JP7797909B2 - Surge suppression circuit and rotating electrical machine - Google Patents

Description

The present invention relates to a surge suppression circuit and a rotating electric machine equipped with the same.

Conventionally, rotating electric machine devices that include a rotating electric machine and a switching circuit with multiple switching elements have been used in a variety of applications, including vehicle drive systems. A typical switching circuit is an inverter that switches DC voltage to generate AC, and a typical rotating electric machine is a three-phase AC motor. The switching circuit and motor are connected by an electric cable with multiple electric wires.

In such rotating electric machine devices, the reactance of the rotating electric machine's windings is large, making it difficult to match the impedance between the electric cable and the rotating electric machine. If there is a large difference between the impedance of the electric cable and the impedance of the rotating electric machine, reflections due to impedance mismatch occur at the input end of the rotating electric machine, generating a large surge voltage. If this surge voltage becomes excessive, there is a risk of damage due to discharges occurring in the rotating electric machine, etc.

Patent document 1 describes a surge suppression circuit that suppresses surges caused by reflections due to impedance mismatch.

Japanese Patent Application Laid-Open No. 2008-283755

Figure 3 is a circuit diagram showing one of the surge suppression circuits described in Patent Document 1. In Figure 3, a three-phase AC motor 7 has a rotor 71 having an N magnetic pole 711 and an S magnetic pole 712, and a stator 72 having U-phase, V-phase, and W-phase windings 721, 722, and 723. Three-phase AC current is supplied to the stator 72 via first to third connecting lines 81, 82, and 83.

The surge suppression circuit 9 includes a first series circuit 91 in which a first resistor 911 and a first capacitor 912 are connected in series, a second series circuit 92 in which a second resistor 921 and a second capacitor 922 are connected in series, and a third series circuit 93 in which a third resistor 931 and a third capacitor 932 are connected in series. One end of each of the first to third series circuits 91 to 93 is connected to the first to third connecting lines 81, 82, and 83, respectively, and the other end is connected to the neutral point N of the inverter via the fourth connecting line 84.

In this surge suppression circuit 9, surge voltages generated in the first to third connection lines 81, 82, and 83 are absorbed by the first to third capacitors 912, 922, and 932. However, the first to third capacitors 912, 922, and 932 are also charged and discharged by the U-phase voltage, V-phase voltage, and W-phase voltage. This increases the power consumption of the first to third resistors 911, 921, and 931, resulting in significant power loss. Furthermore, because the first to third resistors 911, 921, and 931 reach high temperatures, a large cooling structure, such as fins and fans, is required for heat dissipation.

The present invention aims to provide a surge suppression circuit that can suppress surge voltage while suppressing power loss, and a rotating electric machine equipped with the same.

In order to achieve the above object, the present invention provides a surge suppression circuit for use in a rotating electrical machine device in which a switching circuit having a plurality of switching elements and a rotating electrical machine are connected via a plurality of conductive lines, the surge suppression circuit suppressing surge voltages occurring in a plurality of connection lines connecting the plurality of conductive lines to windings of a plurality of phases of the rotating electrical machine, the surge suppression circuit comprising a plurality of upper diodes each having an anode connected to each of the plurality of connection lines, a plurality of lower diodes each having a cathode connected to each of the plurality of connection lines, an upper line to which the cathodes of the plurality of upper diodes are connected, and a plurality of lower diodes each having a cathode connected to each of the plurality of lower diodes. a lower line to which the anodes of the upper and lower lines are connected, and a voltage holding circuit connected between the upper and lower lines, wherein the voltage holding circuit has a storage element that stores charge due to the surge voltage and a discharge unit that discharges the charge of the storage element, the storage element and the discharge unit being connected in parallel between the upper and lower lines, the discharge unit having a discharge resistor and at least one constant voltage diode whose cathode is on the upper line side, the discharge resistor and the constant voltage diode being connected in series, and the negative electrode of the storage element being electrically grounded.

