Power converters, motor drive systems, and refrigeration cycle application equipment

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

Technical Field

[0005] ,

[0001] The present disclosure relates to a power conversion device including a converter that converts alternating current into direct current and outputs it to a load, a motor drive device including the power conversion device, and a refrigeration cycle application device.

Background Art

[0002] The power supply current supplied from an alternating current power supply includes harmonic currents. Harmonic currents are frequency components having a frequency higher than the frequency of the fundamental wave. In order to suppress the disturbances caused by harmonic currents, international regulations are provided for electronic devices that generate harmonic currents. To comply with this regulation, in a converter, measures are taken to suppress the harmonic currents included in the power supply current by chopping in AC (Alternating Current) or DC (Direct Current).

[0003] The following Patent Document 1 discloses a power conversion device including a three-phase PWM (Pulse Width Modulation) converter. The three-phase PWM converter is a converter that performs chopping in AC. Not limited to the three-phase PWM converter, when a converter is used, the power supply current is controlled in a sinusoidal shape, so that it is possible to suppress the power supply harmonics, which are harmonic currents included in the power supply current.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Unlike rectifier circuits, converters contain one or more semiconductor elements. Driving these semiconductor elements requires a drive circuit equipped with a power supply. If a separate power supply is required for each semiconductor element, the drive circuit becomes larger, leading to a larger converter and, consequently, a larger power conversion device.

[0006] This disclosure has been made in view of the above, and aims to provide a power conversion device that can suppress harmonic currents while preventing the device from becoming larger. [Means for solving the problem]

[0007] To solve the above-mentioned problems and achieve the objective, the power conversion device according to this disclosure includes a converter that converts alternating current to direct current and outputs it 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 the upper element of the first semiconductor elements. The boot capacitor is configured to store charge by flowing current through it to the load side of the converter. [Effects of the Invention]

[0008] The power conversion device described herein has the effect of suppressing harmonic currents while preventing the device from becoming larger. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example configuration of a motor drive system including a power converter according to Embodiment 1. [Figure 2] A diagram showing the operating waveforms of the main components of the power converter according to Embodiment 1. [Figure 3] This figure shows an example of the configuration of a drive circuit provided in the power conversion device according to Embodiment 1. [Figure 4] Figure 3 is a diagram illustrating the charging operation of the boot capacitor in the drive circuit shown. [Figure 5]Figure 3 is a diagram illustrating the charge control for the boot capacitor of the drive circuit shown. [Figure 6] Block diagram showing an example of a hardware configuration for realizing the functions of the control unit according to Embodiment 1. [Figure 7] A diagram showing an example configuration of an air conditioner according to Embodiment 2. [Modes for carrying out the invention]

[0010] The power conversion device, motor drive device, and refrigeration cycle application equipment according to the embodiments of this disclosure will be described in detail below with reference to the attached drawings.

[0011] Embodiment 1. Figure 1 shows an example configuration of a motor drive device 100 including a power converter 50 according to Embodiment 1. The power converter 50 according to Embodiment 1 is a power converter that converts the AC voltage output from a three-phase power supply 110, which is a three-phase AC power supply, into a DC voltage and applies it to a load 130. The motor drive device 100 according to Embodiment 1 is a drive device that converts the DC power output from the power converter 50 into AC power, and supplies the converted AC power to a motor 120 to drive the motor 120. As shown in the figure, each phase of the three-phase power supply 110 is represented by R, S, and T, and is called the "R phase," "S phase," and "T phase," respectively.

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

[0013] The load 130 comprises 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, inverter 9, current detection unit 12, drive circuit 17, and 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 the noise current 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 a circuit element that temporarily stores the electrical energy supplied from the three-phase power supply 110. Also, the reactor 2 also operates to reduce the noise current 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 alternating current flowing between the three-phase power supply 110 and the power conversion device 50, and output the detected value of the power supply current to the control unit 14. An example of the current detectors 5a and 5b is an ACCT (Alternating Current Current Transformer). In FIG. 1, an example is shown in which the current detector 5a detects the R-phase current Ir and the current detector 5b detects the T-phase current It, but the present invention is not limited to this example. The current detectors 5a and 5b only need to be able to detect the currents of any two phases of the three phases, and the current of the remaining phase can be obtained by calculation using the fact that the power supply current is three-phase balanced. The phase voltage detection unit 6 detects the R-phase voltage Vr, the S-phase voltage Vs, and the T-phase voltage Vt, which are the phase voltages of each phase of the three phases output by the three-phase power supply 110, and outputs the detected values thereof 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 alternating current voltage output from the three-phase power supply 110 into a direct current voltage and outputs it to the DC buses 19a and 19b. The DC buses 19a and 19b are electrical wirings connecting the converter 3 and the load 130. The voltage between the DC bus 19a and the DC bus 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. The converter current I1 flows through the shunt resistor 7. The converter current I1 is the current flowing into and out of the converter 3. The current detection unit 10 converts the voltage value generated when the converter current I1 flows through the shunt resistor 7 into a current value and outputs it to the control unit 14.

