JP5410213B2 - Control circuit for power conversion circuit and power supply system provided with the control circuit - Google Patents

Description

  The present invention relates to a control circuit for a power conversion circuit and a power supply system including the control circuit.

  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 a connected load or power system. In this type of grid-connected inverter system, when an accident occurs in the power system, the circuit breaker is activated and the grid-connected inverter system is disconnected from the power system and no power is supplied from the power system (power failure In order to prevent the grid-connected inverter system from being in a state of supplying power to the load by a single operation, it is known to have a function to automatically stop the power conversion operation when a power failure occurs ing.

  FIG. 9 is a diagram showing an example of a grid-connected inverter system having a conventional isolated operation automatic stop function.

  In the grid-connected inverter system A100, a power failure determination unit 680 is provided in the control circuit 600 that generates a PWM signal that is a control signal for the power conversion operation of the inverter circuit 200, and the power failure determination unit 680 performs an automatic stop operation of the isolated operation. It is configured to be performed. Based on the output voltage signal Vo of the grid-connected inverter system A100 detected by the voltage sensor 500, the power failure determination unit 680 uses a predetermined power failure determination method when a power failure (an abnormality such as a system fault occurs in the power system C). Whether the circuit breaker D is activated and the power supply from the power system C is stopped) is monitored.

The control circuit 600 includes a PWM signal generation unit 640 and performs feedback control so that the output current Io of the grid-connected inverter system A100 becomes a preset current target value Io ^* (this control is referred to as “current control”). Thus, the PWM signal generation unit 640 controls the generation of the PWM signal. Further, when the power failure determination unit 680 detects the occurrence of a power failure, a stop signal is output from the power failure determination unit 680 to the PWM signal generation unit 640, and the generation of the PWM signal is stopped. The power conversion operation of the circuit 200 is stopped.

  In addition, when the power failure determination unit 680 detects the occurrence of a power failure, a disconnection signal is output from the power failure determination unit 680 to the switch 800 to operate the switch 800, so that the control circuit 600 is connected to the grid when a power failure occurs. The connection between the inverter system A100 and the load B is also disconnected. Thereby, the independent operation state of grid connection inverter system A100 is avoided.

  By the way, in the power failure determination unit 680, for example, it is determined whether or not a power failure has occurred from a change in the detection signal of the voltage sensor 500 (for example, an excessive increase in voltage, etc.). A time delay of about several hundred milliseconds occurs at the shortest time from the occurrence of the occurrence of the failure until the power failure determination unit 680 detects the power failure. For this reason, during this time delay, the grid interconnection inverter system A100 is in a single operation state. Since the grid-connected inverter system A100 performs current control in the single operation state, the output voltage Vo of the grid-connected inverter system A100 increases and an excessive voltage (hereinafter referred to as “overvoltage”) is applied to the load B. There is a possibility that.

  Since it is not preferable that an overvoltage is applied from the grid-connected inverter system A100 to the load B during the time delay from the occurrence of a power failure until the power failure is detected. Japanese Laid-Open Patent Publication No. 2000-228970 proposes a method of stopping the output of a PWM signal when the instantaneous value of the output voltage Vo becomes a predetermined threshold value or more.

  In the grid interconnection inverter system A100 of FIG. 9, the method of this publication is provided with an overvoltage detection unit 650 in parallel with the power failure determination unit 680 as shown by the dotted line in the figure, and the output voltage Vo detected by the voltage sensor 500. When the instantaneous value becomes an overvoltage equal to or greater than a predetermined threshold, the overvoltage detection unit 650 detects the state, outputs a stop signal to the PWM signal generation unit 640, and stops the output of the PWM signal of the PWM signal generation unit 640 It is. When the stop signal is not output from the power failure determination unit 680 even after a predetermined time has elapsed after the overvoltage detection unit 650 outputs the stop signal, the overvoltage detection unit 650 determines that the overvoltage is not due to a power failure, The output of the stop signal to the PWM signal generation unit 640 is stopped, and the output of the PWM signal of the PWM signal generation unit 640 is restarted.

Japanese Patent Laid-Open No. 2000-60000

  By the way, the isolated operation automatic stop function in the conventional grid-connected inverter system A100 stops whether or not the isolated operation state occurs after the occurrence of a power failure, so whether or not a power failure has occurred from the output voltage Vo of the grid-connected inverter system A100. Since the inverter circuit 200 is stopped according to the determination result and the switch 800 is released, a time delay occurs from the time of the power failure to the stop of the inverter circuit 200. There is a problem that an overvoltage may be applied to the load B in a state.

  It has been proposed to deal with the above problem by a method of immediately stopping the inverter circuit 200 when the instantaneous value of the output voltage Vo rises to an overvoltage, but in this method, the inverter circuit 200 is suddenly stopped. Therefore, the connection between the inverter circuit 200 and the filter circuit 300 is substantially cut off, and the polarity of the voltage across the reactor L300 of the filter circuit 300 immediately before the cut-off is reversed and applied to the load B instantaneously. There is a disadvantage of increasing the voltage. When the output current of the inverter circuit 200 is large, the voltage across the reactor L300 also increases. In this case, if the connection between the inverter circuit 200 and the filter circuit 300 is interrupted, the applied voltage to the load B becomes an excessive value. Since the overvoltage is applied to the load B, the problem of the overvoltage application to the load B in the independent operation automatic stop function cannot be completely solved in this respect.

  In addition, the cause of the fluctuation of the instantaneous value of the output voltage Vo is not only when a power failure occurs but also when some abnormality occurs in the system, and the system voltage may fluctuate instantaneously. The process of stopping the inverter circuit 200 every time the voltage rises to an overvoltage is not necessarily an appropriate process. In particular, in Japanese Patent Laid-Open No. 2000-60000, the inverter circuit 200 is restarted when the cause of the instantaneous value of the output voltage Vo rising to an overvoltage is not due to a power failure. This is necessary to stop the inverter circuit 200 unconditionally without stopping the output voltage of the inverter circuit 200 to a voltage smaller than the overvoltage. From the viewpoint of power conversion efficiency of the inverter circuit 200 If it sees, since power conversion efficiency will fall, the process with respect to the overvoltage of the same gazette is not appropriate also in this point.

