Inverter device and refrigeration cycle device

Abstract

This inverter device includes a switching circuit and a controller. The switching circuit includes a plurality of series circuits each having switch elements on the upstream side and switch elements on the downstream side along the direction in which a DC voltage is to be applied, and phase windings of a motor are connected to the respective interconnection points of the switch elements of these series circuits. The controller detects the value of a phase current flowing between the switching circuit and each phase winding for each formation while sequentially forming a plurality of energization paths through which current flows in a predetermined direction of each phase winding through each switch element, and determines abnormality of the motor and abnormality of each switch element on the basis of the ratio of a maximum value and a minimum value among values of each phase current detected by a phase check operation.

Description

Inverter device and refrigeration cycle device

[0001] An embodiment of the present invention relates to an inverter device connected to a motor having a plurality of phase windings and outputting drive power to the motor, and a refrigeration cycle device using the inverter device.

[0002] An inverter device connected to a motor having multiple phase windings and outputting drive power to the motor includes a switching circuit that converts a DC voltage into an AC voltage of a predetermined frequency by switching. The switching circuit includes multiple series circuits, each of which has an upstream switch element and a downstream switch element along the direction of application of the DC voltage. The interconnection points of the switch elements in these series circuits are connected to the respective phase windings of the motor.

[0003] JP 2019-187187 A International Publication No. 2023-181306 A

[0004] If a motor malfunctions, such as poor insulation in one of the phase windings or an open circuit failure in one of the switching elements of the switching circuit, the motor cannot be driven properly. Patent Documents 1 and 2 propose methods for detecting such malfunctions. For example, the malfunction detection method disclosed in Patent Document 2 detects the phase currents flowing through each phase winding of the motor and determines whether the detected phase currents are within an appropriate range. However, because normal current values ​​vary depending on the motor's specifications, it is difficult to determine the appropriate range. In addition to the method disclosed in Patent Document 2 that detects each phase current individually, there is also an example in which a shunt resistor is installed in the DC path of the switching circuit and each phase current is detected through the shunt resistor. In this example, only one phase current can be detected simultaneously, resulting in low current detection accuracy and making it difficult to determine whether the current is normal or abnormal.

[0005] An object of the embodiments of the present invention is to provide an inverter device that can accurately and quickly detect abnormalities in a motor and in each switch element.

[0006] In one embodiment, an inverter device is connected to a motor having multiple phase windings, the inverter device including a switching circuit including a plurality of series circuits each including an upstream switch element and a downstream switch element in a direction of application of a DC voltage, the phase windings being connected to interconnection points of the switch elements of the series circuits, and a controller for controlling the switching circuit. The controller sequentially forms a plurality of current paths through which current flows in a predetermined direction through the phase windings through the switch elements, and performs a phase check operation for each of the paths to detect values ​​of phase currents flowing between the switching circuit and the phase windings, and determines whether there is an abnormality in the motor or each of the switch elements based on the ratio between the maximum and minimum values ​​of the phase currents detected in these phase check operations.

[0007] FIG. 1 is a block diagram showing the circuit configuration of an inverter device according to one embodiment. FIG. 2 is a flowchart showing control details in a controller according to the embodiment. FIG. 3 is a diagram showing a switching pattern of a check operation for each phase according to the embodiment, along with the presence or absence of a current in each phase. FIG. 4 is a diagram showing the current during a W-phase check operation according to the embodiment. FIG. 5 is a diagram showing the current during a V-phase check operation according to the embodiment. FIG. 6 is a diagram showing the current during a U-phase check operation according to the embodiment. FIG. 7 is a diagram showing the current during an X-phase check operation according to the embodiment. FIG. 8 is a diagram showing the current during a Z-phase check operation according to the embodiment. FIG. 9 is a diagram showing the current during a Y-phase check operation according to the embodiment. FIG. 10 is a diagram showing the phase current values ​​during a check of each phase when a short-circuit fault occurs in any of the phase windings of the motor according to the embodiment. FIG. 11 is a diagram showing the phase current values ​​during a check of each phase when an open-circuit fault occurs in any of the switch elements according to the embodiment. FIG. 12 is a diagram showing the configuration of a refrigeration cycle equipped with an inverter device according to the embodiment.

