JP6247433B2 - Frequency detection device and isolated operation detection device including the frequency detection device - Google Patents

Description

  The present invention relates to a frequency detection device that detects the frequency of an AC signal, and an isolated operation detection device that includes the frequency detection device and detects an isolated operation of a grid-connected inverter device that is linked to a power system. .

  The distributed power source connected to the power system is provided with an isolated operation detection device in order to prevent an isolated operation when connected to the power distribution system under conditions of reverse power flow. As a method for detecting the single operation state of the distributed power source, frequency fluctuations that occur during single operation such as frequency change rate detection method, QC mode frequency shift method, slip mode frequency shift method, active power fluctuation method, reactive power fluctuation method, etc. Various systems are known for detecting islanding by detecting. The frequency change rate detection method is a passive method, but the slip mode frequency shift method, the QC mode frequency shift method, the active power fluctuation method, and the reactive power fluctuation method are active methods.

  The frequency change rate detection method is a method for detecting a sudden change in the output frequency of the distributed power source due to an imbalance between the output of the distributed power source and the load. In the slip mode frequency shift method, when the C (capacitance) component of the reactive power load is large during single operation, the output frequency of the distributed power source increases, and when the L (inductance) component is large, the output frequency of the distributed power source decreases. Using this characteristic, when the output frequency of the distributed power source fluctuates from the reference frequency, the amount of fluctuation of the output frequency is amplified and detected. Specifically, the PCS (Power Conditioning System) has frequency-phase characteristics, and when the output frequency of the distributed power source rises with respect to the reference frequency, the phase of the output current of the PCS is advanced and output by positive feedback. When the frequency increase is accelerated and the output frequency of the distributed power source decreases with respect to the reference frequency, the phase of the output current of the PCS is delayed and the decrease in the output frequency is accelerated by positive feedback. This is a method of detecting islanding by the amount of fluctuation.

  The QC mode frequency shift method uses the above frequency characteristics as in the slip mode frequency shift method, but amplifies the phase of the output current of the PCS by positively feeding back the rate of change of the output frequency instead of the output frequency. It is a method to make it.

  The active power variation method is a method in which periodic active power variation is given to the output of the PCS, and the presence or absence of independent operation is detected based on the variation amount of the output voltage, output current, and output frequency of the PCS. In addition, the reactive power fluctuation method is a method in which periodic reactive power fluctuations are given to the output of the PCS, and the presence or absence of an isolated operation is detected based on the fluctuation amounts of the PCS output voltage, output current, and output frequency.

JP 11-41820 A JP 2000-358331 A JP 2002-281684 A JP 2007-252127 A JP 2011-30306 A JP 2006-25550 A

"PLL and frequency detection method to cope with abnormal voltage in case of power system failure" Denki Theory B, Vol. 118, No. 9, 1998

  In a distributed power source using a grid-connected inverter device, when an isolated operation state is detected, for example, it is desired to disconnect the grid-connected inverter device from a customer (load) within 1 second or to stop the operation. ing. The method using the output frequency of the distributed power source as a detection parameter in the above isolated operation detection method requires a high-speed and high-accuracy frequency detection device.

  On the other hand, as a method to detect the output frequency of the distributed power supply, the instantaneous value of the AC voltage output from the distributed power supply is detected, and the time between the points where the detected value crosses the zero level (zero cross point) is measured. Thus, a method of detecting the output frequency of the distributed power supply (zero cross point counting method) is known (see Patent Document 6). Non-Patent Document 1 proposes a method for obtaining the frequency of the AC voltage using a phase detection device that detects the phase of the AC voltage output from the distributed power source using a multiplying PLL (Phase Locked Loop). Has been.

  In addition to the fundamental positive phase component (hereinafter simply referred to as “fundamental wave component”), the frequency of the three-phase power system (hereinafter referred to as “system frequency”) includes low-order harmonic components (for example, 5 Second, seventh, and eleventh harmonic components (hereinafter simply referred to as “harmonic components”) and fundamental wave antiphase components (hereinafter referred to as “unbalanced components”) are often included. Is included in the detection voltage, the waveform of the detection voltage does not accurately become the waveform of the fundamental wave component (waveform distortion occurs), and the zero-cross point of the fundamental wave component cannot be detected accurately, thereby detecting the frequency. There is a problem that accuracy decreases.

  On the other hand, the method of detecting the frequency using the phase detection device of the multiplying PLL system generates a phase in the device, calculates the phase difference between the phase and the phase of the input AC signal, and the phase difference is The phase of the input AC signal is detected by a PLL process that controls the generation phase so as to be zero. If the AC signal contains harmonic components or unbalanced components, these components will affect the PLL processing and the phase of the AC signal cannot be detected accurately, so it is calculated from the detected phase. Frequency accuracy is also reduced. If the frequency detection accuracy decreases, it is not possible to detect the isolated operation at high speed and with high accuracy when the isolated operation is detected using the frequency.

  The present invention has been conceived under the circumstances described above, and can suppress the influence of unbalanced components and harmonic components and detect the frequency of the fundamental component of the AC signal with high accuracy. An object of the present invention is to provide a frequency detection device.

The frequency detection apparatus provided by the first aspect of the present invention is a frequency detection apparatus that detects the frequency of a detection signal that detects a three-phase AC voltage, and the three-phase detection signals are orthogonal to each other in a stationary coordinate system. first signal and the three-phase two-phase conversion means for converting the second signal to output, to extract the fundamental wave component from said first signal and said second signal, the first fundamental signal for And a fundamental wave extraction means for generating a second fundamental wave signal, and a frequency detection means for detecting the frequency of the fundamental wave component of the detection signal using the first fundamental wave signal and the second fundamental wave signal. The fundamental wave extracting means uses a matrix element of a transfer function matrix in which rotational coordinate transformation processing, filter processing, and stationary coordinate transformation processing are combined into one by calculation, and performs linear time-invariant processing. And the first The first signal is processed by a first transfer function, the second signal is processed by a second transfer function, and these are added to generate the first fundamental wave signal, and the first signal Is signal-processed by a third transfer function, the second signal is signal-processed by the first transfer function, and these are added to generate the second fundamental wave signal, and the fundamental wave component When the central angular frequency is ω ₀ and the time constant of the filtering process is T, the first transfer function is
G ₁ (s) = (T · s + 1) / {(T · s + 1) ² + (T · ω ₀ ) ² }
And the second transfer function is
G ₂ (s) = − T · ω ₀ / {(T · s + 1) ² + (T · ω ₀ ) ² }
And the third transfer function is
G ₃ (s) = T · ω ₀ / {(T · s + 1) ² + (T · ω ₀ ) ² }
It is characterized by being.

  The frequency detection device provided by the second aspect of the present invention is a frequency detection device that detects the frequency of a detection signal that detects a single-phase AC voltage, and the first signal and the zero signal that are the detection signals. A fundamental wave extracting means for extracting a fundamental wave component from the second signal and generating a first fundamental wave signal and a second fundamental wave signal; and the first fundamental wave signal and the second fundamental wave Frequency detection means for detecting the frequency of the fundamental wave component of the detection signal using a signal, and the fundamental wave extraction means combines the rotation coordinate conversion process, the filter process, and the stationary coordinate conversion process into one by calculation. The matrix elements of the combined transfer function matrix are used to perform linear time-invariant processing, the first signal is processed by the first transfer function, and the second signal is transferred to the second transfer function. Signal processing by function Then, the first fundamental wave signal is generated by adding them, the first signal is signal-processed by a third transfer function, and the second signal is signal-processed by the first transfer function. By adding these, the second fundamental wave signal is generated, and the center angular frequency of the fundamental wave component is set to ω ₀ When the time constant of the filtering process is T, the first transfer function is
      G ₁ (S) = (T · s + 1) / {(T · s + 1) ² + (T ・ ω ₀ ) ² }
And the second transfer function is
      G ₂ (S) = − T · ω ₀ / {(T · s + 1) ² + (T ・ ω ₀ ) ² }
And the third transfer function is
      G _Three (S) = T · ω ₀ / {(T · s + 1) ² + (T ・ ω ₀ ) ² }
It is characterized by being.

In a preferred embodiment of the present invention, the first transfer function is the G ₁ (S)
Yeah,
      G ’ ₁ (S)
        = (T ² ・ S ² + T · s + T ² ・ Ω ₀ ² ) / {(T · s + 1) ² + (T ・ ω ₀ ) ² }
And

In a preferred embodiment of the present invention, the frequency detecting means detects a zero cross timing at which a signal based on the first fundamental wave signal and the second fundamental wave signal crosses a zero level, and the detection Frequency calculating means for counting the number of pulses of a predetermined clock pulse between the zero cross timings using the zero cross timing detected by means, and calculating the frequency of the fundamental wave component of the detection signal using the count value; Including.

  In a preferred embodiment of the present invention, the apparatus further comprises two-phase / three-phase conversion means for converting the first fundamental wave signal and the second fundamental wave signal into three signals, and the detection means comprises the three signals. The zero cross timing at which each crosses the zero level is detected.

In a preferred embodiment of the present invention, the frequency detection means is input to the filter means including a filter means including a band-pass type complex coefficient filter having a phase characteristic in which the phase linearly changes in the pass band, and the filter means. A phase difference calculating means for calculating a phase difference between an input signal and an output signal output from the filter means; and the detection signal based on the phase difference calculated by the phase difference calculating means using the phase characteristic of the filter means. Frequency calculating means for calculating the frequency of the fundamental wave component.

In a preferred embodiment of the present invention, the angular frequency corresponding to the frequency detected by the frequency detecting means is the central angular frequency ω ₀ .

An isolated operation detection device provided by the third aspect of the present invention includes an AC signal detection means for detecting an output AC signal output from a grid-connected inverter device linked to a power system, and the output AC signal. The frequency detection device provided by the first or second aspect of the present invention that detects the frequency, and the grid-connected inverter device has shifted to the single operation state based on the detection value detected by the frequency detection device. And an isolated operation detecting means for detecting

  In a preferred embodiment of the present invention, the grid-connected inverter device has a power major loop that controls the amount of reactive power output from the grid-connected inverter device, and is detected by the frequency detection device. A reactive power fluctuation value generating means for generating a reactive power fluctuation value for oscillating the reactive power amount based on a frequency to be fed back to the power major loop, wherein the isolated operation detecting means is the frequency detecting means. The variation amount of the frequency detected in step (b) is calculated, and when the variation amount exceeds a predetermined threshold, it is detected that the grid-connected inverter device has shifted to the single operation state.

  In a preferred embodiment of the present invention, the reactive power fluctuation value generation means calculates a frequency change rate using a frequency detected by the frequency detection means, and the reactive power fluctuation varies in proportion to the frequency change rate. A power fluctuation value is generated.

