WO2025121313A1 - Power conversion device and heat pump equipment - Google Patents

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

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 device equipped with the power conversion device.

In order to increase the capacity of the power conversion equipment that drives the motor and to increase the motor's speed, a dual inverter system is known in which an open winding motor, which has independent windings for each phase, is driven by two inverters. However, constantly operating two inverters increases the loss in the switching elements of the inverters. Especially under low load conditions, operating two inverters is a waste of power, even though the motor could originally be driven by only one inverter.

To address this issue, in Patent Document 1, a relay is provided in the wiring between the open winding motor and one of the inverters to short-circuit these wirings. At low rotation speeds when the induced voltage of the motor is low, this relay is shorted to change the windings of the open winding motor to a star connection state and drive it with only one inverter, while the other inverter is stopped, 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 by switching only in the power converter for driving the motor.

Patent document 2 also 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.

In the dual inverter system mentioned 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, the input current cannot be controlled to a sine wave simply by switching in the power converter used to drive the motor, as mentioned above.

Patent document 3 also discloses a system that uses a matrix converter in the primary inverter.

Patent No. 7218131 Patent No. 4391768 Patent No. 5531238

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, and the like must be selected to have a rating equal to or greater than the rated capacity of the power conversion device, resulting in issues such as an increase in the size of the entire power conversion device and increased costs.
Therefore, the present invention provides a power conversion device capable of suppressing harmonics with high efficiency even in a dual inverter system, and a heat pump device equipped with the power conversion device.

The power conversion device of the embodiment includes 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 has one end of a winding of a motor having independent phase windings connected to each phase output terminal, a second power converter has the other end of the winding of the motor connected to each phase output terminal and is configured with a diode and a semiconductor switch, a second storage element connected to the DC side of the second power converter, a reactor branched off from the wiring connecting the AC power source and the rectifier circuit, and a current source between the reactor and the second storage element. a third power converter composed of a diode and a semiconductor switch connected to the third power converter; a short circuit arranged to short 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 so as to suppress harmonics flowing out from the rectifier circuit to the AC power supply side, and switches between an operation mode in which the motor is driven by the first power converter and the second power converter by opening the short circuit, 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.

The power conversion device of the embodiment includes a first power converter having one end of a winding of a motor having independent phase windings connected to each phase output terminal, the first power converter being configured with 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 other end of the winding of the motor being connected to each phase output terminal, the second power converter being configured with a diode and a semiconductor switch, the second storage element connected to the DC side of the second power converter, and a diode and a semiconductor switch connected in parallel to the wiring connecting the AC power source and the rectifier circuit. The third power converter is composed of a reactor connected in a branched manner, a diode and a semiconductor switch connected between the reactor and the second storage element, and suppresses harmonics; 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 the short-circuited and open states of the first short circuit and the second short circuit and the drive state of the motor by the first power converter and the second power converter.

The heat pump device of the embodiment includes the power conversion device of the embodiment and the motor, and drives the compressor with the motor.

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

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, a permanent magnet synchronous motor is used. The motor 10 is a so-called open winding motor, and the three-phase windings are not connected to each other, with both terminals being in an open state. In other words, the motor 10 has six winding terminals Ua, Va, Wa, Ub, Vb, and Wb.

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 a three-phase inverter 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. Each phase output terminal of the first inverter 5 is connected to the winding terminals Ua, Va, and Wa of the motor 10, respectively, and each phase output terminal of the second inverter 9 is connected to the winding terminals Ub, Vb, and Wb of the motor 10, respectively.

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

The second inverter 9 is connected in parallel to both ends of the DC side of the second capacitor 8, which is, for example, an electrolytic capacitor, and the power converter 7. Each of the second capacitor 8 and the first capacitor 4 may be a chargeable and 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 windings of the motor 10, each phase of which is independent.

Furthermore, a short circuit 16 is arranged 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. Figure 1 shows the 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, each phase output terminal of the second inverter 9 is shorted, so that the motor 10 is in a star-connected state at the winding terminals Ub, Vb, and Wb.

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 source 1 via a three-phase reactor 6. Flywheel diodes are connected in an inverse parallel direction to each of the switching elements that make up the first inverter 5, second inverter 9, and power converter 7. All of these are configured by connecting semiconductor switching elements such as IGBTs in a three-phase bridge configuration, and correspond to the first to third power converters, respectively.

