JP2012196072A - Charging method for snubber capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the charging time of an inrush current to a snubber capacitor.
A potential difference between both ends of a snubber capacitor connected between intermediate DC buses 4p and 4n of a matrix converter 1 is detected when a three-phase AC power supply is turned on, and each of the three-phase AC power supplies is detected based on the detection result. Of the two phases, the two phases that are substantially the same as the potential difference of the snubber capacitor 30 are determined, and the phase in which the voltage increases among these two phases is the positive phase of the snubber capacitor 30 and the phase in which the voltage decreases in the two layers And connected to the negative electrode of the snubber capacitor via the matrix converter 1.
[Selection] Figure 2

Description

  The present invention relates to a method for charging a snubber capacitor provided for overvoltage protection in a semiconductor switching circuit.

  The snubber capacitor is used for overvoltage protection. As a cause of the occurrence of the overvoltage, for example, there is one based on an inrush current that flows when the power is turned on. In order to limit the inrush current, for example, in the technique disclosed in Patent Document 1, the inrush current is limited by a resistor.

JP 2006-109582 A

  According to the technique of Patent Document 1, the inrush current can be limited. However, because the current is limited by the resistor, the charging time for completely charging the inrush current to the snubber capacitor is increased. Switching by the switching circuit cannot be started until charging is completed.

  An object of this invention is to provide the charging method of the snubber capacitor which can shorten the charging time of inrush current.

  In the method for charging a snubber capacitor according to one aspect of the present invention, a potential difference between both ends of a snubber capacitor connected between buses of a switching circuit that switches the three-phase AC power supply is detected when the three-phase AC power supply is turned on. Based on the results, two phases that are the same as the potential difference of the snubber capacitor are determined from each phase of the three-phase AC power supply, and the phase in which the voltage increases among the two phases is switched to the positive electrode of the snubber capacitor. While connecting through a circuit, the phase in which the voltage drops among the two phases is connected to the negative electrode of the snubber capacitor through the switching circuit. As the switching circuit, for example, a combination of a converter that rectifies a three-phase alternating current power supply and an inverter that converts the rectified direct current into a three-phase alternating current power supply having a desired frequency and voltage can be used. In this case, the snubber capacitor is provided on the output side of the converter. Alternatively, a matrix converter that converts the voltage and frequency of the three-phase AC power supply can also be used. In this case, the snubber capacitor is connected between the converter unit and the inverter unit of the matrix converter. These switching circuits can use a semiconductor switching element having a self-extinguishing capability, for example, a bridge circuit made of a bipolar transistor, MOSFET or IGFET.

  According to this charging method, since the snubber capacitor is connected between the two phases of the potential difference between both ends of the snubber capacitor and approximately the same potential difference, almost no overcurrent flows. Moreover, since the three-phase AC power supply is connected to the snubber capacitor without using a resistor, the snubber capacitor can be charged in a short time.

  According to another aspect of the present invention, there is provided a method for charging a snubber capacitor. In a switching circuit for switching a three-phase AC power supply, the voltage is the same among the phases of the three-phase AC power supply when the three-phase AC power supply is turned on. The two phases are judged, and the phase in which the voltage rises is connected to the positive electrode of the snubber capacitor in the switching circuit via the switching circuit, and the phase in which the voltage falls in the two phases. And connected to the negative electrode of the snubber capacitor via the switching circuit. As a switching circuit, a converter or a converter part of a matrix converter can be used in the same manner as in the above aspect, and a bipolar transistor, MOSFET, or IGFET can be used as the switching element in the switching circuit as in the above aspect. it can.

  In this charging method, when the two-phase voltage of the three-phase AC power supply is the same, that is, when the potential difference is zero volts, a snubber capacitor is connected to the two phases, so that overcurrent hardly flows and the snubber capacitor is charged. Time can be shortened.

  A charging completion determination step for determining that the snubber capacitor has been charged may be provided. In this charging completion determination step, a charging time is calculated from the frequency of the three-phase AC power supply and the potential difference before the snubber capacitor is charged, and it is determined that the charging time has elapsed.

  If comprised in this way, after a snubber capacitor is fully charged, the next step, for example, switching by a switching circuit, can be started.

  As the charge completion determination step, it may be determined that the potential difference of the snubber capacitor has become a predetermined value or more. With this configuration, the transition to the next step can be made after the potential difference of the snubber capacitor becomes equal to or greater than a predetermined value to such an extent that an excessive inrush current does not flow. Therefore, this transition can be performed at an early stage.