According to the present invention, even if an unbalanced component or a harmonic component is included in the detection signal , the fundamental wave extracting means suitably removes these components and extracts the fundamental wave component. The frequency detection means detects the frequency based on the extracted fundamental wave component. Therefore, even if the AC signal contains unbalanced components and harmonic components other than the fundamental wave component, the frequency of the fundamental wave component of the AC signal is suppressed by suppressing the influence of these components on the frequency detection process. It can be detected accurately.

It is a figure which shows the structure of the grid connection inverter apparatus provided with the isolated operation detection apparatus which concerns on this invention. It is a block diagram which shows the basic composition of the process for producing | generating the PWM signal in a control apparatus. It is a figure which shows the block configuration of 1st Embodiment of a frequency detector. It is a figure for demonstrating the fundamental wave component and unbalance component of a three-phase alternating voltage. It is a figure for demonstrating the frequency component contained in a system | strain voltage. It is a block diagram for demonstrating the method to convert the process accompanied by a rotation coordinate transformation and a stationary coordinate transformation into a linear time invariant process. It is a block diagram for demonstrating the method to convert the process accompanied by a rotation coordinate transformation and a stationary coordinate transformation into a linear time invariant process, and is represented by the matrix. It is a block diagram for demonstrating the calculation of a matrix. It is a block diagram which shows the process which performs a static coordinate transformation after performing a low-pass filter process after performing a rotational coordinate transformation. It is a Bode diagram for analyzing a transfer function which is each element of matrix G _LPF . It is a figure which shows the waveform of the three-phase alternating current voltage containing an unbalance component and a 5th, 7th, 11th harmonic component. It is a figure which shows the waveform of the three-phase alternating current voltage which filtered the three-phase alternating current voltage shown in FIG. 11 by the disturbance removal part. It is a figure for demonstrating the arithmetic processing of the frequency detection part which concerns on 1st Embodiment. It is a figure which shows the result of having simulated the response characteristic of the frequency detector which concerns on 1st Embodiment. It is the figure which expanded the fluctuation state of the frequency output from a frequency detection apparatus 0.3 second after the simulation start of the simulation result shown in FIG. It is a block diagram which shows the process which performs a static coordinate transformation after performing a high-pass filter process after performing a rotational coordinate transformation. It is a Bode diagram for analyzing a transfer function which is each element of matrix G _HPF . It is a block diagram for demonstrating the internal structure of the fundamental wave extraction part which concerns on 2nd Embodiment. It is a figure which shows the frequency characteristic of the fundamental wave extraction part which concerns on 2nd Embodiment. It is a figure which shows the result of having simulated the response characteristic of the frequency detector which concerns on 2nd Embodiment. It is the figure which expanded the fluctuation state of the frequency output from a frequency detection apparatus 0.3 second after the simulation start of the simulation result shown in FIG. It is a figure which shows the block configuration of 3rd Embodiment of a frequency detector.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

  FIG. 1 is a diagram showing a configuration of a grid-connected inverter device including an isolated operation detection device according to the present invention. FIG. 2 is a block diagram showing a basic configuration of processing for generating a PWM signal in the control device 6. In general, a power system includes a three-phase power system and a single-phase power system. In this embodiment, the power system B is a three-phase power system, and the grid-connected inverter device A supplies power to the power system B through a three-phase AC. This will be described as a three-phase inverter device that outputs.

  The grid-connected inverter device A converts DC power generated by the DC power source 1 into AC power by the inverter 2, removes switching noise generated by the inverter 2 by the filter 3, and adjusts the output level by the transformer 4. This is a grid-connected inverter device having a basic configuration for outputting to the power system B via the circuit breaker 5. When the grid-connected inverter device A monitors the control device 6 that controls the output power of the inverter 2 and whether or not the grid-connected inverter device A is in a single operation state, The isolated operation detection device 7 for opening the circuit breaker 5 and disconnecting the grid interconnection inverter device A is provided.

  The control device 6 controls the AC voltage output from the grid interconnection inverter device A by feedback control in order to link the grid interconnection inverter device A to the power grid B. On the other hand, the isolated operation detection device 7 detects the frequency f of the AC voltage output from the grid connection inverter device A as described later, and the system connection inverter device A enters the single operation state using the detected value. Detect that. For feedback control of the control device 6, an AC ammeter 9 and an AC voltmeter 10 that detect an AC current and an AC voltage output from the grid-connected inverter device A are placed at appropriate positions on the output line of the grid-connected inverter device A. Is provided. The isolated operation detection device 7 detects the frequency f of the AC voltage detected by the AC voltmeter 10.

  The DC power source 1 is, for example, a power source that outputs electric energy generated by solar power generation, solar thermal power generation, wind power generation, or the like in a direct current or a battery power source such as a fuel cell. The DC power supply 1 can be applied with a power supply device that outputs any energy such as light energy, mechanical energy, thermal energy, etc., but in the following description, an example using a solar cell as the DC power supply 1 will be described. .

  Inverter 2, for example, six switching elements (IGBT (Insulated Gate Bipolar Transistor), MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), GTO (Gate Turn-Off thyristor) and other semiconductor switching elements) are bridge-connected. This is a voltage controlled inverter composed of a full bridge circuit. A full bridge circuit is a well-known circuit in which three series circuits (arms) in which two switching elements are connected in series are connected in parallel to a pair of power supply lines, and the connection point of each arm is the output terminal. .

  The pair of switching elements of each arm is controlled to be turned on / off by a set of pulse width modulation signals (PWM signals) input from the control device 6. A set of PWM signals input to each arm is a PWM signal whose phases are inverted. Further, the three sets of PWM signals input to the three arms have the same pulse waveform, but are out of phase with each other by 2π / 3. In the inverter 2, the relative voltages at the connection points of the three arms are sequentially switched by three sets of PWM signals, whereby the DC voltage input from the DC power source 1 is converted into a three-phase AC voltage and three Output from the connecting point of the arm.

  The filter 3 removes high frequency switching noise included in the three-phase AC voltage by the switching operation of the switching element in the inverter 2. The filter 3 is composed of a low-pass filter including an L-shaped circuit of a reactor and a capacitor. The transformer 4 is constituted by a three-phase transformer, and boosts or steps down the AC voltage output from the filter 3 to a level almost the same as the system voltage of the power system B.

  The circuit breaker 5 is composed of, for example, an electromagnetic switch. The breaker 5 opens when a detection signal for detecting the isolated operation state of the grid-connected inverter device A is output from the isolated operation detection device 7 and connects the grid-connected inverter device A and the power system B. Disconnect. The circuit breaker 5 is also controlled by the control device 6, and the control device 6 disconnects the connection between the grid connection inverter device A and the power system B by the circuit breaker 5 when the operation of the grid connection inverter device A is abnormal. However, the configuration is omitted in FIG.

The control device 6 is configured by a microcomputer or an FPGA (Field-Programmable Gate Array), and performs a PWM signal generation process by digital arithmetic processing. The control device 6 generates the control targets v _uo , v _vo , and v _wo (sine wave AC voltages that have passed through the filter 3) of the output voltage of the inverter 2 as modulated waves for the U, V, and W phases, A PWM signal is generated by comparing the control targets v _uo , v _vo , and v _wo with a predetermined triangular wave v _t that is a carrier wave.

The control target v _uo of the U phase is that the output current i _u of the inverter 2 is the impedance between the inverter 2 and the power system B (mainly the impedance due to the reactor of the filter 3 and the transformer 4; hereinafter referred to as “reactor for interconnection”) This corresponds to the amplitude of the voltage obtained by vector-combining the voltage corresponding to the voltage drop due to flowing through the system voltage. Since the system voltage is controlled by the power system B, the control device 6 controls the control target v _uo by controlling the voltage of the interconnecting reactor. Since the interconnection reactor is fixed as design values of the filter 3 and the transformer 4, the voltage of the interconnection reactor is controlled by the output current i _u of the inverter 2. Therefore, the control device 6 controls the control target v _uo by substantially controlling the output current i _u of the inverter 2. The same applies to the control targets v _vo and v _wo for the V phase and the W phase.

The bus voltage target value generation unit 6a, the reactive power target value generation unit 6b, the reactive power calculation unit 6c, the uvw-dq conversion unit 6d, the PI compensation units 6e, 6f, 6g, and 6h in the control device 6 illustrated in FIG. The interference units 6i and 6j and the dq-uvw conversion unit 6k are processing blocks for generating output voltage control targets v _uo , v _vo and v _wo by a power major loop. A block surrounded by a dotted line (processing portion by the uvw-dq conversion unit 6d, the PI compensation units 6g and 6h, the non-interacting units 6i and 6j, and the dq-uvw conversion unit 6k) is a portion constituting a current minor loop. The PWM signal generator 6m is a processing block that compares the control targets v _uo , v _vo , and v _wo with the triangular wave v _t to generate a PWM signal. Note that a processing block for adding a system voltage counter component is provided at the front stage or the rear stage of the dq-uvw conversion unit 6k, but the processing block is omitted in FIG.

The control device 6 generates control targets I _do and I _qo for the output current of the inverter 2 in a dq rotating coordinate system (a coordinate system rotating at the frequency of the power system B). That is, the control device 6 sets the reference value V _ref of the direct-current voltage (hereinafter referred to as “bus voltage”) input to the inverter 2 by the bus voltage target value generation unit 6a, and the bus voltage reference value V _ref A deviation ΔV _dc = V _ref −V _dc of the bus voltage V _dc actually measured by the DC voltmeter 8 is obtained, and a predetermined PI compensation calculation is performed on the deviation ΔV _dc by the PI compensation unit 6e. The d-axis component I _dref of the output current control reference is set.

In addition, the control device 6 receives the reactive power target value Q _o generated by the reactive power target value generation unit 6b (Q _o = 0 when operating with a power factor of 1) and is input from the isolated operation detection device 7 described later. The power fluctuation value ΔQ is added to set the reactive power target value Q _o ′ = Q _o + ΔQ for detecting an isolated operation. The reactive power fluctuation value ΔQ is a fluctuation value for actively changing the reactive power target value Q _o output from the inverter 2 in order to detect that the grid-connected inverter device A has shifted to the single operation state. .

The control device 6 uses the output voltages v _u , v _v , v _{w of the} inverter 2 measured with the AC voltmeter 10 and the output currents i _u , i _v , i _w of the inverter 2 measured with the AC ammeter 9. calculating the reactive power Q _r output from the inverter 2 by the reactive power calculator 6c Te 'deviation ΔQ of the reactive power calculated value Q _r for _r = Q _o' the reactive power target value Q _o for islanding detection -Q _{Find r} . Then, the PI compensation unit 6f performs a predetermined PI compensation operation on the deviation ΔQ _r to set the control axis q-axis component I _qref of the output current of the inverter 2 in the dq rotational coordinate system.

