JP2013021795A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device that safely and reliably charges capacitors of bipolar bootstrap circuits without causing a short circuit current.SOLUTION: Arm drive circuits DRuH, DRuL, etc. are individually disposed to apply on/off-driving positive and negative bipolar voltages to switching elements SuH, SuL, etc. of upper and lower arms constituting legs 2-4, capacitors C1u, C2u, etc. are disposed on the upper and lower arms so as to be charged with the positive and negative voltages derived from power from DC power supplies Vg1-Vg3, and thus bipolar bootstrap circuits 5-7 are arranged on the legs 2-4, respectively. A control circuit 8 for performing capacitor charge control repeatedly outputs a control signal to turn on only the switching element of the upper arm of the leg that receives the highest voltage of the phase voltages of a polyphase AC power supply 1 and the switching element of the lower arm of the leg that receives the lowest voltage in response to a voltage change of each phase.

Description

  The present invention relates to a power conversion device having a bipolar bootstrap circuit capable of outputting positive and negative voltages in order to drive a switching element.

  Conventionally, power converters such as a multiphase converter circuit that converts multiphase AC power into DC power and a multiphase inverter circuit that converts DC power into multiphase AC power have been used. In order to output a predetermined voltage, these power conversion devices have a configuration in which switching elements on the upper arm side and switching elements on the lower arm side, which are called legs, are connected in series for the number of input or output phases. It is constituted by a so-called bridge circuit. Further, in order to turn on / off the switching elements of the respective arms, it is common to use a bootstrap type gate drive circuit.

  By the way, in such a power conversion device, instead of a conventional switching element such as a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) or IGBT (Insulated Gate Bipolar Transistor) using a Si (Silicon) semiconductor, a Si and a semiconductor. In comparison, a switching element using a wide band gap semiconductor typified by silicon carbide: SiC (Silicon Carbide) having low loss and high heat resistance is being applied.

  Many of such wide band gap semiconductors have a so-called normally-on characteristic that is conductive even when the gate voltage is zero, or a gate threshold voltage that is lower than that of a Si semiconductor. Therefore, in order to reliably turn off the switching element using the wide band gap semiconductor, a gate driving circuit capable of applying a negative voltage to the gate with respect to the source voltage is required. Therefore, a bipolar bootstrap circuit that can apply positive and negative voltage to the gate is used (for example, see Patent Document 1 below).

  Such a bipolar bootstrap circuit includes capacitors for applying positive and negative voltages, and it is necessary to turn on / off the switching elements of each leg in order to charge the capacitors. Specifically, when charging the upper positive voltage application capacitor for applying a positive voltage to the gate of the switching element on the upper arm side, the upper switching element on the lower arm side is turned off and the switching element on the lower arm side is turned off. Turn on. When charging the upper negative voltage application capacitor for applying a negative voltage to the gate of the switching element on the upper arm side, the switching element on the upper arm side is turned on and the switching element on the lower arm side is turned off. .

JP 2010-35389 A

  However, the conventional bipolar bootstrap circuit has not shown a specific capacitor charging method in consideration of the phase and voltage of the input power supply voltage in a power converter such as a multiphase converter circuit or a multiphase inverter circuit. Therefore, for example, in a multi-phase converter circuit, when a capacitor is charged without considering the voltage phase of each phase, in some cases, a short-circuit current flows to the bridge circuit via the multi-phase AC power supply on the input side, and the power conversion device There was a risk of destroying.

  The present invention has been made in order to solve the above-described problems, and in a power conversion device that performs multi-phase power conversion provided with a bipolar bootstrap circuit, a capacitor is provided at the initial start of the device. It is an object of the present invention to allow safe and reliable capacitor charging without short-circuit current flowing when charging.

  In the first invention, a plurality of legs in which switching elements on the upper arm side and the lower arm side are connected in series to each other are connected in parallel to each other, and a multi-phase AC power source is connected to each midpoint of each leg. A DC / DC converter circuit is a power conversion device in which arm drive circuits that apply positive and negative voltage for on / off drive to each switching element are separately provided on the upper arm side and the lower arm side. In addition, capacitors for positive voltage application and negative voltage application for charging the positive and negative voltages with electric power from a DC power supply are provided separately for the upper arm side and the lower arm side, respectively. Each of the bipolar bootstrap circuit and the control circuit for controlling the arm driving circuit for charging the capacitors. A switching element on the upper arm side of the leg to which the highest voltage among the voltages of each phase of the multiphase AC power source is input to the arm driving circuits on the upper arm side and the lower arm side, and A control signal for turning on only the switching element on the lower arm side of the leg to which a low voltage is input is repeatedly output according to the voltage change of each phase.

