Power conversion device and heat pump equipment

Abstract

A power conversion device according to an embodiment of the present invention comprises a rectifier circuit that rectifies an AC voltage supplied from an AC power source, a first power storage element connected to the DC side of the rectifier circuit, a first power converter connected in parallel to the first power storage element, in which one end of the windings of a motor with independent windings for respective phases is connected to respective phase output terminals of the first power converter, a second power converter in which the other end of the windings of the motor is connected to respective phase output terminals of the second power converter, a second power storage element connected to the DC side of the second power converter, a reactor connected by branching from the wiring connecting the AC power source and the rectifier circuit, a third power converter connected between the reactor and the second power storage element, a short circuit disposed to short-circuit the respective phase output terminals of the first or second power converter, and a control unit that controls the third power converter to suppress harmonics flowing out to the AC power source side and that switches between an operation mode in which the motor is driven by the first and second power converters with the short circuit in the open state and an operation mode in which the motor is driven by either the first or the second power converter with the short circuit in the short-circuit state.

Description

Power conversion equipment and heat pump equipment

[0001] An embodiment of the present invention relates to a power conversion device that drives a motor with an open winding structure, and a heat pump apparatus that includes the power conversion device.

[0002] To increase the capacity of power conversion devices that drive motors and to increase motor speeds, a dual inverter system is known in which an open-winding motor, with independent windings for each phase, is driven by two inverters. However, constantly operating two inverters increases the loss of switching elements in the inverters. Especially under low load conditions, operating two inverters is a waste of power, even though the motor could be driven by just one inverter.

[0003] To address this issue, Patent Document 1 discloses a relay that shorts the wiring between the open-winding motor and one of the inverters. At low rotation speeds with low induced voltage in the motor, the relay is shorted to change the windings of the open-winding motor to a star-connected state, allowing the motor to be driven by only one inverter and stopping the other inverter, thereby reducing power loss. However, in a three-phase input power conversion device, current flows only from the maximum phase to the minimum phase of the three-phase AC, so the input current cannot be controlled to a sine wave simply by switching the power converter used to drive the motor.

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

[0005] In the dual inverter system described above, it is possible to use a small-capacity capacitor in the DC section, but even in this case, if a three-phase AC power supply is used as the power source, it is not possible to control the input current to a sine wave simply by switching in the power converter used to drive the motor, as described above.

[0006] Furthermore, Patent Document 3 discloses a system in which a matrix converter is applied to a primary side inverter.

[0007] Patent No. 7218131 Patent No. 4391768 Patent No. 5531238

[0008] The configuration of Patent Document 3 makes it possible to control the three-phase input current to a sine wave, but the semiconductor devices for the matrix converter, the choke coils used in the AC filter, etc. must be selected to have a rating equal to or higher than the rated capacity of the power conversion device, which causes problems such as an increase in the size and cost of the entire power conversion device. Therefore, we provide a power conversion device that can suppress harmonics with high efficiency even in a dual inverter system, and a heat pump device equipped with that power conversion device.

[0009] The power conversion device of the embodiment includes a first power converter including a rectifier circuit that rectifies an AC voltage supplied from an AC power source, a first storage element connected to the DC side of the rectifier circuit, and a diode and a semiconductor switch connected in parallel to the first storage element, the first power converter having one end of a winding of a motor having independent phase windings connected to each phase output terminal, a second power converter including a diode and a semiconductor switch and having the other end of the winding of the motor connected to each phase output terminal, the second power converter having a second storage element connected to the DC side of the second power converter, a reactor branched off from wiring connecting the AC power source and the rectifier circuit, and a line between the reactor and the second storage element. a third power converter configured with a diode and a semiconductor switch connected to the first power converter or the second power converter; a short-circuit circuit arranged to short-circuit each phase output terminal of the first power converter or the second power converter; and a control unit that switches and executes the third power converter by controlling its switching to suppress harmonics flowing out from the rectifier circuit to the AC power supply side, and by opening the short-circuit, switches between an operation mode in which the motor is driven by the first power converter and the second power converter, and an operation mode in which the motor is driven by only either the first power converter or the second power converter by closing the short-circuit.

[0010] The power conversion device of the embodiment also includes a first power converter, which is composed of a rectifier circuit that rectifies AC voltage supplied from an AC power source, a first storage element connected to the DC side of the rectifier circuit, and a diode and a semiconductor switch connected in parallel to the first storage element, and one end of a winding of a motor having independent phase windings is connected to each phase output terminal; a second power converter, which is composed of a diode and a semiconductor switch and has the other end of the winding of the motor connected to each phase output terminal; a second storage element connected to the DC side of the second power converter; The power converter includes a third power converter configured to suppress harmonics and consisting of a reactor connected in a branched manner, and a diode and a semiconductor switch connected between the reactor and the second storage element, a first short-circuit arranged to short-circuit each phase output terminal of the first power converter, a second short-circuit arranged to short-circuit each phase output terminal of the second power converter, and a control unit that switches between and executes a plurality of operating modes based on combinations of short-circuited and open states of the first short-circuit circuit and the second short-circuit circuit and drive states of the motor by the first power converter and the second power converter.