The control device 6 uses the uvw-dq converter 6d to output the output currents i _u , i _v , i _w of the inverter 2 detected by the AC ammeter 9,
I _d = √ (2/3) · (i _u · cos (θ) + _iv · cos (θ-2π / 3) + i _w · cos (θ-4π / 3))
I _q = √ (2/3) · (−i _u · sin (θ) −i _v · sin (θ−2π / 3) −i _w · sin (θ−4π / 3))
However, θ = 2πf _s · t (f _s : system frequency)
Are converted into the d-axis component I _d and the q-axis component I _q of the dq rotation coordinate system by the uvw-dq coordinate conversion formula, and the dq axis component I _d , in the dq rotation coordinate system of the actually measured values with respect to the control references I _dref and I _{qref Iq} deviations ΔI _d = I _dref −I _d and ΔI _q = I _qref −I _q are calculated, respectively.

Controller 6, as well as a predetermined PI compensation calculation on the deviation [Delta] I _d by PI compensator 6 g, calculating the amount of interference to the q-axis component I _q in the dq rotating coordinate system of the actual measurement value is multiplied by the impedance component ωL of the filter 3 Then, the calculated value is added to the PI compensation calculated value of the deviation ΔI _d to set the control target d-axis component I _do of the output current of the inverter 2 in the dq rotational coordinate system. In addition, the control device 6 performs a predetermined PI compensation calculation on the deviation ΔI _q by the PI compensation unit 6h, and multiplies the d-axis component I _d in the dq rotation coordinate system of the actually measured value by the impedance component ωL of the filter 3 to generate an interference amount. And the calculated value is subtracted from the PI compensation calculated value of the deviation ΔI _q to set the q-axis component I _qo of the control target of the output current of the inverter 2 in the dq rotating coordinate system.

Then, the control device 6 adds a system voltage counter component (not _shown) to the control targets I _do and I _qo , respectively, and dq axis components V _do and V _qo of the control target of the output voltage of the inverter 2 in the dq rotating coordinate system. And the control targets V _do and V _qo are calculated by the dq-uvw converter 6k.
v _uo = [√ (2/3)] · [V _do · cos (θ) −V _qo · sin (θ)]
v _vo = [√ (2/3)] · [V _do · cos (θ−2π / 3) −V _qo · sin (θ−2π / 3)]
v _wo = [√ (2/3)] · [V _do · cos (θ−4π / 3) −V _qo · sin (θ−4π / 3)]
The control targets v _uo , v _vo , and v _wo of the U, V, and W phases are generated by converting the three-phase voltages in the stationary coordinate system using the dq-uvw coordinate conversion formula.

Then, the control device 6 compares the levels of the control targets v _uo , v _vo , and v _{wo with} the level of the triangular wave v _{t in} the PWM signal generation unit 6m, and generates a pulse signal having a level according to the comparison result. PWM signals for U, V, and W phases are generated. The PWM signal for each phase is input to the switching element of each arm of the inverter 2.

  The isolated operation detection device 7 detects whether or not the grid interconnection inverter device A is in an isolated operation state by the QC mode frequency shift method. As described above, in the QC mode frequency shift method, when the output frequency of the grid interconnection inverter device A rises with respect to the reference frequency (system frequency), the phase of the output current of the grid interconnection inverter device A is advanced and corrected. The increase of the output frequency is accelerated by feedback, and when the output frequency of the grid connection inverter device A decreases with respect to the reference frequency (system frequency), the phase of the output current of the grid connection inverter device A is delayed and positive feedback is performed. In this method, the amount of fluctuation in the output frequency is amplified by accelerating the decrease in the output frequency, and the isolated operation is detected based on the amount of fluctuation.

Since the phase of the output current of the grid-connected inverter device A is controlled by controlling the reactive energy, the isolated operation detection device 7 determines the rate of change in the frequency of the alternating current output from the grid-connected inverter device A. A reactive power fluctuation value ΔQ for changing the reactive power target value Q _o is set based on the detected value and fed back to the control device 6.

  Accordingly, the isolated operation detection device 7 includes the reactive power fluctuation controller 71 including the frequency change rate calculating unit 71A and the reactive power fluctuation value generating unit 71B, the frequency detector 72 including the disturbance removing unit 72A and the frequency detecting unit 72B, and the isolated operation. A detector 73 is provided. The isolated operation detection device 7 is constituted by a microcomputer or FPGA, and processes each unit by digital arithmetic processing.

The reactive power fluctuation controller 71 calculates the change rate (df / dt) of the frequency f detected by the frequency detector 72 by the frequency change rate calculation unit 71A, and the reactive power fluctuation value generation unit 71B calculates the change rate (df The reactive power fluctuation value ΔQ for changing the reactive power target value Q _o according to the magnitude and polarity of / dt) is generated. The reactive power fluctuation value generation unit 71B generates a reactive power fluctuation value ΔQ using a relational expression between a preset frequency change rate (df / dt) and the reactive power fluctuation value ΔQ, and controls the reactive power fluctuation value ΔQ. Input to device 6.

In the control device 6, as described above, the process of adding the reactive power fluctuation value ΔQ input from the reactive power fluctuation value generation unit 71B to the reactive power target value Q _o generated by the reactive power target value generation unit 6b is performed. . As a result, the reactive power target value Q _o ′ fluctuates in accordance with the frequency change rate (df / dt), and the control target of the output current of the inverter 2 in the dq rotating coordinate system in accordance with the fluctuation of the reactive power target value Q _o ′. Since the q-axis component I _qo varies, the phases of the three-phase voltage control targets v _uo , v _vo , and v _wo obtained by dq-uvw conversion of the dq-axis components I _do and I _qo vary.

When the grid-connected inverter device A enters the single operation state, the amount of phase fluctuation of the control targets v _uo , v _vo , v _wo of the three-phase voltage increases, and the frequency of the control targets v _uo , v _vo , v _wo Will significantly deviate from the system frequency, so that the isolated operation detector 73 of the isolated operation detection device 7 detects the state and disconnects the grid-connected inverter device A by the circuit breaker 5 as will be described later. Become.

  The frequency detector 72 detects the frequency f of the output voltage of the grid interconnection inverter A detected by the AC voltmeter 10. The isolated operation detection device 7 according to the present embodiment is characterized by the configuration of the frequency detector 72. Hereinafter, the configuration of the frequency detector 72 will be described in detail.

  FIG. 3 is a diagram illustrating a block configuration of the frequency detector 72 according to the first embodiment.

The frequency detector 72 shown in FIG. 3 includes unbalanced components included in three-phase AC voltages (phase voltages of U, V, and W phases) v _u , v _v , and v _w detected by the AC voltmeter 10. A disturbance removing unit 72A that removes harmonic components and the like (components that become disturbances in frequency detection processing) and an AC signal (three-phase AC fundamental wave component) output from the disturbance removing unit 72A by the zero cross point counting method It is comprised with the frequency detection part 72B which calculates a frequency.

The disturbance removing unit 72A converts the three-phase AC voltages v _u , v _v , and v _w (instantaneous values input at a predetermined sampling period) input from the AC voltmeter 10 into two-phase AC voltages vα and vβ that are orthogonal to each other. A three-phase to two-phase converter 721 to convert, an unbalanced component included in the two-phase AC voltages vα and vβ output from the three-phase to two-phase converter 721, and a harmonic component of a predetermined order (mainly a fifth-order harmonic component, A fundamental wave extraction unit 722 that extracts a fundamental wave component by removing harmonic components such as a 7th harmonic component and an 11th harmonic component), and an unbalanced component and a harmonic component output from the fundamental wave extraction unit 722 And a two-phase three-phase conversion unit 723 that converts two-phase AC voltages v _r and v _j that do not include the three-phase AC voltages v _u ′, v _v ′, and v _w ′.

The three-phase to two-phase conversion unit 721 performs processing for converting the three-phase AC voltages v _u , v _v and v _w input from the AC voltmeter 10 into two-phase AC voltages vα and vβ. As shown in FIG. 4A, the horizontal u-axis as a stationary coordinate system is used as a reference axis of phase θ, and the v-axis and w-axis are opposite to each other at an angle of ± 2π / 3 with respect to the u-axis. A uvw coordinate system arranged clockwise and an αβ coordinate system (stationary orthogonal coordinate system) arranged with an α axis along the u axis and a β axis orthogonal to the α axis are provided, and in these coordinate systems, the angular velocity ω Considering the voltage vector V rotating counterclockwise, the symmetric three-phase AC voltages v _u , v _v , and v _w are considered to be the u-axis component, the v-axis component, and the w-axis component of the voltage vector V, and the two-phase AC The voltages vα and vβ can be considered as an α-axis component and a β-axis component of the voltage vector V.

Therefore, the three-phase to two-phase conversion process is a process for converting the u-axis component v _u , v-axis component v _v and w-axis component v _w of the voltage vector V into an α-axis component vα and a β-axis component vβ of the voltage vector V. is there. In the following description, in order to distinguish between an AC signal and an AC signal vector, the AC signal is expressed in lower case and the AC signal vector is expressed in upper case.

The conversion equation for converting the three-phase AC voltages v _u , v _v and v _w into the two-phase AC voltages vα and vβ is as follows:
It is.

The three-phase to two-phase conversion unit 721 calculates the three-phase AC voltages v _u , v _v , and v _w input from the AC voltmeter 10 by performing the calculations of the equations (1) and (2). Convert to vα, vβ.

In general, the three-phase AC voltages v _u , v _v and v _w detected by the AC voltmeter 10 are unbalanced components and odd-order harmonics such as third, fifth, seventh and eleventh in addition to the fundamental component. It is an asymmetric three-phase AC voltage including a wave component (see the frequency component in FIG. 5). Therefore, the three-phase / two-phase conversion unit 721 outputs two-phase AC voltages vα and vβ including the components obtained by the three-phase / two-phase conversion for these components.

The fundamental wave components v _su , v _sv , and v _sw of the three-phase AC voltages v _u , v _v , and v _w are components of u, v, and w in the uvw coordinate system of the fundamental wave voltage vector V _s. Defined. On the other hand, the unbalanced components v _su ′, v _sv ′, v _sw ′ of the three-phase AC voltages v _u , v _v , v _w are represented by the u-axis with respect to the uvw coordinate system, as shown in FIG. In the uwv coordinate system in which the arrangement order of the v-axis and the w-axis is reversed, the components are defined as components in the u, v, and w axis directions of the voltage vector V _s ′ of the unbalanced component.