[0008] An embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 1, an inverter device 10 according to this embodiment is connected to an AC power supply 1. The inverter device 10 includes a diode-bridge full-wave rectifier circuit (rectifier circuit) 2 that full-wave rectifies an AC voltage Vc from the AC power supply 1, a smoothing capacitor 3 that smooths a DC voltage Vd output from the full-wave rectifier circuit 2, a switching circuit 20 that converts the DC voltage V of the smoothing capacitor 3 into a three-phase AC voltage of a predetermined frequency by switching, a positive-side DC current path Lp between the switching circuit 20 and the smoothing capacitor 3, a negative-side DC current path Ln, and a shunt resistor Rs for current detection inserted in series in, for example, the negative-side DC current path Ln, and a controller 30 that controls the switching of the switching circuit 20. The shunt resistor Rs may be located on the positive-side DC current path Lp side, not necessarily on the negative-side DC current path Ln side.

[0009] The output voltage of the switching circuit 20 is supplied as drive power to a brushless DC motor (abbreviated as "motor") M. The full-wave rectifier circuit 2 and smoothing capacitor 3 constitute a DC circuit that converts the AC voltage Vc into a DC voltage Vd and supplies it to the switching circuit 20.

[0010] The motor M is, for example, a compressor motor mounted in an air conditioner, and is composed of a stator having three phase windings Lu, Lv, and Lw star-connected around a neutral point C, and a rotor having a permanent magnet. The unconnected ends of the phase windings Lu, Lv, and Lw are connected to the output terminal of a switching circuit 20. The rotor rotates due to the interaction between the magnetic field generated by the phase windings Lu, Lv, and Lw and the magnetic field created by the permanent magnet. Note that the connection of the phase windings Lu, Lv, and Lw of the motor M is not limited to star connection, and may be a delta connection.

[0011] The switching circuit 20, which is a three-phase inverter circuit, is configured with: input terminals P and N to which the DC voltage Vd of the smoothing capacitor 3 is applied through a positive-side DC current path Lp and a negative-side DC current path Ln; a ​​first series circuit connected between the input terminals P and N and made up of a switch element Tu on the upstream side in the direction of application of the DC voltage Vd and a switch element Tx on the downstream side; a second series circuit connected between the input terminals P and N and made up of a switch element Tv on the upstream side in the direction of application of the DC voltage Vd and a switch element Ty on the downstream side; and a third series circuit connected between the input terminals P and N and made up of a switch element Tw on the upstream side in the direction of application of the DC voltage Vd and a switch element Tz on the downstream side.

[0012] An unconnected end of the phase winding Lu is connected to an interconnection point (output terminal) Qa of the switch elements Tu, Tx in the first series circuit, an unconnected end of the phase winding Lv is connected to an interconnection point (output terminal) Qb of the switch elements Tv, Ty in the second series circuit, and an unconnected end of the phase winding Lw is connected to an interconnection point (output terminal) Qc of the switch elements Tw, Tz in the third series circuit.

[0013] Both ends of the shunt resistor Rs are connected to the controller 30 , and both ends of the smoothing capacitor 3 are connected to the controller 30 .

[0014] The controller 30 includes a current detection unit 30a that detects phase currents Iu, Iv, Iw, Ix, Iy, and Iz flowing through the phase windings Lu, Lv, and Lw based on the voltage generated across the shunt resistor Rs; a voltage detection unit 30b that detects the AC voltage Vc of the AC power supply 1 based on the DC voltage Vd of the smoothing capacitor 3; a determination unit 30c that determines whether there is an abnormality in the motor M and an abnormality in the switch elements Tu to Tz of the switching circuit 20 based on the detection result of the current detection unit 30a; a first control unit 30d that controls the start and stop of the motor M in accordance with the determination result of the determination unit 30c and an external command; and a second control unit 30e that estimates the rotational speed (number of rotations) of the motor M based on the detection result of the current detection unit 30a and controls the switching of the switch elements Tu to Tz so that the rotational speed becomes a target rotational speed (target number of rotations) in accordance with the external command. Here, the phase currents Iu, Iv, Iw, Ix, Iy, and Iz refer to the currents that flow through the switching elements Tu, Tv, Tw, Tx, Ty, and Tz of the switching circuit 20 when the elements are on during the phase check operation described below.

[0015] In particular, the determination unit 30c performs U-phase check operation through Z-phase check operation, which sequentially forms a plurality of current paths (first through sixth current paths) through which current flows in a predetermined direction in the phase windings Lu, Lv, and Lw by turning on a predetermined number of switch elements among the switch elements Tu through Tz of the switching circuit 20, and sequentially detects, via the current detection unit 30a, the values ​​of phase currents Iu, Iv, Iw, Ix, Iy, and Iz flowing between the switching circuit 20 and the motor M for each current path formed. Note that, because a single shunt resistor Rs is used to detect the phase currents Iu through Iz, the determination unit 30c detects only one phase current at each timing of the first through sixth current paths. Then, the judgment unit 30c selects the maximum value Imax and the minimum value Imin from the values ​​of the phase currents Iu to Iz detected in the check operation for each phase, and judges whether there is an abnormality in the motor M or an abnormality in the switch elements Tu to Tz based on the ratio α (= Imax / Imin) between the selected maximum value Imax and minimum value Imin.

