Power conversion device and heat pump apparatus

Abstract

The power conversion device of the embodiment includes: a rectification circuit that rectifies an alternating-current voltage supplied from an alternating-current power source; a first power storage element connected to a direct-current side thereof; a first power converter connected in parallel to the first power storage element, each phase output terminal of which is connected to one end of a winding of a motor independent for each phase winding; a second power converter, each phase output terminal of which is connected to the other end of the winding of the motor; a second power storage element connected to a direct-current side thereof; 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 power storage element; a short-circuit circuit configured to short-circuit each phase output terminal of the first or second power converter; and a control unit that controls the third power converter to suppress a harmonic flowing to the alternating-current power source side, and switches between an operation mode in which the motor is driven by the first and second power converters by setting the short-circuit circuit to an open state, and an operation mode in which the motor is driven by one of the first or second power converters by setting the short-circuit circuit to a short-circuit state.

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] To achieve higher capacity and higher speed in power conversion devices for drive motors, a dual-inverter approach is known, using two inverters to drive open-circuit winding motors with independent windings for each phase. However, if both inverters are always operational, the losses in the switching elements within the inverters increase. Especially under low load conditions, even though only one inverter would be needed to drive the motor, operating both inverters wastes power.

[0003] To address this issue, Patent Document 1 includes a relay that short-circuits the wiring between the open-winding motor and one inverter. At low speeds with low induced voltage, short-circuiting this relay changes the open-winding motor's windings to a star connection, allowing it to be driven by only one inverter, thus stopping the other inverter and reducing power loss. However, in a three-phase input power conversion device, since current flows only from the largest phase to the smallest phase in three-phase AC, the switch in the power converter used for motor drive alone cannot control the input current to a sine wave.

[0004] Furthermore, Patent Document 2 describes a single-phase input power conversion device equipped with a small-capacity thin-film capacitor, which can reduce harmonics of the input current and improve the power factor.

[0005] In the aforementioned dual inverter method, although small-capacity capacitors can be used in the DC section, in this case, when a three-phase AC power supply is used, as mentioned earlier, the input current cannot be controlled as a sine wave using only the switch in the power converter for motor drive.

[0006] In addition, Patent Document 3 discloses a system for applying a matrix converter to a primary-side inverter.

[0007] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 7218131 Patent Document 2: Japanese Patent No. 4391768 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, although the three-phase input current can be controlled as a sine wave, the semiconductor devices used in the matrix converter, the choke coils used in the AC filter, etc., must be selected with the same or higher rated values ​​as the rated capacity of the power conversion device, resulting in technical problems such as the overall enlargement of the power conversion device or increased cost.

[0008] Therefore, a power conversion device that can efficiently suppress harmonics even in a dual-inverter configuration is provided, as well as a heat pump device equipped with the power conversion device.

[0009] Solution to the above technical problems The power conversion device of the embodiment includes: a rectifier circuit for rectifying an AC voltage supplied from an AC power source; a first energy storage element 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 energy storage element, and having one end of a motor winding with independent windings connected to each phase output terminal; a second power converter consisting of a diode and a semiconductor switch connected to the other end of the motor windings connected to each phase output terminal; a second energy storage element 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; and a third power converter consisting of a diode and a semiconductor switch connected to the first energy storage element. The device comprises a diode and a semiconductor switch between the reactor and the second energy storage element; a short-circuit circuit configured to short-circuit each phase output terminal of the first power converter or the second power converter; and a control unit that controls the switching of the third power converter to suppress harmonics flowing from the rectifier circuit to the AC power supply side, and switches between the following operating modes: an operating mode in which the motor is driven by both the first power converter and the second power converter by setting the short-circuit circuit to an open state, and an operating mode in which the motor is driven by only one of the first power converter or the second power converter by setting the short-circuit circuit to a short-circuit state.

[0010] Furthermore, the power conversion device of the embodiment includes: a rectifier circuit for rectifying the AC voltage supplied from the AC power source; a first energy storage element 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 energy storage element, and having one end of a motor winding with independent windings connected to each phase output terminal; a second power converter consisting of a diode and a semiconductor switch connected to the other end of the motor windings connected to each phase output terminal; a second energy storage element connected to the DC side of the second power converter; and a reactor connected to the AC power source and the rectifier circuit. The circuit is connected by wiring branches; a third power converter, which is composed of diodes and semiconductor switches connected between the reactor and the second energy storage element and suppresses harmonics; a first short-circuit circuit, configured to short-circuit each phase output terminal of the first power converter; a second short-circuit circuit, configured to short-circuit each phase output terminal of the second power converter; and a control unit, which switches between multiple operating modes, which are obtained by combining the short-circuit / open states of the first and second short-circuit circuits with the drive states of the motor by the first and second power converters.

