JP2014124040A - Surge reduction circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce surge of a conductor wire connected to a switching circuit.SOLUTION: A switching circuit is connected to a DC power supply and an electric load by a conductor wire. A surge reduction circuit has a feedback path having a sub-conductor wire connected in series to a reflux diode. The feedback path and the conductor wire constitute a current circulation circuit for circulating a reflux current generated by switching of the switching circuit. In an example, the conductor wire connects an inverter and a motor. In another example, the conductor wire connects the inverter and a smoothing capacitor. In another example, the feedback path connects a transistor forming a switch of the switching circuit and a pair of reverse parallel diodes.

Description

The present invention relates to a circuit for reducing a surge voltage of a conductor line connected to a switching element, and more particularly to a surge reduction circuit for reducing a surge voltage of a conductor line connected to a pulse circuit.

For example, in order to reduce the switching loss of an inverter for driving a motor, it is necessary to shorten the transition period of the switching element. This transition period includes an on transition period and an off transition period. The on transition period means a transition period from the off state of the switching element to the on state, and the off transition period means a transition period of the switching element from the on state to the off state. However, due to the shortening of the transition period, a large surge is induced in the wiring connected to the main terminal of the switching element. As a result, the reduction of switching loss due to the shortening of the transition period is limited by the surge. Furthermore, the surge of the cable connecting the inverter and the motor degrades the electrical insulation of the motor coil.

Hereinafter, the surge of the wiring connecting the switching element and the power source is referred to as an input surge. In particular, an input surge that occurs when the switching element is turned off is called a turn-off surge. This turn-off surge applies a high voltage to the main electrode of the switching element. Therefore, the reduction of turn-off surge is important in high voltage switching elements. Further, in the following, the surge of the wiring connecting the switching element and the inductance load is referred to as an output surge.

FIG. 1 shows a surge reduction circuit disclosed in Patent Document 1. As shown in FIG. 1, the surge reduction circuit for reducing the output surge includes a sub-cable connected to a pair of a resistor Rb and a capacitor CA. The sub cable C2 is connected in parallel with the main cable C1 that connects the inverter 3 and the motor 4. The main cable C1 and the sub cable C2 each have an inductance Ls. However, the potential change at the output terminal X of the inverter 3 is transmitted to the motor 4 in parallel through both the main cable C1 and the sub cable C2. Therefore, the direction of the magnetic energy stored in the inductance Ls of the main cable C1 is the same as the direction of the magnetic energy stored in the inductance Ls of the sub cable C2. As a result, the magnetic energy accumulated in the inductance Ls of the sub cable C2 must be consumed in a short time before the current of the main cable C1 flows in the reverse direction through the sub cable C2.

FIG. 2 shows conventional RC snubbers 200U, 200L that reduce the input surge of the half bridge. This half bridge has an upper transistor 31T, a lower transistor 34T, an upper antiparallel diode 31D, and a lower antiparallel diode 34D. The potentials at the positive terminal Y and the negative terminal Z of the half bridge change due to an input surge. This potential change is reduced by the RC circuits 200U and 200L and the smoothing capacitor 6. The half ridge has an internal inductance Li and an external inductance Lo. However, due to the presence of the internal inductance Li, the main electrode of the upper transistor 31T has a large potential oscillation. Furthermore, the large-capacity smoothing capacitor 6 and the RC circuits 200U and 200L increase the cost and loss of the circuit.

U. S. P. No. 7,764,042

An object of the present invention is to provide a switching circuit capable of reducing a surge voltage.

It is known that a conductor wire connected to a switching circuit generates a surge. A resonant circuit having a parasitic (floating) capacitance connected to the conductor wire and an inductance of the conductor wire generates a surge voltage having a high-frequency oscillation voltage. The surge reduction circuit of the present invention has a feedback path connected in parallel with the conductor line. This feedback path has a sub-conductor line connected in series with the freewheeling diode. The feedback path and the conductor line constitute a current circulation circuit for circulating a circulating current generated by switching of the switching circuit.

According to the present invention, since the positive half wave component or the negative half wave component of the surge generated by the conductor line circulates through the feedback path, the surge voltage generated at the end of the conductor line is reduced. According to the present invention, it is possible to realize a surge reduction circuit that is very inexpensive and simple and has excellent reliability.

