JP6484570B2 - Power converter - Google Patents

Description

  The present invention relates to a power converter including a ground fault detection circuit having a zero-phase current transformer provided between a rectifier and a switching element, and a control unit that controls the switching element, and more specifically. The present invention relates to a power conversion device including means for confirming whether or not the ground fault detection circuit is in a state in which a DC ground fault can be detected.

  2. Description of the Related Art Conventionally, there is provided a power conversion device for converting DC power generated by, for example, solar power generation or wind power generation on the power source side into AC power and connecting it to a power company transmission line.

  FIG. 3 is a block diagram showing an example of the electrical configuration of such a power conversion apparatus 100. As shown in FIG.

  The power conversion apparatus 100 includes a rectifier 12 that rectifies input power connected to the input terminal unit 11 on the power supply side, an electrolytic capacitor 14 that smoothes power connected to a subsequent stage of the rectifier 12, and an electrolytic capacitor 14. An intelligent power module (hereinafter also simply referred to as a switching element) 15 for converting DC power into three-phase AC power by various switching elements connected to the rear stage side, and an LC circuit connected to the rear stage side of the switching element 15 Of the reactor 16 and the capacitor 17, the shunt resistor 18 for detecting the current of each phase connected to the rear stage side of the LC circuit, the noise filter 19 connected to the rear stage side of the shunt resistor 18, and the noise filter 19 System-side electromagnetic switch (system-side relay circuit) 20a connected in parallel to the rear stage side and independent-side electromagnetic switch (Self-standing relay circuit) 20b, connected to the downstream side of the system-side electromagnetic switch 20a and connected to the power company transmission line, and connected to the downstream side of the independent-side electromagnetic switch 20b The self-supporting output terminal portion 21b and various controllers A to C that control the switching element 15 are provided. In addition, the block shown with the symbol CT in a figure is a current transformer inserted as needed.

  In the above configuration, the DC line between the rectifier 12 and the switching element 15 is provided with a zero-phase current transformer 13 which is a through-type current sensor, and an output on the secondary side of the zero-phase current transformer 13 is provided. Is input to the DC ground fault detection circuit 22 of the controller B, and the detected value of the DC ground fault is input from the DC ground fault detection circuit 22 to the CPU 23 of the controller A.

  The zero-phase current transformer 13 is a sensor in which almost no current flows when the power conversion device 100 is operating normally. Therefore, when the power conversion apparatus 100 is operating normally, the DC ground fault detection circuit 22 basically does not detect anything, and there is no signal input to the CPU 23.

  On the other hand, when a DC ground fault occurs, the balance of the DC line between the rectifier 12 and the switching element 15 is lost, so a magnetic field is generated around the DC line, and a current flows through the zero-phase current transformer 13. Become. When the current value is detected by the DC ground fault detection circuit 22, the DC ground fault current value is input from the controller B to the CPU 23 of the controller A. The CPU 23 stops switching control of the switching element 15 via the controller C when the current value exceeds the determination value.

  As a power converter equipped with such a DC ground fault detection circuit, for example, in Patent Document 1, an inverter main circuit and an AC relay are interposed between a DC input terminal and an AC output terminal, and a current flows into the inverter main circuit. The main control circuit operates the inverter main circuit with the AC relay opened, and determines whether the inverter main circuit has a fault depending on whether or not current is detected by the DC current sensor during this period. A grid-connected power supply system (power conversion device) is disclosed that is configured to diagnose and close the AC relay only when there is no failure and start the linked operation.

JP-A-6-117066

  As described above, the conventional power converter includes a detection circuit that detects a DC ground fault. However, the zero-phase current transformer 13 for detecting a DC ground fault is a sensor in which almost no current flows when the power converter is operating normally. Basically nothing is detected and no signal is input to the CPU 23.

  This state is the same even when a disconnection or the like occurs in the signal system of the DC ground fault detection circuit 22. Therefore, when a DC ground fault occurs in the power converter in this state, the DC ground fault detection circuit 22. Causes a problem that a DC ground fault cannot be detected and the power converter cannot be stopped. However, a power converter having a function (so-called safety function) for detecting an abnormality such as disconnection of the DC ground fault detection circuit has not been proposed at present.

  The present invention has been made in view of such circumstances, and its purpose is to constantly monitor the state of the DC ground fault detection circuit by adding a function of detecting an abnormality of the detection circuit itself that detects the DC ground fault. Then, when abnormality, such as a disconnection, occurs, it is providing the power converter device which can stop operation | movement immediately.

