Motor drive device and refrigeration cycle device

Abstract

In the present invention, a control unit executes regenerative power absorption control, in which: a mutual conduction path, in which one of the ends of phase windings of a motor are in the state of being mutually conductive, is formed by a first inverter; a rectification circuit for voltages generated at the other ends of the phase windings of the motor is formed by a second inverter; and regenerative power of the motor is absorbed by a second capacitor through the formed rectification circuit.

Description

Motor drive device and refrigeration cycle device

[0001] The present invention relates to a motor drive device and a refrigeration cycle device that drive a permanent magnet synchronous motor, or so-called an open winding motor, having a plurality of phase windings that are not connected to each other.

[0002] Known motors for driving compressors installed in refrigeration cycle devices such as air conditioners and heat source machines include permanent magnet synchronous motors with star-connected phase windings and open-winding motors with disconnected phase windings.

[0003] A motor drive device for driving a permanent magnet synchronous motor having multiple star-connected phase windings includes a rectifier circuit that rectifies the voltage of an AC power supply, a capacitor connected to the terminals of the rectifier circuit, and an inverter connected between the capacitor and each phase winding of the motor, and drives the motor by switching the inverter.

[0004] On the other hand, a motor drive device for driving an open winding motor includes a rectifier circuit that rectifies the voltage of an AC power supply, a capacitor connected to the terminals of the rectifier circuit, a first inverter connected between the capacitor and one end of each phase winding of the motor, and a second inverter connected between the capacitor and the other end of each phase winding of the motor, and drives the motor by switching the first and second inverters in coordination with each other.

[0005] Patent No. 4706987

[0006] In the motor drive device described above, the regenerative power of the motor may be applied to the capacitor through the inverter. In this case, the voltage of the capacitor increases sharply, and this overvoltage may cause damage to electrical components such as the capacitor and rectifier circuit.

[0007] If a large-capacity capacitor is used, the regenerative power of the motor can be absorbed by the capacitor, but if a large-capacity capacitor is used, a large inrush current will flow through the capacitor when the power is turned on, and this inrush current may cause damage to electrical components such as the rectifier circuit and inverter.

[0008] An object of the embodiments of the present invention is to provide a motor drive device and a refrigeration cycle device that are highly safe and can prevent overvoltage caused by regenerative power of a motor.

[0009] A motor drive device according to one embodiment is a motor drive device for a motor having a plurality of mutually disconnected phase windings, and includes: a rectifier circuit that rectifies the voltage of an AC power supply; a first capacitor connected to terminals of the rectifier circuit; a first inverter including a plurality of first switch elements and first diodes connected in anti-parallel to each of the first switch elements, and connected between the first capacitor and one end of each of the phase windings; a second inverter including a plurality of second switch elements and second diodes connected in anti-parallel to each of the second switch elements, and connected to the other end of each of the phase windings; a second capacitor connected to the other end of each of the phase windings via the second inverter; and a control unit. The control unit forms, using the first inverter, a mutual conduction path that brings one ends of the phase windings into a mutually conductive state, and forms, using the second inverter, a rectifier circuit for the voltage generated at the other end of each of the phase windings, and performs regenerative power absorption control to absorb regenerative power of the motor into the second capacitor through the formed rectifier circuit.

[0010] A diagram showing the configuration of the first to fourth embodiments. A flowchart showing the control of the first embodiment. A diagram showing the current path of the regenerative power absorption control in the first to fourth embodiments. A diagram showing the change in voltage of each capacitor before and after the execution of the regenerative power absorption control in the first to fourth embodiments. A diagram showing a modification of the current path of Figure 3. A flowchart showing the control of the second embodiment. A flowchart showing the control of the third embodiment. A flowchart showing the control of the fourth embodiment. A diagram showing the configuration of the main parts of the fifth embodiment.

[0011] [1] A motor drive device according to a first embodiment will be described. As shown in Fig. 1, a three-phase AC power supply 1 is connected to a diode bridge full-wave rectifier circuit 2 that full-wave rectifies an AC voltage Vac of the three-phase AC power supply 1, and a capacitor (first capacitor) C1 is connected to terminals of the full-wave rectifier circuit 2 via a reactor 3. A positive line P1 and a negative line N1 of an inverter (first inverter) 10 are connected to both ends of the capacitor C1, and one ends of phase windings Lu, Lv, Lw of an open-winding motor 4 are connected to three-phase terminals Au, Av, Aw of the inverter 10.

[0012] The open winding motor 4 is a permanent magnet synchronous motor having phase windings Lu, Lv, and Lw that are not connected to one another. Hereinafter, the open winding motor 4 will be abbreviated as motor 4.