[0011] A heat pump device according to an embodiment includes the power conversion device according to the embodiment and the motor, and drives a compressor using the motor.

[0012] FIG. 1 is a diagram showing the configuration of a power conversion device in a first embodiment. FIG. 2 is a diagram showing the configuration of an air conditioner. FIG. 3 is a flowchart showing the process of switching operation modes. FIG. 4 is an equivalent diagram showing the second operation mode. FIG. 5 is a diagram showing the configuration of a power conversion device in a second embodiment. FIG. 6 is a flowchart showing the process of switching operation modes. FIG. 7 is an equivalent diagram showing the third operation mode. FIG. 8 is a diagram showing the configuration of a power conversion device in a third embodiment. FIG. 9 is a flowchart showing the process of switching operation modes. FIG. 10 is an equivalent diagram showing the second operation mode. FIG. 11 is an equivalent diagram showing the third operation mode. FIG. 12 is a flowchart showing the process of regenerative absorption operation in a fourth embodiment. FIG. 13 is a diagram showing the switching state of each inverter when regenerative absorption operation is performed. FIG. 14 is a timing chart showing current and voltage waveforms corresponding to the process shown in FIG. 13. FIG. 15 is a diagram showing the switching state of each inverter when regenerative absorption operation is performed in a fifth embodiment.

[0013] First Embodiment As shown in Fig. 1, the power conversion device of this embodiment drives a motor 10. The motor 10 may be a three-phase permanent magnet synchronous motor or an induction machine, but in this embodiment, it is a permanent magnet synchronous motor. The motor 10 is a so-called open winding motor, and its three-phase windings are not connected to each other, with both terminals being open. In other words, the motor 10 has six winding terminals Ua, Va, Wa, Ub, Vb, and Wb.

[0014] The motor 10 is driven by a dual inverter system using a first inverter 5 and a second inverter 9. The first inverter 5 and the second inverter 9 have the same circuit configuration and are three-phase inverters each having three sets of two series-connected switching elements, one on the upper arm side and one on the lower arm side, with the intermediate connection points of each series-connected switching element serving as three output terminals. The phase output terminals of the first inverter 5 are connected to winding terminals Ua, Va, and Wa of the motor 10, respectively, and the phase output terminals of the second inverter 9 are connected to winding terminals Ub, Vb, and Wb of the motor 10, respectively.

[0015] A rectifier circuit 3 is connected to a three-phase AC power supply 1 via a three-phase reactor 2. The rectifier circuit 3 is configured by connecting six diodes 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.

[0016] The second inverter 9 is connected in parallel to both ends of the DC side of the power converter 7 and a second capacitor 8, which may be, for example, an electrolytic capacitor. Each of the second capacitor 8 and the first capacitor 4 may be a chargeable / dischargeable storage element having a certain amount of capacity, and a storage battery or battery may be used instead of a capacitor. In other words, the first capacitor 4 corresponds to the first storage element, and the second capacitor 8 corresponds to the second storage element. The high-voltage side terminal and the low-voltage side terminal of the first inverter 5, i.e., both ends of the first capacitor 4, are not connected to the second inverter 9, and the second inverter 9 is independent. In other words, the output terminals of the first inverter 5 and the second inverter 9 are connected only via independent windings for each phase of the motor 10.

[0017] A short circuit 16 is also provided at each phase output terminal of the second inverter 9. The short circuit 16 is composed of multiple mechanical relays or multiple semiconductor switches that are simultaneously turned on and off. FIG. 1 shows a case where a mechanical relay with two contacts is used, and when the short circuit 16 is turned on, one relay contact shorts the U-V phase, and the other relay contact shorts the V-W phase. In other words, when the short circuit 16 is turned on, the phase output terminals of the second inverter 9 are shorted, so that the motor 10 is star-connected at the winding terminals Ub, Vb, and Wb.

[0018] The power converter 7, whose DC section is connected to the second capacitor 8, has the same three-phase inverter circuit configuration as the first and second inverters 5 and 9, and each phase output terminal is connected to the three-phase AC power supply 1 via a three-phase reactor 6. A flywheel diode is connected in an anti-parallel direction to each of the switching elements constituting the first inverter 5, the second inverter 9, and the power converter 7. Each of these is configured by connecting semiconductor switching elements such as IGBTs in a three-phase bridge configuration, and corresponds to the first to third power converters, respectively.

[0019] Current sensors 11U and 11V are arranged in the U and V phases of the power supply line connecting the three-phase AC power supply 1 and the three-phase reactor 2. The W-phase current is calculated from the U- and V-phase currents detected by these current sensors 11U and 11V. Furthermore, current sensors 12U and 12V are arranged in the U and V phases of the power supply line connecting the three-phase AC power supply 1 and the three-phase reactor 6. The W-phase current flowing through the three-phase reactor 6 is calculated from the U- and V-phase currents flowing through the three-phase reactor 6 detected by these current sensors 12U and 12V.

