WO2015125377A1

WO2015125377A1 - Power conversion device and power conversion device control method

Info

Publication number: WO2015125377A1
Application number: PCT/JP2014/082190
Authority: WO
Inventors: 智道伊藤; 洋五十嵐; 晃一宮崎
Original assignee: 株式会社日立製作所
Priority date: 2014-02-21
Filing date: 2014-12-05
Publication date: 2015-08-27
Also published as: JP6159271B2; JP2015156772A

Abstract

A stand-alone operation state is detected even when the output power of a power conversion device and the power consumption of a load match each other or when the load includes a capacitor. A power conversion device comprises: a phase calculation unit for calculating, on the basis of an interconnection point voltage, an interconnection point voltage phase; an active current command value calculation unit for calculating, on the basis of a DC voltage, an active current command value indicating an active current to be output by an inverter; a reactive current command value calculation unit for calculating, on the basis of the interconnection point voltage and the output current, a reactive current command value indicating a reactive current to be output by the inverter; a control unit for controlling the inverter according to the output current, the interconnection point voltage phase, the active current command value, and the reactive current command value and thereby changing the output voltage phase of the inverter at predetermined time intervals; and a stand-alone operation detection unit for detecting, on the basis of the change of the interconnection point voltage phase, a stand-alone operation state of the power conversion device.

Description

POWER CONVERTER AND CONTROL METHOD OF POWER CONVERTER

The present invention relates to a power converter and a control method of the power converter.

In recent years, the introduction of distributed power sources using natural energy, such as solar power generation devices and wind power generation devices, has progressed. A distributed power source using natural energy converts power generated by natural energy into grid frequency by a self-excited power converter and transmits the power to the grid. Generally, the output power of such a distributed power supply fluctuates due to the climate, which may impair the stability of the interconnected power system. Under such circumstances, for the purpose of stabilizing the power system, the introduction of a power storage system provided with power storage means represented by a storage battery and a self-excited power converter is progressing mainly on a small scale power system.

When the circuit breaker of the power system is opened by accident detection or system switching in a state where the distributed power source using natural energy or the storage system is connected to the power system, the distributed power source connected to the lower system of the circuit breaker When the generated power of the storage system matches the power consumption of the load connected to the lower system, the voltage of the lower system may be maintained for a long time. The state in which the supply and demand balance is achieved is referred to as an isolated operation state.

The occurrence of an isolated operation interferes with the maintenance of the power system. Therefore, a self-excited power converter for distributed power and a power converter for a storage system have a function to detect an isolated operation, and after an isolated operation is detected according to the grid interconnection technology requirement guidelines in Japan and IEC 62116 overseas. It is defined that the system has a function of quickly disconnecting from the system. In particular, in the grid connection regulations in Japan, for distributed power source linked to a low voltage system, it is defined that the isolated operation is detected within 0.1 s after the isolated operation occurs, and the operation is stopped. Needs to be detected.

As a method of detecting an isolated operation, Patent Document 1 discloses a method of detecting an isolated operation by generating reactive power with a change rate of frequency as a trigger.

As other islanding detection methods, there are known a method of detecting a phase jump of a connection point voltage and a method of detecting a change in system impedance due to harmonic injection.

JP, 2013-099230, A

However, when the power consumed by the load completely matches the power output from the self-excited power converter, it is impossible to detect islanding by phase jump. In addition, when testing the islanding detection function with an RLC parallel circuit with a large-capacity capacitor as described in IEC 62116 as a load, the method using harmonic injection involves absorption of harmonic components by the capacitor. It is difficult to detect solitary operation.

In order to solve the above problems, a power conversion device according to one aspect of the present invention includes an inverter that converts direct current to alternating current and outputs the same to an electric power system, and a DC voltage detection unit that detects a DC voltage input to the inverter , An output current detection unit that detects an output current from the inverter, an interconnection point voltage detection unit that detects an interconnection point voltage at an interconnection point between the inverter and the electric power system, and interconnection based on the interconnection point voltage Based on a phase calculation unit that calculates a point voltage phase, an active current command value calculation unit that calculates an active current command value indicating an active current to be output to the inverter based on a DC voltage, and based on an interconnection point voltage and an output current A reactive current command value calculating unit that calculates a reactive current command value indicating a reactive current to be output to the inverter, and an output current, an interconnection point voltage phase, an active current command value, and an reactive current command value. A control unit that changes the phase of the output voltage of the inverter at predetermined time intervals by controlling the inverter, and a single unit that detects the isolated operation state of the power conversion device based on the change of the interconnection point voltage phase. And a driving detection unit.

According to one aspect of the present invention, the islanding state can be detected even when the output power of the power conversion device matches the power consumption of the load, or even when the load includes a capacitor.