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

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

[0022] Each semiconductor element Q1 to Q6 is equipped with diodes D1 to D6 connected in parallel. Diodes D1 to D6 are connected so that the anode is on the AC side and the cathode is on the DC side. Figure 1 shows the case where semiconductor elements Q1 to Q6 are IGBTs (Insulated Gate Bipolar Transistors), but MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) may be used instead of IGBTs. In the case of MOSFETs, due to their structure, parasitic diodes are built in, so a configuration in which diodes D1 to D6 are not connected in parallel may be adopted.

[0023] The inverter 9 converts direct current to alternating current. More specifically, the inverter 9 converts the DC voltage output from the power converter 50 into an AC voltage to be applied to the motor 120 and outputs it. An example of equipment in which the motor 120 is mounted is a blower or compressor in an air conditioner. An air conditioner is an example of equipment applied to a refrigeration cycle.

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

[0025] The inverter 9 is equipped with six semiconductor elements Q21 to Q26 connected in a three-phase bridge configuration. Semiconductor elements Q21 and Q22 are connected in series in this order, and the connection point 9a of semiconductor elements Q21 and Q22 is electrically connected to the U phase of the motor 120. Semiconductor elements Q23 and Q24 are connected in series in this order, and the connection point 9b of semiconductor elements Q23 and Q24 is electrically connected to the V phase of the motor 120. Semiconductor elements Q25 and Q26 are connected in series in this order, and the connection point 9c of semiconductor elements Q25 and Q26 is electrically connected to the W phase of the motor 120. 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, to distinguish between the semiconductor elements Q1-Q6 in converter 3 and the semiconductor elements Q21-Q26 in inverter 9 without using a sign, the former may be referred to as the "first semiconductor element" and the latter as the "second semiconductor element."

[0026] Each semiconductor element Q21 to Q26 is equipped with diodes D21 to D26 connected in parallel. Diodes D21 to D26 are connected such that their cathodes are on the DC side and their anodes are on the AC side. Figure 1 shows the case where semiconductor elements Q21 to Q26 are IGBTs, but MOSFETs may be used instead of IGBTs. In the case of MOSFETs, due to their structure, they have a built-in parasitic diode, so a configuration in which diodes D21 to D26 are not connected in parallel may be adopted. Alternatively, IGCTs (Integrated Gate Commutated Thyristors) may be used instead of IGBTs.

[0027] The current detectors 18a and 18b detect the three-phase motor current flowing between the inverter 9 and the motor 120, and output the detected motor current value to the control unit 15. An example of current detectors 18a and 18b is ACCT. In Figure 1, an example is shown in which current detector 18a detects the U-phase motor current Iu and current detector 18b detects the W-phase motor current Iw, but the system is not limited to this example. The current detectors 18a and 18b only need to detect the current of any two of the three phases, and the current of the remaining phase can be calculated by taking advantage of the fact that the motor current is three-phase balanced.

[0028] The control unit 14 generates control signals S1 to S6 to control the bus voltage to a desired voltage while controlling the power supply current sinusoidally, based on the detected values ​​of the current detectors 5a and 5b, the phase voltage detection unit 6, the current detection unit 10, and the voltage detection unit 11. Control signals S1 to S6 are control signals for controlling each of the semiconductor elements Q1 to Q6 of the converter 3. 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 rotational speed based on the detected values ​​of the voltage detection unit 11, the current detection unit 12, and the current detectors 18a and 18b. Control signals S21 to S26 are control signals for controlling each of the semiconductor elements Q21 to Q26 of the inverter 9. The control signals S21 to S26 generated by the control unit 15 are input to the drive circuit 17.

[0030] The drive circuit 16 generates drive pulses G1 to G6 based on control signals S1 to S6. The semiconductor elements Q1 to Q6 of the converter 3 are switched by the drive pulses G1 to G6. The drive circuit 17 also generates drive pulses G21 to G26 based on control signals S21 to S26. The semiconductor elements Q21 to Q26 of the inverter 9 are switched by the drive pulses G21 to G26.