[0011] Furthermore, the heat pump device of the embodiment includes the power conversion device of the embodiment and the motor, through which the compressor is driven. Attached Figure Description

[0012] Figure 1 This is a diagram showing the structure of the power conversion device in the first embodiment.

[0013] Figure 2 This is a diagram showing the structure of an air conditioner.

[0014] Figure 3 This is a flowchart illustrating the process of switching action modes.

[0015] Figure 4 This is a diagram that equivalently illustrates the second action mode.

[0016] Figure 5 This is a diagram showing the structure of the power conversion device in the second embodiment.

[0017] Figure 6 This is a flowchart illustrating the process of switching action modes.

[0018] Figure 7 This is a diagram that equivalently illustrates the third action mode.

[0019] Figure 8 This is a diagram showing the structure of the power conversion device in the third embodiment.

[0020] Figure 9This is a flowchart illustrating the process of switching action modes.

[0021] Figure 10 This is a diagram that equivalently illustrates the second action mode.

[0022] Figure 11 This is a diagram that equivalently illustrates the third action mode.

[0023] Figure 12 This is a flowchart showing the processing details of the regeneration and absorption operation in the fourth embodiment.

[0024] Figure 13 This is a diagram showing the switching states of each inverter during regenerative absorption operation.

[0025] Figure 14 It is shown that... Figure 13 The timing diagram shows the current and voltage waveforms corresponding to the processed content.

[0026] Figure 15 This is a diagram showing the switching states of each inverter during the regenerative absorption operation in the fifth embodiment. Detailed Implementation

[0027] (First Embodiment) like Figure 1 As shown, the power conversion device of this embodiment uses motor 10 as the driving object. Motor 10 can be envisioned as a three-phase permanent magnet synchronous motor or an induction motor, but in this embodiment it is set as a permanent magnet synchronous motor. 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, motor 10 has six winding terminals Ua, Va, Wa, Ub, Vb, and Wb.

[0028] Motor 10 is driven by a dual-inverter configuration based on first inverter 5 and second inverter 9. First inverter 5 and second inverter 9 have the same circuit structure, being a three-phase inverter with three sets of two switching elements connected in series on the upper and lower arm sides, and the intermediate connection point of each series-connected switching element serving as three output terminals. The output terminals of each phase of first inverter 5 are connected to the winding terminals Ua, Va, and Wa of motor 10, respectively, and the output terminals of each phase of second inverter 9 are connected to the winding terminals Ub, Vb, and Wb of motor 10, respectively.

[0029] A rectifier circuit 3 is connected to the three-phase AC power supply 1 via a three-phase reactor 2. The rectifier circuit 3 is composed of six diodes connected in a three-phase bridge configuration. A first capacitor 4 and a first inverter 5 are connected to the output terminals of the rectifier circuit 3.

[0030] In the second inverter 9, 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. The second capacitor 8 and the first capacitor 4 can each be any energy storage element capable of charging and discharging with a certain capacity; a storage battery or similar device can also be used instead of a capacitor. In other words, the first capacitor 4 is equivalent to a first energy storage element, and the second capacitor 8 is equivalent to a second energy storage element. The high-voltage and low-voltage 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.

[0031] Furthermore, a short-circuit circuit 16 is provided at each phase output terminal of the second inverter 9. The short-circuit circuit 16 consists of multiple mechanical relays or multiple semiconductor switches that are simultaneously turned on and off. Figure 1 The diagram illustrates the use of a mechanical relay with two contacts. When short-circuit circuit 16 is activated, one relay contact short-circuits the UV phases, and the other relay contact short-circuits the VW phases. That is, if short-circuit circuit 16 is activated, the output terminals of each phase of the second inverter 9 are short-circuited, thus the motor 10 is star-connected on the winding terminals Ub, Vb, and Wb sides.

[0032] The power converter 7, whose DC section is connected to the second capacitor 8, has the same three-phase inverter circuit structure as the first and second inverters 5 and 9. Each phase output terminal is connected to the three-phase AC power supply 1 via a three-phase reactor 6. Freewheeling diodes are connected in anti-parallel to each switching element constituting the first inverter 5, the second inverter 9, and the power converter 7. These are all constructed by a three-phase bridge connection of semiconductor switching elements such as IGBTs (Insulated Gate Bipolar Transistors), respectively corresponding to the first to third power converters.

[0033] 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. The current in phase W is calculated based on the phase U and V currents detected by these current sensors 11U and 11V. Furthermore, 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. The current flowing through phase W of the three-phase reactor 6 is calculated based on the phase U and V currents detected by these current sensors 12U and 12V.