1 shows the configuration of a power conversion device according to a first embodiment. The configuration of the load 200 is shown. The structure of the main circuit of the power converter device 1 is shown. 1 shows the configuration of a controller 100 according to a first embodiment. The configuration of the phase calculator 1004 is shown. The structure of the islanding operation detector 1005 is shown. An example of an output voltage vector of inverter 10 is shown. It is a time chart which shows operation of islanding detection. The structure of the power converter device of a 1st modification is shown. The structure of the power converter device of a 2nd modification is shown. The structure of the power converter device 2 of Example 2 is shown. The structure of the controller 100 of Example 2 is shown. The input / output characteristics of the upper / lower limiter 1077 are shown.

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

A present Example demonstrates the power converter device 1 for solar power generation.

FIG. 1 shows the configuration of the power conversion device of the first embodiment.

A solar panel 30 is connected to the DC circuit of the power converter 1. The power converter 1 converts the DC power generated by the solar panel 30 into AC power having a grid frequency of the power grid 300. , Supply the AC power to the power system 300 and the load 200. A connection point on the power system 300 side of the power conversion device 1 is referred to as an interconnection point (system interconnection point).

The power conversion device 1 and the load 200 are connected in parallel to the power system 300 via the circuit breaker 400. The circuit breaker 400 is opened and closed by the operator of the power system 300 at the time of system fault detection and system maintenance.

The power converter 1 includes a DC voltage sensor 71PT for detecting a DC circuit voltage connected to the solar panel 30, an inverter 10, a harmonic filter 20 for removing harmonics of the output of the inverter 10, and an interconnection point with the inverter 10. Between the contactor 40, output current sensors 72CTu, 72CTw for detecting the output current of the power conversion device 1, interconnection point voltage sensors 70PTuv, 70PTvw for detecting the interconnection point voltage, detected currents and voltages And a controller 100 for calculating a contactor control signal CTTctl for controlling ON / OFF of the contactor 40 and gate signals GateUP to WN (GateUP, GateVP, GateWP, GateUN, GateVN, GateWN) of the inverter 10 on the basis of.

In the inverter 10, the solar panel 30 is connected to the DC circuit terminals P and N, and the harmonic filter 20 is connected to the AC terminals U, V and W. The inverter 10 converts DC power output from the solar panel 30 into three-phase AC power and outputs it. The harmonic filter 20 reduces harmonics flowing out of the inverter 10 into the power system 300 by smoothing the pulse waveform output from the inverter 10 and passing the fundamental wave component.

FIG. 2 shows the configuration of the load 200.

The load 200 is connected in parallel to the interconnection point of the power conversion device 1. The load 200 has its electrical characteristics indicated by a parallel circuit of a resistor, a reactor, and a capacitor.

FIG. 3 shows the configuration of the main circuit of the power conversion device 1.

This figure includes DC voltage sensor 71PT, inverter 10, harmonic filter 20, output current sensors 72CTu, 72CTw, contactor 40, and interconnection point voltage sensors 70PTuv, 70PTvw among power conversion devices 1.

The inverter 10 is an

IGBT module

10 k, 10 l, 10 p, 10 m, 10 n, 10 o, 10 p, and a DC capacitor 10 C in which a diode is connected in antiparallel with a self arc extinguishing semiconductor switching device such as IGBT (Insulated Gate Bipolar Transistor). including. The harmonic filter 20 includes two three-phase reactors 20L1 and 20L2 and a three-phase capacitor 20C. The current sensors 72CTu and 72CTw detect the U-phase current and the W-phase current of the output current of the harmonic filter 20, respectively. The interconnection point voltage sensors 70PTuv and 70PTvw measure the U-phase and V-phase line voltages vsuv at the interconnection points, and the V-phase and W-phase line voltages vsvw, respectively.

FIG. 4 shows the configuration of the controller 100 of the first embodiment.

The line voltages vsuv and vsvw of the interconnection points respectively detected by the interconnection point voltage sensors 70PTuv and 70PTvw are input to the controller 100. Output current detection values isu and isw detected by the output current sensors 72CTu and 72CTw, respectively, are input to the controller 100. A DC voltage detection value vdc detected by the DC voltage sensor 71PT is input to the controller 100. The controller 100 aims to match the voltage command value and the instantaneous average value of the inverter output voltage based on the input voltage and current, as described later, to the

IGBT modules

10k, 10l, 10p, 10m, 10n, Gate signals GateUP, GateVP, GateWP, GateUN, GateVN, and GateWN of 10o and 10p are respectively calculated. The controller 100 further calculates the contactor control signal CTTctl based on the input voltage and current.