[0016] In addition, the first control unit 30d executes the judgment of the judgment unit 30c before starting the motor M, and if the result of the judgment shows that there is no abnormality, starts the motor M, and if the result of the judgment shows that there is an abnormality, stops the start of the motor M and notifies the user of the abnormality.

[0017] Furthermore, during the execution of the determination process of the determination unit 30c, the second control unit 30e variably sets the predetermined period t, which is the on-period of each switch element during the phase check operation, in accordance with the value of the AC voltage Vc detected by the voltage detection unit 30b. Specifically, the second control unit 30e shortens the predetermined period t by a period Δt1 when the AC voltage Vc is higher than a predetermined reference value, and extends the predetermined period t by the period Δt1 when the AC voltage Vc is lower than the reference value, so that the phase current during the normal phase check operation is stable regardless of fluctuations in the AC voltage Vc. In this way, adjusting the predetermined period t in accordance with the value of the AC voltage Vc enables the determination unit 30c to make an appropriate determination regardless of fluctuations in the AC voltage Vc. Furthermore, adjusting the predetermined period t in accordance with the value of the AC voltage Vc prevents damage to the switch elements Tu to Tz due to overcurrent when the AC voltage Vc increases.

[0018] The control executed by the controller 30 will be described with reference to the flowchart of Fig. 2. (W-Phase Check Operation) When starting the motor M is required (YES in S1), the controller 30 executes a W-phase check operation prior to the start of the motor M (S2). Specifically, the controller 30 supplies a pulsed gate signal that turns on the switch elements Tw, Tx, and Ty for a predetermined period t while maintaining the switch elements Tu, Tv, and Tz in an off state as shown in Fig. 3. This establishes a first current path for checking the W-phase, in which current flows from the positive terminal of the smoothing capacitor 3 to the positive-side DC current path Lp, the positive-side terminal P, the switch element Tw, the interconnection point Qc, the phase winding Lw, the phase windings Lu and Lv, the interconnection points Qa and Qb, the switch elements Tx and Ty, the negative terminal N, the negative-side DC current path Ln, the shunt resistor Rs, and the negative terminal of the smoothing capacitor 3, as shown by the dashed line and arrows in Fig. 4. When setting this, the controller 30 adjusts the predetermined period t, which is the on period of the switch elements Tw, Tx, and Ty, in accordance with the value of the AC voltage Vc (or the value of the DC voltage Vd after rectifying the AC voltage Vc), so that the above-mentioned first current path phase current Iw, i.e., the current flowing through the switch element Tw, is stable regardless of fluctuations in the AC voltage Vc.

[0019] Then, the controller 30 detects the value of the phase current Iw based on the voltage generated across the shunt resistor Rs, and stores the detection result in the internal memory (S3).

[0020] (V-Phase Check Operation) Following the W-phase check operation, the controller 30 executes a V-phase check operation (S4). Specifically, the controller 30 supplies pulsed gate signals that turn on the switch elements Tv, Tx, and Tz for a predetermined period t while maintaining the switch elements Tu, Tw, and Ty in an off state as shown in FIG. 3. This sets up a second current path for V-phase check, in which current flows from the positive terminal of the smoothing capacitor 3 to the positive-side DC current path Lp, the positive terminal P, the switch element Tv, the interconnection point Qb, the phase winding Lv, the phase windings Lu and Lw, the interconnection points Qa and Qc, the switch elements Tx and Tz, the negative terminal N, the negative-side DC current path Ln, the shunt resistor Rs, and the negative terminal of the smoothing capacitor 3, as indicated by the dashed lines and arrows in FIG. 5. In this operation, the controller 30 also adjusts the predetermined period t, which is the on period of the switch elements Tv, Tx, and Tz, in accordance with the value of the AC voltage Vc.

[0021] Then, the controller 30 detects the value of the phase current Iv of the second current path based on the voltage generated across the shunt resistor Rs, and stores the detection result in the internal memory (S5).