  According to a second aspect of the present invention, a plurality of legs in which the switching elements on the upper arm side and the lower arm side are connected in series to each other are connected in parallel, and the high voltage side and the low voltage side of the DC power supply are connected to the input side of each leg. A power conversion device connected to both ends, and arm drive circuits for applying positive / negative bipolar voltages for on / off drive to each of the switching elements are individually provided on the upper arm side and the lower arm side. In addition, capacitors for positive voltage application and negative voltage application for charging the positive and negative voltages respectively with electric power from the DC power supply are individually provided on the upper arm side and the lower arm side, and are respectively provided on the legs. A bipolar bootstrap circuit disposed; and a control circuit for controlling each arm drive circuit for charging each capacitor, wherein the control circuit includes the upper stage For each arm drive circuit on the arm side and the lower arm side, a period in which all the switching elements on the upper arm side are turned on and all the switching elements on the lower arm side are turned off, and A control signal for alternately providing a period in which all of the switching elements are turned off and all the switching elements on the lower arm side are turned on is output.

  According to the first and second aspects of the invention, in the power conversion device that performs power conversion for multiple phases to which the bipolar bootstrap circuit is applied, the type of input power source (type of AC power source or DC power source) and the input voltage In consideration of the phase, on / off control of the switching elements on the upper arm side and the lower arm side of the plurality of legs is controlled, so that no short circuit current flows when charging the capacitor at the initial start of the device, etc. The risk of circuit destruction due to short-circuit current can be reduced, and safe and reliable capacitor charging can be performed.

  In particular, according to the first invention, in the power conversion device in which an AC power supply is connected to the middle point of each leg to constitute an AC / DC converter circuit, for applying a positive voltage on the upper arm side of the bipolar bootstrap circuit When charging capacitors and capacitors for applying negative voltage, the switching elements are turned on and off at the timing when no short-circuit current flows in the bridge circuit according to the potential of each phase of the AC energy source. Charging becomes possible.

  According to the second invention, in the power converter in which the high-voltage side and the low-voltage side of the DC power source that is the energy source are connected to both ends of the input side of the leg, the positive voltage application on the upper arm side of the bipolar bootstrap circuit When charging a capacitor for negative voltage and a capacitor for applying a negative voltage, all switching elements on the upper arm side of the multiple legs and all switching elements on the lower arm side are alternately turned on in a time-sharing manner, so that no short circuit current flows. . Further, the DC power supply is connected to both ends of the input side of the leg, and the voltage output from the midpoint of the leg changes in the same phase, so that each voltage is substantially the same potential, and no potential difference is generated. Thereby, safe and reliable capacitor charging is possible.

It is a circuit diagram which shows the structure of the three-phase AC / DC converter circuit in Embodiment 1 of this invention. It is a time chart with which it uses for operation | movement description in Embodiment 1 of this invention. It is a circuit diagram which shows the structure of the three-phase inverter circuit in Embodiment 2 of this invention. It is a time chart with which it uses for operation | movement description in Embodiment 2 of this invention. It is a time chart with which it uses for operation | movement description in Embodiment 3 of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each embodiment, constituent elements having the same functions as those described once are denoted by the same reference numerals and description thereof is omitted.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram showing a configuration of a main part of a three-phase AC / DC converter circuit as a power converter according to Embodiment 1 of the present invention. Although a three-phase AC / DC converter circuit is shown here as a specific example, the present invention is not limited to such a range of applications, and an AC energy source is connected to the midpoint of each leg. The present invention can be similarly applied to any power conversion device, so-called AC / DC converter circuit.

  Each phase of the three-phase AC power source 1 is connected to terminals T1 to T3 of the three-phase AC / DC converter circuit, and supplies AC power to the legs 2 to 4, respectively. Then, the AC power supplied from the three-phase AC power source 1 is converted to DC power by controlling on / off of switching elements SuH to SwH and SuL to SwL of the legs 2 to 4 to be described later, for smoothing Output to a load (not shown) connected to both ends of the terminals T4 and T5 through the capacitor C5.

  In addition, this three-phase AC / DC converter circuit corresponds to each leg 2 to 4 corresponding to each phase (u phase, v phase, w phase) of the three-phase AC power source 1 and to each leg 2 to 4 individually. Each of the bipolar bootstrap circuits 5 to 7 is provided, and a set of these legs 2 to 4 and the bipolar bootstrap circuits 5 to 7 is connected in parallel to each other to form a bridge circuit. . In addition, this three-phase AC / DC converter circuit includes non-isolated DC power supplies Vg1, Vg2, an insulated DC power supply Vg3, and a bipolar bootstrap circuit 5 for supplying gate drive power to the bipolar bootstrap circuits 5-7. Is provided with a control circuit 8 for controlling the arm drive circuits DRuH to DRwH on the upper arm side in order to charge the capacitors C1u to C1w and C2u to C2w on the upper arm side constituting the.

  The legs 2 to 4 and the bipolar bootstrap circuits 5 to 7 to which the u-phase to w-phase AC power is input have the same circuit configuration corresponding to each phase. Therefore, here, focusing on the leg 2 to which the u-phase AC power is input and the bipolar bootstrap circuit 5, the circuit configuration and operation thereof will be described in detail below, taking this as an example.