The controller 100 includes an interconnection point voltage phase detection unit 100a, a DC voltage control unit 100b, a reactive power control unit 100c, a current control unit 100d, and an isolated operation control unit 100e.

First, the connection point voltage phase detection unit 100a will be described.

The interconnection point voltage phase detection unit 100a detects an interconnection point voltage phase that is the phase of the interconnection point voltage. The connection point voltage phase detection unit 100 a includes a phase voltage calculator 1001, an α-β converter 1002, a dq converter 1003, a phase calculator 1004, a cos table 1006, and a sin table 1007.

The phase voltage calculator 1001 sets the phase voltage of the zero-phase component to zero, and calculates phase voltages vsu, vsv, vsw based on the line voltages vsuv, vsvw according to Equation 1.

The α-β converter 1002 performs the α-β conversion of the phase voltages vsu, vsv, vsw according to Equation 2 to calculate vs_alp which is the α component of the interconnection point voltage in the fixed coordinate system and vs_bet which is the β component Do.

The dq converter 1003 performs a dq conversion of vs_alp and vs_bet according to the equation 3 based on a cos table output value cos and a sin table output value sin, which will be described later, to thereby obtain an interconnection point voltage in the rotational coordinate system. D component vsd, q component vsq is calculated.

The phase calculator 1004 calculates the connection point voltage phase theta and the angular frequency omega based on the q component vsq of the connection point voltage.

FIG. 5 shows the configuration of the phase calculator 1004.

The phase calculator 1004 includes a PI controller 10041, an adder 10042, and a time integrator 10043.

The PI controller 10041 calculates del_omeg which is a correction angular frequency based on vsq.

The adder 10042 adds the correction angular frequency del_omeg and the rated angular frequency Omeg0, and outputs the sum omega to the time integrator 10043.

The time integrator 10043 calculates the connection point voltage phase theta by time-integrating the angular frequency omega.

When the connection point voltage phase theta calculated by the controller 100 and the phase of the connection point voltage coincide with each other, the q component vsq of the connection point voltage is zero. On the other hand, when the interconnection point voltage phase theta and the interconnection point voltage phase do not match, the q component vsq of the interconnection point voltage becomes nonzero. Therefore, it becomes possible to detect the interconnection point voltage phase by the configuration of the phase calculator 1004 described above.

The interconnection point voltage phase theta is input to the cos table 1006 and the sin table 1007. The cos table 1006 and the sin table 1007 calculate cos and sin corresponding to the connection point voltage phase theta. The above-mentioned dq converter 1003 performs dq conversion of the interconnection point voltage α component vs_alp and the β component vs_bet using the calculated cos and sin.

The angular frequency omega output from the phase calculator 1004 is output to the isolated operation detector 1005 of the isolated operation detection unit 100e. The d component vsd and the q component vsq of the connection point voltage are output to the reactive power calculator 1070 of the reactive power control unit 100c.

Next, the DC voltage control unit 100b will be described.

The DC voltage control unit 100 b controls the DC voltage to adjust the amount of power from the solar panel 30. The DC voltage control unit 100 b includes a subtractor 1050 and a DC voltage controller 1051.

Subtractor 1050 calculates a difference by subtracting voltage command value Vdc_ref from DC voltage detection value vdc detected by DC voltage sensor 71PT, and outputs the difference to DC voltage controller 1051. The DC voltage controller 1051 is composed of a PI controller, performs PI operation on the difference between the DC voltage command value calculated by the subtractor 1050 and the DC voltage detection value, and uses the result as an effective current command value. It outputs to the subtractor 1013.

Next, the reactive power control unit 100c will be described.

The reactive power control unit 100c calculates a reactive current command value for causing the reactive power to follow the reactive power command value of the target value. Reactive power control unit 100 c includes reactive power calculator 1070, subtractor 1071, reactive power controller 1072, reactive current correction signal calculator 1073, and adder 1074.

Reactive power calculator 1070 outputs reactive power to power system 300 of power conversion device 1 based on interconnection point voltage vsd, vsq, and active current isd of output current and reactive current isq described later according to Equation 4. Is calculated, and the result is output to the subtractor 1071 as the reactive power calculation value Qfb.

Subtractor 1071 calculates a difference between predetermined reactive power command value Qref and Qfb output from reactive power calculator 1070, and outputs the difference to reactive power controller 1072.

The reactive power controller 1072 is configured of a PI controller, performs PI control calculation on the output of the subtractor 1071, and calculates a reactive current command value iqref of the power conversion device 1. Thereby, the reactive power from the power converter device 1 can be brought close to the target value.