[0034] 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 configured between the phase output terminals of the first inverter 5 and the winding terminals Ua, Va, and Wa of the motor 10 to detect the current flowing through each motor winding of the motor 10. The DC sections of the first inverter 5 and the second inverter 9 are connected to the same three-phase AC power supply 1. Therefore, if the first motor 10 is driven by the first inverter 5 and the second inverter 9 in a dual-inverter configuration, a zero-phase current flowing in the same direction with a predetermined period is generated in each phase winding. Therefore, in order to distinguish and detect the zero-phase current and the current flowing in each motor winding, current sensors 15U, 15V, and 15W are provided corresponding to each phase winding.

[0035] The detection signals output by the sensors 11-15 are input to the control unit 20. The control unit 20, which is composed of a microcomputer or the like, 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. In the above structure, the parts other than the motor 10 constitute the power conversion device 41.

[0036] Figure 2 The 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.

[0037] 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.

[0038] 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.

[0039] On the other hand, during cooling, the four-way valve 26 is switched 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 fan 30 and the outdoor fan 31 respectively deliver air to the indoor and outdoor heat exchangers 27 and 29, thereby efficiently facilitating heat exchange between the heat exchangers 27 and 29 and the indoor and outdoor air.

[0040] 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 motor 10, based on instructions from an indoor control unit (not shown) on the indoor unit 24 side. Furthermore, during the operation of the motor 10, the control unit 20 opens and closes the short-circuit circuit 16, for example, according to the load of the motor 10 or its rotational speed. Specifically, when the motor 10 is under high load, high speed, or high input power, the short-circuit circuit 16 is set to the open state, thereby setting the motor 10 to an open winding state; when the motor 10 is under low load, low speed, or low input power, the short-circuit circuit 16 is set to the short-circuit state, thereby switching the motor 10 to a star connection state.

[0041] When the short-circuit circuit 16 is set to the open state, that is, when the motor 10 is set to the open winding state, the control unit 20 uses the current values ​​detected by the current sensors 15U, 15V, and 15W, and the terminal voltages of the first capacitor 4 and the second capacitor 8 detected by the voltage sensors 13 and 14 to perform vector calculations. Based on its 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 from the two inverters 5 and 9 to the windings of the motor 10, thereby providing variable speed drive for the motor 10.

[0042] On the other hand, when the short-circuit circuit 16 is set to a short-circuit state, thereby setting the motor 10 to a star-connected state, the control unit 20 performs vector calculations using the current values ​​detected by current sensors 15U, 15V, and 15W, and the terminal voltage of the first capacitor 4 detected by voltage sensor 13. Based on its calculation results, the control unit 20 only causes the switching elements of the first inverter 5 to operate appropriately, thereby causing the desired current to flow to the windings of the motor 10, and performs variable-speed drive of the motor 10. When the motor 10 is driven in a star-connected state, the second inverter is set to a shut-off state, and all switching elements are turned off.

[0043] On the other hand, even when the motor 10 is in either an open-circuit winding state or a star-connected state, the control unit 20 activates the power converter 7 as an active filter circuit during the operation of the motor 10 to suppress and reduce harmonics flowing through the power lines. Specifically, harmonic currents are extracted from the currents flowing through each phase of the reactor 2 detected by current sensors 11U and 11V, and the terminal voltage of the second capacitor 8 is taken into account. The operation of each switching element of the power converter 7 is then controlled so that the reactor currents of each phase detected by current sensors 12U and 12V become correction currents that cancel out the harmonic currents flowing through phases U, V, and W. Through the operation of this active filter circuit of the power converter 7, the current flowing from the rectifier circuit 3 to the AC power supply 1 side can be made close to a sine wave, thereby suppressing power supply harmonics.

[0044] Furthermore, since the second capacitor 8, which serves as an energy storage element, is used as a power source for the correction current output by the active filter circuit, it has a certain capacity. Additionally, if the generating motor 10 is in a low-load state or where the amount of harmonic current generated is very small, the power converter 7 can be stopped, and the active filter circuit can also be deactivated.

[0045] By configuring the power conversion device 41 as described above, the motor 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. Furthermore, 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. Additionally, since the voltage applied to the windings of the motor 10 becomes multi-level, iron losses generated in the motor 10 can be reduced.

[0046] Furthermore, by improving the driving method of the two inverters 5 and 9 through the control unit 20, 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 insulation components in the drive power supply, preventing the need for larger circuit sizes and increased costs.