  The present invention has been conceived under the circumstances described above, and when the output voltage of the inverter circuit rises to an overvoltage, the application of the overvoltage to the load is suppressed as much as possible to the inverter circuit. At the same time as performing output control, it is determined whether the cause of the overvoltage is due to a power failure, and switching to more appropriate output control according to the determination result, the output of the inverter circuit as much as possible against overvoltage generation It is an object of the present invention to provide a control circuit for an inverter circuit that makes control appropriate.

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

  The control circuit of the power conversion circuit provided by the first aspect of the present invention is a current control that generates a command value signal for controlling the output current of the power conversion circuit detected by the current detection means to a predetermined target current. Command value signal generating means, and PWM signal generating means for generating a PWM signal for controlling the power conversion operation of the power conversion circuit based on the command value signal generated by the current control command value signal generating means, A control circuit for controlling the power conversion operation of the power conversion circuit by the PWM signal generated by the PWM signal generation means, wherein the output voltage of the power conversion circuit detected by the voltage detection means is set to a predetermined target A voltage control command value signal generating means for generating a command value signal for controlling to a voltage, and an output voltage detected by the voltage detecting means satisfies a predetermined condition. Overvoltage detection means for detecting that the overvoltage has occurred, and when the overvoltage detection means detects that the overvoltage has been detected, the command value signal input to the PWM signal generation means is generated as the current control command value signal generation. An overvoltage is detected by a first command value signal switching means for switching from a command value signal generated by the means to a command value signal generated by the voltage control command value signal generation means, and the overvoltage detection means. Determining means for determining whether or not the output current of the power conversion circuit detected by the current detection means is increasing, and determining that the output current of the power conversion circuit is increasing by the determination means. Then, the command value signal input to the PWM signal generating means is converted from the command value signal generated by the voltage control command value signal generating means to the current control instruction. Characterized in that it comprises a second command value signal switching means for switching the command value signal generated by the value signal generating means.

  In a preferred embodiment of the present invention, the overvoltage detection means detects the output voltage when the instantaneous value of the output voltage detected by the voltage detection means is equal to or higher than a predetermined threshold higher than the target voltage. Detects overvoltage.

  In a preferred embodiment of the present invention, the target voltage is “0”.

  In a preferred embodiment of the present invention, the determination unit calculates an effective value at a predetermined cycle from the output current detected by the current detection unit, and an increase in the calculated effective value continues for a predetermined period. Then, it is determined that the output current has increased.

  In a preferred embodiment of the present invention, the determination unit calculates an effective value at a predetermined cycle from the output current detected by the current detection unit, and the calculated effective value is continuously set a predetermined number of times. If it has increased, it is determined that the output current has increased.

  In a preferred embodiment of the present invention, the power conversion circuit is an inverter circuit.

  In a preferred embodiment of the present invention, the power conversion circuit is a DC / DC converter circuit.

  The power supply system provided by the second aspect of the present invention includes the power conversion circuit and the control circuit provided by the first aspect of the present invention.

  A program provided by the third aspect of the present invention is a current control command value for generating a command value signal for controlling the output current of the power conversion circuit detected by the current detection means to a predetermined target current. Signal generation means, and PWM signal generation means for generating a PWM signal for controlling the power conversion operation of the power conversion circuit based on the command value signal generated by the current control command value signal generation means, A program for causing the PWM signal generated by the PWM signal generation means to function as a control means for controlling a power conversion operation of the power conversion circuit, wherein the computer converts the power conversion detected by the voltage detection means. Voltage control command value signal generating means for generating a command value signal for controlling the output voltage of the circuit to a predetermined target voltage; An overvoltage detecting means for detecting that the output voltage detected by the voltage detecting means is overvoltage when a predetermined condition is satisfied; and when the overvoltage detecting means detects that the overvoltage is detected, the PWM signal generation is performed. First command value signal switching means for switching a command value signal input to the means from a command value signal generated by the current control command value signal generating means to a command value signal generated by the voltage control command value signal generating means; When it is detected by the overvoltage detection means that an overvoltage has occurred, the determination means for determining whether or not the output current of the power conversion circuit detected by the current detection means is increasing, and the determination means When it is determined that the output current of the power conversion circuit is increasing, the command value signal input to the PWM signal generating means is transmitted to the voltage control command value signal. It functions as a second command value signal switching means for switching from the command value signal generated by the signal generation means to the command value signal generated by the current control command value signal generation means.

  The recording medium provided by the fourth aspect of the present invention is a computer-readable recording medium that records the program provided by the third aspect of the present invention.

  According to the present invention, when the power conversion operation of the power conversion circuit is controlled by the PWM signal generated based on the command value signal generated by the current control command value signal generation means (the power conversion control of the power conversion circuit is When the output voltage of the power conversion circuit satisfies a predetermined condition during current control), a PWM signal input to the power conversion circuit is generated based on the command value signal generated by the voltage control command value signal generation means Switching to the PWM signal switches the power conversion control of the power conversion circuit from current control to voltage control.

  In the voltage control, since the output voltage of the power conversion circuit is controlled to the target voltage, it is possible to prevent an overvoltage higher than the target voltage from being applied to the load when a load is connected to the power conversion circuit. Voltage control is feedback control that detects the output voltage of the power conversion circuit and controls the PWM signal so that the detected voltage becomes the target voltage. The output voltage of the power conversion circuit is gradually reduced to the target voltage. Therefore, for example, when an LC low-pass filter is provided in the subsequent stage of the power conversion circuit, by suddenly stopping the power conversion circuit, an induced voltage is generated in the LC low-pass filter and the output voltage is jumped up instantaneously. It is possible to avoid the inconvenience of end.

  Further, for example, in the case of a system in which the power conversion circuit is connected to the grid and supplies power, the voltage applied to the load is controlled by the grid, but the power conversion control of the power conversion circuit is switched to voltage control, If the output voltage is reduced, the voltage applied to the load (that is, the output voltage of the power converter circuit) will rise to an overvoltage due to power failure (when the connection to the power system is interrupted) The output current of the converter circuit tends to increase as the output voltage decreases.However, if the cause of the output voltage of the power converter circuit rising to an overvoltage is due to a power failure, such a tendency is not shown. It is possible to specify whether or not it is due to a power failure.

