JP6110093B2 - Inverter device and control method - Google Patents

Description

The present invention, inverter device, and a control method.

  2. Description of the Related Art Conventionally, a grid-connected inverter system has been developed that converts DC power generated by a solar cell or the like into AC power and supplies it to an electric power system.

  FIG. 9 is a block diagram for explaining a conventional general grid-connected inverter system.

The grid interconnection inverter system A100 converts the DC power generated by the DC power source 1 into AC power and supplies it to the power system B. The inverter circuit 2 converts a DC voltage input from the DC power supply 1 into an AC voltage by switching a switching element (not shown) based on the PWM signal input from the control circuit 300. The control circuit 300 generates and outputs a PWM signal for controlling the inverter circuit 2. The control circuit 300 controls the direct current voltage input from the direct current power source 1 to the inverter circuit 2 to be a predetermined voltage. That is, the DC voltage control unit 31 performs feedback control so that the DC voltage e detected by the DC voltage sensor 6 matches the target value e ^* . The control circuit 300 controls the current output from the inverter circuit 2 to be a predetermined current. That is, the current control unit 38 performs feedback control so that the current i detected by the current sensor 4 matches the target value. As the target value, a compensation value output from the DC voltage control unit 31 is used.

  When an instantaneous voltage drop (hereinafter referred to as “instantaneous drop”) occurs in the power system B, the output current of the inverter circuit 2 is increased due to an increase in voltage difference or phase difference between the system voltage and the output voltage of the inverter circuit 2. Soars. When the output current exceeds a predetermined current value, it is determined as an overcurrent by the protection mechanism, and the operation of the inverter circuit 2 is stopped. In the grid-connected inverter system A100, maximum power point tracking (MPPT) control is performed using the power-voltage characteristic of the DC power supply 1 (see FIG. 2). The MPPT control is to control the output voltage so that the output power is maximized. Since MPPT control is performed even if the system voltage is reduced due to the instantaneous drop, the input power of the inverter circuit 2 is not reduced, and the output current in the case of the inverter circuit 2 is increased. Also in this case, when the output current exceeds a predetermined current value, it is determined that the current is an overcurrent, and the operation of the inverter circuit 2 is stopped.

  When the inverter circuit 2 is stopped and the grid-connected inverter system A100 is disconnected from the power grid B, the power supplied to the power grid B is reduced, so that another distributed power source linked to the power grid B May also cause discontinuation. In order to prevent this, a method for suppressing the occurrence of overcurrent has been developed. For example, there is a method of performing pulse-by-pulse overcurrent control when the output current of the inverter circuit 2 exceeds a predetermined value, and limiting the output current of the DC power supply 1 according to the system voltage (see Patent Document 1). There is also a method of increasing the control gain of the current control unit 38 to speed up the current control and suppressing the increase in output current.

JP 2008-228494 A

  When overcurrent is suppressed by pulse-by-pulse overcurrent control or speeding up of current control, the output current of the inverter circuit 2 is suppressed, so the output power Pout of the inverter circuit 2 is reduced. Then, since the output voltage of the DC power supply 1 increases and the output power decreases (see FIG. 2), the input power Pin of the inverter circuit 2 decreases and becomes balanced with the output power Pout. Also, when the output current of the DC power source 1 is limited according to the system voltage, the input power Pin is reduced to balance the output power Pout.

  Thereafter, when the system voltage recovers from the instantaneous drop, the output power Pout is recovered. However, if the recovery of the output power Pout is delayed, the power supplied to the power system B may not be recovered, and there may be a case where other distributed power sources connected to the power system B are disconnected. In order to avoid this, a requirement for defining the voltage drop tolerance of the grid-connected inverter system A100 is beginning to be defined worldwide as a FRT (Fault Ride Through) requirement. Currently, the FRT requirement in Japan is a provisional requirement, but it is stipulated that the output is recovered to 80% or more before the voltage drop within 0.1 second after the voltage is restored.

When the system voltage recovers after recovering from the instantaneous drop, the output voltage of the DC power source 1 decreases and the output power increases as the output power Pout increases (see FIG. 2), so the input power Pin increases. The output power Pout is balanced. However, since the DC voltage control unit 31 performs the control even during the momentary drop and the target value of the current changes, the output current of the inverter circuit 2 changes. When the output current is smaller than the output current before the voltage drop when recovering from the voltage drop, the output power Pout becomes smaller than that before the voltage drop. In this case, when the input power Pin is increased by the MPPT control, the output power Pout is increased and returns to the level before the instantaneous drop. However, since the MPPT control searches for the maximum power point by increasing / decreasing the DC voltage target value e ^* , it takes time to increase the input power Pin. Therefore, 0.1 seconds may elapse until the output power Pout reaches 80% before the instantaneous drop, and the FRT requirement cannot be satisfied.

  On the other hand, when the output current of the inverter circuit 2 is larger than the output current before the voltage drop when recovering from the voltage drop, the output power Pout becomes larger than that before the voltage drop. However, since the input power Pin does not become larger than before the instantaneous drop, the input power Pin may be insufficient and the inverter circuit 2 may be stopped.

  The present invention has been conceived under the circumstances described above, and is a control circuit for an inverter circuit capable of quickly returning the output power Pout to the level before the voltage drop when recovering from the voltage drop. The purpose is to provide.

  In order to solve the above problems, the present invention takes the following technical means.