  Alternatively, as the charge completion determination step, it is also possible to use one that determines that the remaining phase of the three-phase AC power supply has become zero volts. With this configuration, when the voltage of the remaining phase is zero volts, the two phases connected to both ends of the snubber capacitor have the maximum potential difference, so that the snubber capacitor can be sufficiently charged.

  In any one of the above aspects, when the potential difference of the snubber capacitor is greater than or equal to a predetermined value before the start of charging the snubber capacitor, the step of filling the snubber capacitor can be omitted. That is, the filling of the snubber capacitor is performed when the potential difference between both ends of the snubber capacitor is less than a predetermined value. As a result, when the snubber capacitor is charged to such an extent that a dangerous inrush current does not occur, the charging step can be omitted, and the transition to the next step can be performed quickly.

  As described above, according to the present invention, the charging time for the snubber capacitor due to the inrush current can be shortened.

It is a circuit diagram of the principal part of the matrix converter which implements this invention. It is a block diagram of the matrix converter which implemented this invention. It is a flowchart which shows the process which the control circuit 32 of FIG. 2 performs. FIG. 3 is a waveform diagram of each part of the matrix converter of FIG. 2.

  The method of charging a snubber capacitor according to one embodiment of the present invention is performed in an indirect matrix converter 1 as shown in FIG. This indirect matrix converter includes a converter 2, a positive side DC intermediate link 4 p, a negative side DC intermediate link 4 n, and an inverter 6.

  The converter 2 includes upper bidirectional switch circuits 8ur, 8us, and 8ut as upper arms and lower bidirectional switch circuits 8dr, 8ds, and 8dt as lower arms, and the upper bidirectional switch circuit 8ur and lower bidirectional circuits. The switch circuit 8dr is connected in series, the side bidirectional switch circuit 8us and the lower bidirectional switch circuit 8ds are connected in series, and the upper bidirectional switch circuit 8ut and the lower bidirectional switch circuit 8dt are connected in series. Has been. These three series circuits are connected in parallel to each other. Both the upper and lower bidirectional switch circuits 8ur and 8dr have unidirectional switch elements, for example, IGBTs 10a and 10b, their emitters are connected to each other, and diodes 12a and 12b are connected in reverse parallel between the respective collector-emitters. It is connected. The IGBT 10a of each upper bidirectional switch circuit 8ur is connected to the positive direct current intermediate link 4p. The IGBT 10b of each upper bidirectional switch circuit 8ur is connected to the collector of the IGBT 10a of each lower bidirectional switch circuit 8dr. The IGBT 10b of each lower bidirectional switch circuit 8d is connected to the negative direct current intermediate link 4n. The same applies to the other upper bidirectional switch circuits 8us and 8ut and the lower bidirectional switch circuits 8ds and 8dt.

  The R phase of a three-phase AC power supply (not shown) is connected to a connection point Rin between the upper bidirectional switch circuit 8ur and the lower bidirectional switch circuit 8dr via a DC reactor (not shown). The S phase of the three-phase AC power source is connected to a connection point Sin between the directional switch circuit 8us and the lower bidirectional switch circuit 8ds via a DC reactor (not shown), and the upper bidirectional switch circuit 8ut and the lower side A T-phase of a three-phase AC power supply (not shown) is connected to a connection point Tin with the bidirectional switch circuit 8dt via a DC reactor (not shown). A capacitor 14rs is connected between the connection points Rin and Sin, a capacitor 14st is connected between the connection points Sin and Tin, and a capacitor 14tr is connected between the connection points Tin and Rin. These capacitors 14rs, 14st, 14tr and each DC reactor constitute an input filter.

  The inverter 6 has unidirectional switch elements such as IGBTs 16uu, 16uv, and 16uw as upper arms, and unidirectional switch elements such as IGBTs 16du, 16dv, and 16dw as lower arms. The collector of the IGBT 16uu is connected to the positive direct current intermediate link 4p, the emitter of the IGBT 16uu is connected to the collector of the IGBT 16du, and the emitter of the IGBT 16du is connected to the negative direct current intermediate link 4n. Other IGBTs 16uv, 16uw, 16dv, and 16dw are similarly connected. A diode 18u is connected in antiparallel between the collectors and emitters of the IGBTs 16uu, 16uv, and 16uw, and a diode 18d is connected in antiparallel between the collectors and emitters of the IGBTs 16du, 16dv, and 16dw. A load, for example, an electric actuator (not shown) is connected to a connection point u to the IGBTs 16 uu and 16 du, a connection point v to the IGBTs 16 uv and 16 dv, and a connection point w to the IGBTs 16 uu and 16 dw.