[0020] 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 disposed between each phase output terminal 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 both connected to the same three-phase AC power source 1. Therefore, when the first motor 10 is driven using the first inverter 5 and the second inverter 9 in a dual inverter system, a zero-phase current flows in the same direction with a predetermined period in each phase winding. Therefore, current sensors 15U, 15V, and 15W are provided corresponding to each phase winding so that the zero-phase current and the current flowing through each motor winding can be detected separately.

[0021] The detection signals output by the sensors 11 to 15 are input to a control unit 20. The control unit 20 is configured with a microcomputer or the like, and controls the switching of the IGBTs that make up the first inverter 5, the second inverter 9, and the power converter 7 based on the detection signals from the sensors 11 to 15. The above configuration, excluding the motor 10, constitutes a power conversion device 41.

[0022] FIG. 2 shows the configuration of an air conditioner, which is a heat pump device to which a power converter 41 is applied. Heat pump devices to which the power converter 41 is applied include, in addition to air conditioners, hot water generators such as water heaters and hot and cold water generators such as chillers. The air conditioner 21 comprises refrigerant piping and signal communication lines connecting an indoor unit 24 and an outdoor unit 35. The indoor unit 24, which is installed indoors, houses an indoor heat exchanger 27 and an indoor fan 30 inside. Meanwhile, the outdoor unit 35 is located outdoors and houses devices such as the control unit 20, compressor 22, outdoor heat exchanger 29, four-way valve 26, pressure reducing device 28, outdoor fan 31, and outdoor fan motor 53.

[0023] The compressor 22 is configured by housing a compression section 23 and a motor 10 in the same iron hermetic container 25, and the rotor shaft of the motor 10 is connected to the compression section 23. The compressor 22, four-way valve 26, indoor heat exchanger 27, pressure reducing device 28, and outdoor heat exchanger 29 are connected to form a closed loop by pipes that serve as refrigerant passages. The compressor 22 is, for example, a single-cylinder rotary compressor, but is not limited to this and a multi-cylinder rotary compressor, scroll compressor, or reciprocating compressor may also be used.

[0024] During heating, the four-way valve 26 is in the state shown by the solid line, and 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, where it condenses and releases heat into the room, heating the room. It is then decompressed by the pressure reducing device 28, becomes colder, and flows to the outdoor heat exchanger 29, where it absorbs heat from the outside air and evaporates, returning to the compressor 22.

[0025] 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 condenses by releasing heat to the outdoors. It is then decompressed by the pressure reducing device 28, becomes low temperature, and flows to the indoor heat exchanger 27, where the refrigerant evaporates by absorbing heat from the indoor air, cooling the room and returning to the compressor 22. Air is then blown to the indoor and outdoor heat exchangers 27, 29 by an indoor fan 30 and an outdoor fan 31, respectively, so that the blown air efficiently exchanges heat between the indoor air and the outdoor air in each heat exchanger 27, 29.

[0026] Next, the operation of this embodiment will be described. A control unit 20 is provided to control the entire power conversion device 41. The control unit 20 operates or stops the compressor 22, i.e., the motor 10, based on instructions, for example, from an indoor control unit (not shown) on the indoor unit 24 side. During operation of the motor 10, the control unit 20 opens and closes the short circuit 16 depending on, for example, the load on the motor 10 and its rotational speed. Specifically, when the motor 10 is under high load, at a high rotational speed, or with high input power, the short circuit 16 is opened, placing the motor 10 in an open winding state. When the motor 10 is under low load, at a low rotational speed, or with low input power, the short circuit 16 is closed, placing the motor 10 in a star-connected state.

[0027] When the short circuit 16 is opened, i.e., when the motor 10 is in an open winding state, the control unit 20 performs vector calculations using 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. Based on the calculation results, the control unit 20 operates the switching elements of the first inverter 5 and the second inverter 9 in coordination with each other, and causes desired currents to flow from both inverters 5 and 9 to each winding of the motor 10, thereby driving the motor 10 at variable speeds.

[0028] On the other hand, when short circuit 16 is shorted and motor 10 is in a star-connected state, control unit 20 performs vector calculations using the current values ​​detected by current sensors 15U, 15V, and 15W and the terminal voltage of first capacitor 4 detected by voltage sensor 13. Based on the calculation results, control unit 20 appropriately operates only the switching elements of first inverter 5 to pass the desired current through each winding of motor 10, thereby driving motor 10 at a variable speed. When driving motor 10 in a star-connected state, the second inverter is turned off and all switching elements are turned off.

[0029] Meanwhile, during operation of motor 10, whether motor 10 is in an open winding state or a star-connected state, control unit 20 causes power converter 7 to operate as an active filter circuit to suppress and reduce harmonics flowing in the power line. Specifically, harmonic currents are extracted from the currents flowing in each phase of reactor 2 detected by current sensors 11U and 11V, and the control unit controls the operation of each switching element of power converter 7 so that the reactor currents for each phase detected by current sensors 12U and 12V, taking into account the terminal voltage of second capacitor 8, become correction currents that cancel out the harmonic currents flowing in the U, V, and W phases. This active filter circuit operation of power converter 7 makes the current flowing from rectifier circuit 3 to AC power supply 1 closer to a sine wave, thereby suppressing power supply harmonics.

