Power conversion device and heat pump apparatus

Abstract

A power conversion device includes a rectification circuit that rectifies an alternating current voltage supplied from an alternating current power source; a first capacitor connected to a direct current side thereof; a first power converter connected in parallel to the first capacitor and having one end of a winding of a motor independent for each phase connected to each phase output terminal; a second power converter having the other end of the winding of the motor connected to each phase output terminal; a second capacitor connected to a direct current side of the second power converter; a reactor connected from a wiring connecting the alternating current power source and the rectification circuit; a third power converter connected between the reactor and the second capacitor and suppressing harmonics; a relay inserted between the alternating current power source and the third power converter; and a control unit that drives the first and second inverters to charge the second capacitor before starting to activate the motor, and turns on the relay after the charging, an electrostatic capacity of the second capacitor being set to be greater than an electrostatic capacity of the first capacitor.

Description

Technical Field

[0001] Embodiments of the present invention relate to a power conversion device for driving an electric motor with an open-circuit winding structure, and a heat pump device having the power conversion device. Background Technology

[0002] Previously, power conversion devices were known that aimed at miniaturizing passive components and extending the device's lifespan by replacing the large-capacity capacitor used for DC smoothing with a small-capacity capacitor. For example, Patent Document 1 discloses a structure in which a regenerative absorption circuit, consisting of a diode, a resistor, and a capacitor connected in series, is connected in parallel to a small-capacity smoothing capacitor whose maximum pulsating voltage is more than twice its minimum value in the DC section of the power conversion device. In this structure, the capacitance of the capacitor in the DC section can be reduced, but the capacitance of the capacitor used for regenerative energy absorption needs to be appropriately increased to absorb regenerative energy. If the capacitor capacitance is increased, components may sometimes be damaged by surge currents when the power is switched on; therefore, a surge protection circuit is required, posing technical problems in terms of system miniaturization and cost reduction.

[0003] Furthermore, Patent Document 1 describes a single-phase input power conversion device equipped with a small-capacity film capacitor, which can reduce harmonics of the input current and improve the power factor. However, in a three-phase input power conversion device, since the current flows only from the largest phase to the smallest phase in the three-phase AC, the input current cannot be controlled as a sine wave by the switch in the power conversion circuit used to drive the motor alone.

[0004] On the other hand, in order to achieve large-capacity devices and high-speed motors, for example, as shown in Patent Document 2, a dual-inverter method is known that uses two inverters to drive an open-circuit winding motor with independent windings for each phase. In this dual-inverter method, small-capacity capacitors can be used in the DC section; however, for regenerative energy absorption capacitors that ultimately require a certain capacity, a surge protection circuit needs to be provided separately. Furthermore, when connected to multi-phase AC such as three-phase AC, it is impossible to control the input current of the device to be a sine wave.

[0005] In contrast, Patent Document 3 discloses a system that applies a matrix converter to an inverter on the primary side.

[0006] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 4391768 Patent Document 2: Japanese Patent No. 7218131 Patent Document 3: Japanese Patent No. 5531238 Summary of the Invention The technical problem that the invention aims to solve In the structure of Patent Document 3, the three-phase input current can be controlled as a sine wave. However, the semiconductor devices used in the matrix converter and the choke coils used in the AC filter must be selected with a rated value equal to or greater than the rated capacity of the power conversion device, which leads to technical problems such as the overall large size of the power conversion device and increased cost.

[0007] Therefore, a power conversion device is provided that does not require additional surge protection circuits in a dual-inverter configuration, is highly efficient, and can suppress the overall size and cost increase of the device, as well as a heat pump device equipped with the power conversion device.

[0008] Solution to the above technical problems The power conversion device of the embodiment includes: a rectifier circuit for rectifying AC voltage supplied from an AC power source; a first capacitor connected to the DC side of the rectifier circuit; a first power converter consisting of a diode and a semiconductor switch connected in parallel to the first capacitor, with one end of a motor winding, each with an independent phase winding, connected to the output terminal of each phase; a second power converter consisting of a diode and a semiconductor switch connected to the other end of the motor winding at the output terminal of each phase; a second capacitor connected to the DC side of the second power converter; a reactor connected from a wiring branch connecting the AC power source and the rectifier circuit; a third power converter consisting of a diode and a semiconductor switch connected between the reactor and the second capacitor, for suppressing harmonics; a relay inserted between the AC power source and the third power converter; and a control unit that, before starting the motor, drives the first and second inverters to charge the second capacitor, and after charging, connects the relay, wherein the capacitance of the second capacitor is set to be greater than the capacitance of the first capacitor.

