Power conversion device, motor drive device, and refrigeration cycle application device

Abstract

A power conversion device (50) is provided with a converter (3) that converts AC into DC and outputs the DC to a load (130). The converter (3) is provided with semiconductor elements (Q1 to Q6) and a drive circuit (16) for driving the semiconductor elements (Q1 to Q6). The drive circuit (16) is provided with a boot capacitor (64c) for applying a drive voltage to each of the upper elements of the semiconductor elements (Q1 to Q6), and the boot capacitor (64c) is configured such that electric charge is stored by causing a current to flow to the load side of the converter (3).

Description

Power conversion devices, motor drive devices, and refrigeration cycle application equipment

[0001] The present disclosure relates to a power conversion device including a converter that converts AC to DC and outputs the DC to a load, a motor drive device including a power conversion device, and refrigeration cycle equipment.

[0002] Power supply current, which is the current supplied from an AC power supply, contains harmonic currents. Harmonic currents are frequency components with frequencies higher than the fundamental frequency. To suppress interference caused by harmonic currents, international regulations have been established for electronic devices that generate harmonic currents. To comply with these regulations, converters take measures to suppress the harmonic currents contained in the power supply current by chopping AC (Alternating Current) or DC (Direct Current).

[0003] Patent Document 1 listed below discloses a power conversion device equipped with a three-phase PWM (Pulse Width Modulation) converter. The three-phase PWM converter is a converter that performs chopping in AC. The use of any converter, not limited to a three-phase PWM converter, controls the power supply current to a sinusoidal waveform, making it possible to suppress power supply harmonics, which are harmonic currents contained in the power supply current.

[0004] Japanese Patent Application Laid-Open No. 2005-151755

[0005] Unlike rectifier circuits, converters are equipped with one or more semiconductor elements. To drive the semiconductor elements, a drive circuit with a drive power supply is required. If a drive power supply is provided independently for each semiconductor element, the drive circuit will become larger, which will lead to a larger converter and ultimately a larger power conversion device.

[0006] The present disclosure has been made in view of the above, and has an object to provide a power conversion device that can suppress harmonic currents while preventing the device from becoming large.

[0007] To solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure includes a converter that converts AC to DC and outputs the DC to a load. The converter includes a plurality of first semiconductor elements and a first drive circuit that drives the first semiconductor elements. The first drive circuit includes a boot capacitor for applying a drive voltage to upper elements of the first semiconductor elements. The boot capacitor is configured to store charge by passing a current through the load side of the converter.

[0008] The power conversion device according to the present disclosure has the advantage of being able to suppress harmonic currents while preventing the device from becoming large.

[0009] FIG. 1 is a diagram showing an example of the configuration of a motor drive device including a power conversion device according to embodiment 1; FIG. 2 is a diagram showing the operating waveforms of the main parts of the power conversion device according to embodiment 1; FIG. 3 is a diagram showing an example of the configuration of a drive circuit provided in the power conversion device according to embodiment 1; FIG. 4 is a diagram used to explain the charging operation of the boot capacitor of the drive circuit shown in FIG. 3; FIG. 5 is a diagram used to explain the charging control of the boot capacitor of the drive circuit shown in FIG. 3;

[0010] Hereinafter, a power conversion device, a motor drive device, and a refrigeration cycle applied device according to embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0011] First Embodiment Fig. 1 is a diagram showing an example of the configuration of a motor drive device 100 including a power conversion device 50 according to a first embodiment. The power conversion device 50 according to the first embodiment is a power conversion device that converts AC voltage output from a three-phase power supply 110, which is a three-phase AC power supply, into DC voltage and applies the DC voltage to a load 130. The motor drive device 100 according to the first embodiment is also a drive device that converts DC power output from the power conversion device 50 into AC power and supplies the converted AC power to a motor 120 to drive the motor 120. As shown in the figure, the phases of the three-phase power supply 110 are represented by R, S, and T, and are referred to as the "R phase," the "S phase," and the "T phase," respectively.