[0030] The second capacitor 8, which is a storage element, has a certain amount of capacity because it is used as a power source for the correction current output by the active filter circuit. If the motor 10 is in a low load state, causing a state in which the amount of harmonic current generated is very small, the power converter 7 can be stopped, and the active filter circuit operation can be stopped.

[0031] Configuring the power conversion device 41 as described above improves motor controllability using a dual inverter consisting of the first inverter 5 and the second inverter 9 and the motor 10 with an open winding configuration. Furthermore, because voltage is applied to the windings of the motor 10 by the two inverters 5 and 9, the operating range of the motor 10 can be expanded. Furthermore, because the voltage applied to the windings of the motor 10 is multi-level, iron loss generated in the motor 10 can be reduced.

[0032] Furthermore, by devising a method for driving the two inverters 5 and 9 using the control unit 20, it is possible to control the power applied to the motor 10 to a constant level and expand the operating range in the high-speed region by injecting reactive power. Also, by connecting the negative side of the DC section of the power converter 7 with the negative side of the DC section of the second inverter 9, the reference voltage of these circuits becomes common. This makes it possible to reduce the number of insulating points in the drive power supply and prevent increases in circuit size and cost.

[0033] On the other hand, when the motor 10 is running at low speeds and has low input power, the induced voltage of the motor 10 is small, so a lower voltage can be applied, and driving it using the dual inverter method results in lower efficiency compared to driving it with a single inverter as usual, due to the increased conduction loss of the semiconductor switches. By shorting the short circuit 16 to short-circuit the three-phase output of the second inverter 9, and setting the motor 10 in a star-connected state to drive it using only the first inverter 5, driving efficiency at low speeds and low loads can be improved. At high speeds, opening the short circuit 16 will drive the motor 10 with open windings, thereby utilizing the advantages described above.

[0034] Furthermore, while the motor 10 is in operation, regardless of the winding state of the motor 10, the power converter 7 is operated as an active filter circuit that performs switching control so that the current flowing from the rectifier circuit 3 to the AC power supply 1 approaches a sine wave, thereby suppressing power supply harmonics generated by the power conversion device 41.

[0035] Furthermore, the capacitance of the second capacitor 8 is set to be larger than the capacitance of the first capacitor 4. For example, a film capacitor is used for the first capacitor 4, and an electrolytic capacitor is used for the second capacitor 8. This allows for a reduction in the number of electrolytic capacitors used, thereby extending the life of the power conversion device 42. The first capacitor 4 only needs to have a capacitance large enough to cut off high-frequency components generated by switching between the first inverter 5 and the second inverter 9, and large enough so that the current charging the first capacitor 4 when power is turned on does not exceed the tolerance of the diodes that make up the rectifier circuit 3. This capacitance is generally on the order of several tens of μF. This allows for a reduction in the size of the three-phase reactor 2.

[0036] On the other hand, the capacitance of the second capacitor 8 may be determined based on the compensation capacitance of the power converter 7, the output power of the second inverter 9, the ripple current flowing into the second capacitor 8, etc. This capacitance is generally on the order of several hundred μF to several thousand μF. The second capacitor 8 may be any chargeable and dischargeable storage element, and a storage battery or battery may be used instead of an electrolytic capacitor. In this case, the storage capacitance of the storage element is determined based on the compensation capacitance of the power converter 7, the output power of the second inverter 9, the ripple current flowing into the second capacitor 8, etc., just like the second capacitor.

[0037] The following describes a series of operations of the power conversion device 41. In the initial state, the control unit 20 opens the short circuit 16 (S0). In this state, as shown in FIG. 3, when a motor start command is input to the control unit 20 from an external source (YES in S1), the first inverter 5 and the second inverter 9 open-winding drive the motor 10 (S2). The power converter 7 also performs switching control to operate as an active filter circuit, so that the current flowing from the rectifier circuit 3 to the AC power supply 1 approaches a sine wave. This suppresses harmonics generated on the first inverter 5 side (S3). Steps S2 and S3 correspond to the first operating mode. In the initial state, i.e., when the motor 10 is stopped, if no external motor start command is input (NO in S1), the control unit returns to step S1 to wait for an instruction and continues in this state.

[0038] Next, it is determined whether the input power to the motor 10 has fallen below the threshold value α (S4), and if not (NO in S4), the process returns to step S2. If the input power falls below the threshold value α (YES in S4), the short circuit 16 is shorted (S41) and the motor 10 is driven only by the first inverter 5 (S5). Figure 4 shows this state in an equivalent manner.