[0009] Furthermore, the heat pump device of the embodiment includes: the power conversion device of the embodiment, and the motor, which drives the compressor. Attached Figure Description

[0010] Figure 1 This is a diagram showing the structure of the power conversion device in the first embodiment.

[0011] Figure 2 This is a diagram showing the structure of an air conditioner.

[0012] Figure 3 This is a flowchart illustrating the process from power-on to motor startup.

[0013] Figure 4 It is shown that... Figure 3 The timing diagram shows the current and voltage waveforms corresponding to the processed content.

[0014] Figure 5 This is a diagram showing the structure of the power conversion device in the second embodiment.

[0015] Figure 6 This is a flowchart illustrating the processing details of the regeneration and absorption operation in the third embodiment.

[0016] Figure 7 This is a diagram showing the switching states of each inverter during regenerative absorption operation.

[0017] Figure 8 It is shown that... Figure 6 The timing diagram shows the current and voltage waveforms corresponding to the processed content.

[0018] Figure 9 This is a diagram showing the switching states of each inverter during the regenerative absorption operation in the fourth embodiment.

[0019] Figure 10 This is a diagram showing the structure of the power conversion device in the fifth embodiment. Detailed Implementation

[0020] (First Embodiment) like Figure 1 As shown, the power conversion device 41 of this embodiment uses the motor 10 as the driving object. It is conceivable that the motor 10 is a three-phase permanent magnet synchronous motor or an induction motor, but in this embodiment it is set as a permanent magnet synchronous motor. The motor 10 is a so-called open-circuit winding motor, in which its three-phase windings are not connected to each other, and the two terminals are in an open-circuit state. That is, the motor 10 has six winding terminals Ua, Va, Wa, Ub, Vb, and Wb.

[0021] Motor 10 is driven by a dual-inverter configuration consisting of a first inverter 5 and a second inverter 9. The first inverter 5 and the second inverter 9 have the same circuit structure, being three-phase inverters with three sets of two-phase switching elements connected in series, and using the intermediate connection point of each series-connected switching element as three output terminals. The output terminals of the first inverter 5 are connected to the winding terminals Ua, Va, and Wa of motor 10, respectively, and the output terminals of the second inverter 9 are connected to the winding terminals Ub, Vb, and Wb of motor 10, respectively.

[0022] A rectifier circuit 3 is connected to the three-phase AC power supply 1, which serves as the power source for the power conversion device 41, via a three-phase reactor 2 of the power conversion device 41. The rectifier circuit 3 is constructed by connecting six diodes in a three-phase bridge configuration. A first capacitor 4, which serves as a small-capacity film capacitor, and a first inverter 5 are connected to the output terminals of the rectifier circuit 3.

[0023] A second capacitor 8, for example an electrolytic capacitor, and the two ends of the DC side of the power converter 7 are connected in parallel to the second inverter 9. The high-voltage side terminals and low-voltage side terminals of the first inverter 5, i.e., the two ends of the first capacitor 4, are not connected to the second inverter 9; the second inverter 9 is independent. That is, the output terminals of the first inverter 5 and the second inverter 9 are connected only through the independent windings of each phase of the motor 10.

[0024] Each phase output terminal of the power converter 7 is connected to the three-phase AC power supply 1 via the three-phase reactor 6 and the relay 16. The first inverter 5, the second inverter 9, and the power converter 7 are all constructed by a three-phase bridge connection of semiconductor switching elements, such as IGBTs (Insulated Gate Bipolar Transistors), with freewheeling diodes connected in parallel, respectively corresponding to the first to third power converters. Furthermore, the relay 16 can be connected either between the three-phase AC power supply 1 and the three-phase reactor 6, or between the three-phase reactor 6 and the power converter 7. The relay 16 is a single three-phase relay that simultaneously opens and closes the U, V, and W phase power lines without parallel current suppression components. On the other hand, no relay or surge current protection circuit is provided between the three-phase power supply 1 and the rectifier circuit 3. That is, the relay 16 is inserted into the power line that branches off from the three-phase AC power supply 1 and the rectifier circuit 2 to the three-phase reactor 6 and then to the power converter 7.