Furthermore, in order to achieve the above object, the present invention provides a rotating electric machine connected via a plurality of conductive wires to a switching circuit having a plurality of switching elements, the rotating electric machine comprising: a rotating electric machine body having a plurality of phase windings; a plurality of connection lines connecting the plurality of conductive wires to the plurality of phase windings; and a surge suppression circuit for suppressing surge voltages occurring in the plurality of connection lines, the surge suppression circuit comprising a plurality of upper diodes each having an anode connected to each of the plurality of connection lines, a plurality of lower diodes each having a cathode connected to each of the plurality of connection lines, and an upper line to which the cathodes of the plurality of upper diodes are connected. a lower line to which the anodes of the plurality of lower diodes are connected, and a voltage holding circuit connected between the upper line and the lower line, wherein the voltage holding circuit has a storage element that stores charge due to the surge voltage and a discharge unit that discharges the charge of the storage element, the storage element and the discharge unit are connected in parallel between the upper line and the lower line, the discharge unit has a discharge resistor and at least one constant voltage diode whose cathode is on the upper line side, the discharge resistor and the constant voltage diode are connected in series, and the negative electrode of the storage element is electrically grounded.

The surge suppression circuit and rotating electric machine of the present invention make it possible to suppress surge voltage while also reducing power loss.

1 is a circuit diagram showing a configuration of a rotating electrical machine device according to an embodiment of the present invention; 1A shows an example of a U-phase voltage waveform on the switching circuit side, FIG. 1B shows an example of a voltage waveform in the U-phase connection line, and FIG. 1C shows an example of a voltage waveform in the U-phase connection line without a surge suppression circuit. FIG. 1 is a circuit diagram showing an example of a conventional surge suppression circuit.

[Embodiment]
1 is a circuit diagram showing an example of the configuration of a rotating electric machine device according to an embodiment of the present invention. This rotating electric machine device 100 includes a switching circuit 1 that performs DC-AC conversion by switching a plurality of switching elements, an electric cable 2, and a rotating electric machine 3 connected to the switching circuit 1 by the electric cable 2. The rotating electric machine device 100 is mounted on, for example, an electric vehicle or a hybrid vehicle, and the rotating electric machine 3 is used as a drive source for the vehicle.

In this embodiment, the rotating electric machine 3 is a three-phase AC motor, and is used in both a powering mode in which torque is generated, and a regenerative mode in which power is regenerated. In powering mode, a three-phase AC current is output from the switching circuit 1 to the rotating electric machine 3. In regenerative mode, a three-phase AC current is output from the rotating electric machine 3 to the switching circuit 1. In powering mode, the switching circuit 1 functions as an inverter, generating a three-phase AC current by switching a DC voltage. Below, a detailed description is given of the case in which the switching circuit 1 functions as an inverter.

The switching circuit 1 includes first to sixth switching elements 111 to 116 and first to sixth diodes 121 to 126 connected in parallel to the first to sixth switching elements 111 to 116, respectively. The first to sixth switching elements 111 to 116 are connected in series with the first switching element 111 and the second switching element 112, the third switching element 113 and the fourth switching element 114, and the fifth switching element 115 and the sixth switching element 116, respectively, and these series circuits are connected in parallel between the upper bus 13 and the lower bus 14 in a three-phase bridge configuration.

A DC power supply 6 such as a battery is connected to the upper busbar 13, and the lower busbar 14 is electrically grounded. When the rotating electric machine 3 is used as a driving source for a vehicle, the output voltage of the DC power supply 6 is, for example, 500 to 1000 V.

The first to sixth switching elements 111 to 116 are, for example, IGBTs (Insulated Gate Bipolar Transistors) or power MOSFETs, and are switched between an on (conducting) state and an off (blocking) state by an on/off signal output from the control device 10, which performs PWM control. The switching frequency of the first to sixth switching elements 111 to 116 is, for example, 10 kHz.

The switching circuit 1 also has a U-phase output line 15, a V-phase output line 16, and a W-phase output line 17, with the U-phase output line 15 connected between the first switching element 111 and the second switching element 112, the V-phase output line 16 connected between the third switching element 113 and the fourth switching element 114, and the W-phase output line 17 connected between the fifth switching element 115 and the sixth switching element 116.

The electric cable 2 comprises a U-phase electric wire 21, a V-phase electric wire 22, and a W-phase electric wire 23 as multiple conductive wires, and a shield conductor 24 that shields these electric wires 21 to 23. The U-phase electric wire 21, the V-phase electric wire 22, and the W-phase electric wire 23 are insulated electric wires in which a core wire made of, for example, a twisted wire is covered with an insulator, and the shield conductor 24 is, for example, a braided wire in which multiple wires are woven together in a lattice pattern.