[0039] In the next step S6, similar to step S3, the control unit 20 performs a process of operating the power converter 7 as an active filter circuit. Then, the control unit 20 determines whether the input power to the motor 10 exceeds the threshold value β (S7). The threshold value β is set to be greater than the threshold value α to prevent frequent switching of the short circuit 16. If the input power exceeds the threshold value β (YES in S7), the short circuit 16 is switched to an open state (S71) and the process returns to step S2. If the input power does not exceed the threshold value β (NO in S7), the control unit 20 determines whether an external motor stop command has been input (S8). If a motor stop command has not been input (NO in S8), the process returns to step S5. If a motor stop command has been input (YES in S8), the control unit 20 stops all switching operations of the first inverter 5, the second inverter 9, and the power converter 7, thereby stopping the motor 10 (S81). Steps S41, S5, and S6 correspond to the second operating mode.

[0040] As described above, according to this embodiment, in the power conversion device 41, the first capacitor 4 and the first inverter 5 are connected to the DC side of the rectifier circuit 3 that rectifies the AC voltage supplied from the AC power source 1. One end of the winding of the motor 10, which has an open 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 16 is disposed in each of the phase output terminals. The reactor 6, the power converter 7, and the second capacitor 8, which are branched off from the wiring connecting the AC power source 1 and the rectifier circuit 3, are connected to the DC side of the second inverter 7.

[0041] The control unit 20 controls the switching of the power converter 7 so that the current flowing from the rectifier circuit 3 to the AC power supply 1 approaches a sine wave, and switches between a first operating mode in which the motor 10 is driven by the first and second inverters 5 and 9 by opening the short circuit 16, and a second operating mode in which the motor 10 is driven by only the first inverter 5 by shorting the short circuit 16.

[0042] In the first operating mode, the motor 10 is driven using a dual inverter system, which increases the applied voltage and expands the operating range of the motor 10. The multilevel applied voltage reduces iron loss in the motor 10. When a three-phase AC power supply 1 is used, power supply harmonics are largely determined by the capacitance of the current-smoothing reactor 2 and the first capacitor 4, and the input current cannot be controlled by the first inverter 5 and the second inverter 9. Connecting the DC sections of the power converter 7 and the second inverter 9 together, as in this embodiment, reduces the number of insulators in the drive power supply and simplifies the circuit. When the motor 10 rotation speed is low and the input power is relatively low, the system switches to the second operating mode, shorting each phase output of the second inverter 9 using the short circuit 16, and driving the motor 10 in a star connection using only the first inverter 5, thereby improving efficiency. Furthermore, during operation of the motor 10, the power converter 7 operates as an active filter circuit for the rectifier circuit 3, thereby suppressing power supply harmonics in the power conversion device 41.

[0043] Second Embodiment Next, a second embodiment will be described with reference to FIG. 5 . Hereinafter, the same components as those in the first embodiment are denoted by the same reference numerals, and their descriptions will be omitted. The second embodiment focuses on differences. In a power conversion device 42, the short circuit 16 of the power conversion device 41 is disposed on the side of each phase output terminal of the first inverter 5. In the second embodiment, the short circuit 16 shorts each phase output of the first inverter 9. Therefore, in step S9, which replaces step S5, the short circuit 16 is shorted to drive the motor 10 solely by the second inverter 9. Therefore, as shown in FIG. 5 , the current sensors 15U, 15V, and 15W that detect the currents in each phase winding of the motor 10 are moved to the wiring between each phase winding of the motor 10 and the second inverter 9. FIG. 7 illustrates this state in an equivalent manner. Steps S41, S9, and S10 correspond to a third operating mode.

[0044] In step S10, which replaces step S6, the power converter 7 performs harmonic suppression operation on the second inverter 9 side. This harmonic suppression operation functions as a PWM rectifier, stably controlling the terminal voltage of the second capacitor 8 to a target value. The control unit 20 PWM-controls each switching element of the power converter 7 so that the voltage across the second capacitor 8, detected by the voltage sensor 14, is equal to or greater than the DC voltage obtained by rectifying the output of the commercial power source 1. This control operation of the terminal voltage of the second capacitor 8 by the power converter 7 suppresses harmonics generated in the second inverter 9. Generally, a PWM rectifier can suppress harmonics more effectively the higher the boost voltage. However, a higher boost voltage increases losses in the second inverter 9 when driving the motor 10. Therefore, it is desirable to set the boost voltage as low as possible within a range that keeps the amount of harmonics within the target value. Other control operations are the same as those in the first embodiment.

[0045] 8 is a configuration in which a new short circuit 17 is arranged on the side of each phase output terminal of the second inverter 7 in the power conversion device 42. That is, the configuration is a combination of the first and second embodiments.

[0046] In the flowchart shown in FIG. 9 , step numbers identical to those in the flowchart of the first embodiment shown in FIG. 6 indicate that the control unit 20 executes the same operations. In the initial state, both short circuits 16 and 17 are open (S01). If a motor start command is received (YES) in step S1, the control unit 20 determines whether the input power Pm to the motor 10 exceeds a threshold value α (S11). If the threshold value α is exceeded (YES in S11), the control unit 20 opens the short circuits 16 and 17 in step S111, or maintains the open state if the short circuits are already open, and executes steps S2 and S3, i.e., the first operating mode. On the other hand, if the input power Pm does not exceed the threshold value α in step S11 (NO in S11), the control unit 20 proceeds to step S12. If a motor start command is not received in step S1 (NO in S1), the control unit 20 maintains the current state until a motor start command is received.