Current sensors 11U, 11V are arranged in the U and V phases of the power 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, 11V. In addition, current sensors 12U, 12V are arranged in the U and V phases of the power 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, 12V.

Voltage sensors 13, 14 detect the terminal voltages of the first capacitor 4 and the second capacitor 8, respectively. Current sensors 15U, 15V, 15W are arranged between each phase output terminal of the first inverter 5 and the winding terminals Ua, Va, Wa of the motor 10 to detect the current flowing through each motor winding of the motor 10. The DC parts 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 by the dual inverter method using the first inverter 5 and the second inverter 9, a zero-phase current flows in the same direction at a predetermined period in each phase winding. Therefore, current sensors 15U, 15V, 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.

The detection signals output by the above sensors 11 to 15 are input to the control unit 20. The control unit 20 is composed of a microcomputer or the like, and controls the switching of each IGBT constituting the first inverter 5, second inverter 9, and power converter 7 based on the detection signals of the above sensors 11 to 15. The above configuration excluding the motor 10 constitutes the power conversion device 41.

Figure 2 shows the configuration of an air conditioner, which is a heat pump device to which the power conversion device 41 is applied. In addition to air conditioners, heat pump devices to which the power conversion device 41 is applied include hot water generating devices that serve as hot water heaters and hot and cold water generating devices such as chillers. The air conditioner 21 is made up of refrigerant piping and signal communication lines that connect the indoor unit 24 and the outdoor unit 35 to each other. The indoor unit 24, which is installed indoors, houses the indoor heat exchanger 27 and the indoor fan 30 inside. On the other hand, the outdoor unit 35 is placed 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.

The compressor 22 is constructed by housing the compression section 23 and the motor 10 in the same iron sealed 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 one-cylinder rotary compressor, but is not limited to this and a multi-cylinder rotary compressor, scroll compressor, or reciprocating compressor can also be used.

During heating, the four-way valve 26 is in the state shown by the solid line, and the high-temperature refrigerant compressed in 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 cold, and flows to the outdoor heat exchanger 29, where it absorbs heat from the outside air and evaporates, returning to the compressor 22.

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 in the compression section 23 of the compressor 22 is supplied from the four-way valve 26 to the outdoor heat exchanger 29, where it radiates heat to the outdoors and condenses. It is then depressurized by the pressure reducing device 28, becomes a low-temperature refrigerant, 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. Then, the indoor and outdoor heat exchangers 27, 29 are blown with an indoor fan 30 and an outdoor fan 31, respectively, and are configured so that the blowing air efficiently exchanges heat between the indoor air and the outdoor air and between the heat exchangers 27, 29 and the indoor air.

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/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, for example. 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 rotation speed. Specifically, when the motor 10 is under high load, high rotation speed, or when the input power is high, the short circuit 16 is opened to put the motor 10 in an open winding state, and when the load, low rotation speed, or input power is low, the short circuit 16 is shorted to switch the motor 10 to a star connection state.

When the short circuit 16 is opened, that is, 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, and the desired current flows from both inverters 5 and 9 to each winding of the motor 10, thereby driving the motor 10 at a variable speed.

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

On the other hand, the control unit 20 operates the power converter 7 as an active filter circuit to suppress and reduce harmonics flowing in the power line while the motor 10 is operating, regardless of whether the motor 10 is in an open winding state or a star connection state. Specifically, it extracts harmonic currents from the currents flowing in each phase of the reactor 2 detected by the current sensors 11U and 11V, and controls the operation of each switching element of the power converter 7 so that the reactor currents of each phase detected by the current sensors 12U and 12V, taking into account the terminal voltage of the 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 the power converter 7 makes it possible to make the current flowing from the rectifier circuit 3 to the AC power source 1 closer to a sine wave and suppress power source harmonics.

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 very small amount of harmonic current to be generated, the power converter 7 can be stopped to stop the operation of the active filter circuit.

By configuring the power conversion device 41 as described above, the motor controllability is improved using a dual inverter consisting of the first inverter 5 and the second inverter 9, and a 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. In addition, because the voltage applied to the windings of the motor 10 is multi-level, the iron loss generated in the motor 10 can be reduced.