  In order to solve the above problems, a power converter according to the present invention includes a rectifier that rectifies input power, a switching element that converts DC power connected to an output side of the rectifier into AC power, the rectifier, and the switching element. A ground fault detection circuit having a zero-phase current transformer provided between and a control unit for controlling the switching element, wherein the disconnection detection signal from the control unit And a weak current supply circuit for supplying a weak current to the zero-phase current transformer, and the control unit detects a minute current generated in the zero-phase current transformer by the weak current through the ground fault detection circuit. Thus, it is characterized in that it is confirmed whether or not the ground fault detection circuit is in a state where a DC ground fault can be detected.

  According to this configuration, by supplying the weak current from the weak current supply circuit to the zero-phase current transformer, the ground fault detection circuit always detects the minute current generated in the zero-phase current transformer by the weak current. The current value of the minute current is input to the control unit. Therefore, the control unit can check whether the ground fault detection circuit is in a state where it can detect a DC ground fault by constantly monitoring the current value of the minute current while the power conversion device is operating. When the ground fault detection circuit determines that the DC ground fault cannot be detected, the power converter can be immediately stopped.

  According to the power conversion device of the present invention, the control unit outputs a gate block signal synchronized with a switching signal output to the switching element to the weak current supply circuit, and the weak current supply circuit includes the gate Only when a block signal is received, a weak current may be supplied to the zero-phase current transformer based on the disconnection detection signal.

  According to this configuration, wasteful power consumption can be suppressed.

  According to the power conversion device of the present invention, the disconnection detection signal can be a square wave or sine wave AC signal. In other words, any waveform signal may be used as long as the AC signal can be detected by the ground fault detection circuit.

  According to the power conversion device of the present invention, the current value of the minute current is set to a current value lower than the current value when the ground fault is detected. As a result, it is possible to prevent a minute current from being erroneously detected as a ground fault.

  Further, according to the power conversion device of the present invention, when the control unit cannot detect the current value of the minute current input from the ground fault detection circuit, the ground fault detection circuit can detect a DC ground fault. The control of the switching element is stopped when it is determined that there is no state.

  According to this configuration, it is possible to avoid an unexpected situation in which an operation is continued as it is when a ground fault occurs in a state where an abnormality has occurred due to disconnection of the ground fault detection circuit or the like.

  According to the power conversion device of the present invention, by constantly monitoring the current value of the minute current during operation of the power conversion device, whether or not the ground fault detection circuit or the like is operating normally, that is, whether or not there is a disconnection, etc. Anomalies can always be monitored. Therefore, when an abnormality such as disconnection occurs in the ground fault detection circuit or the like, the operation of the power converter can be stopped immediately.

It is a block diagram which shows the electric constitution of the power converter device which concerns on embodiment of this invention. It is a flowchart which shows the processing procedure of the monitoring operation | movement of the direct-current ground fault detection circuit by a power converter device, and the detection operation of direct-current ground fault. It is a block diagram which shows an example of the electrical structure of the conventional power converter device.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an electrical configuration of a power conversion device according to an embodiment of the present invention.

  The basic configuration of the power converter 1 of this embodiment is the same as that of the conventional power converter 100 shown in FIG. 3, and includes an input terminal unit 11, a rectifier 12, an electrolytic capacitor 14, a switching element 15, and a rectifier 12. A zero-phase current transformer 13 which is a feed-through current sensor provided in a DC line between the switching element 15, a reactor 16 and a capacitor 17 constituting an LC circuit, a shunt resistor 18, a noise filter 19, and a system side electromagnetic switching 20a, a self-supporting electromagnetic switch 20b, a system-side output terminal portion 21a, a self-supporting output terminal portion 21b, and various controllers A to C that control the switching element 15.

  The output on the secondary side of the zero-phase current transformer 13 is input to the DC ground fault detection circuit 22 of the controller B, and the detected value of the DC ground fault (from the DC ground fault detection circuit 22 to the CPU 23 of the controller A ( Current value) is input.

  With the above configuration, when a DC ground fault occurs while the power conversion device 1 is operating, the balance of the DC line between the rectifier 12 and the switching element 15 is lost, so a magnetic field is generated around the DC line, and the zero phase A current flows through the current transformer 13. When the current is detected by the DC ground fault detection circuit 22, a DC ground fault detection value (current value) is input from the DC ground fault detection circuit 22 to the CPU 23 of the controller A. When this current value exceeds the determination value, the CPU 23 is configured to immediately stop the switching control of the switching element 15 via the controller C and urgently stop the power conversion device 1.

  In this case, as described in the prior art, the zero-phase current transformer 13 is a sensor that hardly detects current when the power conversion device 1 is operating normally. Therefore, there is no method for confirming whether or not the DC ground fault detection circuit 22 is functioning normally while the power conversion device 1 is operating (that is, whether or not the DC ground fault can be detected).