[0022] (U-Phase Check Operation) Following the V-phase check operation, the controller 30 executes a U-phase check operation (S6). Specifically, the controller 30 supplies pulsed gate signals that turn on the switch elements Tu, Ty, and Tz for a predetermined period t while maintaining the switch elements Tv, Tw, and Tx in an off state as shown in FIG. 3. This sets up a third current path for checking the U-phase, through which current flows from the positive terminal of the smoothing capacitor 3 to the positive DC current path Lp, the positive terminal P, the switch element Tu, the interconnection point Qa, the phase winding Lu, the phase windings Lv and Lw, the interconnection points Qb and Qc, the switch elements Ty and Tz, the negative terminal N, the negative DC current path Ln, the shunt resistor Rs, and the negative terminal of the smoothing capacitor 3, as indicated by the dashed lines and arrows in FIG. 6. Here, too, the controller 30 adjusts the predetermined period t, which is the on period of the switch elements Tu, Ty, and Tz, in accordance with the value of the AC voltage Vc.

[0023] Then, the controller 30 detects the value of the phase current Iu in the third current path based on the voltage generated across the shunt resistor Rs, and stores the detection result in the internal memory (S7).

[0024] (X-Phase Check Operation) Following the U-phase check operation, the controller 30 executes the X-phase check operation (S8). Specifically, the controller 30 supplies pulsed gate signals that turn on the switch elements Tv, Tw, and Tx for a predetermined period t while maintaining the switch elements Tu, Ty, and Tz in an off state as shown in FIG. 3, thereby establishing a fourth current path through which current flows from the positive terminal of the smoothing capacitor 3 to the positive-side DC current path Lp, the positive terminal P, the switch elements Tv and Tw, the interconnection points Qb and Qc, the phase windings Lv and Lw, the phase winding Lu, the interconnection point Qa, the switch element Tx, the negative terminal N, the negative-side DC current path Ln, the shunt resistor Rs, and the negative terminal of the smoothing capacitor 3, as indicated by the dashed lines and arrows in FIG. 7. In this establishment, the controller 30 adjusts the predetermined period t, which is the on period of the switch elements Tv, Tw, and Tx, in accordance with the value of the AC voltage Vc.

[0025] Then, the controller 30 detects the value of the phase current Ix of the fourth current path based on the voltage generated across the shunt resistor Rs, and stores the detection result in the internal memory (S9).

[0026] (Z-Phase Check Operation) Following the X-phase check operation, the controller 30 executes a Z-phase check operation (S10). Specifically, the controller 30 supplies pulsed gate signals that turn on the switch elements Tu, Tv, and Tz for a predetermined period t while maintaining the switch elements Tw, Tx, and Ty in an off state as shown in FIG. 3 , thereby establishing a fifth current path through which current flows from the positive terminal of the smoothing capacitor 3 → positive-side DC current path Lp → positive terminal P → switch elements Tu and Tv → interconnection points Qa and Qb → phase windings Lu and Lv → phase winding Lw → interconnection point Qc → switch element Tz → negative terminal N → negative-side DC current path Ln → shunt resistor Rs → negative terminal of the smoothing capacitor 3, as indicated by the dashed lines and arrows in FIG. 8 . In this establishment, the controller 30 adjusts the predetermined period t, which is the on period of the switch elements Tu, Tv, and Tz, in accordance with the value of the AC voltage Vc.

[0027] Then, the controller 30 detects the value of the phase current Iz of the fifth current path based on the voltage generated across the shunt resistor Rs, and stores the detection result in the internal memory (S11).

[0028] (Y-Phase Check Operation) Following the Z-phase check operation, the controller 30 executes a Y-phase check operation (S12). Specifically, the controller 30 supplies pulsed gate signals that turn on the switch elements Tu, Tw, and Ty for a predetermined period t while maintaining the switch elements Tv, Tx, and Tz in an off state as shown in FIG. 3 , thereby establishing a sixth current path through which current flows from the positive terminal of the smoothing capacitor 3 → positive-side DC current path Lp → positive terminal P → switch elements Tu and Tw → interconnection points Qa and Qc → phase windings Lu and Lw → phase winding Lv → interconnection point Qb → switch element Ty → negative terminal N → negative-side DC current path Ln → shunt resistor Rs → negative terminal of the smoothing capacitor 3, as indicated by the dashed lines and arrows in FIG. 9 . In this establishment, the controller 30 adjusts the predetermined period t, which is the on period of the switch elements Tu, Tw, and Ty, in accordance with the value of the AC voltage Vc.

[0029] Then, the controller 30 detects the value of the phase current Iy in the sixth current path based on the voltage generated across the shunt resistor Rs, and stores the detection result in the internal memory (S13).