[0047] On the other hand, at low input power and low speeds, the induced voltage of the motor 10 is small, so a lower applied voltage is sufficient. If driven by a dual-inverter configuration, the efficiency deteriorates compared to driving with a single inverter as is typically done, due to increased conduction losses in the semiconductor switches. Conversely, by short-circuiting the three-phase output of the second inverter 9 by setting the short-circuit circuit 16 to a short-circuit state, and by setting the motor 10 to a star connection and driving it only by the first inverter 5, the drive efficiency at low speeds and low loads can be improved. At high speeds, if the short-circuit circuit 16 is set to an open state, the motor 10 is driven with an open winding, thus achieving the aforementioned advantages.

[0048] Furthermore, during the operation of the motor 10, regardless of the winding state of the motor 10, the power converter 7 is operated as an active filter circuit that performs switching control to make the current flowing from the rectifier circuit 3 to the AC power supply 1 side approach a sine wave, thereby suppressing the power harmonics generated by the power conversion device 41.

[0049] Furthermore, the capacitance of the second capacitor 8 is set to be greater than that of the first capacitor 4. For example, the first capacitor 4 is a film capacitor, and the second capacitor 8 is an electrolytic capacitor. This reduces the number of electrolytic capacitors used and extends the lifespan of the power conversion device 42. The first capacitor 4 only needs to have a capacitance sufficient to filter out high-frequency components generated by the switching of the first inverter 5 and the second inverter 9, and the current charging the first capacitor 4 when the power is turned on does not exceed the tolerance of the diodes constituting the rectifier circuit 3. This capacitance is typically around tens of μF. This allows for miniaturization of the three-phase reactor 2.

[0050] On the other hand, the capacity of the second capacitor 8 can be determined based on the compensation capacity of the power converter 7 or the output power of the second inverter 9, the ripple current flowing into the second capacitor 8, etc. This capacity is typically around several hundred μF to several thousand μF. Furthermore, the second capacitor 8 can be any energy storage element capable of charging and discharging; a storage battery or battery can be used instead of an electrolytic capacitor. In this case, the energy storage capacity of the energy storage element is determined, similarly to that of the second capacitor, based on the compensation capacity of the power converter 7 or the output power of the second inverter 9, the ripple current flowing into the second capacitor 8, etc.

[0051] The following describes a series of operations of the power conversion device 41. In the initial state, the control unit 20 sets the short-circuit circuit 16 to the open state (S0). In this state, as... Figure 3As shown, when a motor start command is input to the control unit 20 from the outside (Yes in S1), the motor 10 is driven by the open windings of the first inverter 5 and the second inverter 9 (S2). Furthermore, the power converter 7 is switched on and off to operate as an active filter circuit, so that the current flowing from the rectifier circuit 3 to the AC power supply 1 is close to a sine wave. This suppresses harmonics generated on the first inverter 5 side (S3). Steps S2 and S3 correspond to the first operating mode. Additionally, in the initial state, i.e., the stopped state of the motor 10, if no motor start command is input from the outside (No in S1), the system returns to step S1 as a waiting instruction, continuing in the original state.

[0052] Next, it is determined whether the input power to motor 10 is lower than the threshold α (S4). If it is not lower (S4 no), the process returns to step S2. If the input power is lower than the threshold α (S4 yes), the short-circuit circuit 16 is set to a short-circuit state (S41), and motor 10 is driven only by the first inverter 5 (S5). Figure 4 This state is equivalently represented.

[0053] In the next step S6, if the power converter 7 is operated as an active filter circuit in the same way as in step S3, the control unit 20 determines whether the input power to the motor 10 exceeds the threshold β (S7). Furthermore, to prevent frequent switching of the short-circuit circuit 16, the threshold β is set to be greater than the threshold α. If the input power exceeds the threshold β (Yes in S7), after switching the short-circuit circuit 16 to the open state (S71), the process returns to step S2. If the input power does not exceed the threshold β (No in S7), it is determined whether a motor stop command has been input to the control unit 20 from the outside (S8). If no motor stop command is input (No in S8), the process returns to step S5; if a motor stop command is input (Yes in S8), all switching operations of the first inverter 5, the second inverter 9, and the power converter 7 are stopped, thereby stopping the motor 10 (S81). Steps S41, S5, and S6 correspond to the second operating mode.

[0054] As described above, according to this embodiment, in the power conversion device 41, a first capacitor 4 and a first inverter 5 are connected to the DC side of the rectifier circuit 3, which rectifies the AC voltage supplied from the AC power source 1. One end of the winding of the motor 10 with an open-circuit winding structure is connected to each phase output terminal of the first inverter 5, and the other end is connected to each phase output terminal of the second inverter 5. A short-circuit circuit 16 is provided at each phase output terminal. On the DC side of the second inverter 7, a reactor 6, a power converter 7, and a second capacitor 8 are connected, which are connected from a wiring branch connecting the AC power source 1 and the rectifier circuit 3.