According to a preferred embodiment of the invention, the return path consists essentially of a freewheeling diode and a sub-conductor line. The electrical resistance value of the feedback path excluding the resistance value of the freewheeling diode is less than twice the electrical resistance value of the sub conductor wire. In other words, since a special resistor for consuming surge power is not used, the cooling problem of this resistor can be ignored. Furthermore, the inductance value of the feedback path is less than twice the inductance value of the sub conductor wire. In other words, since a transformer that transfers surge power to the outside is not used, the inductance value of the feedback path is not increased by the leakage inductance of the transformer. This means that the reflux current flowing to the return path is increased.

In a preferred example, the conductor wire connects the inverter and the motor. In another preferred embodiment, the conductor line connects the inverter and the smoothing capacitor. In another preferred embodiment, the return path freewheeling diode connects a transistor and an antiparallel diode connected in parallel. In another preferred embodiment, the feedback path connects the high potential main electrode of the upper arm transistor constituting the upper arm switch of the inverter and the cathode electrode of the upper antiparallel diode. In another preferred embodiment, the feedback path connects the low potential main electrode of the lower arm transistor constituting the lower arm switch of the inverter and the anode electrode of the lower antiparallel diode. As a result, recovery of the antiparallel diode can be promoted.

FIG. 1 is a schematic wiring diagram showing a conventional output surge reduction circuit. FIG. 2 is a schematic wiring diagram showing a conventional input surge reduction circuit. FIG. 3 is a schematic wiring diagram showing the output surge reduction circuit of the first embodiment. FIG. 4 is a timing chart showing a surge voltage waveform. FIG. 5 is a schematic wiring diagram showing a first feedback path connected in parallel with the phase cable. FIG. 6 is a schematic wiring diagram showing a second feedback path connected in parallel with the phase cable. FIG. 7 is a schematic wiring diagram showing two feedback paths connected in parallel with the phase cable. FIG. 8 is a schematic wiring diagram showing a modification. FIG. 9 is a schematic wiring diagram showing another modification. FIG. 10 is a schematic wiring diagram showing the input surge reduction circuit of the second embodiment. FIG. 11 is a schematic wiring diagram showing a dead time state. FIG. 12 is a schematic wiring diagram showing the ON state of the lower arm transistor. FIG. 13 is a schematic wiring diagram showing a dead time state. FIG. 14 is a schematic wiring diagram showing the ON state of the upper arm transistor. FIG. 15 is a schematic wiring diagram showing a dead time state. FIG. 16 is a schematic wiring diagram showing an on state of the upper arm transistor. FIG. 17 is a schematic wiring diagram showing a dead time state. FIG. 18 is a schematic wiring diagram showing the ON state of the lower arm transistor. FIG. 19 is a schematic cross-sectional view of a semiconductor chip in which an IGBT chip and a free-wheeling diode constituting the upper arm transistor are integrated. FIG. 20 is a schematic equivalent circuit diagram of the semiconductor chip shown in FIG. FIG. 21 is a schematic wiring diagram showing a surge reduction circuit connected to the upper arm switch. FIG. 22 is a schematic wiring diagram showing a surge reduction circuit connected to the upper arm switch. FIG. 23 is a schematic wiring diagram showing a three-phase motor driving device having six surge reduction circuits.

First Embodiment A first embodiment of the surge reduction circuit according to the present invention will be described with reference to FIGS. According to the first embodiment, a surge reduction circuit for reducing a surge generated in a motor cable is described.

FIG. 3 is a schematic wiring diagram showing the traction motor driving device. The three-phase inverter 3 includes a U-phase leg, a V-phase leg, and a W-phase leg. The U-phase leg consists of a half bridge having an upper arm switch 31 and a lower arm switch 34. The V-phase leg consists of a half bridge having an upper arm switch 32 and a lower arm switch 35. The W-phase leg consists of a half bridge having an upper arm switch 33 and a lower arm switch 36. The U-phase leg has an output terminal 3U. The V-phase leg has an output terminal 3V. The W-phase leg has an output terminal 3W.

The three-phase traction motor 4 has a U-phase terminal 4U, a V-phase terminal 4V, and a W-phase terminal 4W. The three phase cables C1 individually connect U-phase terminal pairs 3U and 4U, V-phase terminal pairs 3V and 4V, and W-phase terminal pairs 3FW and 4W.