[0047] In step S12, it is determined whether the input power Pm is equal to or less than the threshold value α and exceeds the threshold value β. If it is equal to or less than the threshold value α and exceeds the threshold value β (YES in S12), the short circuit 16 is opened and the short circuit 17 is closed (S121), and steps S5 and S6 are executed, i.e., the second operation mode is executed as shown in FIG. 10. If the input power Pm is equal to or less than the threshold value β in step S12 (NO in S12), the short circuit 16 is closed and the short circuit 17 is opened (S122), and steps S9 and S10 are executed, i.e., the third operation mode is executed as shown in FIG. 11. Furthermore, if the determination in step S8 following steps S3, S6, and S10 is "YES" indicating that a motor stop command has been issued, 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). Furthermore, both short circuits 16 and 17 are closed for a very short, predetermined time until the regenerative current disappears (S82), shorting both ends of the windings of motor 10. This causes regenerative energy to be consumed in motor 10, suppressing an increase in the voltage of the DC section on the inverters 5 and 9 side. After that, once the predetermined time has elapsed, the process returns to the start and repeats the process from step S01.

[0048] As described above, according to the third embodiment, the short circuits 16, 17 are arranged at each phase output terminal of the first inverter 5 and each phase output terminal of the second inverter 9, respectively, so that the first to third operating modes can be switched and executed depending on the magnitude of the input power Pm to the motor 10.

[0049] (Fourth Embodiment) In the third embodiment, the operation of the first inverter 5, the second inverter 9, and the power converter 7 was stopped, and both the short circuits 16 and 17 were closed (S81, S82), thereby absorbing regenerative power when the motor 10 was stopped. In the fourth embodiment, an example of regenerative absorption operation using the power conversion device 41 or 42 is shown. This is effective when the capacity of the first capacitor, i.e., the capacitance, is set small to improve the power factor. For example, a film capacitor is used for the first capacitor 4, and a large-capacity electrolytic capacitor is used for the second capacitor 8. By using a film capacitor, which is less susceptible to aging as an individual element, for the first capacitor 43, the life of the power conversion device 42 can be extended.

[0050] The first capacitor 43 only needs to have a capacity sufficient to cut off high frequency components generated by switching between the first inverter 5 and the second inverter 9, and a small capacity sufficient to prevent the current that charges the first capacitor 43 when the power is turned on from exceeding the withstand capacity of the diodes that make up the rectifier circuit 3. This capacity is generally about several tens of μF. This also allows the three-phase reactor 2 to be made smaller.

[0051] On the other hand, the capacitance of the second capacitor 8 is determined based on the compensation capacitance of the power converter 7, the output power of the second inverter 9, the ripple current flowing into the second capacitor 8, etc. The second capacitor 8 may be any storage element that can be charged and discharged, and a storage battery or a battery may be used instead of an electrolytic capacitor.

[0052] Fig. 12 shows an operation flow during regeneration absorption, and Fig. 13 shows only the elements that are energized in the first inverter 5 and the second inverter 9 during regeneration absorption operation. During regeneration absorption in the fourth embodiment, the short circuits 16 and 17 are open, and therefore are not shown in Fig. 13. The operation of the short circuits 16 and 17 is also omitted from the operation flow in Fig. 12. When the voltage across the first capacitor 4 etc. exceeds a predetermined threshold value (YES in S22) during normal operation (S21), the control unit 20 determines that regeneration has occurred in the first motor 10, and performs the regeneration absorption operation shown in Fig. 13 (S23).

[0053] At this time, the power converter 7 is operated as a power regenerative PWM rectifier. Specifically, the power converter 7 is switched to absorb the regenerative power of the motor 10, and the power is returned to the power source 1 so that the voltage across the second capacitor C2 does not exceed the rated voltage range of the element (S24). Since neither the first nor the second inverters 5, 9 are driving the motor 10 during regenerative power absorption, no harmonics are generated. Therefore, the power converter 7 does not need to suppress harmonics, and there is no problem with operating the power converter 7 as a power regenerative PWM rectifier. Then, as long as the voltage across the second capacitor C2 does not fall below the threshold for a set time or more (NO in S25), the process returns to step S3 and the regenerative power absorption operation continues. When the voltage across the second capacitor C2 falls below the threshold for a set time or more (YES in S25), the regenerative power absorption operation and the switching control of the power converter 7 are stopped (S26).

[0054] In the regenerative current absorption operation in step S23 shown in FIG. 13 , 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 a neutral point for the motor 10. Thereafter, no power flows from the motor 10 to the first capacitor 4, preventing overvoltage on the first capacitor 4. Meanwhile, for the second inverter 9, all IGBTs are turned off, making the configuration equivalent to that of the rectifier circuit 3. This allows power to flow from the motor 10 to the second capacitor 8. In this way, by performing the regenerative current absorption operation when the motor 10 generates regenerative current, the regenerative power can be absorbed solely by the second capacitor 8, which has a relatively large capacity. In other words, the capacitance of the second capacitor 8 is set to a value sufficient to absorb the regenerative power generated by the motor 10. Specifically, by setting the capacitance of the second capacitor 8 to approximately several hundred μF to several thousand μF, overvoltage can be prevented even during regeneration. Furthermore, by operating the power converter 7 as a power regenerative PWM rectifier during the regenerative absorption operation (S24), it is also possible to reduce the capacitance of the second capacitor 8.