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

[0032] Next, the configuration and operation of the power converter 50 according to Embodiment 1 will be described. Figure 2 is a diagram showing the operating waveforms of the main parts of the power converter 50 according to Embodiment 1. In Figure 2, the waveforms of the phase voltage of each of the three phases, the phase current of each of the three phases, and the bus voltage Vdc are shown from top to bottom. The horizontal axis of Figure 2 represents time.

[0033] The upper part of Figure 2 shows the waveforms of the R-phase voltage Vr, S-phase voltage Vs, and T-phase voltage Vt, which are sinusoidal voltage waveforms. The meaning of period T1 will be explained later. The middle part of Figure 2 shows the waveforms of the R-phase current Ir, S-phase current Is, and T-phase current It, which are sinusoidal current waveforms. These sinusoidal current waveforms are obtained by PWM control of semiconductor elements Q1 to Q6 of converter 3. By making the R-phase current Ir, S-phase current Is, and T-phase current It sinusoidal current waveforms, power supply harmonics are suppressed. The lower part of Figure 2 shows the waveform of the bus voltage Vdc, which is controlled to be almost constant. By controlling the bus voltage Vdc to be constant, it is possible to drive the load 130 stably. In Embodiment 1, the bus voltage Vdc does not necessarily have to be controlled to be constant.

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

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

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

[0037] In the case of the drive circuit 16 with the configuration shown in Figure 3, charging of the boot capacitor 64c is possible by turning on the semiconductor element Q2, which is the lower element. However, with control using only this method, it is necessary to periodically turn on the lower element of the converter 3 even when the converter 3 does not need to operate. Furthermore, with this control, the duty cycle of the PWM signal when turning on the lower element is constrained by its relationship with the capacitance of the boot capacitor 64c.

[0038] On the other hand, when the drive circuit 16 with the configuration shown in Figure 3 is applied to a three-phase converter 3 as shown in Figure 1, charging of the boot capacitor 64c becomes possible by applying three-phase AC to the converter 3. Here, we will explain using the R-phase drive circuit 16 as an example.

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

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

[0041] In the middle section of Figure 4, the voltage waveform at the point of interest is shown as a solid line, representing the voltage Vr_conv at connection point 3a, while the voltage Vdc_N at the emitter side of the lower semiconductor element Q2 is shown as a dashed line. Voltage Vdc_N is the reference potential voltage on the DC side of converter 3. The second period, period T2, is the period during which voltage Vr_conv is below voltage Vdc_N, and is included in period T1. In the lower section of Figure 4, the change in the drive voltage Vc_boot of the upper element is shown.

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

[0043] Furthermore, in Embodiment 1, in order to drive the upper semiconductor elements Q1, Q3, and Q5 even more stably, the following method is used in combination to control the charging of the boot capacitor 64c.

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

[0045] In the motor drive device 100 according to Embodiment 1, when charging the boot capacitor 64c of the drive circuit 16, the device controls the flow of current to the load 130 side. Specifically, the control unit 14, which controls the operation of the converter 3, transmits an operation command for the inverter 9 to the control unit 15, which controls the operation of the inverter 9. Upon receiving the operation command for the inverter 9, the control unit 15 drives the semiconductor elements Q21 to Q26 so that motor current flows to the motor 120.

[0046] When motor current flows, inverter current I2 flows, causing the voltage across capacitor 4 to drop. When the voltage across capacitor 4 drops, converter current I1 flows, and therefore power supply current also flows. Consequently, if control units 14 and 15 work together to actively control the current flow to the load 130, it becomes possible to stably maintain the drive voltage Vc_boot held by the boot capacitor 64c.

[0047] Next, we will describe the hardware configuration for realizing the functions of the control units 14 and 15 according to Embodiment 1. Figure 6 is a block diagram showing an example of the hardware configuration for realizing the functions of the control units 14 and 15 according to Embodiment 1.

[0048] To implement some or all of the functions of the control units 14 and 15, the system can be configured to include a processor 201 that performs calculations and a memory 202 where the program read by the processor 201 is stored, as shown in Figure 6.

[0049] Processor 201 is an example of a computing means. Processor 201 may be a computing means referred to as a microprocessor, microcomputer, CPU (Central Processing Unit), or DSP (Digital Signal Processor). Memory 202 may include non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), and EEPROM (Electrically EPROM), as well as magnetic disks, flexible disks, optical disks, compact disks, minidiscs, and DVDs (Digital Versatile Discs).

[0050] Memory 202 holds programs that execute the functions of control units 14 and 15. The processor 201 can perform the above-described processes by receiving necessary information and storing it in memory 202, executing the programs stored in memory 202, and referencing the data and tables stored in memory 202. The calculation results from the processor 201 can be stored in memory 202.