[0012] As shown in FIG. 1, the motor drive device 100 according to the first embodiment includes a noise filter 1, a reactor 2, current detectors 5a and 5b, a phase voltage detection unit 6, a power conversion device 50, control units 14 and 15, and a load 130.

[0013] The load 130 includes a shunt resistor 8 for current detection, an inverter 9, a current detection unit 12, a drive circuit 17 which is a second drive circuit, current detectors 18a and 18b, and a motor 120. Of the components of the load 130, the shunt resistor 8, the inverter 9, the current detection unit 12, the drive circuit 17, and the current detectors 18a and 18b, excluding the motor 120, are components of the motor drive device 100.

[0014] The noise filter 1 is disposed between the three-phase power supply 110 and the reactor 2. The noise filter 1 operates to reduce noise currents flowing in and out of the power conversion device 50. The reactor 2 is disposed between the noise filter 1 and the power conversion device 50. The reactor 2 is a device including circuit elements that temporarily store electrical energy supplied from the three-phase power supply 110. The reactor 2 also operates to reduce noise currents flowing in and out of the power conversion device 50.

[0015] The current detectors 5a and 5b detect the power supply current, which is an AC current flowing between the three-phase power supply 110 and the power conversion device 50, and output the detected values ​​of the power supply current to the control unit 14. An example of the current detectors 5a and 5b is an ACCT (Alternating Current Transformer). While FIG. 1 illustrates an example in which the current detector 5a detects the R-phase current Ir and the current detector 5b detects the T-phase current It, the present invention is not limited to this example. It is sufficient for the current detectors 5a and 5b to detect the currents of any two of the three phases; the currents of the remaining phases can be calculated by utilizing the fact that the power supply currents are three-phase balanced. The phase voltage detector 6 detects the phase voltages of the three phases, i.e., the R-phase voltage Vr, the S-phase voltage Vs, and the T-phase voltage Vt, output from the three-phase power supply 110, and outputs the detected values ​​to the control unit 14.

[0016] The power conversion device 50 includes a converter 3 , a drive circuit 16 which is a first drive circuit, a capacitor 4 , a shunt resistor 7 for current detection, a current detection unit 10 , and a voltage detection unit 11 .

[0017] The converter 3 converts the AC voltage output from the three-phase power supply 110 into a DC voltage and outputs it to DC buses 19a and 19b. The DC buses 19a and 19b are electrical wiring that connect the converter 3 to the load 130. The voltage between the DC buses 19a and 19b is called the "bus voltage."

[0018] The output voltage of the converter 3 is applied across the capacitor 4. The capacitor 4 is connected to the DC buses 19a and 19b. Therefore, in the configuration of FIG. 1 , the capacitor voltage, which is the voltage across the capacitor 4, is equal to the bus voltage. The capacitor 4 smoothes the output voltage of the converter 3. The voltage smoothed by the capacitor 4 is applied to the inverter 9.

[0019] The voltage detection unit 11 detects the bus voltage Vdc and outputs the detected value of the bus voltage Vdc to the control units 14 and 15. A converter current I1 flows through the shunt resistor 7. The converter current I1 is a current that flows in and out of the converter 3. The current detection unit 10 converts a voltage value generated when the converter current I1 flows through the shunt resistor 7 into a current value and outputs the current value to the control unit 14.

[0020] The converter 3 includes six semiconductor elements Q1 to Q6 that are connected in a three-phase bridge configuration. The semiconductor elements Q1 and Q2 are connected in series in this order, and a connection point 3a between the semiconductor elements Q1 and Q2 is electrically connected to the R phase of the three-phase power supply 110. The semiconductor elements Q3 and Q4 are connected in series in this order, and a connection point 3b between the semiconductor elements Q3 and Q4 is electrically connected to the S phase of the three-phase power supply 110. The semiconductor elements Q5 and Q6 are connected in series in this order, and a connection point 3c between the semiconductor elements Q5 and Q6 is electrically connected to the T phase of the three-phase power supply 110.