[0013] In the inverter 10, a U-phase series circuit of an upper switch element (first switch element) 11 and a lower switch element (first switch element) 12, a V-phase series circuit of an upper switch element (first switch element) 13 and a lower switch element (first switch element) 14, and a W-phase series circuit of an upper switch element (first switch element) 15 and a lower switch element (first switch element) 16 are connected between a positive side line P1 and a negative side line N1, and the interconnection point between the upper side switch element 11 and the lower side switch element 12 is a U-phase terminal Au, the interconnection point between the upper side switch element 13 and the lower side switch element 14 is a V-phase terminal Av, and the interconnection point between the upper side switch element 15 and the lower side switch element 16 is a W-phase terminal Aw. Inverter 10 converts the DC voltage of capacitor C1 into a three-phase AC voltage of a predetermined frequency by switching in response to commands from control unit 50, and outputs this as drive power for motor 4 from U-phase terminal Au, V-phase terminal Av, and W-phase terminal Aw. In addition, a freewheeling diode (first diode) D1 is connected in anti-parallel to each of six switch elements 11 to 16 of inverter 10 for protecting these switch elements 11 to 16.

[0014] Furthermore, in the inverter 10, by turning on the upper switch elements 11, 13, 15 and turning off the lower switch elements 12, 14, 16, one ends of the phase windings Lu, Lv, Lw can form mutually conductive paths that are mutually conductive through the upper switch elements 11, 13, 15 and the freewheeling diodes D1 of the upper switch elements 11, 13, 15. Alternatively, by turning off the upper switch elements 11, 13, 15 and turning on the lower switch elements 12, 14, 16, the inverter 10 can form mutually conductive paths that are mutually conductive through the lower switch elements 12, 14, 16 and the freewheeling diodes D1 of the lower switch elements 12, 14, 16.

[0015] Meanwhile, the other ends of the phase windings Lu, Lv, Lw of the motor 4 are connected to three-phase terminals Bu, Bv, Bw of an inverter (second inverter) 20. A capacitor (second capacitor) C2 is connected between a positive line P2 and a negative line N2 of the inverter 20. That is, the second capacitor C2 is connected in parallel to the second inverter 20.

[0016] In inverter 20, a U-phase series circuit of upper switch element 21 and lower switch element 22, a V-phase series circuit of upper switch element 23 and lower switch element 24, and a W-phase series circuit of upper switch element 25 and lower switch element 26 are connected between positive side line P2 and negative side line N2, and the interconnection point between upper side switch element 21 and lower side switch element 22 is a U-phase terminal Bu, the interconnection point between upper side switch element 23 and lower side switch element 24 is a V-phase terminal Bv, and the interconnection point between upper side switch element 25 and lower side switch element 26 is a W-phase terminal Bw. As in inverter 10, a freewheeling diode (second diode) D2 is connected in anti-parallel to each of the six switch elements 21 to 26 of inverter 20 for protecting these switch elements 21 to 26.

[0017] In this inverter 20, by turning off all of the switch elements 21 to 26 and by turning on the freewheel diodes D2 of the switch elements 21 to 26, a full-wave rectifier circuit can be formed for the voltage (regenerative power) generated at the other end of each of the phase windings Lu, Lv, and Lw. That is, each freewheel diode D2 in the inverter 20 can function as a regenerative diode D2 in some cases. For this reason, when performing the regenerative power absorption control described below, the freewheel diode D2 is also referred to as a regenerative diode D2. The voltage generated at the other end of each of the phase windings Lu, Lv, and Lw is converted into a DC voltage by the full-wave rectifier circuit formed by each regenerative diode D2, and the DC voltage is applied to the capacitor C2 via the positive line P2 and negative line N2 of the inverter 20.

[0018] The control unit 50 is comprised of a microcomputer and its peripheral circuits, powered by the voltage Vc1 of the capacitor C1, and operates based on a program stored in its internal memory. Alternatively, the control unit 50 may be comprised of a logic circuit. The control unit 50 controls the on / off of the switch elements 11-16 and 21-26 of the inverters 10 and 20 to drive the motor 4 at a variable speed. The control unit 50 is connected to a voltage detector 51 that detects the voltage Vc1 of the capacitor C1, a voltage detector 55 that detects the voltage Vc2 of the capacitor C2, a current detector 52 that detects the motor current (also referred to as the load current or the phase winding current) flowing through the current path between the inverter 10 and one end of the phase windings Lu, Lv, and Lw, and an abnormality detection unit 53. The abnormality detection unit 53 detects abnormalities in the motor 4 and the inverters 10 and 20 based on the detection results of various sensors 54, which are a collection of multiple types of sensors. The various sensors refer to, for example, temperature sensors that detect abnormally high temperatures of the inverters 10 and 20, but are not limited to this and refer to sensors related to various types of abnormality detection.