An inverter device provided by the first aspect of the present invention includes an inverter circuit that is directly input with DC power output from a solar cell, converts the DC power into AC power, and supplies the AC power to a power system, and a control circuit that controls the inverter circuit The control circuit includes a DC voltage control means for generating a DC voltage compensation value for controlling an input voltage of the inverter circuit, and an output current of the inverter circuit. Current control means for generating a current compensation value, and switching means for switching between a first state using the DC voltage compensation value and a second state using a fixed value as a current target value of the current control means. wherein the switching means, when the instantaneous voltage drop in the power system occurs, the switching from the first state to the second state, the DC voltage control means Wherein in the second state, characterized in that it does not perform the control of the input voltage of the inverter circuit.

 The inverter device provided by the second aspect of the present invention includes a DC / DC converter circuit that steps up and down a DC voltage output from a solar cell, and converts DC power output from the DC / DC converter circuit into AC power. An inverter circuit for supplying power to the power system and a control circuit for controlling the inverter circuit, the control circuit having a DC voltage compensation value for controlling an input voltage of the inverter circuit. DC voltage control means for generating, current control means for generating a current compensation value for controlling the output current of the inverter circuit, and a first target that uses the DC voltage compensation value as a current target value of the current control means. Switching means for switching between a state and a second state using a fixed value, wherein the switching means causes an instantaneous voltage drop in the power system. The control circuit switches from the first state to the second state, and the control circuit fixes the step-up ratio of the DC / DC converter circuit while being switched to the second state by the switching means. It is characterized by that.

  In a preferred embodiment of the present invention, the switching means sets the first state by outputting the DC voltage compensation value input from the DC voltage control means as the current target value to the current control means. The fixed state is output to the current control means as the current target value to achieve the second state.

  In a preferred embodiment of the present invention, the switching means sets the first state by outputting a deviation between the input voltage of the inverter circuit and its target value to the DC voltage control means, and sets zero to the DC The second state is obtained by outputting the voltage to the voltage control means.

  In a preferred embodiment of the present invention, the fixed value is the DC voltage compensation value when the first state is switched to the second state.

  In a preferred embodiment of the present invention, the switching means switches from the second state to the first state after recovering from an instantaneous voltage drop.

  In a preferred embodiment of the present invention, the switching means switches from the second state to the first state when the input voltage of the inverter circuit becomes a predetermined value or less.

  In a preferred embodiment of the present invention, the switching means switches from the second state to the first state after a predetermined time has elapsed since the recovery from the instantaneous voltage drop.

A control method provided by the third aspect of the present invention is a control method for controlling an inverter circuit that is directly inputted with direct-current power output from a solar cell, converted into alternating-current power, and supplied to an electric power system. Generated in the first step of generating a DC voltage compensation value for controlling the input voltage of the inverter circuit, the second step of detecting that an instantaneous voltage drop has occurred in the power system, and the second step In the first state until it is detected that the current has been detected, a current compensation value is generated using the DC voltage compensation value as a current target value, and the second state after the occurrence of the current in the second step is detected . And a third step of generating the current compensation value using a fixed value instead of the DC voltage compensation value as the current target value, and in the second state, the input voltage of the inverter circuit that does not control And butterflies.

  According to the present invention, in the first state, since the output current is controlled using the DC voltage compensation value as the current target value, the output current changes according to the input voltage of the inverter circuit. On the other hand, in the second state, the output current is controlled using the fixed value as the current target value, so that the output current is kept constant. If it is in the second state at the time of recovery from the instantaneous drop, the output current does not change and the output voltage increases, so that the output power can be increased immediately. In addition, when a voltage drop occurs, the first state is switched to the second state, and the DC voltage compensation value at this time is used as a fixed value. Can be restored to high speed.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

It is a figure for demonstrating the grid connection inverter system provided with the control circuit which concerns on 1st Embodiment. It is a figure for demonstrating the electric power-voltage characteristic of a solar cell. It is a functional block diagram for demonstrating the internal structure of the control circuit which concerns on 1st Embodiment. It is a flowchart for demonstrating the switching process which a switching part performs. It is a time chart for demonstrating the state of the input electric power of an inverter circuit when an instantaneous drop generate | occur | produces, and the state of output electric power. It is a functional block diagram for demonstrating the internal structure of the control circuit which concerns on 2nd Embodiment. It is a figure for demonstrating the grid connection inverter system which concerns on 3rd Embodiment. It is a functional block diagram for demonstrating the internal structure of the control circuit of the DC / DC converter circuit which concerns on 3rd Embodiment. It is a block diagram for demonstrating the conventional general grid connection inverter system.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings, taking as an example the case where a control circuit according to the present invention is used in a grid-connected inverter system.

  FIG. 1 is a diagram for explaining a grid-connected inverter system including a control circuit according to the first embodiment.

  The grid-connected inverter system A is a distributed power source, and includes a DC power source 1, an inverter circuit 2, a control circuit 3, a current sensor 4, a voltage sensor 5, and a DC voltage sensor 6. The grid interconnection inverter system A is linked to the three-phase power grid B. Hereinafter, the three phases are referred to as a U phase, a V phase, and a W phase. The grid interconnection inverter system A converts the DC power output from the DC power source 1 into AC power by the inverter circuit 2 and supplies it to a load (not shown). The load is also supplied with power from the power system B. The grid interconnection inverter system A is a system with a reverse power flow, and supplies AC power to the power system B. Although not shown, a transformer for boosting (or stepping down) the AC voltage is provided on the output side of the inverter circuit 2. A combination of the inverter circuit 2, the control circuit 3, the current sensor 4, the voltage sensor 5, and the DC voltage sensor 6 is an inverter device, which is called a so-called power conditioner.

  The power system B is provided with a voltage sag detector C, detects that a power sag has occurred in the power system B, and outputs a detection signal to the control circuit 3. Note that the grid interconnection inverter system A may include a voltage sag detector C.

  The DC power supply 1 outputs DC power and includes a solar battery. A solar cell generates direct-current power by converting solar energy into electrical energy. The DC power source 1 outputs the generated DC power to the inverter circuit 2.