[0055] Figure 14 shows the current and voltage waveforms of each part when the flow shown in Figure 13 is executed. Note that although the current waveforms are three-phase, there is no need to distinguish between the three phases here, so the waveforms are not shown separately. In the figure, the "load current" is the current that passes through the three-phase reactor 2, and the "input current" is the current input from the three-phase AC power source 1 to the three-phase reactors 2 and 6. The "power converter current" is the current that flows through the 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 that constitutes the power converter 7.

[0056] In FIG. 14 , regeneration of the motor 10 occurs, and the voltage of the first capacitor 4 (not shown) rises to a threshold value, at which point the regeneration absorption operation begins. When the regeneration absorption operation begins, the voltage across the second capacitor 8 rises temporarily. However, because the power converter 7 operates as a power regeneration PWM rectifier, the voltage is regenerated to the three-phase AC power supply 1, preventing an extremely large rise and gradually increasing. After that, when the regeneration of the motor 10 ends, the voltage across the second capacitor 8 decreases due to the operation of the power regeneration PWM rectifier. When the time during which the voltage across the second capacitor 8 falls below the threshold value exceeds a set time, the switching of the power converter 7 stops, and the regeneration absorption and power regeneration operation ends. As a result, the switching voltage is fixed at Vdc, and the load current, input current, and power converter current all become "0," thereby ending the regeneration absorption operation. While the power converter 7 operates as a power regeneration PWM rectifier, a sinusoidal current synchronized with the voltage of the three-phase AC power supply 1 flows as the input current.

[0057] Furthermore, in determining whether the regenerative absorbing operation has ended in step S25, a "YES" determination may be made when the voltage of the second capacitor 8 shown in Fig. 14 has become stable. Furthermore, because the actual time for which regenerative power is generated is short, the end of the regenerative absorbing operation may be determined based on the elapsed time from the start of the regenerative absorbing operation.

[0058] Fifth Embodiment The fifth embodiment also shows an example of the regenerative absorption operation in the power conversion device 41 or 42. Like FIG. 13 , FIG. 15 shows only the elements that are energized in the first inverter 5 and the second inverter 9 when the regenerative absorption operation is performed. The difference from the third embodiment is that in the first inverter 5, all of the IGBTs on the upper arm side are turned off and all of the IGBTs on the lower arm side are turned on. In this case, since the IGBTs on the lower arm side are turned on for a long period of time, this is effective when the drive power supply for the second inverter 9 is configured as a bootstrap circuit.

[0059] (Other Embodiments) In the above-described embodiment, the generation of regenerative power is detected when the voltage across the first capacitor 4 etc. exceeds a predetermined threshold (S22). Since regenerative power is mainly generated when the motor 10 suddenly stops, i.e., when the first inverter 5 and the second inverter suddenly stop, the terminal voltage of the first capacitor 4 can be prevented from becoming an overvoltage by receiving a stop signal for the motor 10 from the upper control system or by performing a regenerative absorption operation when the motor 10 must be stopped urgently upon detection of an overcurrent abnormality or the like in the first inverter 5.

[0060] The control unit 20 may also perform the following control. The rectifier circuit 3 and first inverter 5 side are designated as a first drive unit, and the power converter 7 and second inverter 9 side are designated as a second drive unit. The control unit 20 performs a fault determination for these first and second drive units. Then, by shorting one of the short circuits 16, 17 connected to the drive unit determined to be in a faulty state, the motor 10 is driven only by the drive unit determined to be in a normal state.

[0061] The semiconductor switch is not limited to an IGBT, and may be, for example, a power MOSFET. The AC power supply may be single-phase. When setting the magnitude relationship between the capacitances C1 and C2 of the first and second capacitors to (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 may be storage batteries or batteries. Furthermore, it is not necessary to set the magnitude relationship between the capacitances C1 and C2 to (C1<C2).

[0062] The switching of the operating mode determined in steps S4 and S7 shown in Fig. 6 and steps S11 and S12 shown in Fig. 9 may be based on, for example, the rotation speed or the load state, in addition to the input power to the motor. The heat pump device is not limited to an air conditioner. Furthermore, the power conversion device may be applied to devices other than heat pump devices.

[0063] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0064] In the drawings, 1 denotes a three-phase AC power supply, 2 denotes a three-phase reactor, 3 denotes a rectifier circuit, 4 denotes a first capacitor (first storage element), 5 denotes a first inverter (first power converter), 6 denotes a three-phase reactor, 7 denotes a power converter (third power converter), 8 denotes a second capacitor (second storage element), 9 denotes a second inverter (second power converter), 10 denotes a motor, 16 and 17 denote short circuits, 20 denotes a control unit, 21 denotes an air conditioner, 22 denotes a compressor, and 41 and 42 denote power conversion devices.