[0019] The control unit 50 drives the motor 4 in a so-called open winding mode by cooperatively controlling the switching of the inverter 10 and the switching of the inverter 20 in accordance with the voltage Vc1 across the capacitor C1, the voltage Vc2 across the capacitor C2, the motor current detected by the current detector 52, and the target speed of the motor 4.

[0020] Furthermore, when the voltage Vc1 of capacitor C1 detected by voltage detector 51 exceeds a predetermined threshold Vcs, the control unit 50 determines that regenerative power is being generated in the phase windings Lu, Lv, and Lw of motor 4 and that this regenerative power is being applied to capacitor C1 through inverter 10, and executes so-called regenerative power absorption control, which is a control to absorb the regenerative power of motor 4 into capacitor C2. Specifically, the control unit 50 forms mutual conductive paths in which one ends of the phase windings Lu, Lv, Lw are mutually conductive through the upper switch elements 11, 13, 15 and the respective freewheel diodes D1 of the upper switch elements 11, 13, 15 in the inverter 10 by turning on the upper switch elements 11, 13, 15 and turning off the lower switch elements 12, 14, 16 (or by turning off the upper switch elements 11, 13, 15 and turning on the lower switch elements 12, 14, 16), and forms a full-wave rectifier circuit for the voltage generated at the other end of the phase windings Lu, Lv, Lw of the motor 4 by turning off all of the switch elements 21 to 26 of the inverter 20 and by bringing the freewheel diodes D2 of the switch elements 21 to 26 into conduction as a result of the switching off, and causes the regenerative power of the motor 4 to be absorbed by the capacitor C2 through the full-wave rectifier circuit.

[0021] By implementing this regenerative power absorption control, it is possible to prevent the regenerative power of the motor 4 from being applied to the capacitor C1 through the inverter 10. In other words, the capacitance of the capacitor C1 is sufficient to remove high-frequency components from the voltage Vc1 generated across the capacitor C1 due to the switching of the inverters 10 and 20, and can be kept to, for example, several tens of μF. This makes it possible to eliminate the need for a circuit to prevent inrush current from the capacitor C1, contributing to the miniaturization and simplification of the circuit while maintaining safety. Furthermore, a small, low-capacity film capacitor can be used for the capacitor C1, rather than an electrolytic capacitor. On the other hand, an electrolytic capacitor with a larger capacitance than the capacitor C1, for example, several hundred μF, is used for the capacitor C2 in order to absorb the regenerative power.

[0022] The full-wave rectifier circuit 2, reactor 3, capacitor C1, inverters 10 and 20, capacitor C2, control unit 50, voltage detector 51, current detectors 52 and 55, abnormality detection unit 53, and various sensors 54 constitute a motor drive device that drives the motor 4.

[0023] The motor 4 is, for example, a motor for driving a compressor 61 in a refrigeration cycle system. The shaft of the compression mechanism (not shown) of the compressor 61 and the rotating shaft of the motor 4 are directly connected, i.e., integrally configured. Rotation of the rotating shaft of the motor 4 operates the compression mechanism of the compressor 61, compressing the refrigerant. One end of an outdoor heat exchanger 63 is connected to the discharge port of the compressor 61 via a four-way valve 62. One end of an indoor heat exchanger 65 is connected to the other end of the outdoor heat exchanger 63 via an electric expansion valve 64, which serves as a pressure reducer. The suction port of the compressor 61 is connected to the other end of the indoor heat exchanger 65 via the four-way valve 62. These piping connections form a heat pump refrigeration cycle. An outdoor fan 66 is disposed near the outdoor heat exchanger 63, and an indoor fan 67 is disposed near the indoor heat exchanger 65.

[0024] During cooling operation, as shown by the solid arrows in FIG. 1 , gas refrigerant discharged from the compressor 61 flows through the four-way valve 62 to the outdoor heat exchanger 63. The gas refrigerant that flows into the outdoor heat exchanger 63 releases heat to the outdoor air and condenses. The liquid refrigerant that flows out of this outdoor heat exchanger (condenser) 63 is depressurized by the electric expansion valve 64 and flows to the indoor heat exchanger 65. The liquid refrigerant that flows into the indoor heat exchanger 65 absorbs heat from the indoor air and evaporates. The gas refrigerant that flows out of this indoor heat exchanger (evaporator) 65 passes through the four-way valve 62 and is drawn into the compressor 61. During heating operation, the flow path of the four-way valve 62 is switched, so that the gas refrigerant discharged from the compressor 61 flows through the four-way valve 62 to the indoor heat exchanger 65 as shown by the dashed arrows in FIG. 1 . The gas refrigerant that flows into the indoor heat exchanger 65 releases heat to the indoor air and condenses. The liquid refrigerant flowing out from the indoor heat exchanger (condenser) 65 is decompressed by the electric expansion valve 64 and flows to the outdoor heat exchanger 63. The liquid refrigerant flowing into the outdoor heat exchanger 63 absorbs heat from the outside air and evaporates. The gas refrigerant flowing out from the outdoor heat exchanger (evaporator) 63 passes through the four-way valve 62 and is drawn into the compressor 61.