  FIG. 2 is a diagram for explaining the power-voltage characteristics of the solar cell.

  In the figure, the horizontal axis represents the output voltage of the solar cell, and the vertical axis represents the output power of the solar cell. As shown in the figure, the output power of the solar cell becomes the maximum output Pmax at the maximum output operating voltage Vpm. When the output voltage is equal to or lower than the voltage Vpm, the output power increases as the output voltage increases, and the output power decreases as the output voltage decreases. On the other hand, when the output voltage is equal to or higher than the voltage Vpm, the output power decreases as the output voltage increases, and the output power increases as the output voltage decreases. The open circuit voltage Voc is a voltage at which the output power becomes zero, and the output voltage of the solar cell does not become larger than the open circuit voltage Voc. The power-voltage characteristics of the DC power supply 1 are also similar.

  Returning to FIG. 1, the inverter circuit 2 converts DC power input from the DC power source 1 into AC power and outputs the AC power. The inverter circuit 2 includes a PWM control inverter and a filter (not shown). The PWM control inverter is a three-phase inverter provided with three sets of six switching elements (not shown). Based on the PWM signal input from the control circuit 3, each switching element is switched on and off to generate DC power. Convert to AC power. The filter removes high frequency components due to switching. Since the positive and negative electrodes on the input side of the inverter circuit 2 are respectively connected to the positive and negative electrodes of the DC power supply 1, the input voltage of the inverter circuit 2 matches the output voltage of the DC power supply 1.

The current sensor 4 detects an instantaneous value of the three-phase output current of the inverter circuit 2. The current sensor 4 converts the detected instantaneous value into a digital signal, and controls the control circuit 3 as current signals i _u , i _v , i _w (the three current signals may be collectively described as “current signal i”). Output to. The voltage sensor 5 detects an instantaneous value of the three-phase output voltage of the inverter circuit 2. The voltage sensor 5 converts the detected instantaneous value into a digital signal and outputs it as a voltage signal v _u , v _v , v _w (the three voltage signals may be collectively described as “voltage signal v”). Output to.

  The DC voltage sensor 6 detects an instantaneous value of the input voltage of the inverter circuit 2 (that is, the output voltage of the DC power supply 1). The DC voltage sensor 6 digitally converts the detected instantaneous value and outputs it to the control circuit 3 as a DC voltage signal e. The DC voltage sensor 6 detects a voltage between terminals of an electrolytic capacitor (not shown) provided between a positive electrode and a negative electrode on the input side of the inverter circuit 2. While the DC voltage control is being performed, the DC voltage is controlled to a constant voltage, and the power stored in the electrolytic capacitor is also constant. Therefore, the power input to the inverter circuit 2 is the power output from the DC power supply 1. Matches.

  The control circuit 3 controls the inverter circuit 2 and is realized by, for example, a microcomputer. The control circuit 3 generates a PWM signal based on the current signal i input from the current sensor 4, the voltage signal v input from the voltage sensor 5, and the DC voltage signal e input from the DC voltage sensor 6. To the inverter circuit 2.

  FIG. 3 is a functional block diagram for explaining the internal configuration of the control circuit 3.

  The control circuit 3 includes a DC voltage control unit 31, a switching unit 32, a reactive power calculation unit 34, a reactive power control unit 35, a switching unit 36, a current control unit 38, and a PWM signal generation unit 39. Although not shown, the control circuit 3 includes an overvoltage detection unit that detects an overvoltage based on the DC voltage signal e input from the DC voltage sensor 6, and an overcurrent based on the current signal i input from the current sensor 4. Is provided with an overcurrent detection unit. When an overvoltage or overcurrent is detected, the generation of the PWM signal by the PWM signal generation unit 39 is stopped, and the connection between the grid-connected inverter system A and the power grid B is cut off. The inverter system A is disconnected from the power system B.

The DC voltage control unit 31 is for controlling the input voltage of the inverter circuit 2. The DC voltage control unit 31 receives a deviation Δe (= e ^* −e) between the DC voltage signal e output from the DC voltage sensor 6 and the DC voltage target value e ^*, and makes the deviation zero. The DC voltage compensation value is output to the switching unit 32. The DC voltage control unit 31 performs, for example, PI control (proportional integration control).

In the grid-connected inverter system A, MPPT control is performed using the power-voltage characteristic of the DC power supply 1 (see FIG. 2). In the present embodiment, the direct current voltage target value e ^* is slightly changed to perform direct current voltage control, thereby changing the output voltage of the direct current power source 1 so that the output power of the direct current power source 1 becomes larger. Change e ^* . As a result, the DC voltage target value e ^* becomes the maximum output operating voltage Vpm, and the power output from the DC power supply 1 is maximized.

The switching unit 32 switches the d-axis current target value used by the current control unit 38. As will be described later, the current control unit 38 performs control by converting the current signals i _u , i _v , and i _w into a d-axis current signal i _d and a q-axis current signal i _q . d-axis current target value is used as a target value of d-axis current signal i _d. The switching unit 32 switches between the DC voltage compensation value and the fixed value input from the DC voltage control unit 31 and outputs them to the current control unit 38 as a d-axis current target value. The state in which the switching unit 32 outputs the DC voltage compensation value as the d-axis current target value is referred to as a “first state”. The state in which the switching unit 32 outputs the fixed value as the d-axis current target value is referred to as a “second state”.