[0025] Current sensors 11U and 11V are installed on phases U and V of the power lines connecting the three-phase AC power supply 1 and the three-phase reactor 2. Additionally, current sensors 12U and 12V are installed on phases U and V of the power lines connecting the three-phase AC power supply 1 and the three-phase reactor 6. Voltage sensors 13 and 14 detect the terminal voltages of the first capacitor 4 and the second capacitor 8, respectively. Current sensors 15U, 15V, and 15W are installed between the output terminals of each phase of the first inverter 5 and the winding terminals Ua, Va, and Wa of the motor 10.

[0026] The detection signals output by the sensors 11-15 are input to the control unit 20. The control unit 20, configured as a microcomputer or similar device, controls the switching of each IGBT constituting the first inverter 5, the second inverter 9, and the power converter 7 based on the detection signals from the sensors 11-15. Furthermore, the control unit 20 also controls the opening and closing of the relay 16. In this structure, the components other than the motor 10 constitute the power conversion device 41.

[0027] Furthermore, the capacitance of the second capacitor 8 is set to be greater than that of the first capacitor 4. Although the first capacitor 4 uses a film capacitor and the second capacitor 8 uses an electrolytic capacitor, this is not a limitation, as long as the capacitance condition is met. For example, both capacitors can be electrolytic capacitors, or both can be film capacitors.

[0028] The capacitance of the first capacitor 4 should be sufficient to interrupt the high-frequency components generated by the switching of the first inverter 5 and the second inverter 9, and the charging current of the first capacitor 4 when the power is on should not exceed the tolerance of the rectifier circuit 3, or more specifically, the tolerance of the diodes that constitute the rectifier circuit 3. This capacitance is typically around tens of μF. This allows for the miniaturization of the three-phase reactor 2.

[0029] By setting the first capacitor 4 to such a small capacity, the surge current to the first capacitor 4 generated when power is supplied to the power conversion device 41 is at an acceptable level, thus eliminating the need for a surge current protection circuit. Furthermore, a typical surge current protection circuit consists of a high-current three-phase or single-phase relay connected in series with the power supply line, and a PTC thermistor connected in parallel with the relay. The relay is pre-disconnected before power is supplied, and after power is supplied, only the current limited by the PTC thermistor flows, slowly charging the capacitor. The relay closes when the capacitor voltage rises and no longer experiences a large surge current. As a result, excessive surge current does not flow into the rectifier circuit, etc., thus protecting the device.

[0030] On the other hand, the capacity of the second capacitor 8 can be determined based on the compensation capacity of the power converter 7, the output power of the second inverter 9, and the ripple current flowing into the second capacitor 8. This capacity is typically around several hundred to several thousand μF. Since the second capacitor 8 has a relatively large capacity, inrush current may flow into the rectifier circuit of the power converter 7 when the power is turned on. Therefore, by preventing the generation of such inrush current through the circuit and control described later, it is not necessary to have an inrush current protection circuit for the second capacitor 8. As a result, the power conversion device 41 as a whole does not require an inrush current protection circuit.

[0031] Figure 2The structure of an air conditioner that is a heat pump device using a power conversion device 41 is shown. In addition to air conditioners, heat pump devices using the power conversion device 41 can also include hot water generating devices such as water heaters and hot / cold water generating devices such as chillers. The air conditioner 21 consists of refrigerant pipes and signal communication lines connecting the indoor unit 24 and the outdoor unit 35 respectively. The indoor unit 24, located indoors, houses an indoor heat exchanger 27 and an indoor fan 30. The outdoor unit 35, located outdoors, houses a control unit 20, a compressor 22, an outdoor heat exchanger 29, a four-way valve 26, a pressure reducing device 28, an outdoor fan 31, and an outdoor fan motor 53.