[0025] The four-way valve 62, electric expansion valve 64, fan motor 66M of outdoor fan 66, and fan motor 67M of indoor fan 67 are connected to an air conditioning controller 70, which is also connected to an abnormality detection unit 71 and various sensors 72. The abnormality detection unit 71 detects abnormalities in the heat pump refrigeration cycle and the fan motors 66M and 67M. The various sensors 72 are a collection of multiple sensors that detect indoor air temperature, outdoor air temperature, heat exchanger temperature, refrigerant temperature, and high-pressure pressure in the refrigeration cycle. The air conditioning controller 70 controls the four-way valve 62, electric expansion valve 64, and fan motors 66M and 67M based on the detection results of the abnormality detection unit 71 and the various sensors 72, and instructs the control unit 50 of the target speed of motor 4.

[0026] The control executed by the control unit 50 will be described with reference to the flowchart of FIG. 2. The control unit 50 performs normal operation (S1), in which the control unit 50 coordinates the switching of the inverter 10 and the inverter 20 to drive the motor 4 in an open winding state (open winding mode) and controls the on / off duty of the inverters 10 and 20 so that the speed of the motor 4 reaches a target speed specified by the air conditioning controller 70. During this normal operation, the control unit 50 compares the voltage Vc1 of the capacitor C1 detected by the voltage detector 51 with a predetermined threshold Vcs (S2). The threshold Vcs is used to determine whether regenerative power from the motor 4 (regenerative power resulting from the inertial energy of the motor 4, magnetic energy stored in the phase windings Lu, Lv, and Lw, and voltages induced in the phase windings Lu, Lv, and Lw due to rotation of the magnets in the rotor of the motor 4) is being applied to the capacitor C1 through the inverter 10.

[0027] For example, if the abnormality detection unit 53 detects an abnormality and the control unit 50 stops the switching of the inverters 10 and 20 to stop the drive of the motor 4 (protective stop), i.e., if all switch elements of the inverters 10 and 20 are turned off, the rotor of the motor 4 may continue to rotate due to inertia. In this case, inertial energy expressed as "(1 / 2) J ω^2" is generated depending on the inertia J and rotational speed ω of the motor 4. This inertial energy passes through the inverter 10 and attempts to be added to the capacitor C1 as regenerative power. In general, the energy that can be absorbed by a capacitor is expressed as "(1 / 2) C (V2^2 - V1^2)," where V1 is the voltage across the capacitor in a steady state, V2 is the voltage across the capacitor after an overvoltage occurs, and C is the capacitance of the capacitor. The voltage V2 across the capacitor is determined by the rated voltage of the full-wave rectifier circuit to which the capacitor is connected. Meanwhile, the amount of regenerative power that can be absorbed by a capacitor is determined by the capacitance C of the capacitor. In other words, the larger the capacitance C of the capacitor, the greater the amount of regenerative power that can be absorbed, and the smaller the capacitance C of the capacitor, the smaller the amount of regenerative power that can be absorbed. A capacitor with a small capacitance C cannot absorb large regenerative power and may malfunction. As described above, the capacitance of capacitor C1 is limited to a value that can remove high-frequency components generated by the switching of inverters 10 and 20. For this reason, the large regenerative power of motor 4 must be absorbed by capacitor C2, which has a larger capacitance than capacitor C1, without being applied to capacitor C1.

[0028] Therefore, when the voltage Vc1 of the capacitor C1 exceeds the threshold Vcs set slightly below the rated tolerance of the capacitor C1 (YES in S2), the control unit 50 determines that the regenerative power of the motor 4 is being generated and applied to the capacitor C1 through the inverter 10, and executes regenerative power absorption control to have the regenerative power of the motor 4 absorbed by the capacitor C2 (S3). That is, as shown in Fig. 3, the control unit 50 forms mutual conductive paths in which one ends of the phase windings Lu, Lv, Lw are mutually conductive through the upper switch elements 11, 13, 15 and the freewheeling diodes D1 of the upper switch elements 11, 13, 15 by turning on the upper switch elements 11, 13, 15 in the inverter 10 and turning off the lower switch elements 12, 14, 16, and turns off all the switch elements 21 to 26 in the inverter 20. When all the switch elements 21 to 26 of the inverter 20 are turned off, a full-wave rectifier circuit for the voltage generated at the other end of the phase windings Lu, Lv, Lw of the motor 4 is formed by the regenerative diodes D2 of the inverter 20.