Therefore, the fundamental wave components v _su , v _sv , v _sw are
v _su = A _s · cos (ω ₀ · t) (3A)
v _sv = A _s · cos (ω ₀ · t -2π / 3) (3B)
v _sw = A _s · cos (ω ₀ · t-4π / 3) (3C)
However, when A _{s is} the amplitude of the fundamental wave component, ω _{0 is} the angular frequency of the fundamental wave component, the unbalanced components v _su ′, v _sv ′, and v _sw ′ are
v _su '= A _s ' · cos (ω ₀ · t) (4A)
v _sv '= A _s ' · cos (ω ₀ · t-4π / 3) (4B)
v _sw '= A _s ' · cos (ω ₀ · t-2π / 3) (4C)
However, A _s ′ is represented by the amplitude of the unbalanced component.

Substituting Equations (3A) to (3C) into Equations (1) and (2) to obtain the two-phase AC voltages v _s α and v _s β of the fundamental wave component,
v _s α = √ (3/2) · A _s · cos (ω ₀ · t) (5)
v _s β = √ (3/2) · A _s · sin (ω ₀ · t) (6)
It becomes. Further, by substituting the equations (4A) to (4C) into the equations (1) and (2), the two-phase AC voltages v _s α ′ and v _s β ′ of the unbalanced components are obtained.
v _s α ′ = √ (3/2) · A _s ' · cos (ω ₀ · t)
v _s β ′ = − √ (3/2) · A _s ′ · sin (ω ₀ · t)
It becomes. Since cos (ω ₀ · t) = cos (−ω ₀ · t) and −sin (ω ₀ · t) = sin (−ω ₀ · t), the two-phase AC voltage vs _{s of the} unbalanced component α ′, v _s β ′ is
v _s α ′ = √ (3/2) · A _s ' · cos (−ω ₀ · t) (7)
v _s β ′ = √ (3/2) · A _s ′ · sin (−ω ₀ · t) (8)
It becomes.

Comparing Equations (7) and (8) with Equations (5) and (6), the angular frequency of the fundamental component is “ω ₀ ”, whereas the angular frequency of the unbalanced component is “−ω _The difference is “ ₀ ”. When the angular frequency ω ₀ is “positive frequency”, the angular frequency −ω ₀ of the unbalanced component becomes “negative frequency”, so the unbalanced components v _su ′, v _sv ′, and v _sw ′ are changed to three-phase two. The two-phase AC voltages v _s α ′ and v _s β ′ obtained by phase conversion can be said to be voltages having a negative frequency.

5, displays a fundamental component in the position of the frequency "f _0" of the positive frequency domain, the frequency "-f ₀ negative frequency domain unbalanced component frequencies of the unbalanced components as" -f ₀ """ Indicates the relationship of the above frequencies. In FIG. 5, only the fifth-order, seventh-order, and eleventh-order harmonic components are depicted as the harmonic components that affect the frequency detection. The harmonic component of an integer multiple of 3 does not appear in the line voltage, and even the phase voltage is removed by the Δ-connected transformer, and the odd-order harmonic component larger than the 11th order has a low level and can be ignored. It is not described in 5.

The fifth order, seventh order, and eleventh order harmonic components v _nu , v _nv , v _nw (where n is the order, n = 5, 7, 11) of the fundamental wave components v _su , v _sv , v _sw are
_{v nu = A n · cos (} n · ω 0 · t) ... (9)
v _nv = A _n · cos (n · ω ₀ · t−n · 2π / 3) (10)
v _nw = A _n · cos (n · ω ₀ · t−n · 4π / 3) (11)
Therefore, by substituting the equations (9) to (11) into the equations (1) and (2), the two-phase AC voltage (V ₅ α, V ₅ beta), when obtaining the _{(V 7 α, V 7 β} ), (V 11 α, V 11 β),
v ₅ α = √ (3/2) · A ₅ · cos (−5ω ₀ · t) (12)
v ₅ β = √ (3/2) · A ₅ · sin (−5ω ₀ · t) (13)
v ₇ α = √ (3/2) · A ₇ · cos (7ω ₀ · t) (14)
v ₇ β = √ (3/2) · A ₇ · sin (7ω ₀ · t) (15)
v ₁₁ α = √ (3/2) · A ₁₁ · cos (−11ω ₀ · t) (16)
v ₁₁ β = √ (3/2) · A ₁₁ · sin (−11ω ₀ · t) (17)
It becomes.

The unbalanced component has a negative frequency because the phase order of the unbalanced component (uvw is clockwise) is opposite to the phase order of the fundamental component (uvw is counterclockwise). is there. Accordingly, two-phase AC voltages v _n α, v _n β (subscript n is a subscript of three-phase two-phase conversion of an n-order harmonic component obtained by multiplying the frequency f ₀ of the fundamental wave component by n (n: an integer of 2 or more). If the angular frequency ω _{n of the} order (the same applies hereinafter) has the same sign as the two-phase AC voltages v _s α and v _s β of the fundamental component, the frequency f _n of the n-order harmonic component is a positive frequency Thus, the phase order of the n-order harmonic components v _nu , v _nv , and v _nw is the same as the phase order of the fundamental wave components v _su , v _sv , and v _sw . Conversely, when the angular frequency ω _n of the two-phase AC voltages v _n α and v _n β has a sign opposite to that of the two-phase AC voltages v _s α and v _s β of the fundamental wave component, the n-order harmonic component The frequency f _n is a negative frequency, and the phase order of the n-th harmonic components v _nu , v _nv , v _nw is opposite to the phase order of the fundamental wave components v _su , v _sv , v _sw .

From equations (12) to (17), the fifth and eleventh harmonic components have negative frequencies, and the seventh harmonic component has a positive frequency. The first harmonic component and the eleventh harmonic component are displayed at the positions of the frequencies “−5f ₀ ” and “−11f ₀ ” in the negative frequency region, respectively, and the negative fifth harmonic component and the eleventh harmonic component are displayed. Are displayed at the positions of the frequencies “5f ₀ ” and “11f ₀ ” in the positive frequency region, respectively. Further, the positive-phase seventh harmonic component is displayed at the position of the frequency “7f ₀ ” in the positive frequency region, and the negative-phase seventh harmonic component is displayed at the position of the frequency “−7f ₀ ” in the negative frequency region. Is displayed.

Therefore, from the three-phase to two-phase conversion unit 721, the fundamental wave component, the unbalanced component, and the fifth, seventh, and eleventh orders represented by the expressions (5) to (8) and (12) to (17) are used. Includes two-phase AC voltages (v _s α, v _s β), (v _s α ′, v _s β ′), (v _n α, v _n β) (n = 5, 7, 11) of harmonic components Two-phase AC voltages vα and vβ are output.

The fundamental wave extraction unit 722 extracts the two-phase AC voltages v _s α and v _s β that are fundamental wave components from the two-phase AC voltages vα and vβ input from the three-phase to two-phase conversion unit 721. The fundamental wave extraction unit 722 performs the same process as the process of performing the stationary coordinate conversion after performing the low-pass filter process after performing the rotational coordinate conversion.

When the two-phase AC voltages vα and vβ are subjected to rotational coordinate conversion based on the phase θ of the fundamental wave of the system voltage, the fundamental wave component is converted into a DC component. When the signal after the rotation coordinate conversion is subjected to low-pass filter processing, only the direct current component is allowed to pass and the alternating current component is blocked, so that only the fundamental wave component converted to the direct current component can be extracted. By performing stationary coordinate transformation on the extracted DC component and returning it to the fundamental wave component, the two-phase AC voltages v _s α and v _s β that are fundamental wave components can be extracted. The fundamental wave extraction unit 722 performs the same processing as these processing as linear time invariant processing.

  First, a method for converting processing involving rotational coordinate transformation and stationary coordinate transformation into linear time-invariant processing will be described.

  FIG. 6A is a diagram for explaining processing involving rotational coordinate conversion and stationary coordinate conversion. In this processing, first, the signals α and β are converted into signals d and q by rotational coordinate conversion. The signals d and q are each processed by a predetermined transfer function F (s), and signals d 'and q' are output. Next, the signals d ′ and q ′ are converted into signals α ′ and β ′ by stationary coordinate transformation. The nonlinear time-varying process shown in FIG. 6A is converted into a process using the matrix G of the linear time-invariant transfer function shown in FIG. 6B.

The rotational coordinate transformation shown in FIG. 6A is represented by a determinant of the following equation (18), and the stationary coordinate transformation is represented by a determinant of the following equation (19).

  Therefore, the process shown in FIG. 6A can be expressed as shown in FIG. 7A using a matrix. The matrix G shown in FIG. 6B can be calculated by calculating the product of the three matrices shown in FIG. 7A and making the calculated matrix a linear time-invariant matrix. At this time, the calculation is performed after converting the matrix of the stationary coordinate conversion and the rotation coordinate conversion into a matrix product.

The matrix of rotational coordinate conversion can be converted into the product of the right-hand side matrix shown in the following equation (20).
Where j is the imaginary unit, exp () is the exponential function of the base e of the natural logarithm,
It is. T ⁻¹ is an inverse matrix of T.

From the Euler's formula, calculating by substituting exp (jθ) = cos θ + jsin θ and exp (−jθ) = cos θ−jsin θ,
It can be confirmed that

Further, the matrix of the static coordinate conversion can be converted into the product of the right-side matrix shown in the following equation (21). The matrix in the middle of the matrix product is a linear time-invariant matrix.
Where j is the imaginary unit, exp () is the exponential function of the base e of the natural logarithm,
It is. T ⁻¹ is an inverse matrix of T.

From the Euler's formula, calculating by substituting exp (jθ) = cos θ + jsin θ and exp (−jθ) = cos θ−jsin θ,
It can be confirmed that

When the product of the three matrices shown in FIG. 7A is calculated using the above equations (20) and (21) and the matrix G is calculated, the following equation (22) is obtained.

When attention is paid to the element in the first row and the first column of the three matrixes in the center of the above equation (22) and this is expressed in a block diagram, the block diagram shown in FIG. 8 is obtained. When calculating the input / output characteristics of the block diagram shown in FIG.
It becomes. Where F (s) is a one-input one-output transfer function having an impulse response f (t).

Here, when θ (t) = ω ₀ t, θ (t) −θ (τ) = ω ₀ t−ω ₀ τ = ω ₀ (t−τ) = θ (t−τ). The input / output characteristics of the block diagram shown in FIG. 8 are equal to those of a linear time invariant system having an impulse response f (t) exp (−jω ₀ t). When the impulse response f (t) exp (−jω ₀ t) is Laplace transformed, a transfer function F (s + jω ₀ ) is obtained. The input / output characteristics when exp (jθ (t)) and exp (−jθ (t)) in the block diagram shown in FIG. 8 are interchanged are the input / output characteristics of the transfer function F (s−jω ₀ ). become.

Therefore, when the calculation is further advanced from the above equation (22),
Is calculated.

  Thereby, the process shown in FIG. 7A can be converted into the process shown in FIG. The process shown in FIG. 7B is a process equivalent to the process of performing the stationary coordinate conversion after performing the process represented by the predetermined transfer function F (s) after performing the rotational coordinate conversion. This system is a linear time-invariant system.