[0032] The compressor 22 is constructed by housing the compression section 23 and the motor 10 within the same sealed iron container 25, with the rotor shaft of the motor 10 connected to the compression section 23. Furthermore, the compressor 22, the four-way valve 26, the indoor heat exchanger 27, the pressure reducing device 28, and the outdoor heat exchanger 29 are connected via pipes serving as refrigerant passages to form a closed loop. The compressor 22 can be, for example, a single-cylinder rotary compressor, but is not limited to this; multi-cylinder rotary compressors, scroll compressors, and reciprocating compressors can also be used.

[0033] During heating, the four-way valve 26 is in the state shown by the solid line. The high-temperature refrigerant compressed by the compression section 23 of the compressor 22 is supplied from the four-way valve 26 to the indoor heat exchanger 27 and condenses, releasing heat into the room to heat the room. Afterwards, the pressure is reduced by the pressure reducing device 28, becoming low-temperature and flowing to the outdoor heat exchanger 29, where it absorbs heat from the outside air, evaporates, and returns to the compressor 22.

[0034] On the other hand, during cooling, the four-way valve 26 switches to the state shown by the dashed line. Therefore, the high-temperature refrigerant compressed by the compression section 23 of the compressor 22 is supplied from the four-way valve 26 to the outdoor heat exchanger 29, where it dissipates heat to the outside and condenses. Afterwards, the pressure is reduced by the pressure reducing device 28, becoming low-temperature refrigerant, which flows to the indoor heat exchanger 27. Here, the refrigerant evaporates by absorbing heat from the indoor air, cooling the room and returning to the compressor 22. Furthermore, the indoor and outdoor heat exchangers 27 and 29 are configured such that they are ventilated by the indoor fan 30 and the outdoor fan 31, respectively, efficiently facilitating heat exchange between the heat exchangers 27 and 29 and the indoor and outdoor air.

[0035] Next, the operation of this embodiment will be explained. A control unit 20 is provided to control the entire power conversion device 41. The control unit 20, for example, operates / stops the compressor 22, i.e., the first motor 10, based on instructions from an indoor control unit (not shown) on the indoor unit 24 side. During the operation of the compressor 22, the control unit 20 performs vector calculations using the current values ​​detected by current sensors 15U, 15V, and 15W, and the terminal voltages of the first capacitor 4 and the second capacitor 8 detected by voltage sensors 13 and 14. Based on the calculation results, the control unit 20 causes the switching elements of the first inverter 5 and the second inverter 9 to operate in coordination, so that the desired current flows through the windings of the first motor 10, thereby providing variable speed drive for the first motor 10.

[0036] Furthermore, during the operation of the motor 10, the control unit 20 causes the power converter 7 to operate as an active filter circuit to suppress and reduce harmonics flowing in the power lines. The control unit 20 extracts the harmonic current from the currents flowing through each phase of the reactor 2 detected by current sensors 11U and 11V, and, taking into account the terminal voltage of the second capacitor 8, controls the operation of each switching element of the power converter 7, so that the reactor currents of each phase detected by current sensors 12U and 12V become correction currents to cancel the harmonic currents flowing in phases U, V, and W. Through the operation of this active filter circuit of the power converter 7, power supply harmonics can be suppressed, making the current flowing from the rectifier circuit 3 to the AC power supply 1 side approach a sine wave.

[0037] Furthermore, since the second capacitor 8 is used as a power source for correcting current when the power converter 7 functions as an active filter circuit, it has a certain capacity. Also, when the power converter 7 operates as an active filter circuit, a high-voltage power supply sufficient to compensate for harmonics is required. Therefore, it is desirable to maintain the terminal voltage of the second capacitor 8, which serves as the power source, above a predetermined value when the active filter circuit is operating. Therefore, the control unit 20 can also control the switching of the power converter 7's switching elements in parallel during active filter circuit operation to maintain the terminal voltage of the second capacitor 8 above a certain value. Moreover, if the motor 10 is under low load, resulting in a very low amount of harmonic current generation, the control unit 20 can detect this state, stop the power converter 7, stop the active filter circuit operation, and reduce the switching losses of the power converter 7's switching elements.

