JP2013236482A - Inverter device, power conversion device, and distribution power-supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter device capable of preventing failure of a switching element and a bi-directional switch when an inverter circuit section returns from an operation stop state.SOLUTION: When an overcurrent is detected during the normal operation of an inverter circuit section and then the inverter circuit section is changed to an operation stop state, all the switching elements in a bridge section 1512 are turned to be off, and two bi-directional switches in a bi-directional section 1511 are turned to be on.

Description

  The present invention relates to an inverter device that performs overcurrent protection.

  Conventionally, inverters that convert DC power into AC power have been used in various fields including solar power generation systems. Various inverter control techniques for protecting against the occurrence of overcurrent have been proposed in the past (see, for example, Patent Documents 1 and 2).

  FIG. 2 shows a conventional DC / AC conversion system including an inverter device having a protection function against occurrence of overcurrent. 2. Description of the Related Art Conventionally, various so-called multilevel inverters have been developed that convert a direct current into an alternating current by generating a pulse voltage waveform having three or more voltage levels. In the multi-level inverter, one having three voltage levels is referred to as a three-level inverter. The inverter device 15 in FIG. 2 is this three-level inverter.

  FIG. 2 shows a DC / AC conversion system that outputs AC power in linkage with a commercial power system using a distributed power source as a DC power source. The inverter device 15 that is a three-level inverter includes an inverter circuit unit 151 and a DSP (Digital Signal Processor) 152. The inverter circuit unit 151 includes a three-level conversion unit 151A and an LC filter unit 151B. The output side of the DC / DC converter 10 to which the DC power supply Vdc is connected to the input side is connected to the input side of the three-level converter 151A. The commercial system 30 is connected to the output side of the LC filter unit 151B. The DC / DC converter 10 and the inverter device 15 constitute a power conversion device.

  The three-level conversion unit 151A includes smoothing capacitors C1 and C2, switching elements Q1, Q2, Q7, and Q8 configured by MOSFETs, and switching elements Q3, Q4, Q5, and Q6 configured by IGBTs. The LC filter unit 151B includes reactors L1 and L2 and an output capacitor C3.

  One end of the high-side smoothing capacitor C1 is connected to the positive output terminal T1 of the DC / DC converter 10, and one end of the low-side smoothing capacitor C2 is connected to the negative output terminal T2 of the DC / DC converter 10. The smoothing capacitors C1 and C2 are connected in series.

  Further, the drain of the switching element Q1 is connected to the plus output terminal T1, the source of the switching element Q7 is connected to the minus output terminal T2, and the source of the switching element Q1 and the drain of the switching element Q7 are connected. An antiparallel diode is connected between the drain and source of each switching element Q1 and Q7. The antiparallel diode may be a parasitic diode (built-in diode) or an externally connected diode, and so on.

  Switching elements Q5 and Q6 are connected in anti-series between the connection point of the smoothing capacitors C1 and C2 and the connection point of the switching elements Q1 and Q7. Anti-parallel diodes are connected between the collectors and emitters of the switching elements Q5 and Q6, and a bidirectional switch is configured by the switching elements Q5 and Q6 and the anti-parallel diodes.

  Further, the drain of the switching element Q2 is connected to the plus output terminal T1, the source of the switching element Q8 is connected to the minus output terminal T2, and the source of the switching element Q2 and the drain of the switching element Q8 are connected. An antiparallel diode is connected between the drain and source of each switching element Q2 and Q8.

  Switching elements Q3 and Q4 are connected in anti-series between the connection point of the smoothing capacitors C1 and C2 and the connection point of the switching elements Q2 and Q8. Anti-parallel diodes are connected between the collectors and emitters of the switching elements Q3 and Q4, and the switching elements Q3 and Q4 and the anti-parallel diodes constitute a bidirectional switch.

  As described above, the switching element Q1, Q2, Q7, and Q8 constitute the bridge portion 1512, and the switching elements Q3 to Q6 constitute the bidirectional portion 1511.

  A connection point between switching elements Q1 and Q7 is connected to one end of reactor L1, and a connection point between switching elements Q2 and Q8 is connected to one end of reactor L2. One end of the output capacitor C3 is connected to the other end of the reactor L1, and the other end of the output capacitor C3 is connected to the other end of the reactor L2 via the current detector 20.