  According to the present invention, when the power conversion control of the power conversion circuit is switched from the current control to the voltage control, it is determined whether or not the output current of the power conversion circuit increases. Therefore, the power conversion control of the power conversion circuit is returned to the current control at the time of connection. On the other hand, if the output current is not increased, the connection with the grid is cut off, and it is estimated that the power conversion circuit is supplying power to the load by the single operation. Then, the suppression control of the output voltage by the voltage control is continued.

  Therefore, after switching to voltage control, the power conversion control of the power conversion circuit is switched to an appropriate control according to the cause of the overvoltage, so even if an overvoltage occurs, the power conversion control is performed with an appropriate control method for the power conversion circuit. Can be performed. In addition, when an overvoltage occurs due to a cause not caused by a power failure, the power conversion circuit is temporarily stopped and then not restarted, so that a reduction in power conversion efficiency of the power conversion circuit can be suppressed.

  Further, by setting the target voltage for voltage control to “0”, the output voltage of the power conversion circuit can be quickly reduced, so that the determination of the increase in output current by the determination means can be performed quickly.

  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 which concerns on 1st Embodiment of this invention. It is a flowchart for demonstrating the determination process which a control switching determination part performs. It is the circuit diagram which simplified the grid connection inverter system which concerns on 1st Embodiment of this invention. It is a vector diagram which shows the relationship between the output voltage of an inverter circuit, output current, a load voltage, and the voltage drop by a reactor. It is a vector diagram showing the relationship between each voltage and current, and shows a change when overvoltage suppression control is performed when the overvoltage is due to a temporary increase in system voltage or the like. It is a vector diagram which shows the relationship between each voltage and electric current, and has shown the change when overvoltage suppression control is performed when overvoltage is due to a power failure. It is a graph which shows the effective value in each time of the output voltage and output current of an inverter circuit. It is a figure for demonstrating the DC / DC converter system which concerns on 2nd Embodiment of this invention. It is a figure for demonstrating the conventional 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 according to a first embodiment of the present invention.

  As shown in the figure, the grid-connected inverter system A includes a DC power source 1, an inverter circuit 2, a filter circuit 3, a current sensor 4, a voltage sensor 5, a control circuit 6, and a switch 8. The grid interconnection inverter system A converts DC power output from the DC power source 1 into AC power by the inverter circuit 2 and supplies the AC power to the load B and the power system C.

  The DC power source 1 outputs DC power and includes, for example, 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. Note that the DC power source 1 is not limited to one that generates DC power from a solar cell. For example, the DC power source 1 may be a fuel cell, a storage battery, an electric double layer capacitor, a lithium ion battery, or AC power generated by a diesel engine generator, a micro gas turbine generator, a wind turbine generator, or the like. It may be a device that converts to DC power and outputs it.

  The inverter circuit 2 converts a DC voltage input from the DC power source 1 into an AC voltage and outputs the AC voltage to the filter circuit 3. The inverter circuit 2 is a so-called PWM control inverter circuit, and converts an input DC voltage into an AC voltage by switching on and off a switching element (not shown) based on a PWM signal input from the control circuit 6. To do.

  The filter circuit 3 removes high frequency components due to switching from the AC voltage input from the inverter circuit 2. The filter circuit 3 includes a low pass filter including a reactor L3 and a capacitor C3. The alternating voltage from which the high frequency component has been removed by the filter circuit 3 is output to the load B and the power system C. The configuration of the filter circuit 3 is not limited to this, and any known filter circuit for removing high frequency components may be used.

  The current sensor 4 detects a current output from the filter circuit 3 (that is, an output current of the grid interconnection inverter system A, hereinafter referred to as “output current Io”). The output current Io detected by the current sensor 4 is output to the control circuit 6 as an output current signal Io. The voltage sensor 5 detects a voltage output from the filter circuit 3 (that is, an output voltage of the grid interconnection inverter system A, hereinafter referred to as “output voltage Vo”). The output voltage Vo detected by the voltage sensor 5 is output to the control circuit 6 as an output voltage signal Vo.

  The switch 8 disconnects the connection between the grid-connected inverter system A and the load B. When the disconnection signal is input from the control circuit 6, the switch 8 disconnects the connection between the grid-connected inverter system A and the load B. Thereby, the independent operation state of the grid connection inverter system A is avoided.

The control circuit 6 controls the inverter circuit 2 and generates a PWM signal based on the output current signal Io input from the current sensor 4 and the output voltage signal Vo input from the voltage sensor 5. Output to the inverter circuit 2. The control circuit 6 performs current control (feedback control performed so that the output current Io becomes a preset current target value Io ^* ) and voltage control (so that the output voltage Vo becomes a preset voltage target value Vo ^*). The output current Io or the output voltage Vo of the grid-connected inverter system A is controlled by controlling the inverter circuit 2 by switching the feedback control to be performed. That is, when the current control is switched, the output current Io is feedback-controlled so as to become the preset current target value Io ^* . When the voltage control is switched, the preset voltage target value is set. The output voltage Vo is feedback-controlled so as to be Vo ^* (in this embodiment, “0”).

  The control circuit 6 normally performs current control. However, when the output voltage Vo becomes an overvoltage, the control is switched to the voltage control to suppress the output voltage Vo (hereinafter referred to as “overvoltage suppression control”). At this time, when the output current Io decreases, the control circuit 6 determines that the increase in the output voltage Vo is due to a power failure, and continues the overvoltage suppression control as it is. On the other hand, when the output current Io increases, the control circuit 6 determines that the increase in the output voltage Vo is not due to a power failure but due to a temporary increase in the system voltage, and switches to current control. Details of the determination of the cause of increase in the output voltage Vo (determination as to whether or not the overvoltage is due to a power failure) due to the increase or decrease in the output current Io during overvoltage suppression control will be described later.

  Further, the control circuit 6 determines a power failure based on the output voltage signal Vo input from the voltage sensor 5. When an abnormality such as a system fault occurs in the power system C, the circuit breaker D is activated and the grid-connected inverter system A is disconnected from the power system C. The control circuit 6 outputs a disconnection signal to the switch 8 when detecting that a state (power failure) in which power is not supplied from the power system C due to the disconnection has occurred.