The leg 2 includes a switching element SuH on the upper arm side and a switching element SuL on the lower arm side.
Hereinafter, the switching element SuH on the upper arm side and the switching element SuL on the lower arm side are simply referred to as an upper arm switching element SuH and a lower arm switching element SuL as necessary.

  In addition, the bipolar bootstrap circuit 5 turns on / off the switching elements SuH and SuL. The upper arm drive circuit DRuH, the lower arm drive circuit DRuL, and the upper arm positive circuit. A capacitor C1u for voltage application, a capacitor C2u for negative voltage application on the upper arm side, a capacitor C3u for positive voltage application on the lower arm side, a capacitor C4u for negative voltage application on the lower arm side, and the upper arm side are provided. It comprises two diodes D1u and D2u.

  In the following description, the arm drive circuit DRuH on the upper arm side and the arm drive circuit DRuL on the lower arm side are simply referred to as the upper arm drive circuit DRuH and the lower arm drive circuit DRuL as necessary. Further, a positive voltage application capacitor C1u on the upper arm side, a negative voltage application capacitor C2u on the upper arm side, a positive voltage application capacitor C3u on the lower arm side, and a negative voltage application capacitor C4u on the lower arm side are: These are simply referred to as an upper-stage positive voltage application capacitor C1u, an upper-stage negative voltage application capacitor C2u, a lower-stage positive voltage application capacitor C3u, and a lower-stage negative voltage application capacitor C4u as necessary.

  Here, as the upper arm switching element SuH and the lower arm switching element SuL, a MOSFET using a wide band gap semiconductor typified by SiC or the like can be used. When a constant positive voltage is applied to the gate terminal, it is turned on. Thus, when a constant negative voltage is applied to the gate terminal, the transistor is turned off.

  Wide band gap semiconductors include gallium nitride-based materials and diamond in addition to silicon carbide (SiC). Since the switching element formed of such a wide band gap semiconductor has high voltage resistance and high allowable current density, the switching element can be reduced in size. By using these reduced switching elements, A semiconductor module incorporating these elements can be miniaturized. Further, since the heat resistance is high, the heat radiation fins of the heat sink can be downsized and the water cooling part can be air cooled, so that the semiconductor module can be further downsized. Furthermore, since the power loss is low, it is possible to increase the efficiency of the switching element, and further increase the efficiency of the semiconductor module. A diode using a wide band gap semiconductor may be used as the diodes D1u and D2u. As a result, an effect similar to that obtained when a MOSFET using a wide band gap semiconductor is used can be obtained.

  The source terminal of the upper arm switching element SuH constituting the leg 2 is connected to the drain terminal of the lower arm switching element SuL, and the terminal T1, which is the contact point, is connected to the u phase of the three-phase AC power source 1. Yes. The drain terminal of the upper arm switching element SuH is connected to one end of the capacitor C5, and the source terminal of the lower arm switching element SuL is connected to the other end of the capacitor C5.

  The upper arm drive circuit DRuH applies either the voltage charged in the upper positive voltage application capacitor C1u or the voltage charged in the upper negative voltage application capacitor C2u to the gate terminal of the upper arm switching element SuH. . Similarly, the lower arm drive circuit DRuL uses either the voltage charged in the lower positive voltage application capacitor C3u or the voltage charged in the lower negative voltage application capacitor C4u as the gate terminal of the lower arm switching element SuL. Apply.

  In this case, the voltage applied to the gate terminals of the switching elements SuH and SuL by the arm driving circuits DRuH and DRuL is applied to the capacitors C1u to C1w and C2u to C2w on the upper arm side, for example, at the start of the power converter. Is required by the gate signals GuH and GuL output from the control circuit 8 in response to the output of a charge command signal X to be described later. Further, in the normal case of performing an operation of converting AC power supplied from the three-phase AC power source 1 into DC power and outputting it, it is for PWM (pulse width modulation) control output from a separate control circuit (not shown). This is done by a gate signal.

  One end of the upper positive voltage application capacitor C1u is connected to the upper arm drive circuit DRuH and the cathode side of the diode D1u, and the other end is connected to the source terminal of the upper arm switching element SuH. One end of the upper negative voltage application capacitor C2u is connected to the source terminal of the upper arm switching element SuH, and the other end is connected to the upper arm drive circuit DRuH and the anode side of the diode D2u.

  One end of the lower positive voltage applying capacitor C3u is connected to the lower arm drive circuit DRuL, and the other end is connected to the source terminal of the lower arm switching element SuL. One end of the lower-stage negative voltage application capacitor C4u is connected to the source terminal of the lower-arm switching element SuL, and the other end is connected to the lower-arm drive circuit DRuL.