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, preventing the circuit size from increasing and the cost from increasing.

On the other hand, when motor 10 is rotating at low speed and has low input power, the induced voltage of motor 10 is small, so a lower voltage can be applied, and driving using the dual inverter method is less efficient than driving using a single inverter as usual, due to the increased conduction loss of the semiconductor switches. In contrast, by shorting short circuit 16, the three-phase output of second inverter 9 is shorted, and motor 10 is connected in a star connection and driven only by first inverter 5, which improves driving efficiency at low speeds and low loads. At high speeds, by opening short circuit 16, motor 10 is driven with open windings, making use of the advantages mentioned above.

Furthermore, while the motor 10 is in operation, 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, regardless of the winding state of the motor 10, thereby suppressing the power supply harmonics generated by the power conversion device 41.

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 the number of electrolytic capacitors used to be reduced, and the life of the power conversion device 42 to be extended. The first capacitor 4 only needs to have a capacity that is large enough to cut off high-frequency components generated by switching between the first inverter 5 and the second inverter 9, and that does not allow the current that charges the first capacitor 4 when the power is turned on to exceed the tolerance of the diodes that make up the rectifier circuit 3. This capacity is generally around several tens of μF. This allows the three-phase reactor 2 to be made smaller.

On the other hand, the capacity of the second capacitor 8 may be determined based on the compensation capacity of the power converter 7, the output power of the second inverter 9, the ripple current flowing into the second capacitor 8, etc. This capacity is generally on the order of several hundred μF to several thousand μF. The second capacitor 8 may be any storage element that can be charged and discharged, and a storage battery or battery may be used instead of an electrolytic capacitor. In this case, the storage capacity of the storage element is determined based on the compensation capacity 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.

The series of operations of the power conversion device 41 will be described below. 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 from the outside to the control unit 20 (YES in S1), the first inverter 5 and the second inverter 9 drive the motor 10 with open windings (S2). In addition, the power converter 7 is switched and controlled so that the current flowing from the rectifier circuit 3 to the AC power source 1 side approaches a sine wave, and is operated as an active filter circuit. This suppresses harmonics generated on the first inverter 5 side (S3). Steps S2 and S3 correspond to the first operation mode. Note that in the initial state, i.e., when the motor 10 is stopped, if a motor start command is not input from the outside (NO in S1), the process returns to step S1 to wait for an instruction, and the state continues as it is.

Then, 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.

In the next step S6, similar to step S3, when the process of operating the power converter 7 as an active filter circuit is performed, the control unit 20 judges 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 in order 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 judges whether a motor stop command has been input from the outside (S8). If the motor stop command has not been input (NO in S8), the process returns to step S5. If the motor stop command has been input (YES in S8), the process stops all switching operations of the first inverter 5, the second inverter 9, and the power converter 7 to stop the motor 10 (S81). Steps S41, S5, and S6 correspond to the second operation mode.

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 with 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 arranged in each phase output terminal. The reactor 6, power converter 7, and second capacitor 8 that are branched off and connected from the wiring that connects the AC power source 1 and the rectifier circuit 3 are connected to the DC side of the second inverter 7.

The control unit 20 controls the power converter 7 to switch 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 closing the short circuit 16.

In the first operating mode, the motor 10 is driven by the dual inverter method, so that the applied voltage can be increased to expand the operating range of the motor 10, and the applied voltage can be multi-leveled to reduce iron loss in the motor 10. When a three-phase AC power supply 1 is used, the power supply harmonics are generally determined by the capacity 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. As in this embodiment, by connecting the DC parts of the power converter 7 and the second inverter 9 to each other, the number of insulations in the driving power supply can be reduced and the circuit can be simplified. When the rotation speed of the motor 10 is low and the input power is relatively small, the operation mode is switched to the second operating mode, each phase output of the second inverter 9 is short-circuited by the short circuit 16, and the motor 10 is star-connected and driven only by the first inverter 5, thereby improving efficiency. Furthermore, during the operation of the motor 10, the power converter 7 is operated as a rectifier circuit 3 active filter circuit, so that the power supply harmonics of the power conversion device 41 can be suppressed.