[0055] The control unit 20 performs switching control on the power converter 7 to make the current flowing from the rectifier circuit 3 to the AC power supply 1 side approach a sine wave, and switches between the following operating modes: a first operating mode in which the motor 10 is driven by the first and second inverters 5 and 9 by setting the short circuit circuit 16 to the open state, and a second operating mode in which the motor 10 is driven only by the first inverter 5 by setting the short circuit circuit 16 to the short circuit state.

[0056] In the first operating mode, by driving the motor 10 using a dual-inverter configuration, the applied voltage can be increased, thereby expanding the operating range of the motor 10, and the applied voltage can be multi-leveled, thereby reducing the iron losses of the motor 10. When using a three-phase AC power supply 1, the power supply harmonics are largely determined by the capacitance of the reactor 2 used for current smoothing and the first capacitor 4, making it impossible to control the input current using the first inverter 5 and the second inverter 9. As in this embodiment, by connecting the DC section of the power converter 7 to the second inverter 9, the insulation of the drive power supply can be reduced, and the circuit can be simplified. If the motor 10 operates at a low speed and the input power is relatively low, the system switches to the second operating mode. The output of each phase of the second inverter 9 is short-circuited by the short-circuit circuit 16, and the motor 10 is driven by the first inverter 5 in a star connection, thereby improving efficiency. Furthermore, during the operation of the motor 10, by making the power converter 7 operate as an active filter circuit of the rectifier circuit 3, the power supply harmonics of the power conversion device 41 can be suppressed.

[0057] (Second Implementation) Next, refer to Figure 5 The second embodiment will be described. In the following description, the same reference numerals will be used for parts identical to those in the first embodiment, and descriptions will be omitted; differences will be described. In the power conversion device 42 of the second embodiment, the short-circuit circuit 16 of the power conversion device 41 is configured to be located at the output terminal side of each phase of the first inverter 5. In the second embodiment, the output of each phase of the first inverter 9 is short-circuited by the short-circuit circuit 16. Therefore, in Figure 6 In the control flowchart shown, in step S9, which replaces step S5, the short-circuit circuit 16 is set to a short-circuit state, and the motor 10 is driven only by the second inverter 9. Therefore, as Figure 5 As shown, current sensors 15U, 15V, and 15W, which detect the current of each phase winding of motor 10, are moved to the wiring between each phase winding of motor 10 and the second inverter 9. Figure 7 This state is equivalently represented. Steps S41, S9, and S10 are equivalent to the third action mode.

[0058] In addition, in step S10, which replaces step S6, harmonic suppression is performed on the second inverter 9 side by the power converter 7. This harmonic suppression operation is the operation of a PWM rectifier that stably controls the terminal voltage of the second capacitor 8 to achieve a target value. Here, the control unit 20 performs PWM control on each switching element of the power converter 7 so that the voltage across the second capacitor 8, detected by the voltage sensor 14, is a value higher than or equal to the DC voltage value after rectification of the output of the commercial power supply 1. By controlling the terminal voltage of the second capacitor 8 by the power converter 7, harmonics generated in the second inverter 9 can be suppressed. Generally, a higher boost voltage of the PWM rectifier results in better harmonic suppression, but if the boost voltage becomes too high, the losses of the second inverter 9 during motor 10 driving will increase. Therefore, it is desirable to set the boost voltage to the lowest possible value while keeping the amount of harmonic generation within the target value. Other controls are the same as in the first embodiment.

[0059] (Third implementation) Figure 8 The power conversion device 43 shown in the third embodiment is a structure in which a new short-circuit circuit 17 is arranged on the output terminal side of each phase of the second inverter 7 in the power conversion device 42. That is, it is a structure that combines the first and second embodiments.

[0060] exist Figure 9 In the flowchart shown, with Figure 6 The same step numbers in the flowchart of the first embodiment shown indicate that the same actions are performed in the control unit 20. In the initial state, both short-circuit circuits 16 and 17 are open (S01). If the determination in step S1 is "yes" as a motor start command is received, it is determined whether the input power Pm to the motor 10 exceeds the threshold α (S11). If it exceeds the threshold α (yes in S11), then in step S111, short-circuit circuits 16 and 17 are opened, or if they are already in the open state, the open state is maintained, and steps S2 and S3, i.e., the first operation mode, are executed. On the other hand, if the input power Pm does not exceed the threshold α in step S11 (no in S11), the process proceeds to step S12. In addition, if there is no motor start command in step S1 (no in S1), the current state is maintained until a motor start command is received.