  The positive side of the non-insulated DC power supply Vg1 is connected to the anode side of the diode D1u and one end of the lower-stage positive voltage application capacitor C3u, and the negative side is connected to the other end of the lower-stage positive voltage application capacitor C3u. As a result, the positive positive voltage applying capacitor C3u is charged with a voltage of + VH with reference to the source potential of the lower arm switching element SuL. When the lower arm switching element SuL is turned on and the upper arm switching element SuH is turned off, the source potential of the upper arm switching element SuH is applied to the upper positive voltage applying capacitor C1u through the path indicated by reference numeral (1) in FIG. A voltage of + VH is charged with reference. The diode D1u is provided to prevent a reverse voltage from being applied to the upper positive voltage application capacitor C1u.

  The positive side of the non-isolated DC power source Vg2 is connected to the negative side of the non-insulated DC power source Vg1 and one end of the lower negative voltage applying capacitor C4u, and the negative side is connected to the other end of the lower negative voltage applying capacitor C4u. Yes. As a result, the voltage of −VL2 is charged in the lower negative voltage applying capacitor C4u with reference to the source potential of the lower arm switching element SuL.

  The positive side of the isolated DC power supply Vg3 is connected to the drain terminal of the upper arm switching element SuH, and the negative side is connected to the cathode side of the diode D2u. As a result, when the upper arm switching element SuH is turned on and the lower arm switching element SuL is turned off, the source potential of the upper arm switching element SuH is applied to the upper negative voltage applying capacitor C2u through the path indicated by reference numeral (2) in FIG. As a reference, the voltage of -VL1 is charged. The diode D2u is provided to prevent the reverse voltage from being applied to the upper negative voltage applying capacitor C2u.

  The non-isolated DC power sources Vg1 and Vg2 and the isolated DC power source Vg3 are similarly connected to the other legs 3 and 4 and the bipolar bootstrap circuits 6 and 7, and the capacitors of the respective gate drive circuits DRvH, DRvL, DRwH and DRWL C1v to C4w are charged.

  Next, the configuration of the control circuit 8 that controls the arm drive circuits DRuH to DRwH on the upper arm side for charging the capacitors C1u to C1w and C2u to C2w on the upper arm side will be described.

  On / off of the switching elements SuH to SwH and SuL to SwL of each phase during capacitor charging reflects the voltage state of each phase of the three-phase AC power supply 1 and the state of the charge command signal X described later by the control circuit 8. Are controlled by gate signals GuH to GwH and GuL to GwL. In this case, the charge command signal X is a control signal input from the outside, and when the capacitors C1u to C1w and C2u to C2w on the upper arm side of the bipolar bootstrap circuits 5 to 7 need to be charged. , Switching from L level to H level.

  Here, when the capacitors C1u to C1w and C2u to C2w on the upper arm side need to be charged includes, for example, the initial start of the power converter. While the charge command signal X is at the H level, as described below, any one of the capacitors C1u to C1w and C2u to C2w on the upper arm side of each bipolar bootstrap circuit 5 to 7 is charged. In addition, normal control which converts the alternating current power supplied from the three-phase alternating current power supply 1 into direct current power and outputs it by controlling on / off the switching elements SuH to SwH and SuL to SwL of each leg 2 to 4 by PWM control. When the operation is performed, the capacitors C1u to C1w and C2u to C2w are charged in accordance with this operation. In this case, the charge command signal X is not particularly output.

  Further, the period during which the charge command signal X is set to the H level may be set in advance, and although not shown in FIG. 1, each capacitor C1u on the upper arm side of each leg 2-4 is not shown. ˜C1w and C2u˜C2w charge voltages are detected, and the charge voltage reaches a constant voltage sufficient to reliably turn on / off each switching element SuH to SwH on the upper arm side of each leg 2 to 4 You may set to the period until.

Next, a specific configuration of the control circuit 8 will be described.
The control circuit 8 compares the input voltage detector 9 that detects the voltage of each phase of the three-phase AC power supply 1 with the voltage value of each phase of the three-phase AC power supply 1 that is input to the input voltage detector 9. Gate signals for the arm drive circuits DRuH to DRwH and DRuL to DRwL on the upper arm side and the lower arm side reflecting the comparison results of the comparators 10 to 15 and the comparison results of the comparators 10 to 15 and the state of the charge command signal X Output determination units 16 to 18 that generate and output GuH to GwH and GuL to GwL. In this case, the input voltage detector 9 is a PLL (Phase Locked Loop) circuit that can generate an output signal having a phase and a frequency that are the same as a reference signal (here, an AC voltage of each phase), for example. And operational amplifiers.

  The configurations and functions of the comparators 10 to 15 and the output determination units 16 to 18 connected to the subsequent stage have the same circuit configuration corresponding to each phase. Therefore, here, focusing on the comparators 10 and 11 and the output determination unit 16 corresponding to the u phase, the circuit configuration and operation will be described in detail below by taking this as an example.