[0021] In this paper, the semiconductor elements Q1, Q3, and Q5 arranged on the upper side of the circuit diagram may be referred to as "upper elements," and the semiconductor elements Q2, Q4, and Q6 arranged on the lower side of the circuit diagram may be referred to as "lower elements." Also, in this paper, the side of the three-phase power supply 110 where connection points 3a to 3c are located, as viewed from the converter 3, may be referred to as the "AC side," and the side of the load 130 may be referred to as the "DC side."

[0022] The semiconductor elements Q1 to Q6 each include a diode D1 to D6 connected in parallel. The diodes D1 to D6 are connected so that their anodes are located on the AC side and their cathodes are located on the DC side. While FIG. 1 illustrates a case where the semiconductor elements Q1 to Q6 are IGBTs (insulated gate bipolar transistors), MOSFETs (metal oxide semiconductor field effect transistors) may be used instead of IGBTs. Note that, because MOSFETs have a built-in parasitic diode due to their structure, a configuration in which the diodes D1 to D6 are not connected in parallel may also be employed.

[0023] The inverter 9 converts DC to AC. More specifically, the inverter 9 converts the DC voltage output from the power conversion device 50 into AC voltage to be applied to the motor 120 and outputs the AC voltage. An example of an apparatus in which the motor 120 is mounted is a blower or compressor in an air conditioner. The air conditioner is an example of an apparatus that applies a refrigeration cycle.

[0024] An inverter current I2 flows through the shunt resistor 8. The inverter current I2 is a current that flows in and out of the inverter 9. The current detection unit 12 converts a voltage value generated when the inverter current I2 flows through the shunt resistor 8 into a current value and outputs the current value to the control unit 15.

[0025] The inverter 9 includes six semiconductor elements Q21 to Q26 that are connected in a three-phase bridge configuration. The semiconductor elements Q21 and Q22 are connected in series in this order, with a connection point 9a between the semiconductor elements Q21 and Q22 electrically connected to the U-phase of the motor 120. The semiconductor elements Q23 and Q24 are connected in series in this order, with a connection point 9b between the semiconductor elements Q23 and Q24 electrically connected to the V-phase of the motor 120. The semiconductor elements Q25 and Q26 are connected in series in this order, with a connection point 9c between the semiconductor elements Q25 and Q26 electrically connected to the W-phase of the motor 120. Note that, from the perspective of the inverter 9, the side of the converter 3 is the DC side, and the side of the motor 120 where the connection points 9a to 9c are located is the AC side. In this paper, in order to distinguish between the semiconductor elements Q1 to Q6 provided in the converter 3 and the semiconductor elements Q21 to Q26 provided in the inverter 9 without using symbols, the former may be referred to as the "first semiconductor elements" and the latter as the "second semiconductor elements."

[0026] The semiconductor elements Q21 to Q26 each include a diode D21 to D26 connected in parallel. The diodes D21 to D26 are connected so that their cathodes are on the DC side and their anodes are on the AC side. While FIG. 1 shows a case where the semiconductor elements Q21 to Q26 are IGBTs, MOSFETs may be used instead of the IGBTs. Note that, in the case of MOSFETs, a parasitic diode is built into the structure, so a configuration in which the diodes D21 to D26 are not connected in parallel may also be employed. Furthermore, an IGCT (Integrated Gate Commutated Thyristor) may be used instead of the IGBTs.

[0027] Current detectors 18a and 18b detect three-phase motor currents flowing between inverter 9 and motor 120 and output the detected motor current values ​​to control unit 15. An example of current detectors 18a and 18b is an ACCT. Note that while FIG. 1 shows an example in which current detector 18a detects U-phase motor current Iu and current detector 18b detects W-phase motor current Iw, this example is not limiting. Current detectors 18a and 18b only need to detect currents in any two of the three phases, and the currents in the remaining phases can be calculated by utilizing the fact that motor currents are three-phase balanced.