  The DSP 152 controls the on / off of each of the switching elements Q1 to Q8 by sending a control signal to the gates of the switching elements Q1 to Q8 via a driver (not shown). Further, the DSP 152 receives a detection signal from the current detector 20.

  Here, if the voltage across the pair of the smoothing capacitors C1 and C2 connected in series is Vin, the smoothing capacitors C1 and C2 have the same capacity. Therefore, the potential at the connection point between the smoothing capacitors C1 and C2 is Vin / 2. It becomes.

  In this case, when the switching elements Q1 and Q8 are turned on, the output voltage Vout of the three-level conversion unit 151A becomes Vin. Further, by turning on the switching elements Q6 and Q8, the output voltage Vout of the three-level conversion unit 151A becomes Vin / 2. Further, when the switching elements Q6 and Q3 are turned on, the output voltage Vout of the three-level converter 151A becomes zero.

  Furthermore, when the switching elements Q2 and Q7 are turned on, the output voltage Vout of the three-level converter 151A becomes −Vin. Further, when the switching elements Q4 and Q7 are turned on, the output voltage Vout of the three-level converter 151A becomes −Vin / 2.

  By switching the switching pattern of such switching elements, for example, as shown in FIG. 3, the output voltage Vout of the three-level converter 151A having three levels can be obtained. Then, by filtering the output voltage Vout by the LC filter unit 151 </ b> B, a sinusoidal output current Iout can be output to the commercial system 30.

JP 2003-153433 A JP-A-9-74685

  The DSP 152 monitors the detection signal from the current detector 20 during normal operation of the inverter circuit unit 151. When an overcurrent occurs during a transient such as a system sudden change, the DSP 152 detects this based on the detection signal from the current detector 20 and controls the gates of the switching elements to turn off all the switching elements Q1 to Q8. Is output. As a result, the operation of the inverter circuit unit 151 is stopped and protection against overcurrent is performed.

  For example, as shown in FIG. 4, when the normal operation is performed with the switching elements Q6 and Q3 turned on in the bidirectional part 1511 and the switching elements Q1 and Q8 turned on in the bridge part 1512, switching is performed from the input terminal on the plus side. A current flows through a route in the order of the element Q1, the reactor L1, the system, the reactor L2, the switching element Q8, and the negative input terminal (solid arrow in FIG. 4).

  Here, when the DSP 152 detects the occurrence of an overcurrent, the DSP 152 turns off all the switching elements Q1 to Q8 as shown in FIG. At this time, due to the action of the reactors L1 and L2, the negative input terminal, the reverse parallel diode of the switching element Q7, the reactor L1, the system, the reactor L2, the reverse parallel diode of the switching element Q2, and the positive input terminal Current flows through the path (solid arrow in FIG. 5). That is, commutation of the switching elements Q2 and Q7 to the antiparallel diode occurs.

  Thereafter, when the DSP 152 detects that the abnormal state has been released, the DSP 152 turns on the switching elements Q6 and Q3 as shown in FIG. 6 in order to cause the inverter circuit unit 151 to return to the normal operation. In the part 1512, the switching elements Q1 and Q8 are turned on. Then, a current flows through the same path as in FIG. 4 (solid arrow in FIG. 6), and at the same time, a recovery current flows through the antiparallel diode due to the commutation of the switching elements Q2 and Q7 to the antiparallel diode. Thereby, an input terminal on the plus side, an antiparallel diode of the switching element Q2, an antiparallel diode of the switching element Q4, a switching element Q3, an antiparallel diode of the switching element Q5, a switching element Q6, an antiparallel diode of the switching element Q7, and A current flows through the path in the order of the input terminal on the minus side (broken arrow in FIG. 6).

  Therefore, a short-circuit mode due to the recovery current occurs, causing a failure of the switching element and the bidirectional switch.

  In view of the above problems, an object of the present invention is to provide an inverter device that can suppress a failure of a switching element and a bidirectional switch when an inverter circuit unit returns from an operation stop state.