[0051] As described above, the power conversion device according to Embodiment 1 includes a converter that converts AC to DC and outputs it 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 the upper element of the first semiconductor elements. The boot capacitor is configured to store charge by flowing current to the load side of the converter. By including a boot capacitor, it is possible to avoid increasing the size of the converter. Therefore, by using the power conversion device according to Embodiment 1, it is possible to suppress harmonic currents while suppressing an increase in the size of the device.

[0052] Furthermore, in the power conversion device according to Embodiment 1, the boot capacitor provided in the first drive circuit is configured to store charge during a first period when the voltage at the AC-side connection point of the first semiconductor element to which the drive voltage from the boot capacitor is applied is smaller than the voltage at the connection points of the other phases. The boot capacitor is also configured to store the most charge during a second period when the voltage at the AC-side connection point of the first semiconductor element to which the drive voltage from the boot capacitor is applied is lower than the reference potential voltage on the DC side of the converter. Using a power conversion device configured in this way makes it possible to stably secure the drive voltage held in the boot capacitor.

[0053] Furthermore, the motor drive device according to Embodiment 1 includes a power converter with the above-described configuration and an inverter that converts the output voltage of the power converter into an AC voltage and applies it to a motor provided in the load. When the motor drive device stores charge in the boot capacitor, it drives a second semiconductor element provided in the inverter so that current flows to the motor. Using a motor drive device configured in this way makes it possible to secure the drive voltage held in the boot capacitor even more stably.

[0054] Embodiment 2. Figure 7 shows 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 equipment applied to a refrigeration cycle and includes a motor drive unit 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 it may be an integrated-type air conditioner in which the compressor 81, indoor heat exchanger 85 and outdoor heat exchanger 83 are provided in a single housing.

[0056] Inside the compressor 81 are a compression mechanism 87 for compressing the refrigerant and a motor 120 for operating the compression mechanism 87. The motor 120 is driven by a motor drive unit 100. In the air conditioner 300, the refrigerant circulates through the compressor 81, four-way valve 82, outdoor heat exchanger 83, expansion valve 84, indoor heat exchanger 85, and refrigerant piping 86, thereby forming a refrigeration cycle.

[0057] Furthermore, 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 Embodiment 2, a motor 120 is used as the drive source for the compressor 81, but the motor 120 may be used as a drive source to drive an indoor unit blower and an outdoor unit blower, respectively, instead of the compressor 81. Alternatively, the motor 120 may be applied as the drive source for the indoor unit blower, the outdoor unit blower, and the compressor 81, and these three motors 120 may be driven by a motor drive device 100.

[0058] According to the air conditioner 300 of Embodiment 2, since it is configured with the motor drive device 100 of Embodiment 1, it is possible to suppress harmonic currents while preventing the converter from becoming larger. This makes it possible to provide a product that is cost-effective and avoids increasing size.

[0059] The configurations shown in the above embodiments are merely examples, and can be combined with other known technologies. It is also possible to omit or modify parts of the configuration without departing from the gist of the invention. [Explanation of Symbols]

[0060] 1 Noise filter, 2 Reactor, 3 Converter, 3a~3c, 9a~9c Connection points, 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 converter, 61 Drive power supply, 62, 63 Gate driver, 64 Bootstrap circuit, 64a Resistor, 64b, D1~D6, D21~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 unit, 110 Three-phase power supply, 120 motor, 130 load, 201 processor, 202 memory, 300 air conditioner, Q1~Q6, Q21~Q26 semiconductor elements.

Claims

1. A power conversion device equipped with a converter that converts alternating current to direct current and outputs it to a load, The aforementioned converter is Multiple first semiconductor elements, A first drive circuit for driving the first semiconductor element, Equipped with, The first drive circuit includes a boot capacitor for applying a drive voltage to the upper element of the first semiconductor element, The boot capacitor is configured such that charge is stored during a first period in which the voltage at the AC-side connection point of the first semiconductor element to which the drive voltage from the boot capacitor is applied is smaller than the voltage at the connection points of the other phases. The second period in which the most charge is stored during the first period is the period in which the voltage at the AC-side connection point of the first semiconductor element to which the drive voltage from the boot capacitor is applied falls below the voltage of the DC-side reference potential of the converter. Power converter.

2. A power conversion device according to claim 1, An inverter that converts the output voltage of the power converter into an AC voltage and applies it to a motor provided in the load, Equipped with, When charging the boot capacitor, the inverter is driven so that current flows to the motor. Motor drive device.

3. The aforementioned inverter is Multiple second semiconductor elements, A second drive circuit that drives the second semiconductor element when charging the boot capacitor, The motor drive device according to claim 2, comprising:

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

Images