Claims

1. An operating mode comprising: a rectifier circuit which rectifies an AC voltage supplied from an AC power source; a first storage element connected to a DC side of the rectifier circuit; a first power converter comprising a diode and a semiconductor switch connected in parallel to the first storage element, and one end of a winding of a motor having independent phase windings connected to each phase output terminal; a second power converter comprising a diode and a semiconductor switch, and the other end of the winding of the motor connected to each phase output terminal; a second storage element connected to the DC side of the second power converter; a reactor connected by branching off from wiring connecting the AC power source and the rectifier circuit; a third power converter comprising a diode and a semiconductor switch connected between the reactor and the second storage element; a short circuit disposed to short-circuit each phase output terminal of the first power converter or the second power converter; a control unit that switches and executes an operation mode in which the motor is driven by only one of the first power converter or the second power converter by putting the short circuit into a short-circuit state.

2. A rectifier circuit which rectifies an AC voltage supplied from an AC power source, a first storage element connected to the DC side of the rectifier circuit, a first power converter comprising a diode and a semiconductor switch connected in parallel to the first storage element, and one end of a winding of a motor having independent phase windings connected to each phase output terminal, a second power converter comprising a diode and a semiconductor switch and having the other end of the motor winding connected to each phase output terminal, a second storage element connected to the DC side of the second power converter, a reactor branched off from wiring connecting the AC power source and the rectifier circuit, and a diode and a semiconductor switch connected between the reactor and the second storage element, and a third power converter which suppresses harmonics, a first short circuit arranged to short-circuit each phase output terminal of the first power converter, and a second short circuit arranged to short-circuit each phase output terminal of the second power converter. a control unit that switches between and executes a plurality of operating modes based on combinations of short-circuited / opened states of the first short-circuit and the second short-circuit and drive states of the motor by the first power converter and the second power converter.

3. The power conversion device according to claim 2, wherein the control unit switches between an operating mode in which the first short-circuit and the second short-circuit are opened, the motor is driven by both the first power converter and the second power converter, and the third power converter is operated as an active filter circuit; an operating mode in which the first short-circuit is opened, the second short-circuit is closed, the motor is driven by only the first power converter, and the third power converter is operated as an active filter circuit; and an operating mode in which the first short-circuit is shorted, the second short-circuit is opened, the motor is driven by only the second power converter, and the third power converter is operated as a PWM rectifier.

4. A power conversion device as described in claim 1 or 2, wherein the maximum amount of energy stored in the second storage element is greater than the maximum amount of energy stored in the first storage element and is set to a capacity capable of absorbing regenerative power generated by the motor.

5. The power conversion device according to claim 4, wherein the first storage element is a film capacitor, and the second storage element is an electrolytic capacitor.

6. A power conversion device as described in claim 1, wherein the control unit, when the short circuit is open and the motor generates regenerative power, turns off all semiconductor switches of the second power converter and turns on or off the semiconductor switches of the first power converter to perform regenerative absorption operation.

7. The power conversion device according to claim 6, further comprising a voltage detection unit that detects a terminal voltage of the first storage element, wherein the control unit performs the regenerative absorption operation when the terminal voltage exceeds a predetermined threshold value.

8. The power conversion device according to claim 6, wherein the control unit performs the regenerative absorption operation when stopping the rotation of the motor.

9. The power conversion device according to claim 2, wherein the control unit brings the first short circuit and the second short circuit into a short state when stopping the rotation of the motor.

10. The power conversion device according to claim 2, wherein the control unit performs fault determination for the rectifier circuit and the first drive unit which is on the first power converter side, and the third power converter and the second drive unit which is on the second power converter side, and drives the motor only using the drive unit which is determined to be in a normal state by putting a short circuit connected to the drive unit which is determined to be in a faulty state into a short circuit state.

11. A power conversion device as claimed in claim 1, wherein the short circuit is arranged to short-circuit each phase output terminal of the first power converter, and the control unit switches between an operating mode in which the short circuit is opened to drive the motor using the first power converter and the second power converter and cause the third power converter to operate as an active filter circuit, and an operating mode in which the short circuit is closed to drive the motor using only the second power converter and cause the third power converter to operate as a PWM rectifier.

12. A power conversion device as claimed in claim 1, wherein the short circuit is arranged to short each phase output terminal of the second power converter, and the control unit switches between an operating mode in which the short circuit is opened to drive the motor using the first power converter and the second power converter and causes the third power converter to operate as an active filter circuit, and an operating mode in which the short circuit is closed to drive the motor using only the first power converter and causes the third power converter to operate as an active filter circuit.

13. The power conversion device according to any one of claims 1, 2 and 12, wherein the control unit switches between a plurality of operation modes based on a parameter related to the input power to the motor.

14. A heat pump device comprising: the power conversion device according to any one of claims 1, 2, or 12; and a motor, wherein the motor drives a compressor.

15. A heat pump device comprising: the power conversion device according to claim 13; and the motor, wherein the motor drives a compressor.

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