The U-phase wire 21, V-phase wire 22, and W-phase wire 23 are connected to the U-phase output wire 15, V-phase output wire 16, and W-phase output wire 17 of the switching circuit 1, respectively, via a connection 201 on the switching circuit 1 side. The shield conductor 24 is electrically grounded on the switching circuit 1 side. The connection 201 is, for example, a connector or terminal block.

The rotating electric machine 3 has a rotating electric machine main body 30 and a surge suppression circuit 4. The rotating electric machine main body 30 has a rotor 31 having an N magnetic pole 311 and an S magnetic pole 312, and a stator 32 having a U-phase winding 321, a V-phase winding 322, and a W-phase winding 323.

The rotating electric machine 3 also has a U-phase connecting line 33, a V-phase connecting line 34, and a W-phase connecting line 35. The U-phase connecting line 33, the V-phase connecting line 34, and the W-phase connecting line 35 connect the U-phase winding 321, the V-phase winding 322, and the W-phase winding 323 to the U-phase electric wire 21, the V-phase electric wire 22, and the W-phase electric wire 23, respectively. This connects the rotating electric machine 3 and the switching circuit 1 via the electric cable 2. The U-phase connecting line 33, the V-phase connecting line 34, and the W-phase connecting line 35 are connected to the U-phase electric wire 21, the V-phase electric wire 22, and the W-phase electric wire 23, respectively, via connecting parts 202 on the rotating electric machine 3 side. The connecting parts 202 are, for example, connectors or terminal blocks.

The surge suppression circuit 4 suppresses surge voltages that occur due to voltage reflection at the ends of the U-phase winding 321, V-phase winding 322, and W-phase winding 323. Such voltage reflection occurs, for example, due to an impedance mismatch between the electric cable 2 and the stator 32 of the rotating electrical machine main body 30. Due to voltage reflection, a voltage of up to approximately twice the output voltage of the DC power supply 6 is generated in the U-phase connecting line 33, V-phase connecting line 34, and W-phase connecting line 35.

The surge suppression circuit 4 includes a first upper diode 411 having an anode connected to the U-phase connecting line 33, a second upper diode 412 having an anode connected to the V-phase connecting line 34, a third upper diode 413 having an anode connected to the W-phase connecting line 35, a first lower diode 421 having a cathode connected to the U-phase connecting line 33, a second lower diode 422 having a cathode connected to the V-phase connecting line 34, and a third lower diode 423 having a cathode connected to the W-phase connecting line 35.

The surge suppression circuit 4 also includes an upper line 401 to which the cathodes of the first to third upper diodes 411 to 413 are connected, a lower line 402 to which the anodes of the first to third lower diodes 421 to 423 are connected, a voltage holding circuit 5 connected between the upper line 401 and the lower line 402, and first and second inrush current suppression resistors 431 and 432 that suppress inrush current to the voltage holding circuit 5.

The voltage holding circuit 5 includes a storage element 51 that stores charge due to surge voltages generated in the U-phase connecting line 33, the V-phase connecting line 34, and the W-phase connecting line 35, and a discharge unit 52 that discharges the charge from the storage element 51. The storage element 51 is, for example, a capacitor. In the example shown in Figure 1, a single capacitor is shown as the storage element 51, but the storage element 51 may also be formed by connecting multiple capacitors in series, parallel, or series-parallel (series and parallel). A ceramic capacitor with a high withstand voltage is preferably used as this capacitor. However, storage devices other than capacitors may also be used as the storage element 51 as long as they are capable of storing charge.

In this embodiment, the discharge unit 52 has a discharge resistor 521 connected in parallel with the storage element 51 between the upper line 401 and the lower line 402, and a constant voltage diode (Zener diode) 522 connected in series with the discharge resistor 521. In the example shown in Figure 1, three constant voltage diodes 522 are connected in series, but the number of constant voltage diodes 522 can be changed as appropriate depending on the breakdown voltage (Zener voltage) of the constant voltage diodes 522. The constant voltage diode 522 is connected so that the upper line 401 side serves as the cathode and the lower line 402 serves as the anode.

The first inrush current suppression resistor 431 is connected between the cathodes of the first to third upper diodes 411 to 413 and the storage element 51. The second inrush current suppression resistor 432 is connected between the anodes of the first to third lower diodes 421 to 423 and the storage element 51. More specifically, the first inrush current suppression resistor 431 is connected between the upper line 401 and the positive electrode of the storage element 51, and the second inrush current suppression resistor 432 is connected between the lower line 402 and the negative electrode of the storage element 51. The resistance values of the first and second inrush current suppression resistors 431 and 432 are, for example, 10 Ω each.