[0061] In step S12, it is determined whether the input power Pm is below threshold α and exceeds threshold β. If it is below threshold α and exceeds threshold β (as in S12), then short-circuit circuit 16 is set to the open state, and short-circuit circuit 17 is closed (S121), and steps S5 and S6 are executed. Figure 10The second operating mode is shown. If the input power Pm is below the threshold β in step S12 (No in S12), then short-circuit circuit 16 is closed and short-circuit circuit 17 is opened (S122), and steps S9 and S10 are executed, i.e. Figure 11 The third operating mode is shown. Furthermore, in step S8 immediately following steps S3, S6, and S10, when the determination is "yes" as a motor stop command is received, the operation of the first inverter 5, the second inverter 9, and the power converter 7 is stopped, and the operation of the motor 10 is stopped (S81). Then, for a predetermined time (S82) during which both short-circuit circuits 16 and 17 are closed until the regenerative current disappears, the two ends of the windings of the motor 10 are short-circuited. This consumes regenerative energy in the motor 10, suppressing the increase in DC voltage on the inverter 5 and 9 sides. After this, if the predetermined time has elapsed, the process returns to the beginning and repeats the steps from step S01.

[0062] As described above, according to the third embodiment, short-circuit circuits 16 and 17 are respectively provided at each phase output terminal of the first inverter 5 and each phase output terminal of the second inverter 9, so that the execution of the first to third operating modes can be switched according to the magnitude of the input power Pm to the motor 10.

[0063] (Fourth implementation) In the third embodiment, regenerative power generated when the motor 10 stops is absorbed by stopping the operation of the first inverter 5, the second inverter 9, and the power converter 7 and closing both short-circuit circuits 16 and 17 (S81, S82). In the fourth embodiment, an example of regenerative absorption operation using power conversion devices 41 or 42 is shown. This is effective when the capacitance of the first capacitor is set to a smaller value, thereby improving the power factor. For example, the first capacitor 4 uses a film capacitor, and the second capacitor 8 uses a large-capacity electrolytic capacitor. Using a film capacitor, which has a lower degree of degradation as a single component over the years, as the first capacitor 43 can extend the lifespan of the power conversion device 42.

[0064] The first capacitor 43 only needs to have a small capacity that can interrupt the high-frequency components generated by the switching of the first inverter 5 and the second inverter 9, and the current charging the first capacitor 43 when the power is turned on does not exceed the tolerance of the diode constituting the rectifier circuit 3. This capacity is usually around tens of μF. As a result, the three-phase reactor 2 can also be miniaturized.

[0065] On the other hand, the capacity of the second capacitor 8 is 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. Furthermore, the second capacitor 8 can be any energy storage element capable of charging and discharging; a storage battery or battery can be used instead of an electrolytic capacitor.

[0066] Figure 12 This refers to the operational process during regeneration and absorption. Figure 13 Only the components energized in the first inverter 5 and the second inverter 9 during regenerative absorption are shown. In the fourth embodiment, during regenerative absorption, since short-circuit circuits 16 and 17 are in an open state, therefore... Figure 13 The diagrams of short-circuit circuits 16 and 17 are omitted. Furthermore, in... Figure 12 The operation of short-circuit circuits 16 and 17 is also omitted in the operation flow. During normal operation (S21), if the voltage across the first capacitor 4, etc., exceeds a preset threshold (S22), the control unit 20 determines that regeneration has occurred in the first motor 10 and proceeds accordingly. Figure 13 The regeneration and absorption action shown is (S23).

[0067] Furthermore, at this time, the power converter 7 is operated as a power regeneration PWM rectifier. That is, the power converter 7 is switched on and off to absorb the regenerated power C2 from the motor 10; the voltage across the second capacitor 8 does not exceed the rated voltage range of the component, and the power is returned to the power supply 1 side (S24). When absorbing regenerated power, since neither the first nor the second inverters 5 and 9 drive the motor 10, no harmonics are generated. Therefore, the power converter 7 does not need to perform harmonic suppression, and it is not a problem to operate the power converter 7 as a power regeneration PWM rectifier. Then, if the voltage across the two terminals does not fall below the threshold for a set time or more (S25, No), the process returns to step S3 and continues the regeneration absorption operation. When the voltage across the two terminals falls below the threshold for a set time or more (S25, Yes), the regeneration absorption operation and the switching control of the power converter 7 are stopped (S26).

[0068] exist Figure 13In the regenerative absorption operation shown in step S23, all IGBTs on the upper arm side of the first inverter 5 are turned on, and all IGBTs on the lower arm side are turned off, thereby forming the neutral point of the motor 10. Afterwards, power will not flow from the motor 10 into the first capacitor 4, and the first capacitor 4 will not become overvoltaged. On the other hand, for the second inverter 9, by turning off all IGBTs, it is equivalent to the structure of the rectifier circuit 3. Thus, power flows from the motor 10 into the second capacitor 8. In this way, by performing the regenerative absorption operation when regeneration occurs from the motor 10, the regenerated power can be absorbed only through the relatively large second capacitor 8. In other words, the capacity of the second capacitor 8 is set to be able to absorb the regenerated power generated by the motor 10. Specifically, by setting the capacity of the second capacitor 8 to around several hundred μF to several thousand μF, overvoltage can be prevented even during regeneration. Furthermore, by operating the power converter 7 as a power regeneration PWM rectifier in the regenerative absorption operation (S24), the capacity of the second capacitor 8 can also be reduced.