  The switching unit 32 includes a recording unit 33 for recording the DC voltage compensation value input from the DC voltage control unit 31. In the first state, the switching unit 32 overwrites and records the input DC voltage compensation value in the recording unit 33 and outputs the overwritten DC voltage compensation value. As a result, the DC voltage compensation value input from the DC voltage control unit 31 is output to the current control unit 38 as the d-axis current target value. On the other hand, in the second state, the switching unit 32 outputs the DC voltage compensation value recorded in the recording unit 33 without overwriting the input DC voltage compensation value in the recording unit 33. As a result, the fixed value is output to the current control unit 38 as the d-axis current target value.

  The switching unit 32 switches between the first state and the second state based on the voltage drop detection signal input from the voltage drop detection device C and the DC voltage signal e input from the DC voltage sensor 6. The switching unit 32 continues the first state until the instantaneous drop occurs, and switches from the first state to the second state when the instantaneous drop occurs. In this embodiment, the voltage sag detection signal is a pulse signal that switches from a low level to a high level when a voltage sag occurs in the power system B and switches from a high level to a low level when the power system B recovers from the voltage sag. Therefore, the switching unit 32 switches from the first state to the second state when the instantaneous drop detection signal is switched from the low level to the high level. Further, the switching unit 32 switches from the second state to the first state when recovering from the instantaneous drop and the output voltage of the DC power supply 1 returns to the level immediately before the occurrence of the instantaneous drop. That is, the switching unit 32 switches from the second state to the first state when the value of the DC voltage signal e becomes equal to or less than the threshold value after the instantaneous drop detection signal is switched from the high level to the low level. In the present embodiment, the threshold value is set to a value obtained by adding a detection error to the DC voltage target value immediately before the occurrence of the instantaneous drop.

  FIG. 4 is a flowchart for explaining the switching process performed by the switching unit 32. The switching process is always executed while the inverter circuit 2 performs the power conversion operation, that is, while the control circuit 3 outputs the PWM signal.

  First, it is determined whether or not an instantaneous drop has occurred (S1). Specifically, it is determined whether or not the voltage sag detection signal input from the voltage sag detector C is switched from a low level to a high level. When the instantaneous drop does not occur (S1: NO), the DC voltage compensation value is input from the DC voltage control unit 31 (S2), and is overwritten and recorded in the recording unit 33 (S3). Then, the overwritten DC voltage compensation value is output to the current control unit 38 (S4), and the process returns to step S1. That is, the output of the DC voltage compensation value (S2 to S4) input from the DC voltage control unit 31 is continued until the instantaneous drop occurs (S1: YES) (first state).

  In step S1, if a voltage drop occurs (S1: YES), that is, if the voltage drop detection signal is switched from a low level to a high level, it is determined whether the voltage drop continues (S5). Specifically, it is determined whether or not the instantaneous drop detection signal is at a high level. When the voltage drop continues (S5: YES), the DC voltage compensation value recorded in the recording unit 33 is output to the current control unit 38 (S6), and the process returns to step S5. In step S5, when recovering from the instantaneous drop (S5: NO), it is determined whether or not the value of the DC voltage signal e input from the DC voltage sensor 6 is equal to or less than a threshold value (S7). If it is equal to or less than the threshold (S7: YES), that is, if the level returns to the level before the voltage drop, the process proceeds to step S2 and returns to the first state. On the other hand, when it is larger than the threshold (S7: NO), that is, when the level has not yet returned to the level before the instantaneous drop, the process proceeds to step S6 and returns to step S5. That is, recovery from the instantaneous drop (S5: NO) and the output of the fixed value (S6) is continued until the value of the DC voltage signal e returns to the level before the instantaneous drop (S7: YES) (the second value) State).

  Note that the switching process performed by the switching unit 32 is not limited to the above-described one, and the switching from the first state to the second state is performed when a voltage sag occurs. What is necessary is just to switch from a 2nd state to a 1st state when it returns to the level before a sag. For example, the DC voltage compensation value input from the DC voltage control unit 31 is output as it is during the first state, and the DC voltage compensation value is recorded in the recording unit 33 when switching from the first state to the second state. The value recorded in the recording unit 33 may be output during the second state.

  The reactive power calculator 34 calculates reactive power output from the inverter circuit 2. The reactive power calculator 34 calculates and outputs a reactive power value Q based on the current signal i input from the current sensor 4 and the voltage signal v input from the voltage sensor 5.

The reactive power control unit 35 is for controlling the reactive power output from the inverter circuit 2. The reactive power control unit 35 receives a deviation ΔQ (= Q ^* −Q) between the reactive power value Q and the reactive power target value Q ^* output from the reactive power calculation unit 34, and sets the deviation to zero. Are output to the switching unit 36. The reactive power control unit 35 performs, for example, PI control.

The switching unit 36 switches the q-axis current target value used by the current control unit 38. The q-axis current target value is used by the current control unit 38 as the target value of the q-axis current signal _iq . The switching unit 36 switches between the reactive power compensation value and the fixed value input from the reactive power control unit 35 and outputs them to the current control unit 38 as a q-axis current target value. The switching unit 36 has the same configuration as the switching unit 32, and includes a recording unit 37 for recording the reactive power compensation value input from the reactive power control unit 35. Further, the switching unit 36 performs the switching process shown in FIG.

  That is, the switching unit 36 uses the reactive power compensation value input from the reactive power control unit 35 as the q-axis current target value as the first state until the instantaneous drop occurs (S1: YES). (S2 to S4). When a voltage drop occurs (S1: YES), the second state is restored until the voltage drop recovers from the voltage drop (S5: NO) and the value of the DC voltage signal e returns to the level before the voltage drop (S7: YES). The reactive power compensation value recorded in the recording unit 37 without being overwritten is output to the current control unit 38 as the q-axis current target value (S6).

  Even if the q-axis current target value at the time of recovery from the voltage sag is different from that before the voltage sag, the ineffective component of the output current of the inverter circuit 2 only changes and does not affect the output power Pout so much. The shaft current target value may not be switched to a fixed value. That is, the switching unit 36 may not be provided.