[0038] By configuring the power conversion device 41 as described above, the controllability of the motor 10, which uses a dual inverter consisting of a first inverter 5 and a second inverter 9 and has an open-circuit winding structure, is improved. By switching the power converter 7, the current flowing from the rectifier circuit 3 to the AC power supply 1 is made approximately sinusoidal, and the converter operates as an active filter circuit, thereby suppressing power supply harmonics. That is, since voltage is applied to the windings of the motor 10 through the two inverters 5 and 9, the operating range of the motor 10 can be expanded. Furthermore, since the voltage applied to the windings of the motor 10 becomes multi-level, iron losses generated in the motor 10 can be reduced.

[0039] Furthermore, by improving the driving method of the control unit 20 for the two inverters 5 and 9, the power applied to the motor 10 can be controlled to be constant, or the operating range in high-speed regions based on ineffective power injection can be expanded. In addition, by connecting the negative DC side of the power converter 7 to the negative DC side of the second inverter 9, the reference voltage of these circuits becomes common. This reduces the number of insulating parts in the drive power supply, preventing the increase in circuit size and cost.

[0040] Here, refer to Figure 3 and Figure 4 The control of the power conversion device 41 without surge current protection circuitry when the power is turned on is explained. The power-on of the power conversion device 41 can be considered to occur during wiring connections at installation, when a circuit breaker (not shown) between the three-phase AC power supply 1 and the power conversion device 41 is switched on from open, and when the three-phase AC power supply 1 is restored from a power outage. In the initial state of the power conversion device 41, when the three-phase AC power supply 1 is not connected, i.e., when the power is not turned on, the relay 16 is in the open state.

[0041] When AC power is supplied from the three-phase AC power supply 1 to the power conversion device 41, the first capacitor 4 is charged via the rectifier circuit 3 (S1). When the terminal voltage of the first capacitor 4 exceeds a threshold (S2 "Yes"), the control unit 20 starts the switching operation of the first and second inverters 5 and 9 (S3). Here, the switching mode for DC excitation of the motor 10 is set. DC excitation is usually used for rotor positioning before the motor 10 starts, and it is an energization that does not generate a rotating magnetic field that only energizes a specific phase of the motor winding 10. In this DC excitation energization mode, the motor 10 does not rotate. The switching mode in this DC excitation pre-adjusts the PWM duty cycle so that a large current does not flow into the second capacitor 8. As a result, the second capacitor 8 is slowly charged via the first and second inverters 5 and 9 (S4), and no temporary excessive current flows through the rectifier circuit 3.

[0042] Next, when the terminal voltage of the second capacitor 8 exceeds the threshold (S5 "Yes"), the control unit 20 activates the relay 16 (S6). At this moment, since the voltage across the second capacitor 8 has already risen to a sufficiently high level, even though the relay 16 is activated, the rectifier section of the power converter 7 will not carry a large current. Then, the drive control of the motor 10 begins (S7).

[0043] In step S5, the threshold value of the terminal voltage of the second capacitor 8 can be set to a value approximately equal to the value after rectifying the AC power supply voltage. However, it can also be set after confirming through experiments that a threshold level will not allow excessive surge current to flow into the second capacitor 8 even when the power is turned on. In addition, the charging of the capacitor in steps S1 and S4 is carried out naturally and is not actively controlled by the control unit 20, but it is described in the flowchart for ease of understanding of the operation.

[0044] As described above, if relay 16 is in the off state when the power is turned on, only the smaller first capacitor 4 is charged. Because the first capacitor 4 has a small capacitance, the surge current generated during its charging will not exceed the tolerance of the components constituting the rectifier circuit 3 and damage them. When the first capacitor 4 is charged to a certain extent, the second capacitor 8 is slowly charged via the open-circuit winding motor 10 and the first capacitor 4 through the DC excitation drive of the first and second inverters 5 and 9. At this time, control is performed by switching the first and second inverters 5 and 9 to prevent the charging current of the second capacitor 8 from becoming excessive.