  The control circuit 6 includes a voltage control unit 61, a current control unit 62, a control switching unit 63, a PWM signal generation unit 64, an overvoltage detection unit 65, a current change detection unit 66, a control switching determination unit 67, and a power failure determination unit 68. ing.

The voltage control unit 61 receives a deviation between the output voltage signal Vo input from the voltage sensor 5 and the voltage target value Vo ^* , and performs control switching using a correction value for setting the deviation as “0” as a command value signal. To the unit 63. In this embodiment, since the voltage target value Vo ^* is set to “0”, overvoltage suppression control is performed so that the output voltage Vo is set to “0”. Since the purpose of the control is to suppress the output voltage Vo, the voltage target value Vo ^* is not limited to “0” and may be any value that is smaller than the system voltage. However, in order to quickly reduce the output voltage Vo by the overvoltage suppression control, it is desirable to set the voltage target value Vo ^* to “0”.

The current control unit 62 receives a deviation between the output current signal Io input from the current sensor 4 and the current target value Io ^* , and performs control switching using a correction value for setting the deviation as “0” as a command value signal. To the unit 63.

  The control switching unit 63 switches between current control and voltage control based on a control switching signal input from the control switching determination unit 67. The control switching unit 63 receives the command value signal from the voltage control unit 61 and the current control unit 62, and outputs one command value signal to the PWM signal generation unit 64. When the control switching signal is a current control command signal (for example, a low level signal), the control switching unit 63 outputs a command value signal input from the current control unit 62 to the PWM signal generation unit 64. On the other hand, when the control switching signal is a voltage control command signal (for example, a high level signal), the control switching unit 63 outputs a command value signal input from the voltage control unit 61 to the PWM signal generation unit 64.

  The PWM signal generation unit 64 generates a PWM signal by a triangular wave comparison method based on the command value signal input from the control switching unit 63 and the carrier signal generated as a triangular wave signal having a predetermined frequency (for example, 4 kHz). To do. For example, a pulse signal that is high when the command value signal is larger than the carrier signal and low when the command value signal is smaller than the carrier signal is generated as a PWM signal. The generated PWM signal is output to the inverter circuit 2. When the stop signal is input from the power failure determination unit 68, the PWM signal generation unit 64 stops generating the PWM signal. Thereby, the power conversion operation of the inverter circuit 2 is stopped.

  The overvoltage detection unit 65 detects that the output voltage Vo has become an overvoltage. The overvoltage detection unit 65 compares the output voltage signal Vo input from the voltage sensor 5 with a preset overvoltage determination value Vmax. This overvoltage determination value Vmax is a voltage several tens of percent higher than the rated output voltage of the inverter circuit 2. The overvoltage detection unit 65 outputs an overvoltage signal to the control switching determination unit 67 when the instantaneous value of the output voltage Vo becomes equal to or higher than the overvoltage determination value Vmax.

  In the present embodiment, the overvoltage determination value Vmax is set as a voltage that is several tens of percent higher than the rated output voltage of the inverter circuit 2, but this is not restrictive. In the present embodiment, the overvoltage detection unit 65 detects the overvoltage by comparing the instantaneous value of the output voltage Vo with the overvoltage determination value Vmax. However, the present invention is not limited to this. For example, the effective value, average value, or peak value of the output voltage Vo may be compared with the overvoltage determination value Vmax to detect the overvoltage. In addition, an overvoltage signal may be output when the state where the overvoltage determination value Vmax or more continues for a predetermined time (or a predetermined number of sampling times).

  In this embodiment, the overvoltage detection unit 65 outputs a low level signal while no overvoltage is detected, and switches to an overvoltage signal (high level signal) and outputs it after detecting the overvoltage. However, it is not limited to this. For example, a high level signal may be output while no overvoltage is detected, and when an overvoltage is detected, it may be switched to a low level signal and output. Further, a detection pulse may be output when an overvoltage is detected or when a state in which the overvoltage is detected continues for a predetermined time.

  The current change detection unit 66 detects increase / decrease in the effective value of the output current Io. The current change detection unit 66 calculates an effective value of the output current (hereinafter referred to as “output current effective value Ie”) from the output current signal Io input from the current sensor 4, and the output current effective value Ie increases. For example, if the output current effective value Ie is unchanged or has decreased, a decrease signal (low level signal) is detected, and if the output current effective value Ie is increased, The increase signal (high level signal) is output to the control switching determination unit 67 as a current change signal.

  In the present embodiment, the current change detection unit 66 outputs a low level signal as a current change signal when the output current effective value Ie does not decrease or does not change, and when the output current effective value Ie increases. The high level signal is output as the current change signal, but it may be reversed.

  In the present embodiment, the current change detection unit 66 detects an increase or decrease in the effective value of the output current, but is not limited thereto. For example, an increase or decrease in the average value or peak value of the output current may be detected.

  The control switching determination unit 67 determines whether to perform current control or voltage control. The control switching determination unit 67 receives an overvoltage signal from the overvoltage detection unit 65, receives a current change signal from the current change detection unit 66, and outputs the determination result to the control switching unit 63 as a control switching signal. The control switching signal is, for example, a low level signal for instructing current control and a high level signal for instructing voltage control. In the present embodiment, the control switching determination unit 67 outputs a current control command signal (low level signal) as a control switching signal and determines to perform voltage control when determining to perform current control. In this case, the voltage control command signal (high level signal) is output as the control switching signal. However, the present invention is not limited to this, and the high level signal and the low level signal may be reversed. Further, when switching control (that is, when switching from current control to voltage control and when switching from voltage control to current control), a pulse signal may be output.

  FIG. 2 is a flowchart for explaining the determination process performed by the control switching determination unit 67.

  Since the control circuit 6 normally performs current control, a current control command signal (low level signal) is output as a control switching signal (S1). Next, it is determined whether or not the output voltage Vo is an overvoltage, that is, whether or not the signal input from the overvoltage detector 65 is an overvoltage signal (high level signal) (S2). If it is not an overvoltage signal (S2: NO), the process returns to step S1 and the output of the current control command signal (low level signal) is continued. In the case of an overvoltage signal (S2: YES), in order to switch current control to voltage control, a voltage control command signal (high level signal) is output as a control switching signal (S3).