The adder 1074 calculates the sum of the reactive current command value iqref and the reactive current correction signal del_iqref output from the reactive current correction signal calculator 1073 described later, and the sum is used as a new reactive current command value iqref2 for current control. It outputs to the subtractor 1014 of the part 100d.

Next, the current control unit 100d will be described.

The current control unit 100d corrects the output voltage based on the active current command value and the reactive current command value. The current control unit 100d includes a subtractor 1010, an α-β converter 1011, a dq converter 1012, a subtracter 1013, a subtractor 1014, a d-axis current controller 1015, a q-axis current controller 1016, an adder 1017, It includes an inverse dq converter 1018, a two-phase to three-phase converter 1019, a carrier wave calculator 1020, and a pulse width modulation (PWM) calculator 1021.

First, a method of calculating the d component isd and the q component isq of the output current will be described.

The subtractor 1010 calculates the v-phase component isv from the u-phase component isu and the w-phase component isw of the output current respectively detected by the output current sensors 72CTu and 72CTw. The α-β converter 1011 calculates the α component is_alp and the β component is_bet by α-β converting the u-phase component isu of the output current, the v-phase component isv, and the w-phase component isw. Note that this α-β conversion is equivalent to Equation 2, and thus redundant description will be omitted.

The dq converter 1012 performs dq conversion of the α component is_alp of the AC output current and the β component is_bet using cos output from the cos table 1006 and sin output from the sin table 1007. Then, the d component isd and the q component isq of the output current are calculated. Note that this dq conversion is equivalent to Equation 3, and therefore redundant description will be omitted. The d component isd of the output current is output to the subtractor 1013, and the q component isq of the output current is output to the subtractor 1014.

Subtractor 1013 calculates a deviation by subtracting d component isd of the output current from the effective current command value output from DC voltage controller 1051, and outputs the deviation to d-axis current controller 1015. The subtractor 1014 subtracts the q component isq of the output current from the reactive current command value iqref2 output from the adder 1074 to calculate a deviation, and outputs the deviation to the q-axis current controller 1016.

The d-axis current controller 1015 and the q-axis current controller 1016 are composed of PI controllers and perform PI control calculation on the input deviation to reduce the deviation by using the d-axis voltage command value of the inverter 10 and q Calculate the axis voltage command value.

The adder 1017 calculates a new d-axis voltage command value vdref by adding a predetermined fixed value Vd0 and the d-axis voltage command value output from the d-axis current controller 1015. Vd0 is a value at which the output voltage of the inverter 10 and the amplitude of the interconnection point voltage are equal when the amplitude of the interconnection point voltage is rated. By adding the d-axis voltage command value to Vd0, it is possible to prevent an excessive current from flowing from the power system 300 into the power conversion device 1 at the gate deblocking of the inverter 10.

The inverse dq converter 1018 includes the vdref output from the adder 1017, the q-axis voltage command value vqref output from the q-axis current controller 1016, the cos output from the cos table 1006, and the sin table 1007 And sin is output from vdref and vqref in accordance with Equation 5 to calculate voltage vectors valp and vbet of the fixed coordinate system.

The two-phase to three-phase converter 1019 converts valp and vbet output from the inverse dq converter 1018 into voltage command values vu_ref, vv_ref and vw_ref of each phase of the inverter 10 according to Equation 6, and performs PWM operation Output to the unit 1021.

Carrier wave calculator 1020 outputs carrier wave tri which is a triangular wave having a frequency equal to the switching frequency of inverter 10. The frequency of the carrier wave is, for example, several kHz.

The PWM computing unit 1021 compares the magnitudes of the carrier wave tri with the voltage command values vu_ref, vv_ref, vw_ref of each phase to calculate gate signals GateUP to WN, and outputs the gate signals GateUP to WN to the inverter 10.

The method of calculating the gate signals GateUP and GateUN will be described by taking the U phase as an example.

When the voltage command value vu_ref is equal to or higher than the carrier wave tri, the PWM computing unit 1021 turns on the gate signal GateUP of the IGBT module 10k and turns off the gate signal GateUN of the IGBT module 10n. Conversely, when voltage command value vu_ref is smaller than carrier wave tri, PWM operation unit 1021 turns off gate signal GateUP of IGBT module 10k and turns on gate signal GateUN of IGBT module 10n. As a result, a pulse voltage for setting the instantaneous average voltage to the voltage command value vu_ref is output to the AC output terminal U of the inverter 10. The PWM computing unit 1021 similarly calculates gate signals for the V-phase and the W-phase, and therefore redundant description will be omitted.