[0028] The control unit 14 generates control signals S1 to S6 for controlling the bus voltage to a desired voltage while controlling the power supply current to a sinusoidal waveform based on the detection values ​​of the current detectors 5a and 5b, the detection value of the phase voltage detection unit 6, the detection value of the current detection unit 10, and the detection value of the voltage detection unit 11. The control signals S1 to S6 are control signals for controlling the semiconductor elements Q1 to Q6 of the converter 3, respectively. The control signals S1 to S6 generated by the control unit 14 are input to the drive circuit 16.

[0029] Furthermore, the control unit 15 generates control signals S21 to S26 for rotating the motor 120 at a desired rotation speed based on the detection values ​​of the voltage detection unit 11, the current detection unit 12, and the current detectors 18a and 18b. The control signals S21 to S26 are control signals for controlling the semiconductor elements Q21 to Q26 of the inverter 9, respectively. The control signals S21 to S26 generated by the control unit 15 are input to the drive circuit 17.

[0030] Drive circuit 16 generates drive pulses G1 to G6 based on control signals S1 to S6. Semiconductor elements Q1 to Q6 of converter 3 perform switching operations in response to the drive pulses G1 to G6. Drive circuit 17 generates drive pulses G21 to G26 based on control signals S21 to S26. Semiconductor elements Q21 to Q26 of inverter 9 perform switching operations in response to the drive pulses G21 to G26.

[0031] 1, the control units 14 and 15 are provided inside the motor drive device 100, but this configuration is not limiting. The control unit 14 may be provided inside the power conversion device 50, and the control unit 15 may be provided inside the load 130. Also, in FIG. 1, the control units 14 and 15 are configured as separate control units, but this configuration is not limiting. The control units 14 and 15 may be integrated into a common control unit that controls both the converter 3 and the inverter 9.

[0032] Next, the configuration and key points of operation of the power conversion device 50 according to the first embodiment will be described. Fig. 2 is a diagram showing the operational waveforms of the main parts of the power conversion device 50 according to the first embodiment. Fig. 2 shows, from top to bottom, the waveforms of the phase voltages of each of the three phases, the phase currents of each of the three phases, and the bus voltage Vdc. The horizontal axis of Fig. 2 represents time.

[0033] The upper part of FIG. 2 shows the waveforms of the R-phase voltage Vr, the S-phase voltage Vs, and the T-phase voltage Vt, which are sinusoidal voltage waveforms. The meaning of period T1 will be described later. The middle part of FIG. 2 shows the waveforms of the R-phase current Ir, the S-phase current Is, and the T-phase current It, which are sinusoidal current waveforms. These sinusoidal current waveforms are obtained by PWM control of the semiconductor elements Q1 to Q6 of the converter 3. By making the R-phase current Ir, the S-phase current Is, and the T-phase current It sinusoidal, power supply harmonics are suppressed. The lower part of FIG. 2 shows the waveform of the bus voltage Vdc, which is controlled to be approximately constant. By controlling the bus voltage Vdc to be constant, it is possible to stably drive the load 130. Note that in the first embodiment, the bus voltage Vdc does not necessarily have to be controlled to be constant.

[0034] Fig. 3 is a diagram showing an example of the configuration of the drive circuit 16 provided in the power conversion device 50 according to the first embodiment. The upper right of Fig. 3 shows the three-phase power supply 110, the reactor 2, the converter 3, the capacitor 4, and the shunt resistor 7 extracted from Fig. 1. The lower left of Fig. 3 shows the circuit configuration of the drive circuit 16 that drives the R-phase leg 3R of the converter 3. The R-phase leg 3R is a circuit section that has semiconductor elements Q1 and Q2 connected in series.