  Next, it is determined whether or not the output current Io is increasing (S4). In the present embodiment, when the period in which the current change signal input from the current change detection unit 66 is an increase signal (high level signal) is a predetermined period, it is determined that the output current Io is increasing. When the output current Io has not increased (S4: NO), the process returns to step S3 and the output of the voltage control command signal (high level signal) is continued. When the output current Io is increasing (S4: YES), the process returns to step S1 to switch the voltage control to the current control, and the current control command signal (low level signal) is output as the control switching signal (S1). ).

  In the present embodiment, the current change detection unit 66 calculates the output current effective value Ie twice after an increase signal is input for a predetermined period for determining whether or not the output current Io is increasing. The period is equivalent to. That is, when the calculated output current effective value Ie increases continuously three times, the control switching signal is switched from the voltage control command signal (high level signal) to the current control command signal (low level signal). Note that the predetermined period is not limited to this, and may be a shorter period or a longer period. As the predetermined period is shortened, the increase in the output current Io can be determined earlier, but the possibility of erroneous detection also increases. On the other hand, the longer the predetermined period, the lower the possibility of false detection, but it takes time to determine the increase in the output current Io.

  In the present embodiment, the current change detection unit 66 detects an increase or decrease in the output current effective value Ie, and the control switching determination unit 67 determines an increase in the output current Io (determines the continuation of a predetermined period of the increase signal). However, the current change detector 66 may detect an increase in the output current Io (detect a continuation of an increase in the output current effective value Ie for a predetermined period). In this case, a signal indicating that the current change detection unit 66 has detected an increase is output to the control switching determination unit 67, and the control switching signal is changed based on the signal indicating that the control switching determination unit 67 has detected the increase. You can do it.

  Further, instead of detecting an increase in the output current Io based on the duration of the increase state of the output current effective value Ie, the output current effective value Ie is set to a preset overcurrent value (for example, a value slightly higher than the rated output current). An increase in output current Io may be detected when Imax or more. In this case, even if the increase rate of the output current effective value Ie is fast, the increase in the output current Io can be detected before the output current effective value Ie exceeds the maximum rated output current. Can be avoided. Further, when the duration of the increase state of the output current effective value Ie reaches a predetermined period, or when the output current effective value Ie becomes equal to or higher than the overcurrent set value Imax, an increase in the output current Io is detected. You may do it.

  Returning to FIG. 1, the power failure determination unit 68 detects the occurrence of a power failure by a predetermined power failure determination method based on the output voltage signal Vo input from the voltage sensor 5. When the power failure determination unit 68 detects the occurrence of a power failure, the power failure determination unit 68 outputs a stop signal to the PWM signal generation unit 64 and outputs a disconnection signal to the switch 8. The PWM signal generation unit 64 to which the stop signal is input stops generating the PWM signal, so that the power conversion operation of the inverter circuit 2 stops. The switch 8 to which the disconnection signal is input disconnects the connection between the grid-connected inverter system A and the load B. Thereby, the independent operation state of the grid connection inverter system A is avoided.

  Next, determination of the cause of increase in the output voltage Vo (determination of whether or not the overvoltage is due to a power failure) due to increase / decrease in the output current Io during overvoltage suppression control will be described with reference to FIGS.

  FIG. 3 shows a simplified circuit diagram of the grid interconnection inverter system A.

  In the figure, an inverter circuit 2 ′ shows a portion of a power source that supplies AC power including the DC power source 1, the inverter circuit 2, and the control circuit 6 in FIG. 1, and a reactor L 3 is a reactor of the filter circuit 3. Only the part of is shown. Note that the current sensor 4 and the voltage sensor 5 are omitted. FIG. 2B shows a state where the grid interconnection inverter A is disconnected from the power system C (power failure state). In this figure, the output voltage of the inverter circuit 2 ′ (the voltage output from the inverter circuit 2 in FIG. 1) is Vinv, the output current (the current output from the inverter circuit 2 in FIG. 1), and the reactor L3 of the filter circuit 3 is (Current flowing) is Iinv, the load voltage at the connection point a of the load B is Vr, the system voltage of the power system C is Vline, and the voltage drop due to the reactor L3 is VL.

When the inverter circuit 2 ′ is connected to the power system C (see FIG. 5A), the voltage of the load B is controlled by the power system C, so the load voltage Vr, the system voltage Vline, and the output voltage Vinv. During the voltage drop VL of the reactor L3,
Vr = Vline
VL = Iinv × ωL, ω = 2πf
Vinv = Vr + VL
There is a relationship. Note that f is the frequency of the system voltage, and ω is the angular frequency of the system voltage.

  4, 5 and 6 are vector diagrams showing the relationship among the output voltage Vinv, the output current Iinv, the load voltage Vr, and the drop voltage VL. FIG. 7 is a diagram for explaining changes in the output voltage Vinv and the output current Iinv.

  FIG. 4A shows the relationship between voltages and currents in a normal state in a state where the grid interconnection inverter A is connected to the power system C (see FIG. 3A). Since the control circuit 6 performs current control with a power factor of 1 in normal times, the phase of the output current Iinv matches the phase of the load voltage Vr (= system voltage Vline). Further, the voltage drop VL is advanced in phase by (1/2) π from the output current Iinv. Accordingly, the vector of the output voltage Vinv is as shown in FIG. 4A by adding the vector of the drop voltage VL to the vector of the load voltage Vr.

FIG. 4B shows the relationship between each voltage and current when the load voltage Vr becomes an overvoltage. The time t at this time is t1, and in order to express each vector when t = t1, for example, the output voltage is displayed as Vinv (t1) (FIGS. 5A to 5D and FIG. 6). Also in (a) to (d), the vectors at time t are displayed in the same manner. The load voltage Vr (t1) is increased due to overvoltage. On the other hand, since the control circuit 6 still performs current control with a power factor of 1, the phase of the output current Iinv (t1) matches the phase of the load voltage Vr (t1). Further, since the output current Io (= output current Iinv) is controlled to the current target value Io ^* , the magnitude of the output current Iinv (t1) has not changed from the normal time (see FIG. 4A). Since the magnitude of the output current Iinv (t1) does not change and the inductive reactance (ωL) of the reactor L3 is constant, the magnitude of the drop voltage VL (t1) does not change. Further, the phase of the drop voltage VL (t1) is advanced by (1/2) π from the phase of the output current Iinv (t1). Therefore, the output voltage Vinv (t1) increases according to the load voltage Vr (t1). At this time, the phase difference between the output voltage Vinv (t1) and the load voltage Vr (t1) is small. At this point, it cannot be determined whether the overvoltage is due to a power failure or due to a temporary increase in the system voltage Vline.