When the isolated operation detection state ISLANDING_FLG output from the isolated operation detector 1005 is 1, the PWM computing unit 1021 does not depend on the magnitude relationship between each of the voltage command values vu_ref, vv_ref, vw_ref and the carrier wave tri, and all gates Turn off the signal. Thereby, when the isolated operation is detected, the PWM computing unit 1021 can stop the switching of the inverter 10 promptly and can avoid the isolated operation state.

Next, the isolated operation control unit 100e will be described.

The isolated operation control unit 100e detects an isolated operation of the power conversion device 1 based on the angular frequency omega of the connection point voltage, and stops the isolated operation of the power conversion device 1 when the isolated operation is detected. The isolated operation control unit 100e includes an isolated operation detector 1005 and a contactor control signal calculator 1008.

The islanding operation detector 1005 receives the angular frequency omega output from the phase calculator 1004, and calculates the islanding detection state ISLANDING_FLG. The islanding operation detector 1005 sets the value of ISLANDING_FLG to 1 when islanding is detected, and sets the value of ISLANDING_FLG to 0 at normal interconnection.

The contactor control signal calculator 1008 turns on the contactor control signal CTTctl when ISLANDING_FLG is 0, and turns off CTTctl when ISLANDING_FLG is 1. The contactor 40 is input when CTT ctl is on and released when CTT ctl is off. Thereby, when an isolated operation is detected, the isolated operation control unit 100e opens the contactor 40 in addition to the gate block of the PWM computing unit 1021, and disconnects the power conversion device 1 from the power system 300 in a power failure. be able to.

FIG. 6 shows the configuration of the isolated operation detector 1005.

The islanding operation detector 1005 includes low pass filters 10051, 10052, a subtractor 10053, and a comparator 10054.

The angular frequency omega of the connection point voltage is input to the low pass filters 10051 and 10052 having different time constants. The time constant τ1 of the low pass filter 10051 is a value shorter than the time constant τ2 of the low pass filter 10052. The subtractor 10053 subtracts the output of the low pass filter 10052 from the output of the low pass filter 10051. The low pass filters 10051 and 10052 and the subtractor 10053 constitute a band pass filter, and output BPF_omeg. Thereby, the direct current component and the high frequency component of the omega fluctuation can be removed. This high frequency component is a harmonic based on the PWM signal of the inverter 10 and is sufficiently higher than the frequency of the reactive current correction signal. Malfunction can be prevented by removing high frequency components.

The comparator 10054 compares the BPF_omeg output from the band pass filter with each of the upper limit determination value TH_H and the lower limit determination value TH_L. When BPF_omeg is equal to or greater than TH_H, or BPF_omeg is equal to or less than TH_L, the comparator 10054 outputs 1 as the isolated operation detection state ISLANDING_FLG.

By this calculation, the islanding operation detector 1005 sets ISLANDING_FLG to 1 when the angular frequency omega changes more than a predetermined value. When a phase jump or a sudden phase change of the connection point voltage occurs, the band pass filter output BPF_omeg largely fluctuates, so ISLANDING_FLG can be set to 1, and an islanding operation can be avoided.

Next, the reactive current correction signal calculator 1073 in the reactive power control unit 100c will be described.

The reactive current correction signal calculator 1073 generates a reactive current correction signal del_iqref. The reactive current command value iqref which is the output of the reactive power controller 1072 is added to the reactive current correction signal del_iqref by the adder 1074, and the sum is output to the current control unit 100d as a new reactive current command value iqref2.

The reactive current correction signal del_iqref is a rectangular wave having a predetermined correction signal period Tperiod. The correction signal cycle Tperiod is set to be equal to or less than twice the detection upper limit time which is the upper limit of the time required from the occurrence of the islanding operation state to the detection. The detection upper limit time is, for example, 0.1 s defined by the grid connection rule. In this case, the correction signal period Tperiod is 0.2 s or less. The waveform of the reactive current correction signal del_iqref is not limited to this shape, and may be pulse or step.

Since the difference between the q component isq of the output current and the reactive current command value iqref2 becomes large at the rising or falling of the rectangular wave of the reactive current correction signal del_iqref, the q-axis current controller 1016 determines the q-axis voltage command value vqred Make a sudden change. By making the reactive current correction signal del_iqref into a rectangular wave of period Tperiod, the output voltage of the inverter 10 can be changed stepwise every half time period of T period.

FIG. 7 shows an example of an output voltage vector of the inverter 10.

This figure shows the interconnection point voltage vector vs and the output voltage vector vind of the inverter 10. When the q-axis voltage command value suddenly changes, the q component of the output voltage vector vinv changes, and the phase difference Δθ with the connection point voltage changes.