[0035] 3, the drive circuit 16 includes a drive power supply 61, gate drivers 62 and 63, and a bootstrap circuit 64. The gate driver 62 is a driver used to drive a semiconductor element Q1, which is an upper element of the R-phase leg 3R. The gate driver 63 is a driver used to drive a semiconductor element Q2, which is a lower element of the R-phase leg 3R. The other two legs of the converter 3 are also driven by two similar gate drivers. The bootstrap circuit 64 includes a resistor 64a, a diode 64b, and a boot capacitor 64c.

[0036] In the drive circuit 16 equipped with the bootstrap circuit 64, the drive voltage for driving the semiconductor element Q2 is applied by the drive power supply 61. On the other hand, the drive voltage for driving the semiconductor element Q1 is applied by the boot capacitor 64c. Therefore, in order to stably drive the semiconductor element Q1, it is necessary to always store a certain amount of charge or more in the boot capacitor 64c.

[0037] 3, the boot capacitor 64c can be charged by turning on the semiconductor element Q2, which is the lower element. However, with this control alone, it is necessary to periodically turn on the lower element of the converter 3 even when the operation of the converter 3 is not required. Furthermore, with this control, the duty ratio of the PWM signal when turning on the lower element is restricted by its relationship with the capacitance of the boot capacitor 64c.

[0038] 3 is applied to the three-phase converter 3 shown in Fig. 1, the boot capacitor 64c can be charged by applying a three-phase AC current to the converter 3. Here, the R-phase drive circuit 16 will be described as an example.

[0039] 2, the first period, period T1, is a period during which the R-phase voltage Vr is smaller than both the S-phase voltage Vs and the T-phase voltage Vt. Period T1 can also be described as a period during which the voltage at node 3a on the AC side of semiconductor element Q1 is smaller than the voltages at nodes 3b and 3c of the other phases. Because the neutral point of the three-phase power supply 110 is grounded, the potential at node 3a during period T1 is lower than zero potential. Therefore, during period T1, charging of boot capacitor 64c becomes possible.

[0040] Fig. 4 is a diagram illustrating the charging operation of the boot capacitor 64c of the drive circuit 16 shown in Fig. 3. The upper part of Fig. 4 shows the three-phase power supply 110, reactor 2, converter 3, capacitor 4, and shunt resistor 7 extracted from Fig. 1. The middle part of Fig. 4 shows the voltage waveform at the target point, and the lower part of Fig. 4 shows the waveform of the drive voltage of the upper element.

[0041] The middle part of Figure 4 shows the voltage waveform of the point of interest, with the voltage Vr_conv at node 3a shown by a solid line and the voltage Vdc_N on the emitter side of semiconductor element Q2, the lower element, shown by a dashed line. Voltage Vdc_N is the voltage of the reference potential on the DC side of converter 3. Period T2, which is the second period, is the period during which voltage Vr_conv falls below voltage Vdc_N and is included in period T1. The bottom part of Figure 4 shows changes in the drive voltage Vc_boot of the upper element.

[0042] As shown in the lower part of Figure 4, the drive voltage Vc_boot rises during period T2, indicating that charging is occurring. Furthermore, the drive voltage Vc_boot has a flat waveform before and after period T2. Therefore, period T2 can be said to be the period in which the greatest amount of charge is stored during period T1.

[0043] In the first embodiment, in order to drive the upper semiconductor elements Q1, Q3, and Q5 more stably, the charging of the boot capacitor 64c is controlled by using the following method in combination.

[0044] Fig. 5 is a diagram illustrating charging control of the boot capacitor 64c of the drive circuit 16 shown in Fig. 3. Fig. 5 shows the three-phase power supply 110, reactor 2, converter 3, capacitor 4, shunt resistor 7, and load 130 extracted from Fig. 1.

[0045] Motor drive device 100 according to the first embodiment controls current to flow to load 130 when charging boot capacitor 64c of drive circuit 16. Specifically, control unit 14, which controls the operation of converter 3, transmits an operation command for inverter 9 to control unit 15, which controls the operation of inverter 9. Having received the operation command for inverter 9, control unit 15 drives semiconductor elements Q21 to Q26 so that a motor current flows through motor 120.