The comparators 10 and 11 are composed of a subtraction circuit or the like. Further, the output determination unit 16 compares the output of the AND gate ANDu and NOR gate NORu, which output the comparison result signal by comparing the output levels of the comparators 10 and 11, and the charge command signal X, for example. The AND gate ANDuH that outputs the gate signal GuH to the upper arm drive circuit DRuH, and the AND gate ANDuL that compares the output of the NOR gate NORu with the charge command signal X and outputs the gate signal GuL to the lower arm drive circuit DRuL. .
The control circuit 8 is not limited to the hardware as described above, but can be configured by software such as a microcomputer.

  In the control circuit 8 configured as described above, the AC voltage of each phase input to the three-phase AC / DC converter circuit is sequentially sent to the input voltage detector 9. The input voltage detector 9 converts the AC voltage of each phase into control signals Vu, Vv, and Vw that can be compared. Subsequently, the control signals Vu, Vv, Vw are sent to the comparators 10-15.

  The comparators 10 and 11 determine whether or not the u-phase AC voltage connected to the terminal T1 of the leg 2 is higher or lower than the AC voltages of the other phases (v-phase and w-phase), and the result Is output. Specifically, one comparator 10 compares the magnitudes of both control signals Vu and Vv, and outputs an H level control signal Yu if the control signal Vu is greater. On the other hand, if the control signal Vu is smaller, the L level control signal Yu is output. Similarly, the other comparator 11 compares the magnitudes of both control signals Vu and Vw, and outputs an H level control signal Zu if the control signal Vu is greater. Conversely, if the control signal Vu is smaller, an L level control signal Zu is output.

  Subsequently, the control signals Yu and Zu are sent to the output determiner 16. Here, based on the control signals Yu and Zu and the charge command signal X, gate signals GuH and GuL to be supplied to the upper gate drive circuit DRuH and the lower gate drive circuit DRuL are generated.

  Specifically, only when the control signals Yu and Zu are both at the H level and the charge command signal X is at the H level, the H level gate signal GuH is output, and the upper gate drive circuit DRuH is caused to output a positive voltage. The upper arm switching element SuH is turned on. In other cases, an L level gate signal GuH is output, a negative voltage is output to the upper gate drive circuit DRuH, and the upper arm switching element SuH is turned off.

  Further, only when the control signals Yu and Zu are both at the L level and the charge command signal X is at the H level, the gate signal GuL at the H level is output, the positive voltage is output to the lower gate drive circuit DRuL, and the lower arm switching is performed. The element SuL is turned on. In other cases, an L level gate signal GuL is output, a negative voltage is output to the lower gate drive circuit DRuL, and the lower arm switching element SuL is turned off.

  The same operation is performed for the comparators 12 to 15 that control the on / off of the switching elements SvH, SwH, SvL, and SwL that constitute the other legs 3 and 4 and the output determiners 17 and 18.

  FIG. 2 shows gate signals GuH to GwH and GuL to GwL for on / off control of the switching elements SuH to SwH and SuL to SwL generated by the control circuit 8, and capacitor charging states of the bipolar bootstrap circuits 5 to 7, respectively. It is a time chart which shows the relationship. Hereinafter, the flow of the charging operation will be described with reference to FIG.

  First, at time t0, the charge command signal X becomes H level, and control for charging the capacitors C1u to C1w and C2u to C2w on the upper arm side of the bipolar bootstrap circuits 5 to 7 is started.

  In the period from time t0 to t1, the w-phase voltage is the highest among the three-phase voltages, and the v-phase voltage is the lowest. Therefore, only the upper gate signal GwH and the lower gate signal GvL are at the H level, and the others are at the L level. Thereby, only the upper arm switching element SwH and the lower arm switching element SvL are turned on. When the upper arm switching element SwH is turned on, the upper negative voltage application capacitor C2w for the W phase is charged by the insulated DC power supply Vg3, and when the lower arm switching element SvL is turned on, the V phase is driven by the non-insulated DC power supply Vg1. The upper positive voltage application capacitor C1v for use is charged.

  Based on the same principle, the u-phase voltage is the highest among the three-phase voltages and the v-phase voltage is the lowest during the period from time t1 to time t2. Therefore, only the upper gate signal GuH and the lower gate signal GvL are at the H level, and the others are at the L level. As a result, only the upper arm switching element SuH and the lower arm switching element SvL are turned on, and the upper negative voltage applying capacitor C2u and the upper positive voltage applying capacitor C1v are charged.

  Based on the same principle, the u-phase voltage is the highest among the three-phase voltages and the w-phase voltage is the lowest during the period from time t2 to t3. Therefore, only the upper gate signal GuH and the lower gate signal GwL are at the H level, and the others are at the L level. As a result, only the upper arm switching element SuH and the lower arm switching element SwL are turned on, and the upper negative voltage applying capacitor C2u and the upper positive voltage applying capacitor C1w are charged.

  Based on the same principle, the v-phase voltage is the highest among the three-phase voltages and the w-phase voltage is the lowest during the period from time t3 to t4. Therefore, only the upper gate signal GvH and the lower gate signal GwL are at the H level, and the others are at the L level. As a result, only the upper arm switching element SvH and the lower arm switching element SwL are turned on, and the upper negative voltage applying capacitor C2v and the upper positive voltage applying capacitor C1w are charged.