  A discharge prevention snubber circuit 20u is connected to each of the IGBTs 16uu, 16uv, and 16uw, and a discharge prevention snubber circuit 20d is connected to the IGBTs 16du, 16dv, and 16dw. In the discharge preventing snubber circuit 20u, a series circuit of a snubber capacitor 22u and a snubber diode 24u is connected in parallel between the collectors and emitters of the IGBTs 16uu, 16uv, and 16uw. One end of the snubber capacitor 22u is connected to the collectors of the IGBTs 16uu, 16uv, and 16uw, the other end is connected to the anode of the snubber diode 24u, and the cathode of the snubber diode 24u is connected to the emitters of the IGBTs 16uu, 16uv, and 16uw. One end of each snubber discharge resistor 26u is connected to a connection point between each snubber capacitor 22u and each snubber diode 24u, and the other end is connected to a connection point between a snubber capacitor 30 and an anode of a diode 28d described later.

  In the discharge prevention snubber circuit 20d, a series circuit of a snubber capacitor 22d and a snubber diode 24d is connected in parallel between the collectors and emitters of the IGBTs 16du, 16dv, and 16dw. The anode of the snubber diode 24d is connected to the collectors of the IGBTs 16du, 16dv, and 16dw, the cathode is connected to one end of the snubber capacitor 22d, and the other end is connected to the emitters of the IGBTs 16du, 16dv, and 16dw. One end of each snubber discharge resistor 26d is connected to a connection point between each snubber capacitor 22d and each snubber diode 24d, and the other end is connected to a connection point between a snubber capacitor 30 and a cathode of a diode 28d described later.

  The upper and lower bidirectional switch circuits 8ur, 8us, 8ut, 8dr, 8ds, 8dt of the converter 2 and the IGBTs 16uu, 16uv, 16uw, 16du, 16dv, 16dw of the inverter 6 are ON / OFF controlled by the control circuit 32 shown in FIG. The In particular, the switching of each of the upper and lower bidirectional switch circuits 8ur, 8us, 8ut, 8dr, 8ds, and 8dt depends on the circulation period of the inverter 6, that is, the IGBTs 16uu, 16uv, and 16uw of the inverter 6 are on, and the IGBTs 16du, 16dv, This is performed when 16dw is off, or when the IGBTs 16uu, 16uv, 16uw of the inverter 6 are off and the IGBTs 16du, 16dv, 16dw are on, and the line voltage to be switched is zero.

  Further, the positive voltage direct current intermediate link 4p is connected to an upper voltage drop means, for example, an anode of a clamp diode 28u, and one end of a snubber capacitor 30 is connected to the cathode. The other end of the snubber capacitor 30 is connected to the lower voltage drop means, for example, the anode of a clamp diode 28d, and the cathode is connected to the negative DC intermediate link 4n. As described above, the other end of each snubber discharge resistor 26u having one end connected to the connection point between each snubber capacitor 22u and each snubber diode 24u is connected to the connection point between the snubber capacitor 30 and the anode of the diode 28d. The other end of each snubber discharge resistor 26d having one end connected to the connection point between each snubber capacitor 22d and each snubber diode 24d is connected to the connection point between the snubber capacitor 30 and the cathode of the diode 28d.

  In the discharge type snubber circuit 20u, for example, the IGBT 16uv corresponding to the turn-on is turned on. However, when the turn-off is performed, the current flowing in the IGBT 16uv flows through the snubber capacitor 22u and the diode 24u, and the wiring inductance and the current at the turn-off time. Is absorbed by the snubber capacitor 22u, the voltage of the snubber capacitor 22u is raised, and the generation of a surge voltage due to the parasitic capacitance of the IGBT 16uv is prevented. When the voltage of the snubber capacitor 22u is higher than the voltage of the positive DC link 4p, the IGBT 16uv is then turned off through the path of the positive DC link 4p, the converter 2, the negative DC link 4n, and the snubber discharge resistor 26u. Is discharged by. Even in the discharge snubber circuit 20d, the direction of current flow is opposite to that in the discharge snubber circuit 20u, but the occurrence of surge is similarly prevented. In this way, the discharge snubber circuits 20u and 20d prevent surges that occur during the switching operation of the inverter 6.