The current control unit 38 is for controlling the output current of the inverter circuit 2. The current control unit 38 performs control by converting the three-phase current signals i _u , i _v and i _w input from the current sensor 4 into a d-axis current signal i _d and a q-axis current signal i _q , and performs compensation. x _d and x _q are converted into three-phase compensation signals x _u , x _v , x _w and output to the PWM signal generator 39.

First, the current control unit 38 converts the three-phase current signals i _u , i _v , and i _w into the α-axis current signal iα and the β-axis current signal by three-phase two-phase conversion (αβ conversion) shown in the following equation (1). It is converted into iβ, and further converted into a d-axis current signal i _d and a q-axis current signal i _q by rotational coordinate conversion (dq conversion) shown in the following equation (2).

Next, the current control unit 38 performs PI control based on the deviation between the d-axis current signal i _d and the d-axis current target value input from the switching unit 32 to generate the compensation signal x _d , and the q-axis current PI control is performed based on the deviation between the signal i _q and the q-axis current target value input from the switching unit 36 to generate the compensation signal x _q .

Then, the current control unit 38 converts the compensation signals x _d and x _q into the compensation signals x α and x β by stationary coordinate transformation (inverse dq transformation) shown in the following equation (3), and further into the following equation (4). By the two-phase three-phase conversion (inverse αβ conversion) shown, the three-phase compensation signals x _u , x _v and x _w are converted.

The PWM signal generation unit 39 generates a PWM signal. The PWM signal generation unit 39 is a command signal for commanding the waveform of the output voltage of each phase of the inverter circuit 2 based on the three-phase compensation signals x _u , x _v , x _w input from the current control unit 38. And a PWM signal is generated by a triangular wave comparison method based on the command signal and the carrier signal. For example, a pulse signal that is high when the command signal is larger than the carrier signal and low when the command signal is equal to or less than the carrier signal is generated as a PWM signal. The generated PWM signal is output to the inverter circuit 2. Note that the PWM signal generation unit 39 is not limited to the case where the PWM signal is generated by the triangular wave comparison method, and the PWM signal may be generated by a hysteresis method, for example.

  The configuration of the control circuit 3 is not limited to the above, and any configuration is possible as long as the DC voltage compensation value can be switched to the d-axis current target value and the fixed value can be switched to the d-axis current target value.

  In this embodiment, although the case where the grid connection inverter system A was a three-phase system was demonstrated, a single phase system may be sufficient. In this case, the current control unit 38 may use the d-axis current target value output from the switching unit 32 as the target value of the single-phase current signal input from the current sensor 4. Alternatively, the single-phase current signal may be converted into two orthogonal current signals by Hilbert transform or the like and used as the α-axis current signal iα and the β-axis current signal iβ.

  In the present embodiment, the case where the control circuit 3 is realized as a digital circuit has been described, but it may be realized as an analog circuit. Further, the processing performed by each unit may be designed by a program, and the computer may function as the control circuit 3 by executing the program. The program may be recorded on a recording medium and read by a computer.

  Next, the operation and effect of the present invention will be described with reference to FIGS.

  FIG. 5 is a time chart for explaining the state of the input power and the output power of the inverter circuit 2 when the instantaneous drop occurs.

  FIG. 4A shows a voltage sag detection signal output from the voltage sag detector C, where a voltage sag occurs at time t = t1, and the level is switched from a low level to a high level. FIG. 4B shows the switching state of the switching units 32 and 36, where the low level indicates the first state and the high level indicates the second state. At time t = t1, the first state is switched to the second state due to the occurrence of a sag. FIG. 3C shows the input voltage Vdc of the inverter circuit 2, that is, the output voltage of the DC power supply 1. FIG. 4D shows the input power Pin of the inverter circuit 2, and FIG. 4E shows the output power Pout of the inverter circuit 2.

  Since DC voltage control is performed before the time t = t1 (first state), the input voltage Vdc is controlled to a constant voltage (maximum output operating voltage Vpm: see FIG. 2). At this time, the input power Pin and the output power Pout are in a balanced state.

  Due to the occurrence of an instantaneous drop at time t = t1, the output power Pout decreases rapidly, and Pin> Pout. At this time, since the first state is switched to the second state (see FIG. 5B), the d-axis current target value and the q-axis current target value are fixed, and the direct-current voltage output from the direct-current voltage control unit 31 Regardless of the compensation value, the output current of the inverter circuit 2 is controlled to be constant. Therefore, since DC voltage control does not function, MPPT control also does not function. Therefore, the output voltage of the DC power supply 1 is freely changed according to the power-voltage characteristics (see FIG. 2). When the output voltage of the DC power supply 1 increases, the operating point moves to the right from the optimal operating point, and the output power of the DC power supply 1 decreases. Therefore, the input power Pin decreases as the input voltage Vdc increases (see FIGS. 5C and 5D).

  At time t = t2, the input power Pin and the output power Pout match, the input power Pin stops decreasing, and the input voltage Vdc also stops increasing. Thereafter, the input power Pin and the output power Pout are balanced while the output is low at the time of the instantaneous drop, and the input voltage Vdc becomes constant. Since the input voltage Vdc does not become equal to or higher than the open circuit voltage Voc of the DC power supply 1, if the threshold for determining the overvoltage is equal to or higher than the open circuit voltage Voc, it is not determined as an overvoltage.