[0045] Subsequently, if the voltage across the second capacitor 8 becomes approximately equal to the value after rectifying the AC power supply voltage, and the relay 16 is switched on, an excessive charging current will not flow from the power converter 7 side, and the larger-capacity second capacitor 8 can be switched to stable operation. Therefore, according to this embodiment, it is possible to safely switch from power-on to stable operation without the need for a protection circuit such as a surge current protection circuit.

[0046] Furthermore, since the relay 16 is located midway through the wiring that supplies power only to the third power converter 7 and the second capacitor 8, which operate as an active filter circuit, only a smaller current flows through it compared to the current flowing in the reactor 2 used to drive the motor by the first and second inverters 5 and 9. Therefore, a small relay with a low rated current value can be used, which contributes to the miniaturization of the device.

[0047] (Second Implementation) Hereinafter, the same reference numerals will be used for parts that are the same as in the first embodiment, and descriptions will be omitted. Different parts will be described. Furthermore, in the accompanying drawings of the power conversion devices of each embodiment shown below, illustrations of sensors 11-15 and the control unit 20 are omitted. Figure 5 In the power conversion device 42 of the second embodiment shown, a third capacitor 17 is connected to the DC section of the power converter 7, which operates as an active filter circuit. The negative terminal of the second capacitor 8 and the negative terminal of the third capacitor 17 are connected in a common manner. The anode of the diode 18 is connected to the positive terminal of the second capacitor 8, and the cathode is connected between the positive terminal of the third capacitor 17 and the positive terminal of the third capacitor 17.

[0048] According to the second embodiment configured as described above, by connecting the negative side of the DC section of the power converter 7 to the negative side of the DC section of the second inverter 9, and inserting a diode 18 between the positive terminals of the second capacitor 8 and the third capacitor 17, the regenerative energy generated when the motor 10 stops can also be absorbed by the third capacitor 17. Therefore, the capacity of the first and second capacitors 4 and 8 can be reduced.

[0049] (Third implementation) The third embodiment shows an example of the regenerative absorption operation in the power conversion device 41 or 42. Figure 6 This refers to the process flow during regeneration and absorption. Figure 7 Only the components energized in the first inverter 5 and the second inverter 9 are shown during regenerative absorption operation. During normal operation (S11), if the voltage across the first capacitor 4, etc., exceeds a preset threshold (S12 "Yes"), the control unit 20 determines that regeneration caused by the motor 10 has occurred and initiates regeneration... Figure 5 The regeneration and absorption operation shown is (S13).

[0050] Furthermore, at this time, the power converter 7 is switched on and off to control the voltage across C2; the second capacitor 8 (S14). That is, the power converter 7 is operated as a power regeneration PWM rectifier. Specifically, the power converter 7 is switched on and off to return the regenerated power to the three-phase AC power supply 1 side, so that the voltage across the second capacitor 8, which absorbs the regenerated power from the motor 10, becomes a specified voltage lower than the rated voltage value of the component. During the regeneration absorption operation, since the first and second inverters 5 and 9 do not drive the motor 10, no harmonics are generated. Therefore, the power converter 7 does not need to perform harmonic suppression operation, and it is not a problem to stop the active filter circuit operation of the power converter 7 and instead make it operate as a power regeneration PWM rectifier. Furthermore, if the voltage across the two ends is not lower than the threshold for a set time or more ("No" in S15), the process returns to step S13 and continues the regeneration absorption operation. If the voltage across the two ends is lower than the threshold for a set time or more ("Yes"), the regeneration absorption operation and the switching control of the power converter 7 are stopped (S16).

[0051] In the regenerative absorption operation in step S13, in the first inverter 5, all IGBTs on the upper arm side are turned on, and all IGBTs on the lower arm side are turned off, thereby forming the neutral point of the motor 10. At this time, power does not flow from the motor 10 into the first capacitor 4. On the other hand, for the second inverter 9, by turning off all IGBTs, its structure is equivalent to that of the rectifier circuit 3. As a result, power flows from the motor 10 into the second capacitor 8. In this way, by performing the regenerative absorption operation when regeneration occurs due to the motor 10, the regenerated power can be absorbed only through the second capacitor 8, which has a larger capacity. By setting the capacity of the second capacitor 8 to about several hundred to several thousand μF, overvoltage can be prevented even during regeneration.