The transfer function of the low-pass filter is represented by F (s) = 1 / (Ts + 1), where T is the time constant. Therefore, the transfer function matrix G _LPF showing the process shown in FIG. 9, that is, the process equivalent to the process of performing the low-pass filter process after performing the rotary coordinate conversion and then performing the static coordinate conversion is expressed by the above equation (23). And is calculated as shown in the following equation (24).

FIG. 10 is a Bode diagram for analyzing a transfer function that is each element of the matrix G _LPF . FIG. 5A shows a 1-row and 1-column element of matrix G _LPF (hereinafter referred to as “(1,1) element”. Other elements are also described in the same manner) and (2,2) element. It shows a transfer function, Fig. (b) shows a transfer function of (1,2) element of the matrix G _LPF, FIG. (c) the transfer function of the (2,1) element of the matrix G _LPF Is shown. The figure shows the case where the center frequency is the system frequency f _s = 60 Hz (that is, the angular frequency ω ₀ = 120π corresponding to the center frequency), and the time constant T is set to “0.1”, “1”. ”,“ 10 ”, and“ 100 ”.

The amplitude characteristics shown in FIGS. 4A, 4B, and 5C all have a peak at the center frequency, and the peak of the amplitude characteristic is −6 dB (= 1/2). Further, as the time constant T increases, the pass band decreases. The phase characteristic shown in FIG. 5A is 0 degree at the center frequency. That is, the transfer function of the (1, 1) element and the (2, 2) element of the matrix G _LPF passes the signal of the center frequency (center angular frequency) without changing the phase. The phase characteristic shown in FIG. 5B is 90 degrees at the center frequency. That is, the transfer function of the (1,2) element of the matrix G _LPF passes the phase of the signal of the center frequency (center angular frequency) by 90 degrees. On the other hand, the phase characteristic shown in FIG. 4C is −90 degrees at the center frequency. That is, the transfer function of the (2, 1) element of the matrix G _LPF passes the signal of the center frequency (center angular frequency) delayed by 90 degrees. In the following, the processing shown in the matrix G _{LPF of the} transfer function for the two-phase AC voltages vα and vβ output from the three-phase to two-phase converter 721 will be considered.

In the two-phase AC voltages v _s α and v _s β of the fundamental wave component of the two-phase AC voltages vα and vβ, as shown in the above formulas (5) and (6), the AC voltage v _s α is an AC voltage. The phase is advanced 90 degrees from v _s β. When the process indicated by the transfer function of the (1, 1) element of the matrix G _LPF is performed on the AC voltage v _s α, the amplitude becomes half and the phase does not change (see FIG. 10A). Further, when the processing indicated by the transfer function of the (1,2) element of the matrix G _LPF is performed on the AC voltage v _s β, the amplitude is halved and the phase advances by 90 degrees (see FIG. 10B). Therefore, since both phases becomes the same phase as the AC voltage v _s alpha, AC voltage v _s alpha is reproduced by adding the both. On the other hand, when the process indicated by the transfer function of the (2, 1) element of the matrix G _LPF is performed on the AC voltage v _s α, the amplitude is halved and the phase is delayed by 90 degrees (see FIG. 10C). In addition, when the process indicated by the transfer function of the (2, 2) element of the matrix G _LPF is performed on the AC voltage v _s β, the amplitude is halved and the phase does not change. Therefore, since both phases becomes the same phase as the AC voltage v _s beta, the AC voltage v _s beta is reproduced by adding the both.

Further, the two-phase AC voltage v?, The two-phase AC voltage v _s alpha unbalanced component of v? ', V _s beta' in the above (7), as shown in equation (8), the AC voltage v _s α 'is the AC voltage v _s β' than 90 degrees out of phase is delayed. When the process indicated by the transfer function of the (1, 1) element of the matrix G _LPF is performed on the AC voltage v _s α ′, the amplitude becomes half and the phase does not change. Further, when the process indicated by the transfer function of the (1,2) element of the matrix G _LPF is performed on the AC voltage v _s β ′, the amplitude is halved and the phase advances by 90 degrees. Therefore, since the phases of both are reversed, adding them together cancels each other. On the other hand, when the process indicated by the transfer function of the (2,1) element of the G _LPF is performed on the AC voltage v _s α ′, the amplitude is halved and the phase is delayed by 90 degrees. In addition, when the process indicated by the transfer function of the (2, 2) element of the matrix G _LPF is performed on the AC voltage v _s β ′, the amplitude becomes half and the phase does not change. Therefore, since the phases of both are reversed, adding them together cancels each other.

That is, the transfer function matrix G _LPF passes the two-phase AC voltages v _s α and v _s β of the fundamental wave component, and blocks the two-phase AC voltages v _s α ′ and v _s β ′ of the unbalanced components. In addition, since signals of frequencies other than the fundamental wave component and the unbalanced component (such as harmonic wave signals) are attenuated by the fundamental wave component, the processing shown in the transfer function matrix G _LPF is a two-phase alternating current of the fundamental wave component. It can be confirmed that the band-pass filter processing is to extract the voltages v _s α and v _s β.

The fundamental wave extraction unit 722 extracts the two-phase AC voltages v _s α and v _s β that are fundamental wave components from the two-phase AC voltages vα and vβ input from the three-phase to two-phase conversion unit 721. The fundamental wave extraction unit 722 outputs the two-phase AC voltages v _r and v _j after extraction of the fundamental wave component to the two-phase three-phase conversion unit 723. The fundamental wave extraction unit 722 performs processing represented by the transfer function matrix G _LPF for extracting the fundamental wave component shown in the above equation (24). That is, the process shown in the following equation (25) is performed. As the angular frequency ω ₀ , the angular frequency ω _s = 120π [rad / sec] corresponding to the system frequency f _s = 60 Hz is set in advance, and the time constant T is designed in advance.

Note that the angular frequency ω ₀ used in the fundamental wave extraction unit 722 is not limited to being set in advance. When the sampling period of the signal processing is a fixed sampling period, the system frequency f _s may be detected by a frequency detection device or the like, and the angular frequency ω ₀ may be calculated and used based on the detected frequency. In this case, the system frequency f _s may be detected from the AC voltage detected by the AC voltmeter provided on the power system B side of the circuit breaker 5, but this frequency detection device has the same configuration as the frequency detector 72. Can be used. Further, the angular frequency ω ₀ may be calculated and used based on the frequency f output from the frequency detector 72.

The two-phase three-phase conversion unit 723 converts the two-phase AC voltages v _r and v _j input from the fundamental wave extraction unit 722 into three-phase AC voltages v _u ′, v _v ′, and v _w ′. The conversion equation for converting the two-phase AC voltages v _r and v _j into the three-phase AC voltages v _u ′, v _v ′, and v _w ′ is
It is.

Therefore, the two-phase / three-phase conversion unit 723 performs the calculations of the equations (26) to (28) to convert the two-phase AC voltages v _r and v _j input from the fundamental wave extraction unit 722 into the three-phase AC voltage. Convert to v _u ', v _v ', v _w '.

FIG. 11 is a diagram illustrating waveforms of three-phase AC voltages v _u , v _v , and v _w each including 10% of unbalanced components and fifth, seventh, and eleventh harmonic components. 12 shows the three-phase AC voltages v _u , v _v , and v _w shown in FIG. 11 as the three-phase two-phase converter 721 and the angular frequency ω ₀ as the system frequency f _s = 60 Hz, and the angular frequency ω _s = 120π [ rad / sec], the three-phase AC voltages v _u ′, v _v ′, and v _w ′ obtained by performing the reverse conversion by the two-phase / three-phase conversion unit 723 after the filtering process by the fundamental wave extraction unit 722 is set. FIG. As shown in FIG. 12, the fundamental wave extraction unit 722 can suitably remove unbalanced components and fifth, seventh, and eleventh harmonic components included in the three-phase AC voltages v _u , v _v , and v _w. I understand.

The frequency detection unit 72B includes a level comparison unit 724 that compares the levels of the three-phase AC voltages v _u ′, v _v ′, and v _w ′ input from the two-phase / three-phase conversion unit 723 with the reference level (0v). A zero-cross detection unit 725 that detects a timing (zero-cross timing) at which each of the three-phase AC voltages v _u ′, v _v ′, v _w ′ crosses the reference level (0v) based on the comparison result of the level comparison unit 724; A pulse generator 726 that generates a clock pulse with a frequency higher than the system frequency f _s, and the count of clock pulses output from the pulse generator 726 according to the zero cross timing output from the zero cross detector 725, thereby controlling each of the three phases. AC voltage _{v u ', v v',} v w ' measures the time of the half period or one period of a frequency calculation unit 72 that calculates the frequency f of the system using the time Including the door.

The level comparison unit 724 compares the voltage level of the three-phase AC voltage v _u ′ input at a predetermined sampling period with a reference level (zero level). Based on the comparison result of the level comparison unit 724, the zero-cross detection unit 725 calculates the frequency of the pulse _Pu that becomes high when the voltage level exceeds the zero level and becomes low when the voltage level falls below the zero level. Output to the unit 727. The level comparison unit 724 and the zero cross detection unit 725 perform the same processing on the three-phase AC voltages v _v ′ and v _w ′, and output the pulse P _v and the pulse P _w to the frequency calculation unit 727, respectively.

As shown in FIG. 13, the pulse rising timing of P _u corresponds to the zero level in t _{u +} a point to cross the positive level of a three-phase AC voltage v _u 'is a negative level, the falling timing of the pulse P _u is This corresponds to the point t _u− where the three-phase AC voltage v _u ′ crosses the zero level from the positive level to the negative level. Negative Similarly, the rising timing and falling timing of the pulse P _v is a three-phase AC voltage v _v 'point crosses the zero level from a negative level to a positive level t _{v +} and three-phase AC voltage v _v' is a positive level Corresponding to the point t _v− where the zero level crosses the level, the rising timing and falling timing of the pulse P _w are the points t _{w +} where the three-phase AC voltage v _w ′ crosses the zero level from the negative level to the positive level. And the point t _{w− at} which the three-phase AC voltage v _w ′ crosses the zero level from the positive level to the negative level.