  At time t = t3, the output voltage of the inverter circuit 2 rises because it recovered from the instantaneous drop (see FIG. 5A). The output current of the inverter circuit 2 is controlled to be constant. Therefore, the output power Pout increases (see FIG. 5E), and Pin <Pout. As a result, the input voltage Vdc decreases (see FIG. 5C). Due to the power-voltage characteristic of the DC power supply 1 (see FIG. 2), when the output voltage of the DC power supply 1 decreases, the operating point moves to the left and the output power of the DC power supply 1 increases. Therefore, the input power Pin increases as the input voltage Vdc decreases (see FIG. 5D).

  At time t = t4, the input voltage Vdc has reached a level immediately before the occurrence of the instantaneous drop, so the state is switched from the second state to the first state (see FIG. 5B). The voltage drop is an instantaneous phenomenon within 1 second, and the temperature and solar radiation intensity do not change immediately before the occurrence of the voltage drop and immediately after recovery from the voltage drop, so the input power Pin at this time is also just before the voltage drop occurs. It is the level of. Therefore, the direct current control can be resumed in the same state as immediately before the occurrence of the instantaneous drop.

  Note that the timing of switching from the second state to the first state is not limited to when the input voltage Vdc returns to the level immediately before the occurrence of the instantaneous drop. For example, the input power Pin may be returned to a level just before the occurrence of the instantaneous drop. Further, after the recovery from the sag, the switching may be performed after a predetermined time (for example, 0.1 seconds) regardless of the input voltage Vdc or the input power Pin. However, when switching to the first state immediately after recovery from the instantaneous drop, MPPT control is started in a state where the output voltage of the DC power supply 1 is large, so it takes time until the maximum power is output. . Therefore, it is difficult to recover the output power of the inverter circuit 2 at an early time after recovery from the instantaneous drop. Further, if the second state is continued indefinitely after recovery from the instantaneous drop, MPPT control does not function, and therefore it cannot follow even if the maximum power point changes due to changes in temperature or solar radiation intensity. Therefore, it is desirable to switch when the input voltage Vdc returns to the level just before the occurrence of the instantaneous drop.

  According to the present embodiment, since the d-axis current target value and the q-axis current target value during the second state are fixed, the output current of the inverter circuit 2 at the time of recovery from the voltage sag is the same as before the voltage sag. It is. Therefore, the output power Pout can be quickly restored to the level before the instantaneous drop. Further, the output power Pout does not become larger than before the instantaneous drop and the input power Pin does not become insufficient.

  The method for switching the DC voltage compensation value (reactive power compensation value) to a fixed value is not limited to the method described above. For example, the DC voltage compensation value (reactive power compensation value) may be fixed by inputting zero instead of the deviation Δe (deviation ΔQ) to the DC voltage control unit 31 (reactive power control unit 35). This case will be described below as a second embodiment.

  FIG. 6 is a functional block diagram for explaining the internal configuration of the control circuit according to the second embodiment. In the figure, the same or similar elements as those of the control circuit 3 (see FIG. 3) according to the first embodiment are denoted by the same reference numerals.

  The control circuit 3 ′ shown in FIG. 6 is the first embodiment in that the switching unit 32 ′ is arranged before the DC voltage control unit 31 and the switching unit 36 ′ is arranged before the reactive power control unit 35. This is different from the control circuit 3 according to FIG.

The switching unit 32 ′ receives a deviation Δe (= e ^* −e) between the DC voltage signal e output from the DC voltage sensor 6 and the DC voltage target value e ^*, and outputs the Δe as it is. The state is set to 1 and the second state is set by outputting zero instead of Δe. When the deviation Δe is input, the DC voltage control unit 31 outputs a DC voltage compensation value for making the deviation zero to the current control unit 38 as a d-axis current target value. On the other hand, when zero is input, the DC voltage compensation value immediately before the zero is input is output to the current control unit 38 as the d-axis current target value. That is, while zero is input, a fixed value is input to the current control unit 38 as the d-axis current target value.

The switching unit 36 ′ is also the same as the switching unit 32 ′. When the deviation ΔQ (= Q ^* −Q) is input and the ΔQ is output as it is, the first state is set, and zero is output instead of ΔQ. By doing so, the second state is obtained. When the deviation ΔQ is input, the reactive power control unit 35 outputs a reactive power compensation value for making the deviation zero to the current control unit 38 as a q-axis current target value. On the other hand, when zero is input, the reactive power compensation value immediately before the zero is input is output to the current control unit 38 as the q-axis current target value. That is, while zero is being input, a fixed value is input to the current control unit 38 as the q-axis current target value.

  Also in the second embodiment, the first state and the second state can be switched as in the first embodiment. Therefore, the same effect as that of the first embodiment can be obtained.

  The present invention can also be applied when a DC / DC converter circuit is provided between the DC power source 1 and the inverter circuit 2. A case where a DC / DC converter circuit is provided will be described below as a third embodiment.

  FIG. 7 is a diagram for explaining the grid interconnection inverter system according to the third embodiment. In the same figure, the same code | symbol is attached | subjected to the element same or similar to the grid connection inverter system A (refer FIG. 1) which concerns on 1st Embodiment. In FIG. 7, illustration of the current sensor 4 and the voltage sensor 5 is omitted.

  A grid-connected inverter system A ′ shown in FIG. 7 is provided with a DC / DC converter circuit 7 and a DC voltage sensor 9 before the DC voltage sensor 6, and a control circuit for controlling the DC / DC converter circuit 7. 8 is different from the grid interconnection inverter system A according to the first embodiment in that 8 is provided.

  The DC / DC converter circuit 7 boosts or steps down the output voltage of the DC power supply 1 and outputs it to the inverter circuit 2. The DC / DC converter circuit 7 boosts or steps down the input voltage by switching on and off a switching element (not shown) based on the PWM signal input from the control circuit 8 and outputs it. Since the positive and negative electrodes on the input side of the DC / DC converter circuit 7 are respectively connected to the positive and negative electrodes of the DC power supply 1, the input voltage of the DC / DC converter circuit 7 matches the output voltage of the DC power supply 1.