[0029] A mutual conductive path is formed between one end of the phase windings Lu, Lv, Lw and the upper switch elements 11, 13, 15 and the respective freewheeling diodes D1 of the upper switch elements 11, 13, 15, so that the regenerative power of the motor 4 is cut off by the inverter 10 and does not flow to the capacitor C1. Then, a full-wave rectifier circuit for the voltage generated at the other end of the phase windings Lu, Lv, Lw is formed by the respective regenerative diodes D2 of the inverter 20, so that the regenerative power of the motor 4 is converted into a DC voltage by the inverter 20 and applied to the capacitor C2.

[0030] An example of the change in the voltage Vc1 of the capacitor C1 and the change in the voltage Vc2 of the capacitor C2 when regenerative power absorption control is being executed is shown in Fig. 4. Here, an example is shown in which the AC voltage Vc of the three-phase AC power supply 1 is set to 200 V and the threshold value Vcs is set to approximately 600 V. In Fig. 4, up to time point A, the motor is normally driven in the open winding mode, and the voltage Vc1 of the capacitor C1 is approximately 300 V, which is the full-wave rectified value of the AC voltage Vc of the three-phase AC power supply 1.

[0031] 4 shows an example in which the voltage Vc2 of the capacitor C2 is controlled to 300 V, which is approximately the same as the voltage Vc1 of the capacitor C1, by controlling the inverters 10 and 20, but other voltage values ​​are also possible. The voltage Vc2 of the capacitor C2 can be controlled to any value by controlling the inverters 10 and 20. Incidentally, a method for generating the voltage Vc2 of the capacitor C2 is described, for example, in Japanese Patent No. 6755845 filed by the applicant of the present application.

[0032] If, at time point A, the inverters 10 and 20 stop operating or the motor speed suddenly decelerates for some reason, regenerative power is generated by the motor 4. This regenerative power is applied to the capacitors C1 and C2, causing the voltages Vc1 and Vc2 of the capacitors C1 and C2 to rise. Then, at time point B, the voltage Vc1 of the capacitor C1 exceeds the threshold Vcs of approximately 600 V. If the voltage Vc1 of the capacitor C1 exceeds the threshold Vcs (YES in S2), the control unit 50 executes the regenerative power absorption control described above. As a result of this execution of the regenerative power absorption control, the current due to the regenerative power stops flowing to the capacitor C1 and instead flows to the capacitor C2, which has a larger capacity. Therefore, after time point B, the voltage Vc1 of the capacitor C1 does not increase any further and remains at the threshold Vcs of approximately 600 V.

[0033] Meanwhile, the voltage Vc2 of capacitor C2 increases due to the regenerative current, but because capacitor C2 has sufficient capacity, it is kept below 500 V even at peak times. At approximately 0.02 seconds in Figure 4, the generation of regenerative power ends, and the regenerative current ceases to flow to capacitor C2. After this point, the voltage Vc2 of capacitor C2 begins to gradually decrease due to the natural discharge of capacitor C2. Furthermore, once time has passed beyond the time shown in Figure 4, the voltage Vc1 of capacitor C1 also gradually decreases, eventually reaching approximately 300 V, the same as during normal operation.

[0034] In this way, by absorbing the regenerative power of the motor 4 into the capacitor C2 without applying it to the capacitor C1, it is possible to eliminate the problem of the voltage Vc1 of the capacitor C1 increasing sharply and becoming an overvoltage. Since no overvoltage occurs, it is possible to prevent damage to electrical components such as the capacitor C1 and the full-wave rectifier circuit 2.

[0035] If the capacitance of capacitor C1 were to be increased to deal with overvoltage, a large inrush current would flow into capacitor C1 when the three-phase AC power supply 1 was turned on, and an inrush current prevention circuit would have to be employed to deal with this inrush current. However, because the regenerative power of motor 4 is absorbed by capacitor C2 without being applied to capacitor C1, there is no need to increase the capacitance of capacitor C1, and this makes it possible to avoid the inrush current from flowing into capacitor C1. By keeping all switch elements 11 to 16 of inverter 10 off when the three-phase AC power supply 1 is turned on, the inrush current does not flow into capacitor C2.

[0036] Since no inrush current flows, there is no need to employ an inrush prevention circuit, and it is also possible to reduce the capacity of the reactor 3. This makes it possible to miniaturize the circuit scale of the motor drive device as much as possible.