  Therefore, in the power conversion device 1 of the present embodiment, whether or not the DC ground fault detection circuit 22 is functioning normally while the power conversion device 1 is operating (that is, whether or not the DC ground fault can be detected). Is added.

  Specifically, in addition to the above configuration, the power conversion device 1 of the present embodiment supplies a weak current to the controller A based on the disconnection detection signal S1 from the CPU 23 to the zero-phase current transformer 13. A circuit 24 is provided. That is, an auxiliary winding is wound around the zero-phase current transformer 13 and a weak current is constantly supplied from the weak current supply circuit 24 to the auxiliary winding.

  Here, the disconnection detection signal S1 is a square wave or sine wave AC signal having a constant frequency. However, any AC waveform signal may be used as long as the DC ground fault detection circuit 22 can detect the AC signal.

  On the other hand, the CPU 3 detects the minute current generated in the zero-phase current transformer 13 by the weak current through the direct current ground fault detection circuit 22, so that the direct current ground fault detection circuit 22 is in a state where the direct current ground fault is detectable. It is configured to check whether or not.

  In this case, the current value of the weak current is set so that the current value of the minute current generated in the zero-phase current transformer 13 by the weak current is lower than the determination value for detecting the DC ground fault. Yes. As a result, it is possible to prevent a minute current generated in the zero-phase current transformer 13 due to a weak current from being erroneously detected as a current value generated due to a DC ground fault.

  Therefore, the CPU 23 constantly monitors the current value of the minute current through the DC ground fault detection circuit 22 to determine whether the DC ground fault detection circuit 22 is functioning normally (that is, in a state in which the DC ground fault can be detected). It is possible to check whether there is.

  Further, in the power conversion device 1 of this embodiment, the CPU 23 is configured to output the gate block signal S <b> 2 synchronized with the switching signal output to the switching element 15 to the weak current supply circuit 24. This gate block signal S2 is a signal of a constant voltage (for example, 5 V, etc.) that is always output during the operation of the power conversion device 1.

  The weak current supply circuit 24 starts supplying weak current to the zero-phase current transformer 13 on the condition that two signals of the disconnection detection signal S1 and the gate block signal S2 are input, and the DC ground fault The monitoring operation of the detection circuit 22 is started. That is, the weak current supply circuit 24 supplies the weak current to the zero-phase current transformer 13 based on the disconnection detection signal S1 only when the gate block signal S2 is received, and the gate block signal S2 is input. If not, the disconnection detection signal S1 from the CPU 23 is not received, and the weak current is not supplied to the zero-phase current transformer 13. According to this configuration, since the DC ground fault detection circuit 22 is monitored only during the operation of the power converter 1, wasteful power consumption can be suppressed.

  Next, the monitoring operation of the DC ground fault detection circuit 22 and the DC ground fault detection operation by the power conversion device 1 having the above configuration will be described.

  As described above, the power conversion device 1 of the present embodiment is configured to constantly supply a minute current to the zero-phase current transformer 13 during the operation of the power conversion device 1. Therefore, even when the power conversion apparatus 1 is operating normally, the current value of a minute current is always input to the CPU 23 through the DC ground fault detection circuit 22. Therefore, it is necessary for the CPU 23 to distinguish and determine the current value of this minute current and the current value generated by the DC ground fault.

  Therefore, in the present embodiment, two threshold values are set for the current value input from the DC ground fault detection circuit 22, and whether the DC ground fault detection circuit 22 is abnormal or not is compared with each threshold value. It is configured to determine whether or not this has occurred.

  Specifically, a current value slightly lower than the minute current is set as the first threshold value Ia, and a current value slightly higher than the minute current and lower than the current value caused by the DC ground fault is set as the second threshold value Ib. Set (Ia <Ib).

  Based on these threshold values Ia and Ib, the CPU 23 performs operation control as follows according to the flowchart shown in FIG.

  During the operation of the power conversion device 1, the CPU 23 constantly monitors the current value input from the DC ground fault detection circuit 22. That is, the input current value is compared with the first threshold value Ia (step S1), and it is confirmed whether or not the input current value is equal to or less than the first threshold value Ia. In this case, the input current value when the power conversion device 1 operates normally and the DC ground fault detection circuit 22 also operates normally is a minute current value, which is higher than the first threshold value Ia. Current value. Therefore, in this case, No is determined in step S1, and the process proceeds to step S2.

  In the next step S2, the CPU 23 compares the input current value with the second threshold value Ib and confirms whether or not the input current value exceeds the second threshold value Ib. In this case, since the input current value is a current value of a minute current and is lower than the second threshold value Ib, it is determined No in step S2, and the process returns to step S1.

  That is, when the input current value input from the DC ground fault detection circuit 22 is between the first threshold value Ia and the second threshold value Ib, the operation is continued as it is. That is, when the power converter 1 operates normally and the DC ground fault detection circuit 22 operates normally, the operation of the power converter 1 is continued as it is.