  5 and 6 show changes in the relationship between each voltage and current thereafter when the control circuit 6 starts overvoltage suppression control when t = t1. FIG. 5 shows changes in the vector diagram when the overvoltage is due to a temporary increase in the system voltage Vline (for reasons other than a power failure), and FIG. 6 shows the case where the overvoltage is due to a power failure. The change of the vector diagram is shown. FIG. 7 shows the effective values of the output voltage Vinv and the output current Iinv at each time t when the control circuit 6 starts overvoltage suppression control when t = t1. FIGS. 7A and 7B show the output voltage Vinv and the output current Iinv, respectively, when the overvoltage is due to a temporary increase in the system voltage Vline. FIGS. 7C and 7D are respectively The output voltage Vinv and the output current Iinv when the overvoltage is due to a power failure are shown.

  When the overvoltage is due to a temporary increase in the system voltage Vline, the load voltage Vr is held at the system voltage Vline because it remains connected to the power system C (Vr (t2) to Vr ( The size of t5) coincides with the size of Vr (t1) in FIG. Therefore, the drop voltage VL increases as the output voltage Vinv decreases due to the overvoltage suppression control (see FIGS. 5A to 5C). Since the inductive reactance (ωL) of the reactor L3 is constant, the output current Iinv increases as the drop voltage VL increases (see FIGS. 5A to 5C). That is, the output current Iinv increases as the output voltage Vinv decreases. FIGS. 7A and 7B show changes in the effective values of the output voltage Vinv and the output current Iinv, respectively. Since the overvoltage suppression control is started at t = t1, the effective value of the output voltage Vinv at t = t2, t3, and t4 decreases (see FIG. 7A). Further, due to the decrease in the output voltage Vinv, the effective value of the output current Iinv at t = t2, t3, t4 increases (see FIG. 7B).

At t = t2, t3, t4, since the effective value of the output current Iinv has increased three times in succession, the control circuit 6 determines that the overvoltage is due to a temporary increase in the system voltage Vline, etc. When t = t4, overvoltage suppression control is canceled and current control with a power factor of 1 is started. Since the power factor is controlled to 1, the phase of the output current Iinv (t5) matches the phase of the load voltage Vr (t5) at t = t5. Further, since the output current Iinv is controlled to the current target value Io ^* by current control, the magnitude of the output current Iinv (t5) matches the magnitude of Iinv (t1) (see FIG. 4B). . Therefore, the magnitude of the drop voltage VL (t5) also matches the magnitude of the drop voltage VL (t1). Further, since the load voltage Vr is held at the system voltage Vline and becomes constant, the magnitude of the load voltage Vr (t5) also matches the magnitude of Vr (t1). Therefore, the magnitude of the output voltage Vinv (t5) also matches the magnitude of the output voltage Vinv (t1). That is, the vector diagram (FIG. 5D) showing the relationship between each voltage and current at t = t5 is the same as that in FIG. 4B. Accordingly, the effective values of the output voltage Vinv and the output current Iinv at t = t5 coincide with the effective values at t = t1 (see FIGS. 7A and 7B).

  In this case, if the system voltage Vline continues to increase temporarily, overvoltage is detected again and overvoltage suppression control is performed. That is, the switching between the overvoltage suppression control and the current control is repeated until the temporary increase in the system voltage Vline is restored. That is, the change in the waveform at t = t1 to t5 in FIGS. 7A and 7B is repeated, and the effective values of the output voltage Vinv and the output current Iinv periodically change. In order to avoid this, when it is determined that the overvoltage is caused by a temporary increase in the system voltage Vline, for example, immediately after the determination (immediately after t = t4 in FIG. 7A), the overvoltage The determination value Vmax may be changed to a large value, or the overvoltage detection unit 65 may not function for a predetermined period (a period until the temporary increase of the system voltage Vline is restored). When the increase of the system voltage Vline continues for a predetermined time, the power failure determination unit 68 determines that the system voltage is abnormal, and the inverter circuit 2 is stopped.

  Even when the control circuit 6 is not controlling the power factor 1, if the overvoltage is not caused by a power failure, the effective value of the output current Iinv is increased by the overvoltage suppression control. That is, although the effective value of the output voltage Vinv is reduced by the overvoltage suppression control, the effective value of the output voltage Vinv is smaller than the effective value of the load voltage Vr because the effective value of the load voltage Vr (= system voltage Vline) is constant. After the effective value of the output voltage Vinv becomes smaller than the effective value of the load voltage Vr, the potential difference between the two increases and the current flowing from the power system C to the inverter circuit 2 increases, so that the output current Iinv The effective value increases.

  On the other hand, when the overvoltage is due to a power failure (see FIG. 3B), no power is supplied from the power system C. Therefore, when the output voltage Vinv is reduced by the overvoltage suppression control, the load voltage Vr is also reduced accordingly. . Therefore, as the output voltage Vinv decreases, the drop voltage VL also decreases (see FIGS. 6A to 6D). Since the inductive reactance (ωL) of the reactor L3 is constant, the output current Iinv decreases as the drop voltage VL decreases (see FIGS. 6A to 6D). That is, the output current Iinv decreases as the output voltage Vinv decreases. FIGS. 7C and 7D show changes in the effective values of the output voltage Vinv and the output current Iinv, respectively. Since the overvoltage suppression control is started at t = t1, the effective value of the output voltage Vinv at t = t2, t3, t4, and t5 decreases (see FIG. 7C). Further, due to the decrease in the output voltage Vinv, the effective value of the output current Iinv at t = t2, t3, t4, and t5 is decreased (see FIG. 7D).