The surge reduction circuit of this embodiment will be described below. This surge reduction circuit includes three first feedback paths and three second feedback paths. Each first feedback path consists of a sub-cable C2 connected in series with the freewheeling diode D1. Each second feedback path consists of a sub-cable C3 connected in series with the freewheeling diode D2. Each phase sub-cable C2 is connected in parallel with each phase cable C1 through a freewheeling diode D1. Each phase sub-cable C3 is connected in parallel with each phase cable C1 through a freewheeling diode D2.

The anode electrodes of the three free-wheeling diodes D1 are individually connected to the output terminals 3U, 3V, and 3W of the inverter 3. The cathode electrodes of the three freewheeling diodes D1 are individually connected to the respective one ends of the three sub cables C2. The cathode electrodes of the three free-wheeling diodes D2 are individually connected to the output terminals 3U, 3V, and 3W of the inverter 3. The anode electrodes of the three freewheeling diodes D2 are individually connected to the respective one ends of the three sub cables C3.

The surge reduction operation of this surge reduction circuit will be described with reference to FIGS. FIG. 4 shows a waveform of the U-phase voltage Vum that arrives at the U-phase terminal 4U of the motor 4 through the phase cable C1. When the upper arm switches 31 and 34 are switched, the U-phase voltage Vum includes a ringing surge voltage. This means that the phase cable C1 has an oscillator Vac that generates a ringing surge, as shown in FIG. Each cable C1-C3 is assumed to have an impedance value Z.

FIG. 5 is a schematic equivalent wiring diagram showing the positive half-wave period of the oscillation voltage of the oscillator Vac. The oscillation power of the oscillator Vac is generated by resonance between the inductance component of the impedance Z and the parasitic capacitance Cs. A positive component of the resonance current Is flows through the impedance Z, the parasitic capacitance Cs, and the ground line GL. The impedance value of the ground line GL is ignored. Furthermore, the circulating current If flows through the sub-cable C3 and the circulating diode D2.

According to FIG. 5, the feedback path consisting of the sub-cable C3 and the freewheeling diode D2 absorbs the energy of the oscillator Vac. This is because the circulating current If flows through the sub-cable 32 and the circulating diode D2. As a result, the energy of the oscillator Vac is reduced, so that the surge of the phase cable C1 is reduced.

FIG. 6 is a schematic equivalent wiring diagram showing the negative positive half-wave period of the oscillation voltage of the oscillator Vac. A negative component of the resonance current Is flows through the impedance Z, the parasitic capacitance Cs, and the ground line GL. Furthermore, the circulating current If flows through the sub-cable C2 and the circulating diode D1. As a result, the feedback path composed of the sub-cable C2 and the freewheeling diode D1 absorbs the energy of the oscillator Vac. This is because the circulating current If flows through the sub-cable C2 and the circulating diode D1. As a result, the energy of the oscillator Vac is reduced, so that the surge of the phase cable C1 is reduced.

Eventually, the circulating current If circulates through the two sub-cables C2 and C3 and the circulating diodes D1 and D2, as shown in FIG. Therefore, the magnetic energy stored in the impedance Z of the sub cables C2 and C3 does not return to the phase cable C1.

According to the first modification shown in FIG. 8, the surge reduction circuit is composed of three pairs each consisting of a sub-cable C3 and a free-wheeling diode D2. Since the electric resistance values of the cables C1 and C3 are small, the attenuation of the circulating current If is small. It is preferable that the decay time constant of the circulating current circulating through the phase cable C1 and the sub cable C3 is longer than the PWM cycle of the inverter 3.

According to the second modification shown in FIG. 9, the surge reduction circuit is composed of three pairs each consisting of a sub-cable C2 and a free-wheeling diode D1. Since the electric resistance values of the cables C1 and C2 are small, the attenuation of the circulating current If is small. It is preferable that the decay time constant of the circulating current circulating through the phase cable C1 and the sub cable C2 is longer than the PWM cycle of the inverter 3.

Further, according to FIGS. 8 and 9, the conductor line Cx having the freewheeling diode Dx connects the positive terminal of the smoothing capacitor 6 and the high potential DC power supply terminal 30 of the inverter 3. By this feedback path composed of the freewheeling diode Dx and the conductor line Cx, the surge of the high potential DC power supply terminal 30 of the inverter 3 is suppressed.

Second Embodiment A second embodiment of the surge reduction circuit of the present invention will be described with reference to FIGS. According to the second embodiment, a surge reduction circuit for reducing turn-off surge is described.