[0046] When the motor current flows, the inverter current I2 flows, causing a drop in the voltage of the capacitor 4. If the voltage of the capacitor 4 drops, the converter current I1 flows, causing the power supply current to also flow. Therefore, if the control units 14 and 15 cooperate to actively control the flow of current to the load 130, it becomes possible to stably ensure the drive voltage Vc_boot held in the boot capacitor 64c.

[0047] Next, a description will be given of a hardware configuration for realizing the functions of the control units 14 and 15 according to embodiment 1. Fig. 6 is a block diagram showing an example of a hardware configuration for realizing the functions of the control units 14 and 15 according to embodiment 1.

[0048] To realize some or all of the functions of the control units 14 and 15, a configuration including a processor 201 that performs calculations and a memory 202 that stores programs read by the processor 201 can be used, as shown in FIG.

[0049] The processor 201 is an example of a computing unit. The processor 201 may be a computing unit called a microprocessor, a microcomputer, a central processing unit (CPU), or a digital signal processor (DSP). Examples of the memory 202 include non-volatile or volatile semiconductor memory such as random access memory (RAM), read-only memory (ROM), flash memory, erasable programmable read-only memory (EPROM), and electrically programmable programmable read-only memory (EEPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a minidisk, and a digital versatile disk (DVD).

[0050] The memory 202 holds programs that execute the functions of the control units 14 and 15. The processor 201 exchanges necessary information and stores it in the memory 202, and the processor 201 executes the programs held in the memory 202 and refers to the data and tables stored in the memory 202, thereby executing the above-mentioned processing. The calculation results by the processor 201 can be stored in the memory 202.

[0051] As described above, the power conversion device according to the first embodiment includes a converter that converts AC to DC and outputs the converted DC to a load. The converter includes a plurality of first semiconductor elements and a first drive circuit that drives the first semiconductor elements. The first drive circuit includes a boot capacitor that applies a drive voltage to upper elements of the first semiconductor elements. The boot capacitor is configured to store charge by passing a current to the load side of the converter. The inclusion of the boot capacitor can prevent the converter from becoming large. Therefore, by using the power conversion device according to the first embodiment, it is possible to suppress harmonic currents while preventing the device from becoming large.

[0052] Furthermore, in the power conversion device according to the first embodiment, the boot capacitor provided in the first drive circuit is configured to store charge during a first period in which the voltage at the connection point on the AC side of the first semiconductor element to which the drive voltage is applied from the boot capacitor is lower than the voltages at the connection points of other phases. Furthermore, the boot capacitor is configured to store the most charge during a second period in which the voltage at the connection point on the AC side of the first semiconductor element to which the drive voltage is applied from the boot capacitor is lower than the voltage of the reference potential on the DC side of the converter. By using a power conversion device configured in this manner, it is possible to stably ensure the drive voltage maintained in the boot capacitor.

[0053] Furthermore, the motor drive device according to the first embodiment includes a power conversion device having the above-described configuration and an inverter that converts the output voltage of the power conversion device into an AC voltage and applies the AC voltage to a motor provided as a load. When storing charge in the boot capacitor, the motor drive device drives a second semiconductor element provided in the inverter so that current flows to the motor. Use of a motor drive device configured in this manner makes it possible to ensure an even more stable drive voltage maintained in the boot capacitor.

[0054] Embodiment 2. Figure 7 is a diagram showing an example of the configuration of an air conditioner 300 according to embodiment 2. The air conditioner 300 according to embodiment 2 is an example of a refrigeration cycle-applied device, and includes a motor drive device 100 and a motor 120 according to embodiment 2. The air conditioner 300 also includes a compressor 81, a four-way valve 82, an outdoor heat exchanger 83, an expansion valve 84, an indoor heat exchanger 85, and refrigerant piping 86.