  Based on the same principle, the v-phase voltage is the highest among the three-phase voltages and the u-phase voltage is the lowest during the period from time t4 to t5. Therefore, only the upper gate signal GvH and the lower gate signal GuL are at the H level, and the others are at the L level. As a result, only the upper arm switching element SvH and the lower arm switching element SuL are turned on, and the upper negative voltage applying capacitor C2v and the upper positive voltage applying capacitor C1u are charged.

  Based on the same principle, the w-phase voltage is the highest among the three-phase voltages and the u-phase voltage is the lowest during the period from time t5 to t6. Therefore, only the upper gate signal GwH and the lower gate signal GuL are at the H level, and the others are at the L level. As a result, only the upper arm switching element SwH and the lower arm switching element SuL are turned on, and the upper negative voltage application capacitor C2w and the upper positive voltage application capacitor C1u are charged.

  As can be seen from the above description, in the three-phase AC / DC converter circuit of the first embodiment, the switching element on the upper arm side of the leg to which the highest input voltage is applied and the lowest input voltage are applied. Only the switching elements on the lower arm side of the leg being turned on simultaneously turn on. For this reason, during the charging period when the charging command signal X is at the H level, such as at the start of the power converter, the potential of each phase of the three-phase AC power supply 1 does not always flow a short-circuit current through the bridge circuit composed of each leg 2-4. Because it depends on the direction, safe and reliable capacitor charging is possible.

  That is, suppose that the v-phase upper arm switching element SvH having a voltage lower than that of the other phase (u-phase, w-phase) is turned on, for example, during the period from t0 to t1 in FIG. 2 without considering the input voltage. In that case, a short-circuit current flows through the path indicated by reference numeral (3) in FIG. On the other hand, in Embodiment 1 of the present invention, switching is performed in accordance with the AC voltage phase of the three-phase AC power supply 1, so that it is ensured that a short-circuit current flows to the bridge circuit via the three-phase AC power supply 1. Can be prevented.

  In addition, even when a wide bandgap semiconductor is applied as a switching element to an AC / DC converter circuit such as a multiphase converter circuit, the bipolar bootstrap circuits 5 to 7 ensure the switching element using the wide bandgap semiconductor. Can be turned off.

Embodiment 2. FIG.
FIG. 3 is a circuit diagram showing a configuration of main parts of a three-phase inverter circuit as a power conversion device according to Embodiment 2 of the present invention. Although a three-phase inverter circuit is shown here as a specific example, the present invention is not limited to such a range of applications, and the high-voltage side and low-voltage side of the DC power source that is the energy source are the input side of the leg. The present invention can be similarly applied to a power conversion device connected to both ends of, for example, a full-bridge type DC / DC converter circuit or a multiphase inverter circuit.

  In the three-phase inverter circuit according to the second embodiment, the DC power supplied from the DC power supply 19 is temporarily charged in the capacitor C6 and further supplied to the legs 2 to 4 constituting the bridge circuit. Each leg 2-4 converts direct-current power into the three-phase alternating current power corresponding to each phase (here u phase, v phase, w phase) of a load, and outputs it from each terminal T8-T10. As a load connected to the output-side terminals T8 to T10, for example, a three-phase motor can be used. Note that the DC power supply 19 may output DC power such as a converter circuit.

  Legs 2 to 4 constituting the three-phase inverter circuit, and bipolar bootstrap circuits 5 to 7 for driving the switching elements SuH to SwH and SuL to SwL constituting the legs 2 to 4, a non-isolated DC power source Since Vg1, Vg2, and insulated DC power supply Vg3 are the same as those described in the first embodiment in terms of their configurations and functions, detailed description thereof is omitted here.

  Next, features of control by the control circuit 20 relating to capacitor charging of the bipolar bootstrap circuits 5 to 7 according to the second embodiment will be described.

  The control circuit 20 controls the output of the gate signals GuH to GwH and GuL to GwL for performing on / off control of the switching elements SuH to SwH and SuL to SwL according to the charge command signal X input from the outside. To do.

  FIG. 4 shows gate signals GuH to GwH and GuL to GwL for on / off control of the switching elements SuH to SwH and SuL to SwL generated by the control circuit 8 and capacitor charging states of the bipolar bootstrap circuits 5 to 7. It is a time chart which shows the relationship.

  First, at time t0, the charge command signal X becomes H level, and control for charging the capacitors C1u to C1w and C2u to C2w on the upper arm side of the bipolar bootstrap circuits 5 to 7 is started.