In order to achieve the above object, the inverter device of the present invention provides:
A first switching element on the high side and a second switching element on the low side that are connected in series, a first bidirectional switch having one end connected to a connection point of the first switching element and the second switching element, and a first switching A first reactor having one end connected to a connection point between the element and the second switching element, a third switching element on the high side and a fourth switching element on the low side connected in series, a third switching element and a fourth switching One end is connected to the connection point between the third switching element and the fourth switching element, the second bidirectional switch having one end connected to the connection point of the elements and the other end connected to the other end of the first bidirectional switch. An inverter circuit unit having a second reactor;
When an overcurrent is detected during normal operation of the inverter circuit unit and the operation is shifted to the stop, the first to fourth switching elements are turned off and the first bidirectional switch and the second bidirectional switch are turned on. A switching control unit,
It is set as the structure provided with.

  According to such a configuration, since the first to fourth switching elements are turned off when an overcurrent is generated during normal operation of the inverter circuit unit, the overcurrent can be suppressed. In addition, since the first bidirectional switch and the second bidirectional switch are turned on, the first reactor and the second bidirectional switch are operated via the first bidirectional switch and the second bidirectional switch by the action of the first reactor and the second reactor. The current flows back through the two reactors. Thereby, it can suppress that an electric current commutates to the antiparallel diode connected to the 1st-4th switching element. Therefore, even when returning to the normal operation, it is possible to suppress the recovery current from flowing through the switching element and to suppress the occurrence of the short-circuit mode. Therefore, the failure of the switching element and the both switches can be suppressed.

  In the above configuration, when overcurrent continues after the first to fourth switching elements are turned off and the first bidirectional switch and the second bidirectional switch are turned on, The switching control unit may be configured to turn off the first bidirectional switch and the second bidirectional switch while turning off the first to fourth switching elements. According to such a configuration, overcurrent can be more reliably suppressed.

  Moreover, the power converter device of this invention is provided with the inverter apparatus of one of the said structures, and the DC / DC converter connected to the front | former stage side of the said inverter apparatus.

  Moreover, the distributed power supply system of this invention is equipped with the said power converter device and the solar cell, fuel cell, or storage battery connected to the front | former stage side of the DC / DC converter which the said power converter device has.

  ADVANTAGE OF THE INVENTION According to this invention, when an inverter circuit part returns from an operation stop state, failure of a switching element and a bidirectional switch can be suppressed.

It is a figure which shows the switching control at the time of the operation stop in the inverter circuit part which concerns on one Embodiment of this invention. It is a figure which shows the structure of the prior art example of a DC / AC conversion system. It is a figure which shows an example of the output voltage waveform of a 3 level conversion part, and the output current waveform of an inverter circuit part. It is a figure which shows the switching control at the time of the normal driving | operation in the conventional inverter circuit part. It is a figure which shows the switching control at the time of the operation stop in the conventional inverter circuit part. It is a figure which shows the switching control at the time of the return from the operation stop in the conventional inverter circuit part.

  An embodiment of the present invention will be described below with reference to the drawings. Since the configuration of the DC / AC conversion system according to the embodiment of the present invention is the same as the configuration of FIG. 2 described above, detailed description thereof is omitted here.

  Here, as shown in FIG. 4 described above, the switching elements Q6 and Q3 are turned on in the bidirectional part 1511, the switching elements Q1 and Q8 are turned on in the bridge part 1512, and the inverter circuit part 151 is performing normal operation. And In this case, current flows from the positive input terminal through the switching element Q1, the reactor L1, the system, the reactor L2, the switching element Q8, and the negative input terminal in this order (solid arrow in FIG. 4).

  When the DSP 152 detects the occurrence of overcurrent based on the detection signal from the current detector 20, the DSP 152 controls the switching elements Q1, Q2, Q7, and Q8 in the bridge unit 1512 to be off, but the bidirectional unit 1511. The switching elements Q6 and Q3 are controlled to be on and the switching elements Q5 and Q4 are controlled to be off.

  As described above, the overcurrent can be suppressed by turning off the switching element in the bridge portion 1512. In addition, due to the action of reactors L1 and L2, current flows back through the system, reactor L2, antiparallel diode of switching element Q4, switching element Q3, antiparallel diode of switching element Q5, switching element Q6, and reactor L1. (Solid arrow in FIG. 1). That is, since current flows through reactors L1 and L2 via the bidirectional switch in bidirectional unit 1511, current can be suppressed from flowing to the antiparallel diode of the switching element in bridge unit 1512.