FIG. 10 is a schematic equivalent circuit diagram showing the U-phase leg of inverter 3 shown in FIG. This U-phase leg has an upper arm switch 31 and a lower arm switch 34 connected in series. The U-phase leg further has free-wheeling diodes D7 and D8. The upper arm switch 31 includes an upper transistor 31T and an upper antiparallel diode 31D connected in parallel. The lower arm switch 34 includes a lower transistor 34T and a lower antiparallel diode 34D connected in parallel.

With the exception of the free-wheeling diodes D7 and D8, this U-phase leg consists of a known half bridge. The U-phase cable C1 is connected to the high potential DC link line 7 through the transistor 31T and the antiparallel diode 31D. The U-phase cable C1 is connected to the low potential DC link line 8 through the transistor 34T and the antiparallel diode 34D.

The collector electrode (high potential main electrode) of the transistor 31T is connected to the cathode electrode of the antiparallel diode 31D through the bypass conductor line C7 having the freewheeling diode D7. The anode electrode of the freewheeling diode D7 is connected to the collector electrode (high potential main electrode) of the transistor 31T.

Similarly, the collector electrode (low potential main electrode) of the transistor 34T is connected to the anode electrode of the antiparallel diode 34D through the bypass conductor line C8 having the freewheeling diode D8. The cathode electrode of the freewheeling diode D8 is connected to the emitter electrode (low potential main electrode) of the transistor 34T.

The collector electrode of the transistor 31T is connected to the high potential DC link line 7 through the conductor line 1U. The cathode electrode of the antiparallel diode 31D is connected to the high potential DC link line 7 through the conductor line 2U. Similarly, the emitter electrode of the transistor 34T is connected to the low potential DC link line 8 through the conductor line 1L. The anode electrode of the antiparallel diode 34D is connected to the low potential DC link line 8 through the conductor line 2L.

The conductor lines 1U, 1L, 2U and 2L have an internal inductance Li and an external inductance Lo, respectively. The internal inductance Li means an inductance value inside the U-phase leg module surrounded by a broken line. This external inductance Lo means the external inductance value of this U-phase leg module. The high potential DC link line 7 is connected to the low potential DC link line 8 through the smoothing capacitor 6.

The switching operation of the half bridge constituting the U-phase leg will be described with reference to FIGS. FIGS. 11 to 14 show modes in which the U-phase cable C1 flows U-phase current from the U-phase winding of the motor 4 to the inverter 3. FIGS. 15 to 18 show modes in which the U-phase cable C1 flows U-phase current from the inverter 3 to the U-phase winding of the motor 4. Each of the conductor lines 1U and 1L has an inductance LT (= Li + Lo). Each of the conductor lines 2U and 2L has an inductance LD (= Li + Lo). FIG. 11 shows a dead time state in which the transistor 31T is turned off. The U-phase current Im flows to the high potential DC link line 7 through the antiparallel diode 31D.

FIG. 12 shows a point in time when the transistor 34T is turned on. The U-phase current Im flows to the low potential DC link line 8 through the transistor 34T. Due to the magnetic energy accumulated in the inductance LD of the conductor wire 2U, the circulating current If circulates through the conductor wire 1U, the circulating diode D7 and the conductor wire 2U. The conductor line 1U and the bypass conductor line C7 constitute a sub conductor line of the return path. Therefore, the potential drop of the cathode electrode of the antiparallel diode 31D is suppressed. As a result, since the recovery of the antiparallel diode 31D is promoted, the reverse recovery loss of the antiparallel diode 31D is reduced.

FIG. 13 shows a dead time state in which the transistor 34T is turned off. The U-phase current Im flows to the high potential DC link line 7 through the antiparallel diode 31D. If the circulating current If flowing in the antiparallel diode 31D remains, the rise of the U-phase current Im is promoted. Due to the magnetic energy accumulated in the inductance LT of the conductor wire 1L, the circulating current If circulates through the conductor wire 2L, the circulating diode D8 and the conductor wire 1L. The conductor line 2L and the bypass conductor line C8 constitute a sub conductor line of the return path. Therefore, the potential drop of the emitter electrode of the transistor 34 is suppressed. In other words, the turn-off surge of the transistor 34 is suppressed.