  On the other hand, when an abnormality such as disconnection occurs in the system from the zero-phase current transformer 13 through the DC ground fault detection circuit 22 to the CPU 23 of the controller A during the operation of the power converter 1 as described above, Even if a weak current is supplied to the current transformer 13, the current value of the minute current generated by the weak current is not input to the CPU 23. Further, when an abnormality such as a disconnection occurs in the system from the CPU 23 through the weak current supply circuit 24 to the zero phase current transformer 13, the weak current is not supplied to the zero phase current transformer 13 in the first place. The CPU 23 does not receive a current value of a minute current that should be generated by a weak current.

  Therefore, in these cases, the CPU 23 determines that the input current value is equal to or less than the first threshold value Ia in Step S1 (Yes is determined), and proceeds to Step S3. That is, an abnormality such as disconnection from the zero-phase current transformer 13 to the CPU 23 of the controller A via the DC ground fault detection circuit 22 or the system from the CPU 23 to the zero-phase current transformer 13 via the weak current supply circuit 24. Is determined to have occurred. In other words, it is determined that the DC ground fault detection circuit 22 cannot detect the occurrence of the DC ground fault. And a process is advanced to step S5 and operation | movement of the power converter device 1 is stopped urgently (namely, switching control of the switching element 15 is stopped).

  On the other hand, when a DC ground fault occurs during the operation of the power converter 1, the balance of the DC line between the rectifier 12 and the switching element 15 is lost, a magnetic field is generated around the DC line, and zero A large current flows through the phase current transformer 13. Since this current value is higher than the second threshold value Ib, the CPU 23 determines Yes in step S2, and advances the process to step S4. That is, in this case, it is determined that a DC ground fault has occurred in the power conversion device 1. And a process is advanced to step S5 and operation | movement of the power converter device 1 is stopped urgently (namely, switching control of the switching element 15 is stopped).

  Thus, according to the present invention, the DC ground fault detection circuit 22 is supplied to the zero-phase current transformer 13 by the weak current by always supplying the weak current from the weak current supply circuit 24 to the zero-phase current transformer 13. The configuration is such that the minute current generated is always detected and the current value of this minute current is input to the CPU 23. Therefore, the CPU 23 constantly monitors the current value of the minute current during operation of the power conversion device 1 to determine whether the DC ground fault detection circuit 22 is in a state where the DC ground fault can be detected in real time. Since it can be confirmed, when the DC ground fault detection circuit 22 determines that the DC ground fault cannot be detected, the power converter 1 can be immediately stopped.

  The present invention can be implemented in various other forms without departing from the spirit or main features thereof. Therefore, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is set forth in the claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Power converter 11 Input terminal part 12 Rectifier 13 Zero phase current transformer 14 Electrolytic capacitor 15 Intelligent power module (switching element)
Reference Signs List 16 Reactor 17 Capacitor 18 Shunt Resistor 19 Noise Filter 20a System Side Electromagnetic Switch 20b Self Standing Electromagnetic Switch 21a System Side Output Terminal Section 21b Self Standing Output Terminal Section 22 DC Ground Fault Detection Circuit (Ground Fault Detection Circuit)
23 CPU (control unit)
24 Weak current supply circuit

Claims (5)

A ground having a rectifier for rectifying input power, a switching element for converting DC power connected to the output side of the rectifier to AC power, and a zero-phase current transformer provided between the rectifier and the switching element A power conversion device comprising a fault detection circuit and a control unit that controls the switching element,
A weak current supply circuit that supplies a weak current to the zero-phase current transformer based on a disconnection detection signal from the control unit,
The control unit detects whether or not the ground fault detection circuit is capable of detecting a DC ground fault by detecting a minute current generated in the zero-phase current transformer by the weak current through the ground fault detection circuit. The power converter characterized by confirming. The power conversion device according to claim 1,
The control unit outputs a gate block signal synchronized with a switching signal output to the switching element to the weak current supply circuit,
The weak current supply circuit supplies a weak current to the zero-phase current transformer based on the disconnection detection signal only when the gate block signal is received. The power conversion device according to claim 1 or 2, wherein
The disconnection detection signal is a square wave or sine wave AC signal. It is a power converter device as described in any one of Claim 1- Claim 3, Comprising:
The power conversion device according to claim 1, wherein the current value of the minute current is a current value lower than a current value when a ground fault is detected. A power conversion device according to any one of claims 1 to 4, wherein
When the current value of the minute current input from the ground fault detection circuit cannot be detected, the control unit determines that the ground fault detection circuit is not in a state in which a DC ground fault can be detected and determines the switching element. The power converter characterized by stopping control.

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