The frequency calculation unit 727 generates zero-cross timings of the three-phase AC voltages v _u ′, v _v ′, and v _w ′ based on the rise or fall of the pulses P _u , P _v , and P _w input from the zero cross detection unit 725. Is detected. As shown in FIG. 12, the three-phase AC voltages v _u ′, v _v ′, v _w ′ input from the two-phase three-phase converter 723 are the fundamental waves of the three-phase AC voltages v _u , v _v , v _w . Since the components (symmetric three-phase alternating current) are extracted, the frequencies f _su , f _sv , and f _sw of the three-phase alternating voltages v _u ′, v _v ′, and v _w ′ are the same. Therefore, the zero cross timing of the three-phase AC voltages v _u ′, v _v ′, v _w ′ is detected at a timing that is 1/6 of the period of the fundamental wave component of the AC signal. In addition, a clock pulse CK having a frequency several hundred to several hundreds of times the system frequency f _s is input from the pulse generator 726 to the frequency calculator 727. The frequency calculation unit 727 counts the clock pulse CK according to the detection of the zero cross timing, and calculates the frequency f from the count value.

Frequency calculator 727, as shown in FIG. 13, and starts counting the clock pulses CK by a pulse P _u rise timing t _u input from the zero-cross detector 725 _+, the rising timing t _{u +} subsequent pulse P _w The count of the clock pulse CK is stopped at the falling timing _tw− , and the count value N is temporarily stored. The frequency calculation unit 727 multiplies the count value N by the period τ [sec] of the clock pulse CK to calculate the time T = τ · N [sec] between the zero cross points t _{u +} -t _{w−, and} between the zero cross points The frequency f = 1 / (6T) = 1 / (6 · τ · N) of the fundamental wave component is calculated by calculating the inverse of the time six times the time T, and the calculation result is output as a frequency detection value.

Further, the frequency calculation unit 727 starts counting the clock pulse CK at the falling timing t _w− of the pulse P _w input from the zero-cross detection unit 725, and the rising of the pulse P _v following the falling timing t _w−. At the timing t _{v +} , the counting of the clock pulse CK is stopped, and the count value N is also multiplied by the period τ [sec] of the clock pulse CK to calculate the time T [sec] between the zero cross points t _w−− t _{v +} . Hereinafter, the frequency calculation unit 727 calculates the pulse P _v , P _u , P _w every time the rising timing and falling timing are detected in order, between the zero cross points t _{v +} -t _u-, between t _u- -t _{w +} , Each time T [sec] of t _{w +} -t _v- , t _v- -t _{u +} , t _{u +} -t _w- ,... is calculated, and the reciprocal of the time 6 times the time T between the zero cross points. Is calculated to calculate the frequency f of the fundamental wave component, and the calculation result is output as a frequency detection value. That is, the frequency calculation unit 727 calculates the frequency f of the fundamental wave component every time zero cross timing is detected.

In the zero cross point counting method, the level of the three-phase AC voltages v _u , v _v , and v _w is sampled at a predetermined cycle. If the zero cross point enters during the sampling cycle, the zero cross point is detected by linear interpolation or the like. There is a need to. When the three-phase AC voltages v _u , v _v , and v _w include an unbalanced component or a harmonic component, the cycle of the zero cross point accurately corresponds to the frequency f ₀ of the fundamental component due to the distortion of the voltage waveform. Therefore, it is necessary to calculate the frequency f over several cycles and take the average value of the calculation results to suppress the adverse effects of unbalanced components and harmonic components.

In the frequency detector 72 according to the present embodiment, the three-phase AC voltage input to the frequency detector 72B is the three-phase AC voltage v _u ′, v _v ′, v _w ′ obtained by extracting the fundamental wave component. And the influence of harmonic components are suppressed, and the period of the zero cross point is exactly six times the period corresponding to the frequency f ₀ of the fundamental wave component. Therefore, according to the frequency detector 72 according to the present embodiment, the sampling frequency is increased to such an extent that the error between the zero cross point and the sampling point can be ignored, so that it is faster and more accurate than the conventional zero cross point counting method. Can detect the frequency f. Moreover, since the frequency component of the noise mixed in with the AC voltmeter 10 or the like is suppressed, it is not necessary to newly provide a filter for removing this noise.

FIG. 14 shows the result of simulating the response characteristic of the frequency f detected by the frequency detector 72 (see FIG. 3) according to the first embodiment. Specifically, the simulation is started in a state where the frequency of the three-phase AC voltage of the power system is stable at the system frequency f _s = 60 [Hz], and the system frequency f _s is instantaneously 0.2 seconds after the simulation starts. Specifically, the response characteristic of the frequency detector 72 when the frequency is changed to 60.3 [Hz] is shown. FIG. 15 is an enlarged view of the fluctuation state of the frequency f output from the frequency detector 72 after 0.3 seconds from the start of the simulation. The content condition of the unbalanced component and the fifth, seventh and eleventh harmonic components included in the input three-phase AC voltages v _u , v _v and v _w is 10%, respectively, and the frequency of the clock pulse CK is 100 The frequency is [kHz]. Further, the angular frequency ω ₀ of the fundamental wave extraction unit 722 is set to an angular frequency ω _s = 120π [rad / sec] corresponding to the system frequency f _s = 60 Hz.

As shown in FIG. 14, when the system frequency f _s is instantaneously increased from 60.0 [Hz] to 60.3 [Hz] 0.2 seconds after the simulation starts, the frequency output from the frequency detector 72 Although f fluctuates in a pulse shape in an attempt to follow a sudden change in the system frequency f _s , it may converge to around 60.3 [Hz] approximately 0.05 seconds after the sudden frequency change (time 0.2 seconds). I understand. Further, when 0.1 second has elapsed since the sudden frequency change (time 0.3 second), the frequency f output from the frequency detector 72 is 60.24 [Hz] and 60 as shown in FIG. . 315 [Hz]. In the zero cross point counting method, the frequency f is calculated using the reciprocal of the count number of the clock pulses CK, and therefore an error occurs when the frequency f cannot be divided. Since the accuracy is improved by increasing the frequency of the clock pulse CK, in practice, the frequency of the clock pulse CK may be designed in consideration of the performance of the microcomputer or the like constituting the control device 6. Even if the input three-phase AC voltages v _u , v _v , and v _w include an unbalanced component and a harmonic component, the frequency f output from the frequency detector 72 is a frequency change ( It can be said that the system frequency f _s after the change is settled within 0.1 seconds from the time 0.2 seconds).

Note that the frequency calculation method in the frequency calculation unit 727 is not limited to the above-described one. For example, counting the number of pulses 3N of clock pulses CK during the rising timing t _{u +} and pulse P _u which is input from the zero-cross detector 725 and the falling timing t _u-, the period of the clock pulse CK to the count value 3N Multiplying τ [sec] to calculate the high level period T _u [sec] of the pulse P _u and calculating the reciprocal of the period twice the high level period T _u , the frequency f = 1 / (2T _u ) = 1 / (6N · τ) may be calculated. The same applies to the pulses P _v and P _w input from the zero cross detector 725.

Further, for example, the clock pulse CK is counted from the rising timing t _{u +} of the pulse P _u to the next rising timing t _{u +,} and the fundamental value component is obtained by multiplying the count value N _u = 6N by the cycle τ [sec] of the clock pulse CK. The frequency f may be calculated by calculating the period 2T [sec] of the first and calculating the reciprocal 1 / (6N · τ) of the calculated value. The same applies to the pulses P _v and P _w .

Further, the frequency may be calculated using the two-phase AC voltages v _r and v _j without providing the two-phase / three-phase converter 723. That is, the level comparison unit 724 compares each or one of the two-phase AC voltages v _r and v _j with the reference level (0 v), and the zero cross detection unit 725 determines the zero cross timing based on the comparison result of the level comparison unit 724. And the frequency f may be calculated from the number of clock pulses CK counted by the frequency calculation unit 727 based on the zero cross timing.

Returning to FIG. 1, the isolated operation detector 73 calculates a fluctuation amount Δf (= f−f _s ) of the frequency f detected by the frequency detector 72 from the system frequency f _s , and the fluctuation amount Δf is set in advance. It is determined whether the threshold value f _th is exceeded. When the fluctuation amount Δf exceeds the threshold f _th , the isolated operation detector 73 outputs a disconnect signal to the circuit breaker 5 on the assumption that the grid-connected inverter device A has shifted to the isolated operation state. The circuit breaker 5 disconnects the connection between the grid interconnection inverter device A and the power system B by the disconnection signal from the isolated operation detector 73.

  As described above, according to the present embodiment, since the frequency detector 72 can detect the frequency of the output voltage of the grid interconnection inverter device A at high speed and with high accuracy, the grid interconnection inverter device A is operated independently. The transition to the state can be detected at high speed and with high accuracy, and the grid-connected inverter device A can be disconnected from the power system B.

  In the first embodiment, the case where the fundamental wave extraction unit 722 extracts a fundamental wave component by performing processing instead of the low-pass filter has been described, but the present invention is not limited thereto. If the unbalanced component and the harmonic component to be suppressed are known, the fundamental wave component may be extracted by suppressing those components. In this case, it can function as a notch filter by performing processing in place of the high-pass filter. A case where the fundamental wave extraction unit 722 extracts a fundamental wave component by processing instead of the high-pass filter will be described below as a second embodiment.

The transfer function of the high-pass filter is represented by F (s) = Ts / (Ts + 1), where T is the time constant. Therefore, the transfer function matrix G _HPF showing the process shown in FIG. 16, that is, the process equivalent to the process of performing the static coordinate conversion after performing the high-pass filter process after performing the rotation coordinate conversion, And is calculated as shown in the following equation (29).

FIG. 17 is a Bode diagram for analyzing a transfer function which is each element of the matrix G _HPF . FIG (a) shows a transfer function of (1, 1) element and (2,2) element of the matrix G _HPF, FIG (b) the transfer function of the (1,2) element of the matrix G _HPF FIG. 4C shows the transfer function of the (2, 1) element of the matrix G _HPF . This figure shows the case where the center frequency is the system frequency f _s = 60 Hz, and the time constant T is “0.1”, “1”, “10”, “100”.

The amplitude characteristic shown in FIG. 6A is attenuated in the vicinity of the center frequency, and the amplitude characteristic at the center frequency is −6 dB (= ½). Further, as the time constant T increases, the cutoff band decreases. The amplitude characteristics shown in FIGS. 5B and 5C both have a peak at the center frequency, and the peak of the amplitude characteristics is −6 dB (= ½). Further, as the time constant T increases, the pass band decreases. Further, the phase characteristic shown in FIG. 5A is 0 degree at the center frequency. That is, the transfer function of the (1, 1) element and the (2, 2) element of the matrix G _HPF passes the signal of the center frequency without changing the phase. The phase characteristic shown in FIG. 5B is −90 degrees at the center frequency. That is, the transfer function of the (1,2) element of the matrix G _HPF passes the signal of the center frequency signal delayed by 90 degrees. On the other hand, the phase characteristic shown in FIG. 4C is 90 degrees at the center frequency. That is, the transfer function of the (2, 1) element of the matrix G _HPF passes the phase of the signal at the center frequency by 90 degrees. In the following, the process shown in the matrix G _{HPF of the} transfer function for the two-phase AC voltages vα and vβ output from the three-phase to two-phase converter 721 will be considered.