[0052] Figure 8 Show execution Figure 6 The flowchart shows the current and voltage waveforms of each component. Regarding the current waveforms, although they are three-phase, they are not shown separately since it is not necessary to distinguish between the three phases here. The "load current" in the diagram is the current flowing in the three-phase reactor 2, and the "input current" is the current input from the three-phase AC power supply 1 to the three-phase reactors 2 and 6. The "power converter current" is the current flowing in the power converter 7, i.e., the current flowing in the three-phase reactor 6. The "second capacitor voltage" is the terminal voltage of the second capacitor 8, and the "switching voltage" is the collector-emitter voltage of the IGBT constituting the power converter 7.

[0053] exist Figure 8In this process, when regeneration of motor 10 occurs and the voltage of the first capacitor 4 (not shown) rises to a threshold, the regeneration absorption operation begins. If the regeneration absorption operation begins, the voltage across the second capacitor 8 temporarily rises. However, since the power converter 7 operates in parallel as a power regeneration PWM rectifier, the regeneration current flowing into the second capacitor 8 is regenerated to the three-phase AC power supply 1, and does not rise excessively. Afterward, if the regeneration of motor 10 ends, the voltage across the second capacitor 8 drops due to the operation of the power regeneration PWM rectifier in the power converter 7. Furthermore, when the voltage across the second capacitor 8 remains below the threshold for a set period of time, the switching operation of the power converter 7 stops, and the regeneration absorption and power regeneration operations end. As a result, the switching voltage is fixed to the DC voltage Vdc obtained after full-wave rectification and smoothing of the AC power supply 1, and the load current, input current, and power converter current all become "0", thus ending the regeneration absorption operation. In addition, during the operation of the power converter 7 as a power regeneration PWM rectifier, a sinusoidal current synchronized with the voltage of the three-phase AC power supply 1 flows through the input current.

[0054] Additionally, in the termination determination of the regeneration absorption operation in step S15, it is also possible to... Figure 8 The condition is determined as "yes" when the voltage of the second capacitor 8 shown becomes stable. Furthermore, since the actual regenerated power generation time is short, the end can also be determined by the elapsed time from the start of the regeneration absorption operation. Additionally, the threshold value in step S15 does not necessarily have to be set to the same value as the threshold value in step S13.

[0055] (Fourth implementation) The fourth embodiment also shows an example of regenerative absorption operation in the power conversion device 41 or 42. Figure 6 Similarly, Figure 9 Only the components energized in the first inverter 5 and the second inverter 9 during regenerative absorption operation are shown. The difference from the third embodiment is that in the first inverter 5, all IGBTs on the upper arm side are turned off, while all IGBTs on the lower arm side are turned on. In this case, since the IGBTs on the lower arm side are turned on for an extended period, it is effective when the drive power supply for the second inverter 9 is configured using a bootstrap circuit.

[0056] (Fifth implementation) Figure 10 The power conversion device 43 shown in the fifth embodiment is a structure in which the three-phase reactor 2 is removed from the power conversion device 41, and a reactor 44 is inserted on the positive side between the rectifier circuit 3 and the first capacitor 8. In this way, by inserting the reactor 44 into the DC section, the number of reactors used can be reduced compared to the case where it is inserted into the AC section. Furthermore, the reactor inserted into the DC section can be configured only in... Figure 10 The high-potential side lines shown can also be distributed across the high-potential and low-potential side lines. With this distributed distribution, the inductance of each reactor is only about half that of a single reactor inserted.

[0057] (Other implementation methods) Semiconductor switches are not limited to IGBTs; for example, they can also be power MOSFETs.

[0058] Alternating current power can also be single-phase.

[0059] When the capacitances C1 and C2 of the first and second capacitors are set to be in a relationship of (C1 < C2), it is not necessary to set the first capacitor 4 as a film capacitor and the second capacitor 8 as an electrolytic capacitor. The second capacitor can also be a supercapacitor or a double-layer capacitor, such as a storage battery.