[0037] The voltage Vc2 of the capacitor C2 can be adjusted to any value by controlling the input power from the motor 4 to the inverter 20. This makes it possible to suppress pulsation of the motor 4 by instantaneously outputting active power from the capacitor C2 and the inverter 20, and also makes it possible to expand the operating speed range of the motor 4 by instantaneously outputting reactive power from the capacitor C2 and the inverter 20.

[0038] Subsequently, after the execution of the regenerative power absorption control, the control unit 50 determines whether a condition for canceling the regenerative power absorption control is satisfied (S4). Examples of conditions for the cancellation include the passage of a predetermined period of time, cancellation of the abnormality detection by the abnormality detection unit 53 (cancellation of the protective stop), and a change in the target speed instructed by the air conditioning controller 70. The compressor 61 is a high-load device that requires a high torque to compress the refrigerant to a high pressure. Therefore, once the supply of power to the motor 4 that drives the compressor 61 is stopped, the compressor rotates for a very short time due to inertia. Therefore, if time is used as a criterion for determining whether to cancel the regenerative power absorption control, 0.1 seconds from the start of the regenerative power absorption control is sufficient.

[0039] If the voltage Vc1 is equal to or lower than the threshold value Vcs in step S2 (NO in S2), the control unit 50 determines that the situation is not such that regenerative power is generated by the motor 4, and continues normal operation (S1). In the above embodiment, in the regenerative power absorption control, as shown in Fig. 3, mutual conduction paths are formed by turning on the upper switch elements 11, 13, 15 and turning off the lower switch elements 12, 14, 16 in the inverter 10, whereby one ends of the phase windings Lu, Lv, Lw are mutually connected through the upper switch elements 11, 13, 15 and the respective freewheel diodes D1 of those upper switch elements 11, 13, 15. However, this is not limiting, and mutual conduction paths may also be formed by turning off the upper switch elements 11, 13, 15 and turning on the lower switch elements 12, 14, 16 in the inverter 10, whereby one ends of the phase windings Lu, Lv, Lw are mutually connected through the lower switch elements 12, 14, 16 and the respective freewheel diodes D1 of those lower switch elements 12, 14, 16, as shown in Fig. 5. Regenerative power can also be absorbed by the capacitor C2 with this switching pattern.

[0040] [2] A second embodiment will be described. In the first embodiment, the start of regenerative power absorption control is determined based on an increase in the voltage Vc1 of the capacitor C1. In the second embodiment, however, the control unit 50 executes regenerative power absorption control when the decrease amount "-ΔH" of the speed H of the motor 4 exceeds a predetermined threshold value "-ΔHs". The other configurations are the same as those of the first embodiment.

[0041] As shown in the flowchart of Fig. 6, during normal operation (S1), the control unit 50 controls the switching of the inverter 10 so that the speed of the motor 4 becomes the target speed specified by the air conditioning controller 70. The control unit 50 compares the amount of decrease "-ΔH" in the speed H of the motor 4 with a predetermined threshold value "-ΔHs" (S2a). The amount of decrease "-ΔH" in the speed H of the motor 4 corresponds to the amount of decrease in the target speed specified by the air conditioning controller 70. The threshold value "-ΔHs" is used to determine whether a sudden decrease in the target speed (a sudden decrease in the output frequency of the inverter 10) is causing an induced voltage (regenerative power) to be generated in the phase windings Lu, Lv, and Lw of the motor 4.

[0042] For example, if the target speed suddenly decreases but the rotor continues to rotate due to inertia according to the target speed up to that point, regenerative energy is generated in the motor 4. This regenerative energy is intended to be added to the inverter 10 and the capacitor C1 as regenerative power of the motor 4.

[0043] If the decrease in speed H "-ΔH" is equal to or less than the threshold value "-ΔHs" (NO in S2a), the control unit 50 determines that the situation is not such that regenerative power is generated by the motor 4, and continues normal operation (S1).

[0044] If the reduction amount "-ΔH" of the speed H exceeds the threshold value "-ΔHs" (YES in S2a), the control unit 50 determines that the motor 4 is generating regenerative power and executes regenerative power absorption control (S3). This regenerative power absorption control is the same as the regenerative power absorption control of the first embodiment, and the effects obtained by executing this regenerative power absorption control are also the same as those of the first embodiment. Note that, although the reduction amount of the speed H of the motor 4 is the reduction amount of the target speed instructed by the air conditioning controller 70 here, the actual motor speed may be detected or estimated, and the reduction amount of this actual speed of the motor 4 may be replaced with the above-mentioned speed H.

[0045] As the regenerative power absorption control is executed, the control unit 50 determines whether a condition for canceling the regenerative power absorption control is met (S4). The condition for canceling the control may be met when a predetermined period of time has elapsed, when the target speed instructed by the air conditioning controller 70 is changed, or the like.