[0069] Figure 14 Show execution Figure 13 The flowchart shows the current and voltage waveforms for each component. Regarding the current waveforms, although it is a three-phase circuit, there is no need to distinguish between the three phases here, so these waveforms are not shown separately. The "load current" in the diagram is the current flowing through three-phase reactor 2, and the "input current" is the current input from three-phase AC power supply 1 to three-phase reactors 2 and 6. The "power converter current" is the current flowing through three-phase reactor 6. The "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.

[0070] exist Figure 14 In 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. When the regeneration absorption operation begins, the voltage across the second capacitor 8 temporarily rises, but because the power converter 7 operates as a power regeneration PWM rectifier, the voltage rises gradually rather than extremely sharply when regenerating from the three-phase AC power supply 1. Subsequently, when the regeneration of motor 10 ends, the voltage across the second capacitor 8 begins to decrease due to the operation of the power regeneration PWM rectifier. Furthermore, when the voltage across the second capacitor 8 remains below the threshold for a set period of time or longer, the power converter 7 stops switching, and the regeneration absorption and power regeneration operations end. As a result, the switching voltage is fixed at Vdc, and the load current, input current, and power converter current all become "0", ending the regeneration absorption operation. Additionally, 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.

[0071] Furthermore, in the termination determination of the regeneration absorption operation in step S25, it is also possible to... Figure 14 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.

[0072] (Fifth implementation) The fifth embodiment also shows an example of the regenerative absorption operation in the power conversion device 41 or 42. Figure 15 and Figure 13 Similarly, only the components energized in the first inverter 5 and the second inverter 9 during regenerative absorption operation are shown. Unlike the third embodiment, in the first inverter 5, all IGBTs on the upper arm side are turned off, and 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 composed of a bootstrap circuit.

[0073] (Other implementation methods) In the above embodiment, the generation of regenerative power is detected when the voltage across the first capacitor 4 exceeds a preset threshold (S22). Since regenerative power is mainly generated during the emergency stop of the motor 10, i.e., the emergency stop of the first inverter 5 and the second inverter, the regenerative absorption operation is performed when the motor 10 must be stopped urgently due to receiving a stop signal from the upper control system or detecting an overcurrent abnormality in the first inverter 5, thereby preventing the terminal voltage of the first capacitor 4 from becoming an overvoltage.

[0074] Furthermore, the control unit 20 can also perform the following control: The rectifier circuit 3 and the first inverter 5 side are designated as the first drive unit, and the power converter 7 and the second inverter 9 side are designated as the second drive unit. The control unit 20 performs fault diagnosis on these first and second drive units. Furthermore, by setting either of the short-circuit circuits 16 and 17 connected to the drive unit side that is determined to be faulty to a short-circuit state, the motor 10 is driven only through the drive unit side that is determined to be in a normal state.

[0075] Semiconductor switches are not limited to IGBTs; for example, they can also be power MOSFETs.

[0076] Alternating current power can also be single-phase.

[0077] 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 for the first capacitor 4 to be a film capacitor and the second capacitor 8 to be an electrolytic capacitor. The first and second capacitors 4 and 8 can also be used as storage batteries or batteries. Furthermore, it is not necessary for the capacitances C1 and C2 to be set to be in a relationship of (C1 < C2).

[0078] exist Figure 6 Steps S4, S7 and S8 shown Figure 9 The switching of the operation mode determined in steps S11 and S12 can be based on the input power of the motor, or for example, on the speed or load status.

[0079] Heat pump equipment is not limited to air conditioners. In addition, power conversion devices can also be applied to equipment other than heat pump equipment.

[0080] 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.

[0081] Explanation of reference numerals in the attached figures 1 Three-phase AC power supply 2 Three-phase reactors 3 Rectifier Circuit 4. First capacitor (first energy storage element) 5. First Inverter (First Power Converter) 6 Three-phase reactors 7. Power converter (3rd power converter) 8. Second capacitor (second energy storage element) 9. Second Inverter (Second Power Converter) 10 motors 16 and 17 Short-circuit circuits 20 Control Department 21 Air conditioner 22 Compressor 41 and 42 Power conversion devices.