In the two-phase AC voltages v _s α and v _s β of the fundamental wave component of the two-phase AC voltages vα and vβ, as shown in the above formulas (5) and (6), the AC voltage v _s α is an AC voltage. The phase is advanced 90 degrees from v _s β. When the processing shown in the transfer function of the (1, 1) element of the matrix G _HPF is performed on the AC voltage v _s α, the amplitude is halved and the phase does not change (see FIG. 17A). Further, when the processing shown in the transfer function of the (1,2) element of the matrix G _HPF is performed on the AC voltage v _s β, the amplitude is halved and the phase is delayed by 90 degrees (see FIG. 17B). Therefore, since the phases of both are reversed, adding them together cancels each other. On the other hand, when the process indicated by the transfer function of the (2,1) element of the matrix G _HPF is performed on the AC voltage v _s α, the amplitude is halved and the phase is advanced by 90 degrees (see FIG. 17C). Further, when the process indicated by the transfer function of the (2, 2) element of the matrix G _HPF is performed on the AC voltage v _s β, the amplitude becomes half and the phase does not change. Therefore, since the phases of both are reversed, adding them together cancels each other.

Further, the two-phase AC voltage v?, The two-phase AC voltage v _s alpha unbalanced component of v? ', V _s beta' in the above (7), as shown in equation (8), the AC voltage v _s α 'is the AC voltage v _s β' than 90 degrees out of phase is delayed. When the processing indicated by the transfer function of the (1, 1) element of the matrix G _HPF is performed on the AC voltage v _s α ′, the amplitude becomes half and the phase does not change. Further, when the process indicated by the transfer function of the (1,2) element of the matrix G _HPF is performed on the AC voltage v _s β ′, the amplitude is halved and the phase is delayed by 90 degrees. Therefore, 'since the same phase as the AC voltage v _s alpha by adding both' both phase AC voltage v _s alpha is reproduced. On the other hand, when the process indicated by the transfer function of the (2,1) element of the matrix G _HPF is performed on the AC voltage v _s α ′, the amplitude is halved and the phase advances by 90 degrees (see FIG. 17C). . In addition, when the processing indicated by the transfer function of the (2, 2) element of the matrix G _HPF is performed on the AC voltage v _s β ′, the amplitude is halved and the phase does not change. Therefore, 'since the same phase as the AC voltage v _s beta by adding both' both phase AC voltage v _s beta is reproduced.

That is, the matrix G _{HPF of the} transfer function passes the two-phase AC voltages v _s α ′ and v _s β ′ that are unbalanced components, and blocks the two-phase AC voltages v _s α and v _s β that are fundamental wave components. In addition, signals of frequencies other than the fundamental wave component and the unbalanced component (such as harmonic component signals) were processed as shown in the transfer functions of the (1, 1) element and (2, 2) element of the matrix G _HPF . In this case, it passes as it is (see FIG. 17A), and when the processing shown in the transfer function of the (1,2) element and the (2,1) element is performed, it attenuates (FIGS. 17B and 17C). )), Pass almost as it is. Therefore, it can be confirmed that the process shown in the matrix G _HPF of the transfer function is a notch filter process that removes only the two-phase AC voltages v _s α and v _s β of the fundamental wave component.

When the (1,2) and (2,1) elements of the matrix G _HPF of the transfer function are interchanged, the two-phase AC voltages v _s α ′ and v _s β ′ of the unbalanced components are reversed from the above. The two-phase AC voltages v _s α and v _s β of the fundamental wave component and the signal of the harmonic component are passed. In other words, the processing shown in the matrix in which the (1,2) element and the (2,1) element of the transfer function matrix G _HPF are exchanged is only the two-phase AC voltages v _s α ′ and v _s β ′ of the unbalanced components. Is a notch filter process. Further, the matrix can be considered to be obtained by setting “−ω ₀ ” instead of the angular frequency ω ₀ in the transfer function matrix G _HPF . That is, the process shown in the transfer function matrix G _HPF is a notch filter process that removes only the frequency component set as the angular frequency ω ₀ .

For example, when the frequency components to be suppressed are an unbalanced component (−f ₀ ) and fifth, seventh, and eleventh harmonic components (−5f ₀ , + 7f ₀ , −11f ₀ ), a notch is provided for each frequency component. If the filter process is performed, only the fundamental wave component can be extracted.

  The block diagram of the frequency detection apparatus according to the second embodiment is different from the frequency detector 72 according to the first embodiment shown in FIG. 3 in that the fundamental wave extraction unit 722 is replaced with a fundamental wave extraction unit 722 ′ (a diagram to be described later). 18) (the illustration other than the fundamental wave extraction unit 722 'is omitted). In order to distinguish from the frequency detector 72 according to the first embodiment, the frequency detector according to the second embodiment is referred to as a frequency detector 72 ′.

  FIG. 18 is a block diagram for explaining the internal configuration of the fundamental wave extraction unit 722 'according to the second embodiment.

The fundamental wave extraction unit 722 ′ includes an unbalanced component removal unit 722a, a fifth harmonic removal unit 722b, a seventh harmonic removal unit 722c, and an eleventh harmonic removal unit 722d. The unbalanced component removal unit 722a suppresses the passage of unbalanced component signals, and removes unbalanced components from the two-phase AC voltages vα and vβ input from the three-phase to two-phase conversion unit 721 (see FIG. 3). Remove and output. The unbalanced component removing unit 722a performs a process of setting “−ω ₀ ” in place of the angular frequency ω ₀ in the transfer function matrix G _HPF shown in the above equation (29), and the unbalanced component removing unit 722a. Assuming that the signals output from vα ′ and vβ ′ are the processing shown in the following equation (30). As the angular frequency ω ₀ , the angular frequency ω _s = 120π [rad / sec] corresponding to the system frequency f _s = 60 Hz is set in advance, and the time constant T is designed in advance.

The 5th harmonic removal unit 722b, the 7th harmonic removal unit 722c, and the 11th harmonic removal unit 722d suppress the passage of the 5th harmonic, the 7th harmonic, and the 11th harmonic, respectively. in the matrix G _HPF transfer function shown in the equation (29), respectively "-5Omega _0" in place of the angular frequency omega _0, "7Omega _0", "- 11ω _0" and the process which is the one that performs. As the angular frequency ω ₀ , an angular frequency ω _s = 120π [rad / sec] corresponding to the system frequency f _s = 60 Hz is set in advance.

Note that the angular frequency ω ₀ used in the fundamental wave extraction unit 722 ′ is not limited to being set in advance. When the sampling period of the signal processing is a fixed sampling period, the system frequency f _s may be detected by a frequency detection device or the like, and the angular frequency ω ₀ may be calculated and used based on the detected frequency. Further, the angular frequency ω ₀ may be calculated and used based on the frequency f output from the frequency detector 72.

FIG. 19 is a diagram illustrating the frequency characteristics of the fundamental wave extraction unit 722 ′. The unbalanced component removing unit 722a, the fifth harmonic removing unit 722b, the seventh harmonic removing unit 722c, and the eleventh harmonic removing unit 722d are respectively an unbalanced component (−f ₀ ), a fifth harmonic component ( −5f ₀ ), seventh harmonic component (7f ₀ ), and eleventh harmonic component (−11f ₀ ) have a frequency characteristic that suppresses the passage, so that the fundamental wave extraction unit 722 ′ as a whole has a frequency characteristic. Is as shown in FIG. According to the figure, the unbalanced component (−f ₀ ), the fifth harmonic component (−5f ₀ ), the seventh harmonic component (7f ₀ ), and the eleventh harmonic component (−11f ₀ ) are suppressed, The fundamental wave component (f ₀ ) that is the other component passes. Therefore, the fundamental wave extraction unit 722 ′ can suitably pass the fundamental wave component, and extracts the two-phase AC voltages v _s α and v _s β that are the fundamental wave components from the two-phase AC voltages vα and vβ.

Generally, the harmonics superimposed on the electric power system include many fifth-order, seventh-order, and eleventh-order harmonics. In the present embodiment, these and the unbalanced components are suppressed. The fundamental wave extraction unit 722 ′ may be designed according to the harmonic order that needs to be suppressed. For example, when it is desired to suppress only the fifth harmonic as the harmonic, it is not necessary to include the seventh harmonic removing unit 722c and the eleventh harmonic removing unit 722d, and further, the thirteenth harmonic is also desired to be suppressed. In the transfer function matrix G _HPF shown in the above equation (29), a 13th-order harmonic removal unit in which “13ω ₀ ” is set as the angular frequency ω ₀ may be further provided. Moreover, when there are few harmonic components superimposed on the electric power system and can be disregarded, it is good also as only the unbalanced component removal part 722a. Further, in order to remove noise mixed in with the AC voltmeter 10 or the like, a removing unit for removing the frequency component of the noise may be further provided in the fundamental wave extracting unit 722 ′.

  Also in the second embodiment, since the fundamental wave extraction unit 722 ′ can extract only the fundamental wave component by removing the unbalanced component and the harmonic component of the predetermined order, the same effect as the first embodiment can be obtained. Can play.

  FIG. 20 shows the result of simulating the response characteristic of the frequency f detected by the frequency detector 72 'according to the second embodiment. FIG. 21 is an enlarged view of the fluctuation state of the frequency f output from the frequency detector 72 '0.3 seconds after the simulation starts. The simulation conditions are the same as the simulation results shown in FIGS.

As shown in FIG. 20, also in the case of the second embodiment, when the system frequency f _s is instantaneously increased from 60.0 [Hz] to 60.3 [Hz] after 0.2 seconds from the start of the simulation, the frequency detection is performed. It can be seen that the frequency f output from the device 72 'suddenly changes in a pulse shape, but converges to approximately 60.3 [Hz] approximately 0.02 seconds after the sudden frequency change (time 0.2 seconds). Further, as shown in FIG. 21, when 0.1 second has elapsed since the sudden frequency change (time 0.3 second), the frequency f output from the frequency detector 72 ′ is 60.24 [Hz] and 60. .315 [Hz], and the same error as in the simulation (FIGS. 14 and 15) in the first embodiment occurs. Therefore, in response speed, it was confirmed that the frequency detector 72 ′ according to the second embodiment had higher performance than the frequency detector 72 according to the first embodiment. In other words, faster frequency detection characteristics can be obtained by using the fundamental wave extraction unit 722 ′ as a notch filter than using the fundamental wave extraction unit 722 as a bandpass filter.