  Thereafter, when the DSP 152 detects that the abnormal state has been released, the DSP 152 turns on the switching elements Q6 and Q3 as shown in FIG. 4 to cause the inverter circuit unit 151 to return to the normal operation. In the part 1512, the switching elements Q1 and Q8 are turned on. At this time, since no commutation of current to the antiparallel diode of the switching element in the bridge portion 1512 occurs, no recovery current is generated, and the occurrence of a short-circuit mode as shown by the dashed arrow in FIG. 6 is suppressed. it can. Therefore, the failure of the switching element can be suppressed.

  In addition, the control method is the same in the combination operation of the opposite phase to the above. That is, the switching elements Q4 and Q5 of the bidirectional unit 1511 are turned on, and the switching elements Q2 and Q7 are performing PWM switching operation. In this case, if it is detected that an output overcurrent has occurred, the switching elements Q1, Q2, Q7 and Q8 of the bridge unit 1512 are controlled to be off, and the switching elements Q4 and Q5 in the bidirectional unit 1511 are controlled to be on. If the switching elements Q3 and Q6 are controlled to be off, the current does not flow to the antiparallel diode of the switching element of the bridge unit 1512 as described above. Therefore, after the overcurrent state is released, the switching element Q3 and Q6 are reversed. No recovery current is generated by the parallel diode.

  Further, for example, when the DSP 152 detects that overcurrent continues even after a certain period of time has elapsed since the start of control to turn on some of the switching elements of the bidirectional unit 1511 as shown in FIG. The DSP 152 turns off all the switching elements in the bidirectional unit 1511 in addition to the bridge unit 1512. Thereby, an overcurrent can be suppressed more reliably.

  The embodiment of the present invention has been described above, but the embodiment can be variously modified within the scope of the gist of the present invention.

  For example, as the bidirectional switch in the inverter circuit unit, one configured by connecting two switching elements in antiparallel to each other may be used.

  Further, in the above embodiment, the voltage-type current control type inverter device for the purpose of system interconnection in the distributed power supply system is used, but the same applies to the voltage-type voltage control capable of AC output independently. Regardless of the method, the effect of the present invention is the same. Further, the DC power source Vdc may be a DC power source such as a storage battery or a fuel cell in addition to the solar battery.

DESCRIPTION OF SYMBOLS 10 DC / DC converter 15 Inverter apparatus 151 Inverter circuit part 151A 3 level conversion part 151B LC filter part 1511 Bidirectional part 1512 Bridge part 152 DSP (Digital Signal Processor)
20 Current detector 30 Commercial system T1 Positive output terminal T2 Negative output terminal C1, C2 Smoothing capacitor Q1-Q8 Switching element L1, L2 Reactor C3 Output capacitor Vdc DC power supply

Claims (6)

A first switching element on the high side and a second switching element on the low side that are connected in series, a first bidirectional switch having one end connected to a connection point of the first switching element and the second switching element, and a first switching A first reactor having one end connected to a connection point between the element and the second switching element, a third switching element on the high side and a fourth switching element on the low side connected in series, a third switching element and a fourth switching One end is connected to the connection point between the third switching element and the fourth switching element, the second bidirectional switch having one end connected to the connection point of the elements and the other end connected to the other end of the first bidirectional switch. An inverter circuit unit having a second reactor;
When an overcurrent is detected during normal operation of the inverter circuit unit and the operation is shifted to the stop, the first to fourth switching elements are turned off and the first bidirectional switch and the second bidirectional switch are turned on. A switching control unit,
An inverter device comprising:   When the overcurrent continues after the first to fourth switching elements are turned off and the first bidirectional switch and the second bidirectional switch are turned on, the switching control unit The inverter device according to claim 1, wherein the first to fourth switching elements are turned off and the first bidirectional switch and the second bidirectional switch are turned off.   A power conversion device comprising: the inverter device according to claim 1 or 2; and a DC / DC converter connected to a front stage side of the inverter device.   A distributed power supply system comprising: the power conversion device according to claim 3; and a solar cell connected to a front stage side of a DC / DC converter included in the power conversion device.   A distributed power supply system comprising: the power conversion device according to claim 3; and a fuel cell connected to a front stage side of a DC / DC converter included in the power conversion device.   A distributed power supply system comprising: the power conversion device according to claim 3; and a storage battery connected to a front stage side of a DC / DC converter included in the power conversion device.

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