[0060] exist Figure 3 In step S3, before the relay 16 is turned on, the motor 10 is DC-excited by the output of the first and second inverters 5 and 9, thereby charging the second capacitor 8. However, the power-on mode at this time is not limited to the DC-excited switching mode. It can be any switching mode that allows the first and second inverters 5 and 9 to slowly charge the second capacitor 8 without rotating the motor 10.

[0061] Heat pump equipment is not limited to air conditioners. Furthermore, power conversion devices can also be applied to equipment other than heat pumps.

[0062] While several embodiments of the invention have been described, these embodiments are merely illustrative and not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, with various omissions, substitutions, and modifications possible without departing from the spirit of the invention. These embodiments and their variations are included within the scope and spirit of the invention, and are included within the scope of the invention as described in the claims and its equivalents.

[0063] Explanation of reference numerals in the attached figures 1 Three-phase AC power supply 2 Three-phase reactors 3 Rectifier Circuit 4. First capacitor 5. First Inverter (First Power Converter) 6 Three-phase reactors 7. Power converter (3rd power converter) 8. Second capacitor 9. Second Inverter (Second Power Converter) 10 motors 16 Relays 20 Control Department 21 Air conditioner 22 Compressor 31 Fans 41-43 Power conversion device 44. Reactor.

Claims

1. A power conversion device, characterized in that, have: A rectifier circuit rectifies the AC voltage supplied from an AC power source. The first capacitor is connected to the DC side of the rectifier circuit; The first power converter is composed of diodes and semiconductor switches connected in parallel to the first capacitor, and each phase output terminal is connected to one end of the winding of a motor with independent phase windings. The second power converter is connected to the other end of the motor winding at each phase output terminal and is composed of diodes and semiconductor switches; The second capacitor is connected to the DC side of the second power converter; The reactor is connected from a wiring branch that connects the AC power supply to the rectifier circuit; The third power converter, consisting of a diode and a semiconductor switch connected between the reactor and the second capacitor, suppresses harmonics; A relay is inserted between the AC power source and the third power converter; as well as The control unit drives the first and second inverters to charge the second capacitor before starting the motor, and then connects the relay after charging. The capacitance of the second capacitor is set to be greater than that of the first capacitor.

2. The power conversion device as described in claim 1, characterized in that, The first capacitor is a film capacitor, and the second capacitor is an electrolytic capacitor.

3. The power conversion device as described in claim 1, characterized in that, The capacity of the first capacitor is such that it can cut off the high-frequency components generated by the switching of the first power converter and the second power converter, and the current charging the first capacitor when the power is turned on does not exceed the tolerance of the rectifier circuit 3.

4. The power conversion device as described in claim 1, characterized in that, The control unit causes the third power converter to operate as an active filter circuit.

5. The power conversion device as described in claim 1, characterized in that, It includes a third capacitor connected to the DC section of the third power converter. The negative terminal of the second capacitor is connected in a common manner to the negative terminal of the third capacitor. The power conversion device further includes a diode, the anode of which is connected to the positive terminal of the second capacitor, and the cathode of which is connected to the positive terminal of the third capacitor.

6. The power conversion device as described in claim 1, characterized in that, When regenerating power from the motor, the control unit turns off all the semiconductor switches of the second power converter and turns on or off the semiconductor switches of the first power converter, causing one of the winding terminals of the motor to be short-circuited, thereby performing a regeneration absorption operation in which the second capacitor absorbs the regenerated power.

7. The power conversion device as described in claim 6, characterized in that, If the control unit detects that the voltage across the first capacitor exceeds a predetermined threshold, the regeneration absorption operation is performed.

8. The power conversion device as described in claim 6, characterized in that, When performing the regenerative absorption operation, the control unit causes the third power converter to operate as a power regeneration PWM rectifier that regenerates power to the AC power source.

9. The power conversion device as claimed in claim 1, characterized in that, It includes a reactor that is inserted between the AC power supply and the rectifier circuit.

10. The power conversion device as claimed in claim 1, characterized in that, It includes a reactor inserted between the rectifier circuit and the first power converter.

11. A heat pump device, characterized in that, have: The power conversion device as described in any one of claims 1 to 10; and The motor, The compressor is driven by the motor.

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