It is noted that either the first inrush current suppression resistor 431 or the second inrush current suppression resistor 432 may be omitted. Even if either the first inrush current suppression resistor 431 or the second inrush current suppression resistor 432 is omitted, the inrush current to the storage element 51 can still be suppressed. In other words, it is sufficient that an inrush current suppression resistor is connected either between the cathode of each of the first to third upper diodes 411 to 413 and the storage element 51, or between the anode of each of the first to third lower diodes 421 to 423 and the storage element 51.

The positive electrode 511 of the storage element 51 is connected between the first inrush current suppression resistor 431 and the discharge resistor 521, and the negative electrode 512 is electrically grounded. By electrically grounding the negative electrode 512, even if a surge voltage occurs when the first switching element 111, the third switching element 113, and the fifth switching element 115 between the U-phase output line 15, the V-phase output line 16, and the W-phase output line 17 and the upper bus 13 are all in the on state, this surge voltage can be appropriately suppressed.

In other words, if the negative electrode 512 of the storage element 51 is not electrically grounded, and the first switching element 111, the third switching element 113, and the fifth switching element 115 are all on, the first to third lower diodes 421-423 of the surge suppression circuit 4 will all be non-conductive, and the negative electrode 512 of the storage element 51 will be in an electrically floating state. As a result, even if a surge voltage occurs, the storage element 51 will not be charged, and the surge voltage cannot be suppressed. However, in this embodiment, because the negative electrode 512 of the storage element 51 is electrically grounded, the negative electrode 512 of the storage element 51 will not be in a floating state, and the surge voltage can be absorbed by the storage element 51. Note that a situation in which the first switching element 111, the third switching element 113, and the fifth switching element 115 are all on can occur momentarily, for example, at the change in the PWM period.

In this embodiment, the negative electrode 512 of the storage element 51 is electrically grounded via the shield conductor 24 of the electric cable 2. By grounding the voltage hold circuit 5 via the shield conductor 24 of the electric cable 2, it is possible to prevent an increase in the amount of wiring (ground wire) between the switching circuit 1 and the rotating electric machine 3. However, the negative electrode 512 of the storage element 51 may also be electrically grounded on the rotating electric machine 3 side without going through the shield conductor 24 of the electric cable 2.

The time constant of the storage element 51 and the discharge resistor 521 is longer than the switching period during which the first to sixth switching elements 111 to 116 of the switching circuit 1 are switched. This allows the storage element 51 to appropriately absorb surge voltages for a period longer than at least one switching period. The capacitance of the storage element 51 is, for example, 1 μF, and the resistance of the discharge resistor 521 is, for example, 300 kΩ.

2(a) is an example of a U-phase voltage waveform at the connection part 201 on the switching circuit 1 side. FIG. 2(b) is an example of a voltage waveform in the U-phase connecting line 33. FIG. 2(c) is an example of a voltage waveform in the U-phase connecting line 33 when the surge suppression circuit 4 is not included. In FIGS. 2(a) to 2(c), the horizontal axis represents time, and the vertical axis represents voltage. V _DC on the vertical axis represents the output voltage of the DC power supply 6.

Without the surge suppression circuit 4, impedance mismatch between the electric cable 2 and the stator 32 of the rotating electric machine main body 30 causes the voltage from the switching circuit 1 to be reflected at the end of the U-phase winding 321 side of the U-phase connecting line 33, resulting in a large surge voltage as shown in Figure 2(c). However, in this embodiment, the surge suppression circuit 4 suppresses the surge voltage as shown in Figure 2(b). This makes it possible to prevent damage to the rotating electric machine 3 due to the surge voltage.

Furthermore, in this embodiment, charge is stored in the storage element 51 only when a surge voltage occurs that exceeds the voltage at both ends of the storage element 51. As a result, the capacitor is not frequently charged or discharged due to the interphase voltage, as in the conventional example shown in Figure 3, for example, and power loss can be significantly reduced. In other words, this embodiment makes it possible to suppress surge voltage while also suppressing power loss.

In addition, in this embodiment, the negative electrode 512 of the storage element 51 is electrically grounded, so surge voltage can be suppressed even when the first switching element 111, the third switching element 113, and the fifth switching element 115 are all in the on state.