Second Embodiment
Next, the second embodiment will be described with reference to FIG. 5. In the following, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description will be omitted, and the different parts will be described. In the power conversion device 42 of the second embodiment, the short circuit 16 of the power conversion device 41 is arranged on the side of each phase output terminal of the first inverter 5. In the second embodiment, each phase output of the first inverter 9 is short-circuited by the short circuit 16. Therefore, in the control flow chart shown in FIG. 6, in step S9 instead of step S5, the short circuit 16 is shorted to drive the motor 10 only by the second inverter 9. Therefore, as shown in FIG. 5, the current sensors 15U, 15V, and 15W that detect the current of 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 shows this state in an equivalent manner. Steps S41, S9, and S10 correspond to the third operation mode.

In addition, in step S10, which replaces step S6, the power converter 7 performs harmonic suppression operation on the second inverter 9 side. The harmonic suppression operation here is an operation as a PWM rectifier that stably controls the terminal voltage of the second capacitor 8 to a target value. Here, the control unit 20 PWM controls each switching element of the power converter 7 so that the voltage between both ends of the second capacitor 8 detected by the voltage sensor 14 becomes a value equal to or higher than the DC voltage value obtained by rectifying the output of the commercial power source 1. This terminal voltage control operation of the second capacitor 8 by the power converter 7 can suppress harmonics generated in the second inverter 9. In general, the higher the boost voltage of a PWM rectifier, the greater the suppression effect of harmonics. However, as the boost voltage increases, the loss during driving of the motor 10 in the second inverter 9 increases, so it is desirable to set the boost voltage value as low as possible within the range in which the amount of harmonics generated can be suppressed within the target value. Other controls are the same as those in the first embodiment.

Third Embodiment
A power conversion device 43 of the third embodiment shown in Fig. 8 has a configuration in which, in the power conversion device 42, new short circuits 17 are arranged on the side of each phase output terminal of the second inverter 7. That is, the configuration is a combination of the first and second embodiments.

In the flowchart shown in FIG. 9, the same step numbers as 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 it is determined in step S1 that there is a motor start command and the answer is "YES", it is determined whether the input power Pm to the motor 10 exceeds the threshold value α (S11). If it exceeds the threshold value α (YES in S11), the short circuits 16 and 17 are opened in step S111, or if they are already in an open state, the open state is maintained, and steps S2 and S3, that is, the first operation mode, are executed. On the other hand, if the input power Pm does not exceed the threshold value α in step S11 (NO in S11), the process proceeds to step S12. Note that if there is no motor start command in step S1 (NO in S1), the current state is maintained until there is a motor start command.

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 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 as shown in FIG. 11. Furthermore, in step S8 following steps S3, S6, and S10, when it is determined that there is a motor stop command and the answer is "YES," 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 (S82) for a very short, predetermined time until the regenerative current disappears, shorting both ends of the windings of motor 10. This causes the 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, when the predetermined time has elapsed, the process returns to the start and repeats the process from step S01.

As described above, according to the third embodiment, short circuits 16, 17 are provided at each phase output terminal of the first inverter 5 and each phase output terminal of the second inverter 9, 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.

Fourth Embodiment
In the third embodiment, the operation of the first inverter 5, the second inverter 9, and the power converter 7 is stopped, and both the short circuits 16 and 17 are closed (S81, S82) to absorb regenerative power when the motor 10 is 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 for the first capacitor 43, which is a single element that is less susceptible to deterioration over time, the life of the power conversion device 42 can be extended.

The first capacitor 43 only needs to have a capacity large enough to cut off high-frequency components generated by switching between the first inverter 5 and the second inverter 9, and a small capacity so that the current that charges the first capacitor 43 when the power is turned on does not exceed the tolerance of the diodes that make up the rectifier circuit 3. This capacity is generally around several tens of μF. This also makes it possible to miniaturize the three-phase reactor 2.

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, 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 battery may be used instead of an electrolytic capacitor.