[0046] This method makes it possible to detect or predict the generation of regenerative energy before the voltage Vc1 of the capacitor C1 in the first embodiment exceeds the threshold Vcs. However, since this method can only handle cases where the rotation speed of the motor 4 suddenly decreases, it is desirable to use it in combination with the first embodiment.

[0047] [3] A third embodiment will be described. In the third embodiment, the control unit 50 executes regenerative power absorption control when the power P supplied from the inverter 10 to the phase windings Lu, Lv, Lw of the motor 4 becomes negative, and also executes regenerative power absorption control when the decrease "-ΔP" in the power P supplied from the inverter 10 to the phase windings Lu, Lv, Lw of the motor 4 exceeds a predetermined threshold "-ΔPs". The other configurations are the same as those of the first embodiment.

[0048] As shown in the flowchart of FIG. 7 , during normal operation, the control unit 50 controls the switching of the inverter 10 so that the speed of the motor 4 becomes the target speed instructed by the air conditioning controller 70 (S1). In this operation, the control unit 50 calculates the supply power P from the inverter 10 to the phase windings Lu, Lv, Lw based on the output voltage of the inverter 10 corresponding to the output frequency of the inverter 10 and the motor current (load current) detected by the current detector 52, and if there is a downward change in the calculated supply power P, calculates the amount of decrease "-ΔP" (S21).

[0049] The control unit 50 then determines whether the calculated supply power P is a negative value (S22). The supply power P will be a positive value if no regenerative power is being generated by the motor 4, and will be a positive value if the supply power P is greater than the regenerative power even if the motor 4 is generating regenerative power, but will be a negative value if the supply power P is less than the regenerative power of the motor 4.

[0050] If the supply power P is not a negative value (YES in S1), the control unit 50 compares the calculated decrease amount "-ΔP" with a predetermined threshold value "-ΔPs" (S23). The threshold value "-ΔPs" is used to determine whether a sudden decrease in the target speed (a sudden decrease in the output frequency of the inverter 10) is causing the motor 4 to generate regenerative power.

[0051] For example, if the target speed suddenly decreases but the rotor continues to rotate due to inertia according to the target speed up to that point, regenerative energy is generated in the motor 4. This regenerative energy is intended to be added to the inverter 10 and the capacitor C1 as regenerative power of the motor 4.

[0052] If the decrease in the supply power P "-PH" is equal to or less than the threshold value "-ΔPs" (NO in S23), the control unit 50 determines that the situation is not such that regenerative power is being generated by the motor 4, and continues normal operation (S1).

[0053] If the decrease amount "-P" of the supplied power P exceeds the threshold value "-ΔPs" (YES in S23), the control unit 50 determines that the situation is such that regenerative power is being generated by the motor 4, and executes regenerative power absorption control (S3). This regenerative power absorption control is the same as the regenerative power absorption control in the first embodiment, and the effects obtained by executing this regenerative power absorption control are also the same as those in the first embodiment.

[0054] As the regenerative power absorption control is executed, the control unit 50 determines whether a condition for canceling the regenerative power absorption control is met (S4). The condition for canceling the control may be met when a predetermined period of time has elapsed, when the target speed instructed by the air conditioning controller 70 is changed, or the like.

[0055] [4] A fourth embodiment will be described. In the fourth embodiment, the control unit 50 executes the regenerative power absorption control when a stop command to the motor 4 is received from the air conditioning controller 70. The other configurations are the same as those in the first embodiment.

[0056] As shown in the flowchart of Fig. 8, during normal operation, the control unit 50 controls the switching of the inverter 10 so that the speed of the motor 4 becomes the target speed instructed by the air conditioning controller 70 (S1), and monitors stop instructions for the motor 4 (S2b). Stop instructions for the motor 4 include a stop instruction from the air conditioning controller 70, a stop instruction (protective stop) issued when the abnormality detection unit 53 detects an abnormality, and a stop instruction (overcurrent abnormality stop instruction) issued by the control unit 50 itself when the motor current detected by the current detector 52 abnormally increases. Note that abnormalities detected by the abnormality detection unit 53 include an abnormal increase or decrease in the AC voltage of the three-phase AC power supply 1, an abnormal AC current of the three-phase AC power supply 1, and loss of synchronization of the motor 4.

[0057] If there is no instruction to stop the motor 4 (NO in S2b), the control unit 50 determines that the situation is not such that regenerative power is generated by the motor 4, and continues normal operation (S1).

[0058] When a stop command is issued to the motor 4, the control unit 50 immediately stops the switching of the inverter 10, but the rotor of the motor 4 may continue to rotate due to inertia and generate regenerative energy. This regenerative energy attempts to be applied to the inverter 10 and the capacitor C1 from the phase windings Lu, Lv, and Lw as regenerative power.