  Further, in order to prevent a surge from occurring in the IGBTs 16 uu, 16 uv, and 16 uw of the inverter 6 due to the switching operation in the converter 2, as described above, one end is provided at the connection point between each snubber capacitor 22u and each snubber diode 24u. Is connected to the connection point between the snubber capacitor 30 and the anode of the diode 28d, and one end is connected to the connection point between each snubber capacitor 22d and each snubber diode 24d. The other end of the snubber discharge resistor 26d is connected to a connection point between the snubber capacitor 30 and the cathode of the diode 28d.

  That is, the capacitors 14rs, 14st, and 14tr are charged approximately equal to the line voltage of the three-phase AC power supply, and the snubber capacitor 30 and the upper clamp diode 28u The potential at the connection point with the cathode is clamped to a potential obtained by subtracting the voltage drop at the clamp diode 28u from the peak potential of the absolute values of the interphase voltages Vrs, Vst, Vts of the three-phase AC power supply. The potential at the connection point of the clamp diode 28d with the anode is clamped at a potential obtained by adding the voltage drop of the clamp diode 28d to the cross potential of the absolute values of Vrs, Vst, and Vts, and does not vary.

  The other end of the snubber discharge resistor 26d of the lower discharge prevention snubber circuit 20d is connected to the connection point between the capacitor 30 where the potential does not change and the cathode of the upper clamp diode 28u, and the potential does not change. The other end of the snubber discharge resistor 26u of the upper discharge prevention snubber circuit 20u is connected to a connection point between the upper electrode 30 and the anode of the lower clamp diode 28d. Therefore, even if the DC intermediate potential fluctuates due to switching in the converter 2, the snubber capacitor 22u only discharges to the potential at the connection point between the capacitor 30 and the anode of the clamp diode 28d, and the snubber capacitor 22d It discharges only to the potential at the connection point between the clamp diode 28u and the cathode. Therefore, even if switching is performed by the converter 2, the potential of the snubber capacitor 22u does not become lower than the potential of the capacitors 14rs, 14st, 14tr, and no current flows from the capacitors 14rs, 14st, 14tr to the snubber capacitor 22u. There will be no surge.

  In order to prevent the occurrence of surge in this way, the snubber capacitor 30 needs to be charged. For this reason, it is necessary to charge the snubber capacitor 30 by the converter 2 when the supply of the three-phase AC power to the matrix converter is started. At this time, a large inrush current may flow. In order to charge the snubber capacitor 30 without flowing a large inrush current, the following configuration is adopted.

  As shown in FIG. 2, the voltage detection circuit 34 detects the voltage between the positive direct current intermediate link 4p and the negative intermediate link 4n, which is supplied to the control circuit 32, and the potential difference Vc between both ends of the snubber capacitor 30 is calculated. Calculated.

  Further, the phase voltages Vr, Vs, Vt of the three-phase AC power supply are detected by the phase voltage detector 36, and the detection results are supplied to the control circuit 32. Further, one of the phases of the three-phase AC power source, for example, the phase of T phase in this embodiment is detected by the phase detector 38, and the detection result is supplied to the control circuit 32.

  The control circuit 32 performs the processing shown in FIG. 3 every time the phase is advanced 60 degrees from the reference phase, for example, the phase of the R phase is 90 degrees as shown in FIG. 4 according to the phase detection result by the phase detector 38. Execute.

  In the process shown in FIG. 3, the control circuit 32 first determines whether the potential difference between both ends of the snubber capacitor 30 is equal to or smaller than a predetermined value, that is, whether the snubber capacitor 30 needs to be charged (step 2). When the answer to this determination is no, that is, when charging is not necessary, the control circuit 32 stops the charging process of the snubber capacitor 30 and starts the next process, for example, control of the converter 2 and the inverter 4 not shown.