Furthermore, in this embodiment, multiple constant voltage diodes 522 are connected in series to the discharge resistor 521, so the voltage across the storage element 51 is maintained at a value higher than the breakdown voltage of the multiple constant voltage diodes 522. This further reduces the power consumed by the discharge resistor 521.

(Summary of the embodiment)
Next, the technical ideas grasped from the above-described embodiments will be described by using the reference numerals and the like in the embodiments. However, the reference numerals in the following description do not limit the components in the claims to the members and the like specifically shown in the embodiments.

[1] A surge suppression circuit (4) used in a rotating electric machine device (1) in which a switching circuit (1) having a plurality of switching elements (111-116) and a rotating electric machine (3) are connected via a plurality of conductive wires (21-23), and which suppresses surge voltages generated in a plurality of connection lines (33, 34, 35) connecting the plurality of conductive wires (21-23) and the plurality of phase windings (321, 322, 323) of the rotating electric machine (3), comprising a plurality of upper diodes (411-413) each having an anode connected to each of the plurality of connection lines (33, 34, 35) and a cathode connected to each of the plurality of connection lines (33, 34, 35). a plurality of lower diodes (421-423) connected to the upper line (401); an upper line (401) to which the cathodes of the plurality of upper diodes (411-413) are connected; a lower line (402) to which the anodes of the plurality of lower diodes (421-423) are connected; and a voltage holding circuit (5) connected between the upper line (401) and the lower line (402), wherein the voltage holding circuit (5) has a storage element (51) that stores charge due to the surge voltage and a discharge unit (52) that discharges the charge of the storage element (51), and the negative electrode of the storage element (51) is electrically grounded.

[2] The surge suppression circuit (4) described in [1] above, wherein the storage element (51) is a capacitor connected between the upper line (401) and the lower line (402).

[3] The surge suppression circuit (4) described in [1] or [2] above, wherein the discharge section (52) has a discharge resistor (521) connected in parallel with the storage element (51) between the upper line (401) and the lower line (402).

[4] The surge suppression circuit (4) described in [3] above, wherein the discharge section (52) has at least one constant voltage diode (522) whose cathode is on the upper line (401) side, and the discharge resistor (521) and the constant voltage diode (522) are connected in series.

[5] A surge suppression circuit (4) described in any of [2] to [4] above, wherein the time constant of the storage element (51) and the discharge resistor (521) is longer than the switching period during which the multiple switching elements (111-116) are switched.

[6] A surge suppression circuit (4) described in any of [1] to [5] above, in which inrush current suppression resistors (431, 432) that suppress inrush current to the storage element (51) are connected at least between the cathodes of each of the plurality of upper diodes (411-413) and the storage element (51), and between the anodes of each of the plurality of lower diodes (421-423) and the storage element (51).

[7] A surge suppression circuit (4) according to any one of [1] to [6] above, in which the switching circuit (111-116) and the rotating electric machine (3) are connected via an electric cable (2) having a plurality of electric wires (21-23) as the plurality of conductive wires and a shield conductor (2) that shields the plurality of electric wires (21-23), and the negative electrode of the storage element (51) is electrically grounded via the shield conductor (24).

[8] A rotating electric machine (3) connected to a switching circuit (1) having a plurality of switching elements (111-116) via an electric cable (2) having a plurality of electric wires (21-23), the rotating electric machine (30) having a plurality of phase windings (321, 322, 323), a plurality of connection lines (33-35) connecting the plurality of electric wires (21-23) to the plurality of phase windings (321, 322, 323), and a surge suppression circuit (4) that suppresses surge voltages generated in the plurality of connection lines (33-35), the surge suppression circuit (4) comprising a plurality of upper diodes (411-413) whose anodes are connected to each of the plurality of connection lines (33, 34, 35), and a plurality of upper diodes (411-413) whose anodes are connected to each of the plurality of connection lines (33, 34, 35), The rotating electric machine (3) comprises a plurality of lower diodes (421-423) whose cathodes are connected to the respective connecting lines (33, 34, 35), an upper line (401) to which the cathodes of the plurality of upper diodes (411-413) are connected, a lower line (402) to which the anodes of the plurality of lower diodes (421-423) are connected, and a voltage holding circuit (5) connected between the upper line (401) and the lower line (402), wherein the voltage holding circuit (5) has a storage element (51) that stores charge due to the surge voltage and a discharge unit (52) that discharges the charge of the storage element (51), and the negative electrode of the storage element (51) is electrically grounded.