  Since the effective value of the output current Iinv does not increase, the control circuit 6 determines that the overvoltage is due to a power failure (not to determine that the overvoltage is due to a temporary increase in the system voltage Vline), and the output voltage The overvoltage suppression control is continued until Vinv becomes “0”.

  The control circuit 6 may be realized as an analog circuit or a digital circuit. Further, the processing performed by each unit may be designed by a program, and the computer may function as the control circuit 6 by executing the program. The program may be recorded on a recording medium and read by a computer.

  Next, the operation of the control circuit 6 will be described.

The control circuit 6 normally performs current control. That is, the current control unit 62 outputs a command value signal based on the deviation between the output current signal Io input from the current sensor 4 and the current target value Io ^* . The PWM signal generation unit 64 generates a PWM signal based on a command value signal input from the current control unit 62 via the control switching unit 63 and outputs the PWM signal to the inverter circuit 2.

  When the overvoltage detection unit 65 detects an overvoltage, the control circuit 6 performs overvoltage suppression control by switching the current control to voltage control. That is, when the overvoltage detection unit 65 detects an overvoltage based on the output voltage signal Vo input from the voltage sensor 5, the overvoltage detection unit 65 outputs an overvoltage signal. When the overvoltage signal is input from the overvoltage detection unit 65, the control switching unit 67 outputs a voltage control command signal as a control switching signal to the control switching unit 63 (step S3 in FIG. 2: step S3 from YES).

The voltage control unit 61 outputs a command value signal based on the deviation between the output voltage signal Vo input from the voltage sensor 5 and the voltage target value Vo ^* (= 0). The PWM signal generation unit 64 generates a PWM signal based on a command value signal input from the voltage control unit 61 via the control switching unit 63 and outputs the PWM signal to the inverter circuit 2. Thereby, the control circuit 6 performs overvoltage suppression control for controlling the output voltage Vo to “0”.

  When the output current Io increases during overvoltage suppression control, the control circuit 6 stops the voltage suppression control and switches the voltage control to current control. That is, when the control switching determination unit 67 detects an increase in the output current Io based on the current change signal input from the current change detection unit 66, the control switching determination unit 67 outputs a current control command signal to the control switching unit 63 as a control switching signal. (Step S4 in FIG. 2: Step S1 from YES). The PWM signal generation unit 64 generates a PWM signal based on a command value signal input from the current control unit 62 via the control switching unit 63 and outputs the PWM signal to the inverter circuit 2. Thereby, the control circuit 6 stops overvoltage suppression control and performs current control. When the control switching determination unit 67 does not detect an increase in the output current Io, the voltage suppression control is continued.

  When the power failure determination unit 68 detects a power failure while continuing the overvoltage suppression control, the power failure determination unit 68 outputs a stop signal to the PWM signal generation unit 64 and outputs a disconnection signal to the switch 8. The PWM signal generation unit 64 to which the stop signal is input stops outputting the PWM signal, so that the output voltage Vinv becomes “0”. The switch 8 to which the disconnection signal is input disconnects the connection between the grid-connected inverter system A and the load B. Thereby, the independent operation state of the grid connection inverter system A is avoided.

  Next, the operation of the control circuit 6 will be described.

In the present embodiment, when the inverter circuit 2 is current-controlled by the PWM signal generated by the PWM signal generation unit 64 based on the command value signal generated by the current control unit 62, the overvoltage detection unit 65 is overvoltage. Is detected, the control switching unit 63 switches the command value signal input to the PWM signal generation unit 64 to the command value signal generated by the voltage control unit 61, and the inverter circuit 2 performs voltage control (overvoltage suppression control). Start. In the overvoltage suppression control, the output voltage Vo of the inverter circuit 2 is controlled to the voltage target value Vo ^* (= 0). Therefore, it is possible to prevent an overvoltage from being applied to the load B.

The overvoltage suppression control is feedback control for detecting the output voltage Vo of the inverter circuit 2 and controlling the detected voltage to be the voltage target value Vo ^* (= 0). Therefore, since the output voltage Vo of the inverter circuit 2 is gradually decreased, an induction voltage is generated in the reactor L3 provided in the filter circuit 3 by instantaneously stopping the inverter circuit 2, and the output voltage Vo is instantaneously jumped. The inconvenience of raising can also be avoided.

  In the present embodiment, when an increase in the output current Io is detected when overvoltage suppression control is being performed, the command value signal input to the PWM signal generation unit 64 by the control switching unit 63 is a current value. The command value signal generated by the control unit 62 is switched, and output control by the inverter circuit 2 is switched from voltage control to current control. On the other hand, when the increase in the output current Io is not detected, the inverter circuit 2 continues the overvoltage suppression control. That is, when the cause of the output voltage Vo of the inverter circuit 2 rising to an overvoltage is not due to a power failure but due to a temporary increase in the system voltage, the output control by the inverter circuit 2 is returned to the current control. When the cause is due to a power failure, overvoltage suppression control is continued in the output control by the inverter circuit 2. Therefore, when an overvoltage occurs, it is possible to cause the inverter circuit 2 to perform power conversion control by an appropriate control method according to the cause of the overvoltage.

  Further, when an overvoltage occurs due to a cause not caused by a power failure, the inverter circuit 2 is temporarily stopped and then not restarted, so that a reduction in power conversion efficiency of the inverter circuit 2 can be suppressed.

  In addition, although the case where the control circuit which concerns on this invention was used for the grid connection inverter system was demonstrated in the said 1st Embodiment, it is not restricted to this. The control circuit according to the present invention can also be used in a power supply system such as a DC / DC converter system.

  FIG. 8 is a diagram for explaining a DC / DC converter system according to a second embodiment of the present invention. In the figure, the same or similar elements as those in the grid interconnection inverter system A shown in FIG.

  The DC / DC converter system A ′ is different from the grid-connected inverter system A (see FIG. 1) of the first embodiment in that a DC / DC converter circuit 7 is provided instead of the inverter circuit 2. The internal configuration of the control circuit 6 is the same as that of the control circuit 6 of FIG.

  The DC / DC converter system A 'boosts or lowers the DC voltage output from the DC power supply 1 by the DC / DC converter circuit 7 and supplies the DC voltage to the load B and the storage battery E.