  During the period of time t0 to t1, the upper gate signals GuH to GwH at the H level and the lower gate signals GuL to GwL at the L level are output. As a result, all the upper arm switching elements SuH to SwH are turned on, and at the same time, all the lower arm switching elements SuL to SwL are turned off. Accordingly, all the upper-stage negative voltage applying capacitors C2u to C2w are charged through the path indicated by reference numeral (4) in FIG. Note that the period of time t0 to t1 in the second embodiment is sufficiently shorter than the period of t0 to t1 in the third embodiment to be described later.

  In the period from time t1 to time t2, all L level gate signals GuH, GuL,... Are output. Thereby, all the switching elements SuH to SwH and SuL to SwL are turned off. This is to prevent an arm short circuit due to simultaneous turn-on of the upper arm switching elements SuH to SwH and the lower arm switching elements SuL to SwL of the legs 2 to 4.

  During the period from time t2 to time t3, L level upper gate signals GuH to GwH and H level lower gate signals GuL to GwL are output. As a result, all the upper arm switching elements SuH to SwH are turned off, and at the same time, all the lower arm switching elements SuL to SwL are turned on. Therefore, all the upper-stage positive voltage applying capacitors C1u to C1w are charged through the path indicated by reference numeral (5) in FIG. The period from time t2 to t3 in the second embodiment is sufficiently shorter than the period from t2 to t3 in the third embodiment to be described later.

  In the period from time t3 to t4, all the L level gate signals GuH, GuL,... Are output again. Thereby, all the switching elements SuH to SwH and SuL to SwL are turned off. This is also for preventing an arm short circuit as in the period from time t1 to time t2.

  Thereafter, during the period in which the charge command signal X is at the H level, the operation at the times t0 to t4 is repeated, and the capacitors C1u to C1w and C2u to C2w on the upper arm side of the bipolar bootstrap circuits 5 to 7 are each non-insulated DC The power supply voltage Vg1 and the insulated DC power supply Vg3 are gradually charged up to the power supply voltages VH and VL1.

  As can be seen from the above description, in the three-phase inverter circuit of the second embodiment, the upper positive voltage applying capacitors C1u to C1w and the upper negative voltage applying capacitors C2u to C2w of the bipolar bootstrap circuits 5 to 7 are used. The upper arm switching elements SuH to SwH of the legs 2 to 4 and the lower arm switching elements SuL to SwL are not turned on at the same time during the charging period. Further, the DC power source 19 is connected to both ends of the input terminals T6 and T7 of the legs 2 to 4, and when charging the capacitor, unlike the case of the first embodiment, outputs from the middle points of the legs 2 to 4. Since the applied voltage changes in the same phase, the voltage applied to the output side terminals T8 to T10 becomes substantially the same potential, and no potential difference occurs.

  Therefore, even if all the upper switching elements SuH to SwH of each leg 2 to 4 and all the lower switching elements SuL to SwL are alternately turned on in a time-sharing manner, no short-circuit current flows, and safe and reliable capacitor charging is possible. It becomes possible. Even when a wide bandgap semiconductor is applied as a switching element constituting a multiphase inverter circuit, a full bridge type DC / DC converter circuit, etc., the wide bandgap semiconductor is used by the bipolar bootstrap circuits 5-7. The switching element can be reliably turned off.

  Furthermore, since both the upper stage positive voltage application capacitors C1u to C1w and the upper stage negative voltage application capacitors C2u to C2w are gradually charged, even if the upper arm switching elements SuH to SwH are turned on by mistake, the circuit is destroyed by a short circuit current. Can reduce the risk.

Embodiment 3 FIG.
FIG. 5 shows the gate signals GuH to GwH and GuL to GwL for the on / off control of the switching elements SuH to SwH and SuL to SwL generated by the control circuit 8 and the bipolar bootstrap circuit 5 according to the third embodiment. It is a time chart which shows the relationship with the capacitor charge state of -7.

  The basic configuration of the circuit in the third embodiment is the same as that of the three-phase inverter circuit shown in the second embodiment, and only the control by the control circuit 20 is partially different. Therefore, description of the circuit configuration and operation is omitted here.

Hereinafter, the control method according to the third embodiment will be described with reference to FIG.
First, at time t0, the charge command signal X becomes H level, and control for charging the capacitors C1u to C1w and C2u to C2w on the upper arm side of the bipolar bootstrap circuits 5 to 7 is started.

  During the period from time t0 to t1, the upper gate signals GuH to GwH at the H level and the lower gate signals GuL to GwL at the L level are output. As a result, all the upper arm switching elements SuH to SwH are turned on, and at the same time, all the lower arm switching elements SuL to SwL are turned off. Accordingly, all the upper-stage negative voltage applying capacitors C2u to C2w are charged through the path indicated by reference numeral (4) in FIG.

  In the period from time t1 to time t2, all L level gate signals GuH, GuL,... Are output. Thereby, all the switching elements SuH to SwH and SuL to SwL are turned off. This is to prevent an arm short circuit due to simultaneous turn-on of the upper arm switching elements SuH to SwH and the lower arm switching elements SuL to SwL of the legs 2 to 4, and the period from t1 to t2 in the second embodiment. The same.