When the power system 300 is normal and the circuit breaker 400 is turned on, the interconnection point voltage is determined by the voltage of the power system 300. Therefore, even if the power converter 1 changes the output voltage vector phase of the inverter 10 by the reactive current correction signal, almost no phase change of the connection point voltage occurs. As a result, in the non-islanding state, the addition of the reactive current correction signal to the reactive current command value has almost no influence. On the other hand, in the isolated operation state in which circuit breaker 400 is opened, there is no element for stabilizing the connection point voltage phase, so the phase change of the output voltage of inverter 10 is the secondary side of circuit breaker 400 (power converter 1 Side, and the q-axis voltage command value periodically and rapidly changes based on the reactive current correction signal, so that the isolated operation can be detected quickly.

FIG. 8 is a time chart showing an operation of islanding detection.

This time chart includes the waveforms of reactive current correction signal del_iqref and reactive current command value iqref2, the waveform of interconnection point voltage phase theta, the waveform of angular frequency band pass filter output BPF_omeg, and the waveform of islanding detection state ISLANDING_FLG The waveform of the contactor control signal CTTctl is shown. Here, the waveform of the reactive current correction signal del_iqref is represented by a broken line, and the waveform of the reactive current command value iqref2 after correction is represented by a solid line.

The reactive current correction signal del_iqref is a rectangular wave having a correction signal period Tperiod, and changes its value stepwise at time t1, t2, t4 for each half period. The current control unit 100 d changes the voltage command value of the inverter 10 so as to follow the reactive current command value iqref 2, so the reactive current and reactive power output from the power conversion device 1 change.

When the reactive current command value iqref2 is changed into a rectangular wave by del_iqref, the reactive current output from the inverter 10 substantially matches iqref2 although the delay of the current control system remains as an error. On the other hand, the reactive power controller 1072 changes the reactive current command value iqref so that the reactive power output from the power conversion device 1 matches the reactive power command value Qref. Since the reactive power controller 1072 responds by regarding the reactive current correction signal del_iqref as a disturbance, the reactive current command value iqref also fluctuates in the same cycle as the reactive current correction signal del_iqref.

Therefore, the waveform of the reactive current command value iqref2 after correction is slightly different from the waveform of the reactive current correction signal del_iqref. The waveform of the reactive current output from the inverter 10 according to the reactive current command value iqref2 is not a rectangular wave itself of the reactive current correction signal del_iqref but a substantially rectangular wave due to the delay of the response of the current control unit 100d. Thus, the periodic phase change of the output voltage of inverter 10 based on reactive current command value iqref2 is compared to the phase change of voltage of power system 300 (the voltage at the connection point when the power conversion device is not in the isolated operation state). It becomes steep. In other words, the output voltage of inverter 10 based on reactive current command value iqref 2 includes a component of a higher frequency than the voltage of power system 300.

It is assumed that circuit breaker 400 is opened due to an accident or the like of power system 300 at time t3. Here, it is assumed that the load 200 and the power output from the power conversion device 1 completely match. In this case, as shown in the waveform of the connection point voltage phase theta, no deviation occurs in the connection point voltage phase theta.

At time t4, which is the first change point of the reactive current correction signal del_iqref after time t3, a change occurs in the interconnection point voltage phase theta due to a change in the reactive current correction signal del_iqref, and a change occurs in the angular frequency, The BPF_omeg also changes. Here, BPF_omeg becomes equal to or less than the lower limit judgment value TH_L, and the islanding operation detector 1005 detects an islanding state. When the islanding operation detector 1005 detects the islanding state, the islanding detection state ISLANDING_FLG changes from 0 to 1, all the gate signals of the inverter 10 are turned off, and the contactor control signal CTTctl changes from on to off.

Since the BPF_omeg can generate a large fluctuation by periodically and rapidly changing the reactive current command value, it is possible to reliably detect an isolated operation. It is also possible to generate a change in angular frequency by changing the reactive power command value, but the control response of reactive power controller 1072 having a current control system in the minor loop is slower than the response of current control unit 100d. As the correction signal calculator 1073 changes the reactive current command value, it is possible to cause the BPF_omeg fluctuation to be larger than changing the reactive power command value.

By setting the correction signal cycle Tperiod to be twice or less of the upper limit time, the reactive current correction signal suddenly changes every time the upper limit time or less. That is, the timing at which the reactive current command value suddenly changes can always be received within the upper limit time from the occurrence of the isolated operation state. As a result, the time required to detect the islanding state becomes equal to or less than the upper limit time, and the grid connection regulation can be satisfied.

According to the present embodiment, even if the output power of the power conversion device 1 matches the power consumption of the load 200 connected in parallel to the power conversion device 1 when the power conversion device 1 generates an isolated operation state, It is possible to detect the islanding state reliably and promptly, stop the power generation of the power conversion device 1, and disconnect from the power system 300.