  The inverter circuit 2 converts the DC power input from the DC / DC converter circuit 7 into AC power. Since the positive and negative electrodes on the input side of the inverter circuit 2 are respectively connected to the positive and negative electrodes on the output side of the DC / DC converter circuit 7, the input voltage of the inverter circuit 2 becomes the output voltage of the DC / DC converter circuit 7. Match.

  The DC voltage sensor 9 detects an instantaneous value of the input voltage of the DC / DC converter circuit 7 (that is, the output voltage of the DC power supply 1). The DC voltage sensor 9 digitally converts the detected instantaneous value and outputs it to the control circuit 8 as a DC voltage signal e '. The DC voltage sensor 9 detects a voltage between terminals of an electrolytic capacitor (not shown) provided between the positive electrode and the negative electrode on the input side of the DC / DC converter circuit 7. While the DC voltage control is being performed, the DC voltage is controlled to a constant voltage, and the electric power stored in the electrolytic capacitor is also constant. Therefore, the electric power input to the DC / DC converter circuit 7 It matches the output power.

  The control circuit 8 controls the DC / DC converter circuit 7, and is realized by, for example, a microcomputer. The control circuit 8 generates a PWM signal based on the DC voltage signal e ′ input from the DC voltage sensor 9 and outputs the PWM signal to the DC / DC converter circuit 7.

  FIG. 8 is a functional block diagram for explaining the internal configuration of the control circuit 8. The control circuit 8 includes a DC voltage control unit 81, a switching unit 82, and a PWM signal generation unit 84.

The DC voltage control unit 81 is for controlling the input voltage of the DC / DC converter circuit 7. The DC voltage controller 81 receives a deviation Δe ′ (= e ′ ^{* −} e ′) between the DC voltage signal e ′ output from the DC voltage sensor 9 and the DC voltage target value e ′ ^*, and calculates the deviation. A DC voltage compensation value for making it zero is output to the switching unit 82. The DC voltage control unit 81 performs, for example, PI control (proportional integration control). In the grid-connected inverter system A ′, the DC / DC converter circuit 7 performs MPPT control. In the present embodiment, the direct current voltage target value e ′ ^* is slightly changed to perform direct current voltage control, thereby changing the output voltage of the direct current power supply 1 so that the output power of the direct current power supply 1 becomes larger. Change the value e ' ^* . Thus, the DC voltage target value e ′ ^* becomes the maximum output operating voltage Vpm, and the power output from the DC power supply 1 is maximized.

  The switching unit 82 switches a signal input to the PWM signal generation unit 84. The switching unit 82 outputs the DC voltage compensation value input from the DC voltage control unit 81 in the first state, and outputs a fixed value in the second state. The switching unit 82 has the same configuration as the switching unit 32 and includes a recording unit 83 for recording the DC voltage compensation value input from the DC voltage control unit 81. Further, the switching unit 82 performs the switching process shown in FIG.

  That is, the switching unit 82 outputs the DC voltage compensation value input from the DC voltage control unit 81 to the PWM signal generation unit 84 as the first state until the instantaneous drop occurs (S1: YES) (S2). ~ S4). When the voltage drop occurs (S1: YES), the second voltage is restored until the voltage drop is restored (S5: NO) and the value of the DC voltage signal e ′ returns to the level before the voltage drop (S7: YES). As a state, the DC voltage compensation value recorded in the recording unit 83 without being overwritten is output to the PWM signal generating unit 84 (S6).

  The PWM signal generation unit 84 generates a PWM signal output to the DC / DC converter circuit 7. The PWM signal generation unit 84 generates a PWM signal by a triangular wave comparison method based on the signal input from the switching unit 82 and the carrier signal. The generated PWM signal is output to the DC / DC converter circuit 7. The PWM signal generation unit 84 is not limited to the case where the PWM signal is generated by the triangular wave comparison method. For example, the PWM signal generation unit 84 may generate the PWM signal by a hysteresis method.

  The configuration of the control circuit 8 is not limited to the above. For example, as in the case of the second embodiment, the switching unit 82 may be arranged upstream of the DC voltage control unit 81. In the present embodiment, the control circuit 8 is realized as a digital circuit, but may be realized as an analog circuit. Further, the processing performed by each unit may be designed by a program, and the computer may function as the control circuit 8 by executing the program. The program may be recorded on a recording medium and read by a computer.

  In the first state, the DC / DC converter circuit 7 is input with the PWM signal generated based on the DC voltage compensation value output from the DC voltage control unit 81, so the input voltage (that is, the DC power supply 1). Output voltage) to a DC voltage target value. At this time, the inverter circuit 2 performs control to make the input voltage of the inverter circuit 2 (that is, the output voltage of the DC / DC converter circuit 7) constant. On the other hand, in the second state, the DC / DC converter circuit 7 receives the PWM signal generated based on the DC voltage compensation value (fixed value) when the first state is switched to the second state. Therefore, the boost ratio of the DC / DC converter circuit 7 is fixed to the boost ratio when the first state is switched to the second state. Therefore, the DC / DC converter circuit 7 boosts or steps down the input voltage at a fixed boost ratio and outputs the boosted voltage to the inverter circuit 2. Thereby, according to the change of the input voltage of the inverter circuit 2, the input voltage of the DC / DC converter circuit 7 (that is, the output voltage of the DC power supply 1) changes similarly. Therefore, also in this embodiment, the state of the input power and the output power of the inverter circuit 2 when the instantaneous drop occurs is the same as the time chart (see FIG. 5) in the case of the first embodiment. The same effect as the form can be achieved.