  Also in this embodiment, when overvoltage is detected, current control is stopped and overvoltage suppression control is performed. Therefore, when the DC / DC converter system A ′ is disconnected from the storage battery E due to an abnormality of the storage battery E, it is possible to prevent an overvoltage from being applied to the load B. Further, since the output voltage Vo is slowly decreased by the overvoltage suppression control, it is possible to prevent an induced voltage from being generated in the reactor of the filter circuit and jumping up the output voltage Vo.

  In addition, when an increase in the absolute value of the output current Io is detected when overvoltage suppression control is being performed, it is considered that the DC / DC converter system A ′ is connected to the storage battery E. The suppression control is stopped and current control is performed. On the other hand, when the increase in the absolute value of the output current Io is not detected, it is considered that the DC / DC converter system A ′ is disconnected from the storage battery E, and thus the overvoltage suppression control is continued. Therefore, when an overvoltage occurs, it is possible to cause the DC / DC converter circuit 7 to perform power conversion control by an appropriate control method according to the cause of the overvoltage.

  In addition, when the overvoltage is due to a temporary increase in the voltage of the storage battery E, the DC / DC converter circuit 7 is temporarily stopped and then not restarted. A reduction in conversion efficiency can be suppressed.

  The control circuit of the present invention can also be applied to an AC / DC converter system that converts AC power output from an AC power source into DC power and supplies the DC power to the load B and the storage battery E.

  The control circuit of the power conversion circuit according to the present invention and the power conversion system including the control circuit are not limited to the above-described embodiments. The specific configuration of the control circuit of the power conversion circuit according to the present invention and each part of the power conversion system including the control circuit can be varied in design in various ways.

A Grid-connected inverter system 1 DC power supply 2 Inverter circuit 3 Filter circuit 4 Current sensor 5 Voltage sensor 6 Control circuit 61 Voltage control unit (voltage control command value signal generating means)
62 Current control unit (current control command value signal generating means)
63 Control switching section (first command value signal switching means, second command value signal switching means)
64 PWM signal generation unit 65 Overvoltage detection unit 66 Current change detection unit (determination means)
67 Control switching determination unit (first command value signal switching means, second command value signal switching means, determination means)
68 Power failure judgment unit 7 DC / DC converter circuit 8 Switch A 'DC / DC converter system B Load C Power system D Breaker E Storage battery

Claims (10)

Current control command value signal generating means for generating a command value signal for controlling the output current of the power conversion circuit detected by the current detection means to a predetermined target current;
PWM signal generation means for generating a PWM signal for controlling the power conversion operation of the power conversion circuit based on the command value signal generated by the current control command value signal generation means;
A control circuit for controlling a power conversion operation of the power conversion circuit by the PWM signal generated by the PWM signal generation means,
Voltage control command value signal generation means for generating a command value signal for controlling the output voltage of the power conversion circuit detected by the voltage detection means to a predetermined target voltage;
Overvoltage detection means for detecting that the output voltage detected by the voltage detection means is overvoltage when a predetermined condition is satisfied;
When it is detected by the overvoltage detection means that an overvoltage has occurred, a command value signal input to the PWM signal generation means is converted from the command value signal generated by the current control command value signal generation means to the voltage control command value signal. First command value signal switching means for switching to the command value signal generated by the generating means;
A determination means for determining whether or not an output current of the power conversion circuit detected by the current detection means has increased when it is detected by the overvoltage detection means that an overvoltage has occurred;
When the determination means determines that the output current of the power conversion circuit is increasing, the command value signal to be input to the PWM signal generation means is determined from the command value signal generated by the voltage control command value signal generation means. Second command value signal switching means for switching to the command value signal generated by the current control command value signal generating means;
A control circuit for a power conversion circuit, comprising:   The overvoltage detection unit detects that the output voltage has become an overvoltage when an instantaneous value of an output voltage detected by the voltage detection unit is equal to or higher than a predetermined threshold higher than the target voltage. Item 2. The control circuit according to Item 1.   The control circuit according to claim 1, wherein the target voltage is “0”.   The determination means calculates an effective value from the output current detected by the current detection means in a predetermined cycle, and the output current increases when the calculated effective value continues to increase for a predetermined period. The control circuit according to any one of claims 1 to 3, wherein   The determination means calculates an effective value from the output current detected by the current detection means at a predetermined cycle, and the output current is calculated when the calculated effective value increases continuously for a preset number of times. The control circuit according to claim 1, wherein the control circuit determines that is increasing.   The control circuit according to claim 1, wherein the power conversion circuit is an inverter circuit.   The control circuit according to claim 1, wherein the power conversion circuit is a DC / DC converter circuit.   A power supply system comprising: the power conversion circuit; and the control circuit according to claim 1. Computer
Current control command value signal generating means for generating a command value signal for controlling the output current of the power conversion circuit detected by the current detection means to a predetermined target current;
PWM signal generation means for generating a PWM signal for controlling the power conversion operation of the power conversion circuit based on the command value signal generated by the current control command value signal generation means;
And a program for causing the PWM signal generated by the PWM signal generation means to function as a control means for controlling a power conversion operation of the power conversion circuit,
The computer,
Voltage control command value signal generation means for generating a command value signal for controlling the output voltage of the power conversion circuit detected by the voltage detection means to a predetermined target voltage;
Overvoltage detection means for detecting that the output voltage detected by the voltage detection means is overvoltage when a predetermined condition is satisfied;
When it is detected by the overvoltage detection means that an overvoltage has occurred, a command value signal input to the PWM signal generation means is converted from the command value signal generated by the current control command value signal generation means to the voltage control command value signal. First command value signal switching means for switching to the command value signal generated by the generating means;
A determination means for determining whether or not an output current of the power conversion circuit detected by the current detection means has increased when it is detected by the overvoltage detection means that an overvoltage has occurred;
When the determination means determines that the output current of the power conversion circuit is increasing, the command value signal to be input to the PWM signal generation means is determined from the command value signal generated by the voltage control command value signal generation means. Second command value signal switching means for switching to the command value signal generated by the current control command value signal generating means;
Program to make it function.   A computer-readable recording medium on which the program according to claim 9 is recorded.

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