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 energy storage element 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 energy storage element, 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 energy storage element 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 consists of a diode and a semiconductor switch connected between the reactor and the second energy storage element; A short-circuit circuit is configured to short-circuit each phase output terminal of the first power converter or the second power converter; as well as The control unit performs switching control on the third power converter to suppress harmonics flowing from the rectifier circuit to the AC power supply side, and Switching to the following operating modes: an operating mode in which the motor is driven by the first power converter and the second power converter by setting the short-circuit circuit to an open state, and... The motor is operated by setting the short-circuit circuit to a short-circuit state and driving it only by either the first power converter or the second power converter.

2. A power conversion device, characterized in that, have: A rectifier circuit rectifies the AC voltage supplied from an AC power source. The first energy storage element 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 energy storage element, 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 energy storage element 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 is composed of a diode and a semiconductor switch connected between the reactor and the second energy storage element and suppresses harmonics; The first short-circuit circuit is configured to short-circuit each phase output terminal of the first power converter; The second short-circuit circuit is configured to short-circuit each phase output terminal of the second power converter; as well as The control unit switches between multiple operating modes, which are obtained by combining the short-circuit / open states of the first and second short-circuit circuits with the drive states of the motor by the first and second power converters.

3. The power conversion device as described in claim 2, characterized in that, The control unit switches to the following operating modes: setting the first short-circuit circuit and the second short-circuit circuit to the open state, driving the motor by both the first power converter and the second power converter, and making the third power converter operate as an active filter circuit. The operation mode in which the first short-circuit circuit is set to the open state, the second short-circuit circuit is set to the short-circuit state, the motor is driven only by the first power converter, and the third power converter operates as an active filter circuit; and The operation mode is to set the first short-circuit circuit to a short-circuit state and the second short-circuit circuit to an open state, so that only the second power converter drives the motor and the third power converter operates as a PWM rectifier.

4. The power conversion device as described in claim 1 or 2, characterized in that, The maximum energy stored in the second energy storage element is set to be greater than the maximum energy stored in the first energy storage element and to be able to absorb the regenerative power generated by the motor.

5. The power conversion device as described in claim 4, characterized in that, The first energy storage element is a film capacitor, and the second energy storage element is an electrolytic capacitor.

6. The power conversion device as described in claim 1, characterized in that, When the motor generates regenerative power while the short-circuit circuit is open, the control unit turns off all the semiconductor switches of the second power converter and performs regenerative absorption by turning the semiconductor switches of the first power converter on or off.

7. The power conversion device as described in claim 6, characterized in that, It includes a voltage detection unit for detecting the terminal voltage of the first energy storage element. If the terminal voltage exceeds a predetermined threshold, the control unit performs the regeneration absorption operation.

8. The power conversion device as described in claim 6, characterized in that, The control unit performs the regenerative absorption operation when the rotation of the motor is stopped.

9. The power conversion device as described in claim 2, characterized in that, When the control unit stops the rotation of the motor, it sets the first short-circuit circuit and the second short-circuit circuit to a short-circuit state.

10. The power conversion device as claimed in claim 2, characterized in that, The control unit performs fault diagnosis on the first drive unit, which serves as the side between the rectifier circuit and the first power converter, and the second drive unit, which serves as the side between the third power converter and the second power converter. By setting the short-circuit circuit connected to the drive unit side that is determined to be in a faulty state to a short-circuit state, the motor is driven only by the drive unit side that is determined to be in a normal state.

11. The power conversion device as claimed in claim 1, characterized in that, The short-circuit circuit is configured to short-circuit each phase output terminal of the first power converter. The control unit switches between the following operating modes: an operating mode in which the short-circuit circuit is set to the open state, the motor is driven by the first power converter and the second power converter, and the third power converter operates as an active filter circuit; and an operating mode in which the short-circuit circuit is set to the short-circuit state, the motor is driven only by the second power converter, and the third power converter operates as a PWM rectifier.

12. The power conversion device as claimed in claim 1, characterized in that, The short-circuit circuit is configured to short-circuit each phase output terminal of the second power converter. The control unit switches between the following operating modes: an operating mode in which the short-circuit circuit is set to the open state, the motor is driven by the first power converter and the second power converter, and the third power converter operates as an active filter circuit; and an operating mode in which the short-circuit circuit is set to the short-circuit state, the motor is driven only by the first power converter, and the third power converter operates as an active filter circuit.

13. The power conversion device according to any one of claims 1, 2, and 12, characterized in that, The control unit switches between multiple operating modes based on parameters related to the input power to the motor.

14. A heat pump device, characterized in that, have: The power conversion device as described in any one of claims 1, 2, and 12; and The motor, The compressor is driven by the motor.

15. A heat pump device, characterized in that, have: The power conversion device as claimed in claim 13; and The motor, The compressor is driven by the motor.

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