  Further, in the grid-connected inverter system A ′, when the switching to the second state is not performed, the output power Pout of the inverter circuit 2 becomes small and the input voltage of the inverter circuit 2 becomes large when the instantaneous drop occurs. When this input voltage exceeds a predetermined voltage value, it is determined as an overvoltage, and the operation of the inverter circuit 2 is stopped. However, since the step-up ratio of the DC / DC converter circuit 7 is fixed by switching to the second state when an instantaneous drop occurs, the input voltage of the inverter circuit 2 is suppressed. That is, since the input voltage of the DC / DC converter circuit 7 does not exceed the open circuit voltage Voc of the DC power supply 1, the output voltage of the DC / DC converter circuit 7 (the input voltage of the inverter circuit 2) is fixed to the open circuit voltage Voc. The voltage does not exceed the voltage multiplied by the boost ratio. Therefore, in the case of the third embodiment, an effect of suppressing the overvoltage of the input voltage of the inverter circuit 2 can also be achieved.

  In the present embodiment, the case where the control circuit 8 fixes the step-up ratio of the DC / DC converter circuit 7 by fixing the DC voltage compensation value has been described, but the present invention is not limited to this. Since it is only necessary to fix the step-up ratio of the DC / DC converter circuit 7 in the second state, the PWM signal generator 84 may fix the pulse width of the PWM signal, for example.

  In this embodiment, the second state is switched to the first state based on the DC voltage signal e (see FIG. 7) output from the DC voltage sensor 6, but the DC voltage output from the DC voltage sensor 9 is used. Switching may be performed based on the signal e ′. Further, the switching may be performed based on the input power of the DC / DC converter circuit 7, or may be switched after a predetermined time (for example, 0.1 seconds) has elapsed after the recovery from the sag.

Engaging Louis inverter device according to the present invention, and control method is not limited to the embodiments described above. The specific structure of each part of the engagement Louis inverter apparatus, and control method of the present invention may be varied in design in many ways.

A System interconnection inverter system 1 DC power supply 2 Inverter circuit 3, 3 'control circuit 31 DC voltage control unit 32, 32' switching unit 33 recording unit 34 reactive power calculation unit 35 reactive power control unit 36, 36 'switching unit 37 recording Unit 38 Current control unit 39 PWM signal generation unit 4 Current sensor 5 Voltage sensor 6 DC voltage sensor 7 DC / DC converter circuit 8 Control circuit 81 DC voltage control unit 82 Switching unit 83 Recording unit 84 PWM signal generation unit 9 DC voltage sensor B Power system C Instantaneous voltage drop detection device

Claims (9)

An inverter device that includes an inverter circuit that is directly inputted with DC power output from a solar cell, converts the AC power into AC power, and supplies the AC power to a power system, and a control circuit that controls the inverter circuit,
The control circuit includes:
DC voltage control means for generating a DC voltage compensation value for controlling the input voltage of the inverter circuit;
Current control means for generating a current compensation value for controlling the output current of the inverter circuit;
Switching means for switching between a first state using the DC voltage compensation value and a second state using a fixed value as a current target value of the current control means;
With
The switching means switches from the first state to the second state when an instantaneous voltage drop occurs in the power system ,
The DC voltage control means does not control the input voltage of the inverter circuit in the second state.
An inverter device characterized by that. A DC / DC converter circuit that steps up and down a DC voltage output from a solar cell, an inverter circuit that converts DC power output from the DC / DC converter circuit into AC power, and supplies the AC power, and controls the inverter circuit An inverter device comprising a control circuit for
The control circuit includes:
DC voltage control means for generating a DC voltage compensation value for controlling the input voltage of the inverter circuit;
Current control means for generating a current compensation value for controlling the output current of the inverter circuit;
Switching means for switching between a first state using the DC voltage compensation value and a second state using a fixed value as a current target value of the current control means;
With
The switching means switches from the first state to the second state when an instantaneous voltage drop occurs in the power system,
The control circuit fixes the step-up ratio of the DC / DC converter circuit while being switched to the second state by the switching means.
An inverter device characterized by that. The switching means is
The DC voltage compensation value input from the DC voltage control means is output to the current control means as the current target value to the first state,
By outputting the fixed value as the current target value to the current control means, the second state is set.
The inverter device according to claim 1 or 2. The switching means is
The deviation between the input voltage of the inverter circuit and its target value is output to the DC voltage control means to the first state,
By outputting zero to the DC voltage control means, the second state is established.
The inverter device according to claim 1 or 2. The fixed value is the DC voltage compensation value when switching from the first state to the second state.
The inverter apparatus in any one of Claims 1 thru | or 4. The switching means switches from the second state to the first state after recovering from an instantaneous voltage drop,
The inverter apparatus in any one of Claim 1 thru | or 5. The switching means switches from the second state to the first state when the input voltage of the inverter circuit becomes a predetermined value or less.
The inverter device according to claim 6. The switching means switches from the second state to the first state after a predetermined time has elapsed since the recovery from the instantaneous voltage drop.
The inverter device according to claim 6. A control method for controlling an inverter circuit that is directly inputted with direct-current power output from a solar cell, converted into alternating-current power, and supplied to an electric power system,
A first step of generating a DC voltage compensation value for controlling an input voltage of the inverter circuit;
A second step of detecting that an instantaneous voltage drop has occurred in the power system;
In the first state until the occurrence of occurrence in the second step is detected, a current compensation value is generated using the DC voltage compensation value as a current target value, and the occurrence of occurrence in the second step is detected. In a second state after being performed, a third step of generating the current compensation value using a fixed value as the current target value instead of the DC voltage compensation value;
With
In the second state, the input voltage of the inverter circuit is not controlled.
A control method characterized by that.