FIG. 14 shows a point in time when the transistor 31T is turned on. The U-phase current Im flows to the high potential DC link line 7 through the transistor 31T. Due to the magnetic energy accumulated in the inductance LD of the conductor wire 2U, the circulating current If circulates through the conductor wire 1U, the circulating diode D7 and the conductor wire 2U. The conductor line 1U and the bypass conductor line C7 constitute a sub conductor line of the return path. Therefore, the potential drop of the cathode electrode of the antiparallel diode 31D is suppressed. As a result, since the recovery of the antiparallel diode 31D is promoted, the reverse recovery loss of the antiparallel diode 31D is reduced.

FIG. 15 shows a dead time state in which the transistor 34T is turned off. The U-phase current Im flows to the U-phase cable C1 through the antiparallel diode 34D. FIG. 16 shows a point in time when the transistor 31T is turned on. The U-phase current Im flows through the transistor 31T to the U-phase cable C1. Due to the magnetic energy accumulated in the inductance LD of the conductor wire 2L, the circulating current If circulates through the conductor wire 2L, the circulating diode D8 and the conductor wire 1L. The conductor line 1L and the bypass conductor line C8 constitute a sub conductor line of the return path. Therefore, the potential increase of the anode electrode of the antiparallel diode 34D is suppressed. As a result, the recovery of the antiparallel diode 34D is promoted, so that the reverse recovery loss of the antiparallel diode 34D is reduced.

FIG. 17 shows a dead time state in which the transistor 31T is turned off. The U-phase current Im flows to the U-phase cable C1 through the antiparallel diode 34D. Due to the magnetic energy accumulated in the inductance LT of the conductor wire 1U, the circulating current If circulates through the conductor wire 1U, the circulating diode D7, and the conductor wire 2U. The conductor line 2U and the bypass conductor line C7 constitute a sub conductor line of the return path. Therefore, the potential increase of the collector electrode of the transistor 31 is suppressed. In other words, the turn-off surge of the transistor 31 is suppressed.

FIG. 18 shows a point in time when the transistor 34T is turned on. The U-phase current Im flows to the U-phase cable C1 through the transistor 34T. Due to the magnetic energy accumulated in the inductance LD of the conductor wire 2L, the circulating current If circulates through the conductor wire 2L, the circulating diode D8 and the conductor wire 1L. The conductor line 1L and the bypass conductor line C8 constitute a sub conductor line of the return path. Therefore, the potential increase of the anode electrode of the antiparallel diode 34D is suppressed. As a result, the recovery of the antiparallel diode 34D is promoted, so that the reverse recovery loss of the antiparallel diode 34D is reduced.

FIG. 19 is a schematic cross-sectional view showing a silicon chip on which the IGBT forming the transistor 31T and the freewheeling diode D7 are integrated. The insulating part 301 of the silicon chip separates the freewheeling diode D7 from the IGBT 31T. The P + substrate 300 of the silicon chip constitutes both the collector electrode of the IGBT 31T and the anode electrode of the freewheeling diode D7. Therefore, the circuit structure of the transistor 31T and the freewheeling diode D7 is simplified, and the inductance of the conductor line C7 can be reduced. FIG. 20 is an equivalent circuit diagram showing an IGBT 31T having the freewheeling diode D7 shown in FIG.

FIG. 21 shows a modification of the surge reduction circuit connected to the upper arm switch 31. This surge reduction circuit includes freewheeling diodes D7T and D7D and a conductor line 400. The conductor wire 400 has an inductance L400. The freewheeling diode D7T and the conductor line 400 form a return path for the conductor line 1U. The freewheeling diode D7D and the conductor line 400 form a return path for the conductor line 2U.

FIG. 22 shows another variation of the surge reduction circuit connected to the upper arm switch 31. This surge reduction circuit comprises freewheeling diodes D7T and D7D and conductor lines 400 and 401. The conductor wire 400 has an inductance L400. The conductor wire 401 has an inductance L401. The freewheeling diode D7T and the conductor line 400 form a return path for the conductor line 1U. The freewheeling diode D7D and the conductor line 401 form a return path for the conductor line 2U.

FIG. 23 is a schematic wiring diagram of a three-phase motor driving device showing another modification. This motor drive device has seven surge reduction circuits. Each of the three surge reduction circuits has a feedback path with a freewheeling diode D7. Each of the three surge reduction circuits has three feedback paths with a freewheeling diode D2. One surge reduction circuit has a feedback path with a freewheeling diode Dx. The inverter 3 incorporates freewheeling diodes D2 and D7.