[0059] Therefore, when a stop command to the motor 4 is issued (YES in S2b), the control unit 50 determines that there is a high possibility that regenerative power will be generated by the motor 4, and executes regenerative power absorption control (S3). This regenerative power absorption control is the same as the regenerative power absorption control of the first embodiment, and the effects obtained by executing this regenerative power absorption control are also the same as those of the first embodiment.

[0060] As the regenerative power absorption control is executed, the control unit 50 determines whether a condition for canceling the regenerative power absorption control is met (S4). The condition for canceling the control may be, for example, when the stop instruction to the motor 4 is released, a predetermined period of time has elapsed, or when the target speed instructed by the air conditioning controller 70 is changed.

[0061] [5] A fifth embodiment will be described. As shown in Fig. 9, a positive line P3 and a negative line N3 of an inverter (third inverter) 30 are connected to both ends of a capacitor C2, and a fan motor (three-phase permanent magnet synchronous motor) 67M of the indoor fan 67 in Fig. 1 is connected to three-phase terminals Cu, Cv, and Cw of the inverter 30. Furthermore, a positive line P4 and a negative line N4 of an inverter (fourth inverter) 40 are connected to both ends of the capacitor C2, and a fan motor (three-phase permanent magnet synchronous motor) 68M of the outdoor fan 68 in Fig. 1 is connected to three-phase terminals Du, Dv, and Dw of the inverter 40.

[0062] According to this configuration, the regenerative power absorbed by the capacitor C2 can be effectively used as power to drive the fan motors 67M and 68M. The other configurations and effects are the same as those of the first embodiment.

[0063] The first to fifth embodiments described above each illustrate an example in which different criteria are used when generating or predicting regenerative power. The criteria in each of these embodiments may be appropriately selected and combined. The above-described embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. These novel embodiments and modifications may be embodied in various other forms, and various omissions, rewrites, and modifications may be made without departing from the spirit of the invention. These embodiments and modifications are intended to fall within the spirit of the invention, as well as within the scope of the claims and their equivalents.

[0064] 1...Three-phase AC power supply, 2...Full-wave rectifier circuit, 3...Reactor, 4...Open winding motor, Lu, Lv, Lw...Phase windings, C1...Capacitor (first capacitor), 10...Inverter (first inverter), 20...Inverter (second inverter), C2...Capacitor (second capacitor), 50...Control unit, 61...Compressor, 62...Four-way valve, 63...Outdoor heat exchanger, 65...Indoor heat exchanger, 66...Outdoor fan, 67...Indoor fan, 70...Air conditioning controller.

Claims

1. A motor drive device for a motor having a plurality of phase windings that are not connected to each other, comprising: a rectifier circuit that rectifies the voltage of an AC power source; a first capacitor connected to a terminal of the rectifier circuit; a first inverter including a plurality of first switch elements and a first diode connected in anti-parallel to each of the first switch elements, and connected between the first capacitor and one end of each of the phase windings; a second inverter including a plurality of second switch elements and a second diode connected in anti-parallel to each of the second switch elements, and connected to the other end of each of the phase windings; a second capacitor connected to the other end of each of the phase windings via the second inverter; and a control unit that performs regenerative power absorption control such that the regenerative power of the motor is absorbed by the second capacitor through the rectifier circuit formed.

2. A motor drive device as described in claim 1, wherein the capacitance of the first capacitor is large enough to remove high-frequency components from the voltage generated in the first capacitor that are generated by switching of the first inverter and the second inverter, and the capacitance of the second capacitor is larger than the capacitance of the first capacitor.

3. The motor drive device according to claim 1, wherein the control unit executes the regenerative power absorption control when the voltage of the first capacitor exceeds a threshold value.

4. The motor drive device according to claim 1 or 3, wherein the control unit executes the regenerative power absorption control when an amount of decrease in speed of the motor exceeds a threshold value.

5. A motor drive device as described in claim 1 or 3, wherein the control unit executes the regenerative power absorption control when the power supplied from the first inverter to each phase winding becomes a negative value, and executes the regenerative power absorption control when the amount of decrease in the power supplied from the first inverter to each phase winding exceeds a threshold value.

6. The motor drive device according to claim 1 or 3, wherein the control unit executes the regenerative power absorption control when a stop command is issued to the motor.

7. The motor drive device according to claim 1, further comprising a third inverter that converts the voltage of the second capacitor into power for driving another motor.

8. A refrigeration cycle device equipped with the motor drive device according to claim 1, comprising a compressor driven by the motor for sucking in, compressing and discharging a refrigerant, and a heat pump type refrigeration cycle in which the refrigerant discharged from the compressor is passed through a four-way valve, a condenser, a pressure reducer and an evaporator before being returned to the suction side of the compressor.

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