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

Also, at this time, the power converter 7 is operated as a power regeneration PWM rectifier. That is, the power converter 7 is switched and controlled to absorb the regenerative power of the motor 10; power is returned to the power source 1 side so that the voltage across the second capacitor 8 does not exceed a value within the rated voltage range of the element (S24). When absorbing regenerative power, the first and second inverters 5 and 9 are not driving the motor 10, so no harmonics are generated. Therefore, the power converter 7 does not need to suppress harmonics, and there is no problem in operating the power converter 7 as a power regeneration PWM rectifier. Then, while the voltage across both ends does not fall below the threshold for a set time or more (NO in S25), the process returns to step S3 and the regenerative absorption operation is continued. When the voltage across both ends falls below the threshold for a set time or more (YES in S25), the regenerative absorption operation and the switching control of the power converter 7 are stopped (S26).

In the regenerative absorption operation in step S23 shown in FIG. 13, all the IGBTs on the upper arm side of the first inverter 5 are turned on, and all the IGBTs on the lower arm side are turned off to form a neutral point for the motor 10. After this, no power flows from the motor 10 to the first capacitor 4, and the first capacitor 4 does not become overvoltage. On the other hand, the second inverter 9 is made equivalent to the configuration of the rectifier circuit 3 by turning off all the IGBTs. This allows power to flow from the motor 10 to the second capacitor 8. In this way, by performing the regenerative absorption operation when regeneration occurs by the motor 10, the regenerative power can be absorbed only by the second capacitor 8, which has a relatively large capacity. In other words, the capacity of the second capacitor 8 is set to a capacity that can absorb the regenerative power generated by the motor 10. Specifically, by setting the capacity of the second capacitor 8 to about several hundred μF to several thousand μF, it is possible to prevent overvoltage from occurring even during regeneration. Furthermore, by operating the power converter 7 as a power regenerative PWM rectifier during regenerative absorption operation (S24), it is also possible to reduce the capacity of the second capacitor 8.

FIG. 14 shows the current and voltage waveforms of each part when the flow shown in FIG. 13 is executed. Note that although the current waveforms are three-phase, they are not shown separately here as there is no need to distinguish between the three phases. The "load current" in the figure 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.

In FIG. 14, regeneration of the motor 10 occurs, and the voltage of the first capacitor 4 (not shown) rises to a threshold value, and the regeneration absorption operation is started. When the regeneration absorption operation starts, the voltage across the second capacitor 8 rises once, but since the power converter 7 operates as a power regeneration PWM rectifier, the voltage does not rise extremely high because it is regenerated to the three-phase AC power source 1, and it gradually rises. 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. Then, when the time during which the voltage across the second capacitor 8 falls below the threshold value becomes equal to or longer than the 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 to Vdc, and the load current, input current, and power converter current all become "0", and the regeneration absorption operation ends. Note that while the power converter 7 operates as a power regeneration PWM rectifier, a sine wave current synchronized with the voltage of the three-phase AC power source 1 flows in the input current.

In addition, in determining whether the regenerative absorption operation has ended in step S25, a "YES" determination may be made if the voltage of the second capacitor 8 shown in FIG. 14 has become stable. In addition, because the actual time for which regenerative power is generated is short, the end of the regenerative absorption operation may be determined based on the elapsed time from the start of the operation.

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 the IGBTs on the upper arm side are turned off and all 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.

Other Embodiments
In the above 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 is suddenly stopped, i.e., when the first inverter 5 and the second inverter are suddenly stopped, the terminal voltage of the first capacitor 4 can be prevented from becoming an overvoltage by performing a regenerative absorption operation when a stop signal for the motor 10 is received from the upper control system or an overcurrent abnormality or the like is detected in the first inverter 5 and the motor 10 must be stopped urgently.

The control unit 20 may also perform the following control. The rectifier circuit 3 and first inverter 5 side are the first drive unit, and the power converter 7 and second inverter 9 side are the 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.

The semiconductor switch is not limited to an IGBT, but may be, for example, a power MOSFET.
The AC power supply may be single phase.
When the magnitude relationship between the capacitances C1 and C2 of the first and second capacitors is set to (C1<C2), it is not necessary to use a film capacitor for the first capacitor 4 and an electrolytic capacitor for the second capacitor 8. The first and second capacitors 4 and 8 may be storage batteries or batteries. In addition, it is not necessary to use a magnitude relationship between the capacitances C1 and C2 to be (C1<C2).

The switching of the operation mode determined in steps S4 and S7 shown in FIG. 6 and steps S11 and S12 shown in FIG. 9 may be performed based on, for example, the rotation speed or the load state other than 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.