Hereinafter, the modification of a present Example is demonstrated.

FIG. 9 shows the configuration of the power conversion device of the first modification.

The power conversion device 1 of the first modification is a power conversion device for a storage system. A storage battery 31 is connected to the DC circuit of the power conversion device for a storage system. The power conversion device for a storage system exhibits the same effect as the above-described power conversion device 1 for solar power generation.

FIG. 10 shows the configuration of the power conversion device of the second modification.

The power converter 1 of the second modification is a power converter for a wind power generation system. A wind power generation system is connected to the DC circuit of the power conversion device for wind power generation system. The wind power generation system obtains rotational torque by receiving wind by the blades 32, and transmits the rotational torque to the rotor of the permanent magnet generator 34 via the shaft 33, and the stator winding of the permanent magnet generator 34. The induced voltage generated in the line is rectified by the diode rectifier 35 to obtain DC power. The power conversion device for a wind power generation system exhibits the same effect as the power conversion device 1 for solar power generation described above. The diode rectifier 35 for rectifying the power of the permanent magnet generator 34 may be a self-excitation converter.

According to this embodiment, a steep phase change at the interconnection point can be generated only at the time of isolated operation without generating at the time of grid connection, and the isolated operation can be detected at an early stage. Also, by setting the change cycle of the reactive current command value to within 0.2 s, it becomes possible to detect an isolated operation within 0.1 s.

The power conversion device of the present embodiment changes the amplitude of the reactive current correction signal in accordance with the active current output from the power conversion device. By this operation, it is possible to limit the amount of change of the reactive current in a state where the effective current is small, and to suppress the efficiency reduction of the power conversion device due to the excessive reactive current. Here, when the effective current is small and matches the consumed effective current of the load, it means that the capacity of the load is small (light load). When the effective current is small, the imbalance ratio of the reactive current becomes large even with a small change of the reactive current, and the phase change of the interconnection point voltage can be made large. Therefore, it is possible to achieve both the detection of the islanding state and the suppression of the efficiency decrease of the power converter at all times.

FIG. 11 shows the configuration of the power conversion device 2 of the second embodiment.

Compared to the power conversion device 1 of the first embodiment, the power conversion device 2 of the present embodiment has a controller 101 instead of the controller 100. In the present embodiment, the same parts as those of the first embodiment are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 12 shows the configuration of the controller 100 of the second embodiment.

Compared to the controller 100, the controller 101 has a reactive power control unit 101c instead of the reactive power control unit 100c. Reactive power control unit 101 c adjusts reactive current correction signal del_iqref in accordance with the effective current command value output from DC voltage controller 1051. The reactive power control unit 101 c has a multiplier 1076, an upper / lower limiter 1077, and a multiplier 1078 in addition to the elements of the reactive power control unit 100 c.

The multiplier 1076 multiplies the effective current command value by a predetermined gain. The upper and lower limit limiter 1077 has an upper limit of 1.0 and limits the output of the multiplier 1076 with the ratio of the reactive current command value necessary for detecting the no-load single running state as the lower limit.

FIG. 13 shows the input / output characteristics of the upper and lower limit limiter 1077.

This figure shows the relationship between the direct current command value and the output of the upper / lower limiter 1077. The output of the upper and lower limit limiter 1077 has a characteristic of monotonically increasing with respect to the direct current command value, and limits the output to a range between a lower limit value and an upper limit value set in advance. As a result, even if the load is reduced, the reactive current command value can maintain the minimum amplitude. Further, even when the ratio of reactive power to active power is limited, reactive power can be suppressed.

The multiplier 1078 multiplies the output of the reactive current correction signal calculator 1073 by the upper / lower limiter 1077 to calculate the reactive current correction signal del_iqref.

In this embodiment, by using the output of the multiplier 1078 as a reactive current correction signal, it is possible to output a reactive current correction signal according to the active current. Thereby, since the reactive current at the time of light load of the power conversion device 2 can be reduced, it is possible to suppress the efficiency decrease due to reactive current output, and it is possible to output the reactive current necessary for the islanding state detection.

According to this embodiment, even when the power conversion device 2 generates an isolated operation state, the output power from the power conversion device 2 and the power consumption of the load 200 connected in parallel to the power conversion device 2 match. Thus, it becomes possible to detect the islanding state reliably and promptly, to stop the output of the power conversion device 2, and to disconnect the power system 300.

Furthermore, by limiting the range of the reactive current correction signal and making the reactive current correction signal a monotonically increasing characteristic with respect to the active current command value, the loss due to the light load reactive current output of the power conversion device 2 is reduced. It is possible to suppress the decrease in efficiency.