  As is well known, if the notch filter and the bandpass filter have a multi-stage configuration, it is possible to achieve steep filter characteristics and easily adjust the removal characteristics and responsiveness of unbalanced components and harmonic components. When mounting, a multi-stage configuration with an appropriate number of stages is preferable. For example, in the frequency detector 72 (see FIG. 3) according to the first embodiment, a fundamental wave extraction unit 722 may be further provided after the fundamental wave extraction unit 722. In addition, when a notch filter and a bandpass filter are combined, a synergistic effect of both characteristics can be expected, and a faster and more accurate frequency detection characteristic can be obtained. Therefore, for example, in the frequency detector 72 (see FIG. 3) according to the first embodiment, a fundamental wave extraction unit 722 ′ may be further provided after the fundamental wave extraction unit 722.

  Note that the configuration of the frequency detection unit 72B is not limited to that described above. For example, the phase of the AC voltage is detected by the phase detector of the multiplying PLL system described in Non-Patent Document 1, and the input of the integrator is set to the frequency by setting the numerator of the integrator built in the phase detector to 2π. The frequency may be detected by assuming that the frequency is obtained, or the angular frequency input to the integrator may be divided by 2π to obtain the frequency. In addition, as in the frequency detection device described in Japanese Patent Application No. 2011-208365 filed by the applicant, the phase characteristics in the passband of the bandpass type complex coefficient filter (complex coefficient bandpass filter) The frequency may be calculated from the phase difference between the input signal and the output signal of the complex-coefficient bandpass filter using the fact that the (characteristic) has a characteristic represented by linear approximation.

  In the first and second embodiments, the QC mode frequency shift type isolated operation detection device has been described. However, the present invention can also be applied to other frequency shift type isolated operation detection devices such as a slip mode frequency shift method. . For example, in the slip mode frequency shift method, the frequency change rate calculation unit 71A in FIG. 1 is removed, and the reactive power fluctuation value generation unit 71B sets the reactive power fluctuation value ΔQ using the frequency f detected by the frequency detector 72. You just have to do it. In addition, the present invention can be widely applied to other systems other than the frequency shift system as long as the system detects the frequency and performs the isolated operation detection using the fluctuation amount of the frequency.

In the first and second embodiments, the case where the three-phase AC voltages v _u , v _v , and v _w are input as input signals has been described. However, the frequency detection device according to the present invention is a single-phase AC voltage. The present invention can also be applied when v is input. A frequency detection device for detecting the frequency of the single-phase AC voltage v will be described below as a third embodiment.

  FIG. 22 is a block diagram of a frequency detector 72 ″ according to the third embodiment, except that a three-phase / two-phase converter 721 is not provided for the frequency detector 72 of FIG. In the case of a single phase, only the single-phase AC voltage v is input, so that sampling data of the single-phase AC voltage v and “0” are input to the fundamental wave extraction unit 722. In the frequency detector 72 of FIG. 3, the three-phase / two-phase converter 721 may be removed and sampling data of the AC voltage v of any of U, V, and W phases may be input.

In the fundamental wave extraction unit 722, even when the single-phase AC voltage v is input, the two-phase AC voltages v _r and v _j (sine wave and cosine wave signals) that are orthogonal to each other are output as in the case of the three-phase. Therefore, the fundamental wave extraction unit 722, the two-phase three-phase conversion unit 723, and the frequency detection unit 72B can be realized with the same configuration as the three-phase frequency detector 72 shown in FIG.

  In the first to third embodiments, the case where the isolated operation detecting device 7 detects the isolated operation of the grid interconnection inverter device A has been described. However, the present invention is not limited to this. The isolated operation detection device according to the present invention can also be used when detecting isolated operation of a grid interconnection device such as a synchronous generator.

In the first to third embodiments, the case where the frequency detector 72 (72 ′, 72 ″) is used in the isolated operation detection device 7 has been described, but the present invention is not limited to this. The frequency detection device according to the present invention is It can also be used for other systems, or can be used alone as a detection device for detecting the frequency of a predetermined AC signal, for example, as a frequency detection device for detecting the system frequency f _s of the power system B. You can also

  The frequency detection device and the isolated operation detection device according to the present invention are not limited to the above-described embodiments. The specific configuration of each part of the frequency detection device and the isolated operation detection device according to the present invention can be varied in design in various ways.

A system interconnection inverter device B power system 1 DC power supply 2 inverter 3 filter 4 transformer 5 circuit breaker 6 control device 6a bus voltage target value generation unit 6b reactive power target value generation unit 6c reactive power calculation unit 6d uvw-dq conversion unit 6e, 6f, 6g, 6h PI compensation unit 6i, 6j Decoupling unit 6k dq-uvw conversion unit 6m PWM signal generation unit 7 Independent operation detection device 71 Reactive power fluctuation controller 71A Frequency change rate calculation unit 71B Reactive power fluctuation value Generation unit 72, 72 ', 72 "Frequency detector 72A Disturbance removal unit 72B Frequency detection unit 721 Three-phase to two-phase conversion unit 722, 722' Fundamental wave extraction unit 722a Unbalanced component removal unit 722b 5th harmonic removal unit 722c 7 Second harmonic removal unit 722d 11th harmonic removal unit 723 Two-phase three-phase conversion unit 724 Level comparison unit (detection means)
725 Zero cross detector (detection means)
726 Pulse generator 727 Frequency calculator 73 Independent operation detector 8 DC voltmeter 9 AC ammeter 10 AC voltmeter (AC signal detection means)

Claims (10)

A frequency detection device that detects the frequency of a detection signal that detects a three-phase AC voltage ,
Three-phase two-phase conversion means for converting the three-phase detection signal into a first signal and a second signal orthogonal to each other in a stationary coordinate system and outputting the same;
It extracts the fundamental wave component from said first signal and said second signal, and the fundamental wave extracting means for generating a first fundamental signal and the second fundamental signal,
Frequency detecting means for detecting a frequency of a fundamental wave component of the detection signal using the first fundamental wave signal and the second fundamental wave signal;
With
The fundamental wave extracting means includes
Using the matrix elements of the transfer function matrix that combines the rotation coordinate transformation process, the filter process and the static coordinate transformation process into one by calculation,
It performs linear time invariant processing,
The first signal is signal-processed by a first transfer function, the second signal is signal-processed by a second transfer function, and these are added to generate the first fundamental wave signal, The first signal is signal-processed by a third transfer function, the second signal is signal-processed by the first transfer function, and these are added to generate the second fundamental wave signal,
When the central angular frequency of the fundamental wave component is ω ₀ and the time constant of the filter processing is T,
The first transfer function is:
G ₁ (s) = (T · s + 1) / {(T · s + 1) ² + (T · ω ₀ ) ² }
And
The second transfer function is
G ₂ (s) = − T · ω ₀ / {(T · s + 1) ² + (T · ω ₀ ) ² }
And
The third transfer function is
G ₃ (s) = T · ω ₀ / {(T · s + 1) ² + (T · ω ₀ ) ² }
Is,
A frequency detection apparatus characterized by that. A frequency detection device that detects a frequency of a detection signal that detects a single-phase AC voltage ,
Fundamental wave extraction means for extracting a fundamental wave component from the first signal that is the detection signal and the second signal that is a zero signal to generate a first fundamental wave signal and a second fundamental wave signal;
Frequency detecting means for detecting a frequency of a fundamental wave component of the detection signal using the first fundamental wave signal and the second fundamental wave signal;
With
The fundamental wave extracting means includes
Using the matrix elements of the transfer function matrix that combines the rotation coordinate transformation process, the filter process and the static coordinate transformation process into one by calculation,
It performs linear time invariant processing,
The first signal is signal-processed by a first transfer function, the second signal is signal-processed by a second transfer function, and these are added to generate the first fundamental wave signal, The first signal is signal-processed by a third transfer function, the second signal is signal-processed by the first transfer function, and these are added to generate the second fundamental wave signal,
When the central angular frequency of the fundamental wave component is ω ₀ and the time constant of the filter processing is T,
The first transfer function is:
G ₁ (s) = (T · s + 1) / {(T · s + 1) ² + (T · ω ₀ ) ² }
And
The second transfer function is
G ₂ (s) = − T · ω ₀ / {(T · s + 1) ² + (T · ω ₀ ) ² }
And
The third transfer function is
G ₃ (s) = T · ω ₀ / {(T · s + 1) ² + (T · ω ₀ ) ² }
Is,
A frequency detection apparatus characterized by that. Instead of the first transfer function G ₁ (s),
G ' ₁ (s)
= (T ² · s ² + T · s + T ² · ω ₀ ² ) / {(T · s + 1) ² + (T · ω ₀ ) ² }
And
The frequency detection apparatus according to claim 1 or 2 . The frequency detection means includes
Detecting means for detecting a zero cross timing at which a signal based on the first fundamental wave signal and the second fundamental wave signal crosses a zero level;
Frequency calculation means for counting the number of pulses of a predetermined clock pulse between the zero cross timings using the zero cross timing detected by the detection means and calculating the frequency of the fundamental wave component of the detection signal using the count value. When,
including,
Frequency detection apparatus according to any one of claims 1 to 3. Two-phase three-phase conversion means for converting the first fundamental wave signal and the second fundamental wave signal into three signals;
The detecting means detects a zero cross timing at which each of the three signals crosses a zero level.
The frequency detection apparatus according to claim 4 . The frequency detection means includes
Filter means comprising a bandpass type complex coefficient filter having a phase characteristic in which the phase varies linearly in the passband;
A phase difference calculating means for calculating a phase difference between an input signal input to the filter means and an output signal output from the filter means;
Frequency calculating means for calculating the frequency of the fundamental component of the detection signal from the phase difference calculated by the phase difference calculating means using the phase characteristic of the filter means;
including,
Frequency detection apparatus according to any one of claims 1 to 3. The angular frequency corresponding to the frequency detected by the frequency detection means is the central angular frequency ω ₀ ,
Frequency detection apparatus according to any one of claims 1 to 6. AC signal detecting means for detecting an output AC signal output from the grid-connected inverter device linked to the power system;
The frequency detection device according to any one of claims 1 to 7 , which detects a frequency of the output AC signal;
Isolated operation detecting means for detecting that the grid-connected inverter device has shifted to the isolated operation state based on the detection value detected by the frequency detection device;
An isolated operation detection device comprising: The grid-connected inverter device has a power major loop that controls the amount of reactive power output from the grid-connected inverter device,
Reactive power fluctuation value generating means for generating a reactive power fluctuation value for oscillating the reactive power amount based on the frequency detected by the frequency detection device and feeding back to the power major loop;
The islanding detection means calculates a fluctuation amount of the frequency detected by the frequency detection means, and detects that the grid-connected inverter device has shifted to an islanding state when the fluctuation amount exceeds a predetermined threshold. To
The isolated operation detection device according to claim 8 . The reactive power fluctuation value generating means, said generating a reactive power fluctuation value calculating a frequency change rate varies in proportion to the frequency change rate by using the frequency detected by said frequency detecting means, claim 9 The isolated operation detection device according to 1.