  When the answer to the determination in step S2 is yes, that is, when the snubber capacitor 30 needs to be charged, the control circuit 32 determines whether the predetermined two-phase potential difference is substantially the same as the potential difference of the snubber capacitor 30 ( Step S4). The predetermined two phases are, for example, as shown in FIG. 4, in the section 1 from the reference phase of phase 0 degrees (the phase of the R phase is 90 degrees) to 60 degrees, the potential difference Vst between the phase voltage Vs and the phase voltage Vt. In the section 2 from 60 degrees to 120 degrees, the potential difference Vsr between the phase voltage Vs and the phase voltage Vr, and in the section 3 from 120 degrees to 180 degrees, the potential difference Vtr between the phase voltage Vt and the phase voltage r. In the section 4 from 180 degrees to 240 degrees, the potential difference Vts between the phase voltage Vt and the phase voltage Vs, and in the section 5 from 240 degrees to 300 degrees, the potential difference Vrs between the phase voltage Vr and the phase voltage Vs, 300 In the interval 6 degrees from 0 degree, the potential difference Vrt between the phase voltage Vr and the phase voltage Vt.

  If the answer to this determination at step S4 is no, step S4 is repeated until the answer is yes. If the answer to the determination in step S4 is yes, the upper bidirectional switch circuit of the rising phase of the two phase voltages is turned on, and the lower bidirectional switch circuit of the falling phase is turned on (step S6).

  For example, in the section 1, since the phase voltage Vs increases and the phase voltage Vt decreases, the upper bidirectional switch circuit 8us and the lower bidirectional switch circuit 8dt are turned on.

  In section 2, since the phase voltage Vs rises and the phase voltage Vr falls, the upper both-side switch 8us is turned on and the lower bidirectional switch 8dr is turned on.

  In section 3, since the phase voltage Vt increases and the phase voltage Vr decreases, the upper bidirectional switch 8ut is turned on and the lower bidirectional switch 8dr is turned on.

  In section 4, since the phase voltage Vt rises and the phase voltage Vs falls, the upper bidirectional switch 8ut is turned on and the lower bidirectional switch 8ds is turned on.

  In section 5, since the phase voltage Vr rises and the phase voltage Vs falls, the upper bidirectional switch 8ur is turned on and the lower bidirectional switch 8ds is turned on.

  In section 6, since the phase voltage Vr rises and the phase voltage Vt falls, the upper bidirectional switch 8ur is turned on and the lower bidirectional switch 8dt is turned on.

  When the determination in step S6 is yes, charging of the snubber capacitor 30 is started. That is, step S6 functions as a charging start step. Since the potential difference of the snubber capacitor 30 and the two-phase potential difference for charging the snubber capacitor 30 are substantially equal at the start of charging, a large inrush current does not flow through the snubber capacitor 30.

  Following step S6, it is determined whether the remaining one phase is 0V (step S8). If the answer to this determination is no, step S8 is repeated until the answer is yes. During this time, the charging of the snubber capacitor 30 is continued. Then, when the answer to the determination in step S8 is yes, the potential difference between the two phases, that is, Vst is the maximum in the section 1, and even if charged more than this, it is not charged depending on the potential difference between the two phases. End the processing in the section. That is, step S8 functions as a charging completion determination step.

  In addition, before the end of one section, for example, section 1, the next section, for example, section 2 is started. For example, in section 1 and section 2, the upper bidirectional switch 8us that is turned on is common. The lower bidirectional switch 8dr that is turned on is common to the sections 2 and 3, the upper bidirectional switch 8ut that is turned on is common to the sections 3 and 4, and is turned on to the sections 4 and 5. The lower bidirectional switch 8ds is common, the upper switches 8ur that are turned on are common in the sections 5 and 6, and the lower bidirectional switch 8dt that is turned on is common in the sections 6 and 1. Therefore, problems such as short circuit do not occur.

  Thus, by charging the snubber capacitor 30 when the power is turned on, it is possible to prevent a large inrush current from flowing through the snubber capacitor 30. Moreover, since it is not necessary to limit the inrush current using a resistor, the time required for charging can be shortened, and the time until the switching operation of the converter 2 can be drastically shortened. Specifically, for example, in section 1, if the charging time is the longest, charging starts at the beginning of section 1 (phase 0 degree) and charging ends when the R phase reaches 0V. However, this section is 90 degrees in terms of phase, and the charging time does not become longer than this. That is, the maximum charging time is 90 degrees in terms of the phase, and the time until the switching operation of the converter 2 is started can be drastically reduced. Further, since it is not necessary to use a resistor or a switch for intermittently connecting the resistor to the snubber capacitor, it is not necessary to add a new part.