  During the period from time t2 to time t3, L level upper gate signals GuH to GwH and H level lower gate signals GuL to GwL are output. As a result, all the upper arm switching elements SuH to SwH are turned off, and at the same time, all the lower arm switching elements SuL to SwL are turned on. Therefore, all the upper-stage positive voltage applying capacitors C1u to C1w are charged through the path indicated by reference numeral (5) in FIG.

The control operation of the third embodiment differs from the control operation of the second embodiment in two points.
First, the first negative voltage application capacitors C2u, C2v and C2w are insulated by one charge by making the charging periods t0 to t1 sufficiently longer than the charging periods t0 to t1 of the second embodiment. It is a point which charges to voltage VL1 of DC power supply Vg3. The second point is that the charging periods t2 to t3 of the upper positive voltage applying capacitors C1u, C1v, and C1w are sufficiently longer than the charging periods t2 to t3 of the second embodiment, so that non-insulated direct current can be obtained by one charge. It is a point which charges to the voltage VH of the power supply Vg1.

  As can be seen from the above description, the three-phase inverter circuit of the third embodiment can obtain the same operations and effects as those of the second embodiment, and further, has the unique features of the third embodiment. As described above, the upper-stage positive voltage applying capacitors C1u to C1w and the upper-stage negative voltage applying capacitors C2u to C2w can be charged each time with one charge, so that switching loss during charging can be reduced.

1 Three-phase AC power supply, 2-4 legs, 5-7 bipolar bootstrap circuit,
8 control circuit, 9 input voltage detector, 10-15 comparator, 16-18 output determiner,
19 DC power supply, 20 control circuit.

Claims (8)

A plurality of legs in which the switching elements on the upper arm side and the lower arm side are connected in series to each other are connected in parallel to each other, and a polyphase AC power source is connected to each midpoint of each leg to constitute an AC / DC converter circuit A power conversion device,
Arm driving circuits for applying positive / negative bipolar voltages for on / off driving to each switching element are provided individually on the upper arm side and the lower arm side, and the positive and negative voltages are supplied by power from a DC power source. A bipolar bootstrap circuit in which each capacitor for positive voltage application and negative voltage application for charging each is provided separately on the upper arm side and the lower arm side, and disposed on each leg,
A control circuit for controlling each arm drive circuit for charging each capacitor,
The control circuit performs switching on the upper arm side of the leg to which the highest voltage among the voltages of each phase of the multiphase AC power source is input to the arm drive circuits on the upper arm side and the lower arm side. A power converter that repeatedly outputs a control signal for turning on only the switching element on the lower arm side of the leg to which the element and the lowest voltage are input according to the voltage change of each phase. The control circuit compares the voltage value of each phase of the multi-phase AC power source and the multi-phase AC power supply with respect to the upper and lower arm drive circuits according to the comparison result of the comparator. Control that turns on only the switching element on the upper arm side of the leg to which the highest voltage is input and the switching element on the lower arm side of the leg to which the lowest voltage is input. The power converter of Claim 1 provided with the output determination device which outputs a signal. The power conversion device according to claim 1, wherein each of the switching elements is formed of a wide band gap semiconductor. The power converter according to claim 3, wherein the wide band gap semiconductor is silicon carbide, a gallium nitride-based material, or diamond. A plurality of legs in which the switching elements on the upper arm side and the lower arm side are connected in series to each other, and the high-voltage side and the low-voltage side of the DC power supply are connected to both ends of the input side of each leg. A conversion device,
Arm drive circuits for applying positive / negative bipolar voltages for on / off drive to the switching elements are provided individually on the upper arm side and the lower arm side, and the positive and negative voltages are generated by power from the DC power source. Bipolar bootstrap circuits, each of which is provided with a positive voltage application capacitor and a negative voltage application capacitor for charging a voltage individually on the upper arm side and the lower arm side, and are respectively disposed on the legs.
A control circuit for controlling each arm drive circuit for charging each capacitor,
The control circuit is configured to turn on all the switching elements on the upper arm side and turn off all the switching elements on the lower arm side with respect to the arm drive circuits on the upper arm side and the lower arm side. A power converter that outputs a control signal that alternately turns off all the switching elements on the upper arm side and turns on all the switching elements on the lower arm side. In the control signal output period in which the control circuit turns on all the switching elements on the upper arm side and turns off all the switching elements on the lower arm side, the negative voltage applying capacitor on the upper arm side is completely turned off. The control signal output period for turning off all the switching elements on the upper arm side and turning on all the switching elements on the lower arm side is set to the positive voltage on the upper arm side. The power conversion device according to claim 5, wherein the power conversion device is set to a period for completely charging the capacitor for application. The power converter according to claim 5 or 6, wherein each of the switching elements is formed of a wide band gap semiconductor. The power converter according to claim 7, wherein the wide band gap semiconductor is silicon carbide, a gallium nitride-based material, or diamond.

Images