Although the example which applied the power converter device 2 to the inverter for solar power generation was demonstrated in the present Example, it is the same even if it applies to the inverter for electrical storage systems and the inverter for wind power generation similarly to the modification of Example 1. Play an effect.

The terms in one embodiment of the present invention will be described. The DC voltage detection unit corresponds to the DC voltage sensor 71PT or the like. The output current detection unit corresponds to the output current sensors 72CTu, 72CTw, and the like. The interconnection point voltage detection unit corresponds to the interconnection point voltage sensors 70PTuv, 70PTvw, and the like. The phase calculation unit corresponds to the connection point voltage phase detection unit 100 a and the like. The direct current command value calculation unit corresponds to the direct current voltage control unit 100b and the like. The reactive current command value calculation unit corresponds to the reactive power control unit 100c and the like. The control unit corresponds to the current control unit 100d and the like. The isolated operation detection unit corresponds to the isolated operation control unit 100e and the like. The basic reactive current command value corresponds to the reactive current command value iqref or the like. The correction command value corresponds to the reactive current correction signal del_iqref or the like. The reactive current command value corresponds to iqref 2 or the like.

The present invention is not limited to the embodiments described above, and can be modified in other various forms without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Power converter, 10 ... Inverter, 10k, 10l, 10m, 10n, 10o, 10p ... IGBT module, 10C ... Capacitor, 20 ... Harmonic filter, 20L1, 20L2 ... Reactor, 20C ... Capacitor, 30 ... Solar panel , 31: storage battery, 32: blade, 33: shaft, 34: permanent magnet generator, 35: diode rectifier, 40: contactor, 70PTuv, 70PTvw: interconnection point voltage sensor, 71PT: DC voltage sensor, 72CTu, 72CTw: output Current sensor, 100, 101 ... controller, 200 ... load, 300 ... power system, 400 ... circuit breaker

Claims

An inverter that converts direct current into alternating current and outputs it to the power system;
A DC voltage detection unit that detects a DC voltage input to the inverter;
An output current detection unit that detects an output current from the inverter;
An interconnection point voltage detection unit that detects an interconnection point voltage at an interconnection point between the inverter and the power system;
A phase calculation unit that calculates an interconnection point voltage phase based on the interconnection point voltage;
An active current command value calculation unit that calculates an active current command value indicating an active current to be output to the inverter based on the DC voltage;
A reactive current command value calculation unit that calculates a reactive current command value indicating a reactive current to be output to the inverter based on the output current and the interconnection point voltage;
By controlling the inverter based on the output current, the connection point voltage phase, the effective current command value, and the reactive current command value, the phase of the output voltage of the inverter is determined at predetermined time intervals. A control unit to change
An isolated operation detection unit that detects an isolated operation state of the power conversion device based on a change in the connection point voltage phase;
Power converter comprising:
The phase change of the output voltage generated at each time interval is sharper than the phase change of the voltage in the power system.
The power converter device according to claim 1.
The time interval is equal to or less than an upper limit time predetermined as an upper limit of time from occurrence of the islanding state to detection.
The power converter device according to claim 2.
The reactive current output from the inverter periodically changes with a period of twice the time interval,
The power converter device according to claim 3.
The reactive current command value calculation unit calculates, based on the output current and the interconnection point voltage phase, a basic reactive current command value indicating reactive current by control to bring reactive power from the power conversion device closer to a target value. Calculating the reactive current command value by calculating a correction command value that changes at the time interval, and adding the correction command value to the basic reactive current command value;
The power converter device according to claim 4.
The waveform of the correction command value is a rectangular wave having a cycle of twice the time interval,
The power converter device according to claim 5.
The change in the phase of the output voltage of the inverter changes in accordance with the active current output from the inverter.
The power converter device according to any one of claims 1 to 6.
The reactive current command value calculation unit increases the correction command value according to an increase of the active current command value.
The power converter device according to claim 5 or 6.
A control method of a power conversion device including an inverter which converts direct current into alternating current and outputs it to a power system,
Detecting a DC voltage input to the inverter;
Detecting the output current from the inverter,
Detecting an interconnection point voltage at an interconnection point between the inverter and the power system;
The interconnection point voltage phase is calculated based on the interconnection point voltage,
Based on the DC voltage, an active current command value indicating an active current to be output to the inverter is calculated;
A reactive current command value indicating a reactive current to be output to the inverter is calculated based on the connection point voltage and the output current,
By controlling the inverter based on the output current, the connection point voltage phase, the effective current command value, and the reactive current command value, the phase of the output voltage of the inverter is determined at predetermined time intervals. Change,
Detecting the islanding state of the power conversion device based on a change in the connection point voltage phase.