  In the above embodiment, charging of the snubber capacitor is started when the potential difference between both ends of the snubber capacitor 30 becomes substantially equal to the predetermined two-phase potential difference in each section, but the predetermined two-phase voltage is The snubber capacitor can be charged as soon as they are almost equal. In this case, there may be a difference between the potential difference between both ends of the snubber capacitor 30 and a predetermined two-phase voltage, but the snubber capacitor 30 is charged from the state where the two-phase potential difference is almost zero. A too large inrush current does not flow through the snubber capacitor 30. Further, even when the two-phase voltages determined in advance are not substantially equal, if the difference between the two-phase potential difference and the potential difference between both ends of the snubber capacitor 30 is a difference that does not cause excessive inrush current, The snubber capacitor 30 can be charged by these two phases.

  In the above embodiment, when the voltage of the phase not involved in the charging of the snubber capacitor 30 becomes 0 V, it is determined that the charging is completed and the charging is stopped. However, both ends of the snubber capacitor measured before the charging is started. Charge to a predetermined voltage based on the potential difference between the two phases, the phase of the two phases at the start of charging (the phase difference with respect to the reference phase (which is determined from the phase detection result of the phase detector 38) and the frequency of the three-phase AC power It is also possible to calculate the time required for the charging, and when the time has elapsed, it can be determined that the charging time has elapsed and charging can be stopped.

  In the above embodiment, when the voltage of the phase not involved in the charging of the nava capacitor 30 becomes 0 V, it is determined that the charging is completed and the charging is stopped, but the snubber capacitor 30 measured by the voltage detector 34 is used. When the control circuit 32 determines that the potential difference is equal to or greater than a predetermined value, charging may be stopped.

  In the above embodiment, the snubber capacitor 30 is connected to the positive side DC intermediate link 4p and the negative side DC intermediate link 4n via the clamp diodes 28u and 28d. However, the clamp diodes 28u and 28d are removed and the positive side DC intermediate link is connected. It can also be connected to the link 4p and the negative side DC intermediate link 4n. In the above embodiment, the present invention is implemented in a matrix converter. However, the present invention is not limited to this. For example, the present invention can be implemented when a normal converter and an inverter are used in combination, or only a converter is used. It can also be implemented.

1 Matrix converter (switching circuit)
30 Snubber capacitor 32 Control circuit 34 Voltage detector 36 Phase voltage detector 38 Phase detector

Claims (6)

A potential difference between both ends of a snubber capacitor connected between buses of a switching circuit that switches a three-phase AC power source is detected when the three-phase AC power source is turned on,
Based on this detection result, among the phases of the three-phase AC power supply, determine two phases that are the same as the potential difference of the snubber capacitor,
The phase in which the voltage increases among the two phases is connected to the positive electrode of the snubber capacitor via the switching circuit, and the phase in which the voltage decreases in the two phases is connected to the negative electrode of the snubber capacitor. To charge the snubber capacitor. In the switching circuit for switching the three-phase AC power supply, when the three-phase AC power supply is turned on, the two phases having the same voltage are determined among the phases of the three-phase AC power supply,
The phase in which the voltage rises among the two phases is connected to the positive electrode of the snubber capacitor in the switching circuit via the switching circuit, and the phase in which the voltage drops in the two phases is connected to the negative electrode of the snubber capacitor A method for charging a snubber capacitor connected to the via via the switching circuit. The method of charging a snubber capacitor according to claim 1 or 2,
A charging completion determining step for determining that the snubber capacitor has been charged, wherein the charging completion determining step calculates a charging time from a frequency difference of the three-phase AC power supply and a potential difference before charging the snubber capacitor; A method of charging a snubber capacitor that determines that the time has elapsed. The method of charging a snubber capacitor according to claim 1 or 2,
A method for charging a snubber capacitor, comprising: a charge completion determination step for determining that the snubber capacitor has been charged, wherein the charge completion determination step determines that the potential difference of the snubber capacitor has reached a predetermined value or more. The method of charging a snubber capacitor according to claim 1 or 2,
A method for charging a snubber capacitor, comprising: a charge completion determination step for determining that the snubber capacitor has been charged, wherein the charge completion determination step determines that the remaining phase of the three-phase AC power supply has reached zero volts. In the charging method of the snubber capacitor in any one of Claims 1 thru | or 5,
A method of charging a snubber capacitor that omits the filling step of the snubber capacitor when the potential difference of the snubber capacitor is greater than or equal to a predetermined value before the start of charging the snubber capacitor.

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