The first embodiment described above shows a surge reduction circuit that reduces the output surge of the inverter 3. Similarly, the second embodiment describes a surge reduction circuit that reduces the input surge of the inverter 3. However, these surge reduction circuits can reduce a surge caused by an intance component of a conductor line connected to various switching circuits such as an oscillator, an inverter, and a DCDC converter.

Claims (8)

In a surge reduction circuit connected to a DC power source and a switching circuit connected to an electrical load by a conductor wire,
The surge reduction circuit has a feedback path having a sub conductor wire connected in series with a freewheeling diode;
The surge reduction circuit, wherein the feedback path and the conductor wire constitute a current circulation circuit for circulating a circulating current (If) generated by switching of the switching circuit. The return path consists only of a free-wheeling diode and a sub conductor wire,
The electrical resistance value of the feedback path excluding the electrical resistance value of the freewheeling diode is less than twice the electrical resistance value of the sub conductor wire,
The surge reduction circuit according to claim 1, wherein an inductance value of the feedback path is less than twice an inductance value of the sub conductor wire. The switching circuit comprises an inverter (3) for driving a motor (4) as the electric load,
The phase cable (C1) forming the conductor wire connects the terminal (4U) of the motor (4) to the output terminal (3U) of the inverter (3),
The feedback path has a sub-cable (C3) and a free-wheeling diode (D2) connected in series,
The return path is connected in parallel with the phase cable (C1) in order to flow a circulating current (If) from the terminal (4U) of the motor (4) to the output terminal (3U) of the inverter (3). 1. The surge reduction circuit according to 1. The switching circuit comprises an inverter (3) for driving a motor (4) as the electric load,
The phase cable (C1) forming the conductor wire connects the terminal (4U) of the motor (4) to the output terminal (3U) of the inverter (3),
The return path has a sub-cable (C2) and a free-wheeling diode (D1) connected in series,
The feedback path is connected in parallel with the phase cable (C1) in order to flow a circulating current (If) from the output terminal (3U) of the inverter (3) to the terminal (4U) of the motor (4). 1. The surge reduction circuit according to 1. The switching circuit comprises an inverter (3) for driving a motor (4) as the electric load,
The high potential DC power supply terminal (30) of the inverter (3) is connected to the positive terminal of the smoothing capacitor (6) through the high potential DC link line (7) forming the conductor line.
The feedback path has a sub cable (CX) and a freewheeling diode (DX) connected in series,
The feedback path is connected in parallel with the high potential DC link line (7) in order to flow the circulating current (If) from the DC power supply terminal (30) of the inverter (3) to the positive terminal of the smoothing capacitor (6). The surge reduction circuit according to claim 1. The switching circuit has an upper arm switch (31) having an upper transistor (31T) and an upper antiparallel diode (31D) connected in parallel,
The high potential main electrode of the upper transistor (31T) is connected to the high potential DC link line (7) through the conductor line (1U),
The cathode electrode of the upper antiparallel diode (31D) is connected to the high potential DC link line (7) through the conductor line (2U),
The feedback path includes a bypass conductor wire (C7) and a free-wheeling diode (D7) connected in series,
The bypass conductor line (C7) and the freewheeling diode (D7) are provided with a conductor line (If) for flowing a freewheeling current (If) from the high potential main electrode of the upper transistor (31T) to the cathode electrode of the upper antiparallel diode (31D). The surge reduction circuit according to claim 1, wherein 1U) is connected to the conductor wire (2U). The surge reduction circuit according to claim 6, wherein the upper transistor (31T) and the freewheeling diode (D7) are integrated on a common semiconductor chip. The switching circuit includes a lower arm switch (34) having a lower transistor (34T) and a lower antiparallel diode (34D) connected in parallel,
The low potential main electrode of the lower transistor (34T) is connected to the low potential DC link line (8) through the conductor line (1L),
The anode electrode of the antiparallel diode (34D) is connected to the low potential DC link line (8) through the conductor line (2L),
The return path has a bypass conductor line (C8) and a free-wheeling diode (D8) connected in series,
The feedback path is in parallel with the conductor line (1L) and the conductor line (2L) in order to flow a circulating current (If) from the anode electrode of the lower antiparallel diode (34D) to the low potential main electrode of the lower transistor (34T). The surge reduction circuit according to claim 1, which is connected to the circuit.

Images