[0055] The air conditioner 300 may be a separate type air conditioner in which the outdoor unit is separated from the indoor unit, or an integrated type air conditioner in which the compressor 81, indoor heat exchanger 85, and outdoor heat exchanger 83 are provided within a single housing.

[0056] The compressor 81 contains a compression mechanism 87 that compresses the refrigerant and a motor 120 that operates the compression mechanism 87. The motor 120 is driven by a motor drive device 100. In the air conditioner 300, a refrigeration cycle is formed by circulating the refrigerant through the compressor 81, the four-way valve 82, the outdoor heat exchanger 83, the expansion valve 84, the indoor heat exchanger 85, and the refrigerant piping 86.

[0057] The components of the air conditioner 300 can also be applied to appliances such as refrigerators or freezers equipped with a refrigeration cycle. In addition, in the second embodiment, the motor 120 is used as the drive source for the compressor 81, but the motor 120 may also be used as the drive source for an indoor unit blower and an outdoor unit blower (not shown) instead of the compressor 81. Alternatively, the motor 120 may be used as the drive source for each of the indoor unit blower, the outdoor unit blower, and the compressor 81, and these three motors 120 may be driven by the motor drive device 100.

[0058] The air conditioner 300 according to the second embodiment is configured to include the motor drive device 100 according to the first embodiment, and therefore can suppress harmonic currents while preventing the converter from becoming large. This makes it possible to provide a product that is inexpensive and avoids large size.

[0059] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, and parts of the configurations may be omitted or modified without departing from the spirit of the invention.

[0060] 1 noise filter, 2 reactor, 3 converter, 3a to 3c, 9a to 9c connection point, 3R R-phase leg, 4 capacitor, 5a, 5b, 18a, 18b current detector, 6 phase voltage detection unit, 7, 8 shunt resistor, 9 inverter, 10, 12 current detection unit, 11 voltage detection unit, 14, 15 control unit, 16, 17 drive circuit, 19a, 19b DC bus, 50 power conversion device, 61 drive power supply, 62, 63 gate driver, 64 bootstrap circuit, 64a resistor, 64b, D1 to D6, D21 to D26 diode, 64c boot capacitor, 81 compressor, 82 four-way valve, 83 outdoor heat exchanger, 84 expansion valve, 85 indoor heat exchanger, 86 refrigerant piping, 87 compression mechanism, 100 motor drive device, 110 Three-phase power supply, 120 motor, 130 load, 201 processor, 202 memory, 300 air conditioner, Q1 to Q6, Q21 to Q26 semiconductor elements.

Claims

1. A power conversion device including a converter that converts AC to DC and outputs the converted DC to a load, The converter comprises: a plurality of first semiconductor elements; a first drive circuit that drives the first semiconductor element; Equipped with the first drive circuit includes a boot capacitor for applying a drive voltage to an upper element of the first semiconductor element; the boot capacitor is configured to store charge during a first period in which a voltage at a connection point on the AC side of the first semiconductor element to which a drive voltage is applied from the boot capacitor is smaller than voltages at connection points of other phases; The second period during which the largest amount of charge is stored in the first period is a period during which the voltage at the connection point on the AC side of the first semiconductor element to which the drive voltage is applied from the boot capacitor falls below the voltage of the reference potential on the DC side of the converter. Power conversion device.

2. The power conversion device according to claim 1; an inverter that converts the output voltage of the power conversion device into an AC voltage and applies the AC voltage to a motor provided in the load; Equipped with When storing electric charge in the boot capacitor, the inverter is driven so that a current flows through the motor. Motor drive device.

3. The inverter is a plurality of second semiconductor elements; a second drive circuit that drives the second semiconductor element when storing charge in the boot capacitor; The motor drive device according to claim 2 , comprising:

4. A refrigeration cycle device comprising the motor drive device according to claim 2 or 3.