The above describes embodiments of the present invention, but the above-described embodiments do not limit the scope of the invention as defined in the claims. It should also be noted that not all combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention.

The present invention can be modified as appropriate without departing from the spirit and scope of the invention. For example, in the above embodiment, the U-phase wire 21, V-phase wire 22, and W-phase wire 23 of the electric cable 2 are used as the conductive wires connecting the switching circuit 1 and the rotating electric machine 3. However, this is not limiting. The conductive wires connecting the switching circuit 1 and the rotating electric machine 3 may also be plate-shaped bus bars made of a conductive metal material such as a copper alloy.

1... Switching circuit 100... Rotating electric machine devices 111 to 116... First to sixth switching elements 2... Electric cable 21... U-phase electric wire (conductive wire)
22...V-phase electric wire (conductive wire)
23...W-phase electric wire (conductive wire)
24...shield conductor 3...rotating electric machine 30...rotating electric machine main body 321...U-phase winding 322...V-phase winding 323...W-phase winding 33...U-phase connecting line 34...V-phase connecting line 35...W-phase connecting line 4...surge suppression circuit 411-413...first to third upper diodes 421-423...first to third lower diodes 431...first inrush current suppression resistor 432...second inrush current suppression resistors 441-446...first to sixth inrush current suppression resistors 5...voltage holding circuit 51...storage element 52...discharge unit 521...discharge resistor 522...constant voltage diode

Claims (6)

A surge suppression circuit used in a rotating electric machine device in which a switching circuit having a plurality of switching elements and a rotating electric machine are connected via a plurality of conductive wires, the surge suppression circuit suppressing surge voltages occurring in a plurality of connection lines connecting the plurality of conductive wires to windings of a plurality of phases of the rotating electric machine,
a plurality of upper diodes each having an anode connected to each of the plurality of connection lines; a plurality of lower diodes each having a cathode connected to each of the plurality of connection lines; an upper line to which the cathodes of the plurality of upper diodes are connected; a lower line to which the anodes of the plurality of lower diodes are connected; and a voltage holding circuit connected between the upper line and the lower line,
the voltage holding circuit has a storage element that stores an electric charge due to the surge voltage, and a discharge unit that discharges the electric charge of the storage element, the storage element and the discharge unit being connected in parallel between the upper line and the lower line,
the discharge unit has a discharge resistor and at least one constant voltage diode whose cathode is on the upper line side, the discharge resistor and the constant voltage diode being connected in series;
The negative electrode of the storage element is electrically grounded.
Surge suppression circuitry. the storage element is a capacitor connected between the upper line and the lower line;
2. The surge suppression circuit of claim 1. a time constant of the storage element and the discharge resistor is longer than a switching period in which the plurality of switching elements are switched;
3. The surge suppression circuit according to claim 1 . an inrush current suppression resistor for suppressing an inrush current to the storage element is connected between at least one of the cathodes of the plurality of upper diodes and the storage element and the anodes of the plurality of lower diodes and the storage element;
4. The surge suppression circuit according to claim 1. the switching circuit and the rotating electric machine are connected via an electric cable having a plurality of electric wires as the plurality of conductive wires and a shield conductor that shields the plurality of electric wires,
The negative electrode of the storage element is electrically grounded via the shield conductor.
5. A surge suppression circuit according to claim 1. A rotating electric machine connected to a switching circuit having a plurality of switching elements via a plurality of conductive wires,
a rotating electrical machine body having windings of multiple phases; a plurality of connection lines connecting the plurality of conductive wires to the windings of the multiple phases; and a surge suppression circuit for suppressing surge voltages occurring in the plurality of connection lines,
the surge suppression circuit comprises a plurality of upper diodes each having an anode connected to one of the plurality of connection lines, a plurality of lower diodes each having a cathode connected to one of the plurality of connection lines, an upper line to which the cathodes of the plurality of upper diodes are connected, a lower line to which the anodes of the plurality of lower diodes are connected, and a voltage holding circuit connected between the upper line and the lower line;
the voltage holding circuit has a storage element that stores an electric charge due to the surge voltage, and a discharge unit that discharges the electric charge of the storage element, the storage element and the discharge unit being connected in parallel between the upper line and the lower line,
the discharge unit has a discharge resistor and at least one constant voltage diode whose cathode is on the upper line side, the discharge resistor and the constant voltage diode being connected in series;
The negative electrode of the storage element is electrically grounded.
Rotating electric motor.