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 gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims.

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

Claims (15)

a rectifier circuit that 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 including a diode and a semiconductor switch connected in parallel to the first storage element, the first power converter having an output terminal for each phase connected to one end of a winding of a motor having independent windings for each phase;
a second power converter including a diode and a semiconductor switch, the second power converter being connected to the other end of the winding of the motor at each phase output terminal;
a second storage element connected to a DC side of the second power converter;
a reactor that is branched off from a line that connects the AC power supply and the rectifier circuit;
a third power converter including a diode and a semiconductor switch connected between the reactor and the second storage element;
a short circuit arranged to short-circuit each phase output terminal of the first power converter or the second power converter;
switching control of the third power converter so as to suppress harmonics flowing out from the rectifier circuit to the AC power supply side;
and a control unit that switches between and executes an operation mode in which the motor is driven by the first power converter and the second power converter by bringing the short circuit into an open state, and an operation mode in which the motor is driven by only one of the first power converter or the second power converter by bringing the short circuit into a short state. a rectifier circuit that 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 including a diode and a semiconductor switch connected in parallel to the first storage element, the first power converter having an output terminal for each phase connected to one end of a winding of a motor having independent windings for each phase;
a second power converter including a diode and a semiconductor switch, the second power converter being connected to the other end of the winding of the motor at each phase output terminal;
a second storage element connected to a DC side of the second power converter;
a reactor that is branched off from a line that connects the AC power supply and the rectifier circuit;
a third power converter configured to suppress harmonics and including 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;
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. an operation mode in which the control unit drives the motor by both the first power converter and the second power converter with the first short circuit and the second short circuit in an open state, and operates the third power converter as an active filter circuit;
an operation mode in which the first short circuit is in an open state, the second short circuit is in a short state, the motor is driven only by the first power converter, and the third power converter is operated as an active filter circuit;
3. The power conversion device according to claim 2, wherein an operating mode is switched between a first operating mode and an operating mode in which the first short-circuit is in a short-circuited state and the second short-circuit is in an open state, and the motor is driven by only the second power converter, and the third power converter is operated as a PWM rectifier. The power conversion device according to 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 the regenerative power generated by the motor. 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. The power conversion device according to claim 1, wherein the control unit performs a regenerative absorption operation by turning off all semiconductor switches of the second power converter and turning on or off the semiconductor switches of the first power converter when the motor generates regenerative power in an open state of the short circuit. a voltage detection unit that detects a terminal voltage of the first storage element,
The power conversion device according to claim 6 , wherein the control unit performs the regenerative absorption operation when the terminal voltage exceeds a predetermined threshold value. The power conversion device according to claim 6, wherein the control unit performs the regenerative absorption operation when stopping the rotation of the motor. The power conversion device according to claim 2, wherein the control unit shorts the first short circuit and the second short circuit when stopping the rotation of the motor. The control unit includes a first drive unit which is a side of the rectifier circuit and the first power converter,
3. The power conversion device according to claim 2, wherein a fault determination is performed for the third power converter and a second drive unit on the second power converter side, and a short circuit connected to the drive unit determined to be in a faulty state is short-circuited, thereby driving the motor only using the drive unit determined to be in a normal state. the short circuit is arranged to short-circuit each phase output terminal of the first power converter;
2. The power conversion device according to claim 1, wherein the control unit switches between an operating mode in which the short circuit is opened, the motor is driven by the first power converter and the second power converter, and the third power converter is operated as an active filter circuit, and an operating mode in which the short circuit is closed, the motor is driven by only the second power converter, and the third power converter is operated as a PWM rectifier. the short circuit is arranged to short-circuit each phase output terminal of the second power converter;
2. The power conversion device according to claim 1, wherein the control unit switches between an operating mode in which the short circuit is opened, the motor is driven by the first power converter and the second power converter, and the third power converter is operated as an active filter circuit, and an operating mode in which the 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. The power conversion device according to any one of claims 1, 2, or 12, wherein the control unit switches between a plurality of operating modes based on a parameter related to the input power to the motor. A power converter according to any one of claims 1, 2 and 12;
The motor,
A heat pump device in which the motor drives a compressor. The power conversion device according to claim 13;
The motor,
A heat pump device in which the motor drives a compressor.

Images