[0030] (Determination of Abnormality) After the Y-phase check operation is completed, the controller 30 selects the maximum value Imax and the minimum value Imin from the values ​​of the six phase currents Iu, Iv, Iw, Ix, Iy, and Iz stored in the internal memory (S14). The controller 30 then calculates the ratio α (= Imax / Imin) between the selected maximum value Imax and minimum value Imin (S15), and determines whether the calculated ratio α is less than a threshold value αs (α<αs) (S16).

[0031] If the ratio α is less than the threshold value αs (YES in S16), the controller 30 determines that the motor M and the switch elements Tu to Tz are normal (S17), and starts the motor M (S18).

[0032] If the ratio α is equal to or greater than the threshold value αs (NO in S16), the controller 30 determines that there is an abnormality in the motor M or one of the switch elements Tu to Tz (S19), and does not start the motor M, maintaining it in a stopped state (S20).The controller 30 then stores the details of the abnormality in its internal memory and notifies an external maintenance person or the like by displaying the details on the display or communicating via network (S21).

[0033] The current values ​​during normal operation vary depending on the specifications of the motor M. When a large-capacity motor M is used, the phase current values ​​Iu to Iz are generally larger, while when a small-capacity motor M is used, the phase current values ​​Iu to Iz are generally smaller. For this reason, it is difficult to determine whether a motor M has an abnormality using the same phase current value (threshold value). Even when the specifications of the motor M are the same, variations in the phase current values ​​occur due to manufacturing variations in the phase windings and differences in the rotor's stopping position during phase check operations—specifically, the position of the magnets attached to the rotor. Taking these factors into consideration, it has been found that it is preferable to use the ratio α (= Imax / Imin) of the maximum value Imax of each phase current to the minimum value Imin of each phase current as an indicator for determining whether a malfunction occurs. That is, regardless of the specifications and various variations of the motor M, when the motor M and switching circuit 20 are normal, the ratio α (= Imax / Imin) of the maximum value Imax of each phase current to the minimum value Imin of each phase current falls within a low value close to "1." On the other hand, if some abnormality occurs, the ratio α (= Imax / Imin) of the maximum value Imax of each phase current to the minimum value Imin of each phase current will be large. Therefore, by using the ratio α of the maximum value Imax of each phase current to the minimum value Imin of each phase current for abnormality determination, it becomes extremely easy to set the determination threshold αs, and it becomes possible to use the same threshold, for example, "2", even if the specifications of the motor M are different.

[0034] If a short-circuit fault occurs in the phase winding Lv of the motor M, that is, if there is current leakage from the phase winding Lv, the phase currents Iv and Iy will each increase significantly as shown in FIG. 10 during a V-phase check (FIG. 5) in which the phase current Iv flows through the phase winding Lv and currents branching from the phase current Iv flow through the phase windings Lu and Lw, and during a Y-phase check (FIG. 9) in which the phase current Iy branches off into the phase windings Lu and Lw and the currents passing through the phase windings Lu and Lw join together and flow through the phase winding Lv.

[0035] In this case, the controller 30 selects the larger of the phase currents Iv and Iy, that is, approximately 32 A, as the maximum value Imax, and selects the smallest phase current Iw, that is, 11 A, as the minimum value Imin (S14), and calculates the ratio α between the maximum value Imax and the minimum value Imin (= Imax / Imin = 32 / 11 = 2.91) (S15). This ratio α is a value equal to or greater than the threshold value αs (= 2).

[0036] If the calculated ratio α is equal to or greater than the threshold value αs (NO in S16), the controller 30 determines that there is a short-circuit fault in one of the phase windings Lu, Lv, Lw (S19), and keeps the motor M stopped without starting it (S20). It also stores in its internal memory the fact that there is a short-circuit fault in one of the phase windings Lu, Lv, Lw and notifies an external maintenance person or the like by displaying the fault on a display screen or communicating via a network (S21).

[0037] Furthermore, for example, if an open circuit fault occurs in the switch element Tx of the switching circuit 20, that is, if the switch element Tx cannot be turned on even when an attempt is made to turn it on, of the phase current Iw ( FIG. 4 ) during a W-phase check operation in which the switch elements Tw, Tx, and Ty are turned on to form the first current path, the phase current Iv ( FIG. 5 ) during a V-phase check operation in which the switch elements Tv, Tx, and Tz are turned on to form the second current path, and the phase current Ix ( FIG. 7 ) during an X-phase check operation in which the switch elements Tv, Tw, and Tx are turned on to form the fourth current path, only the phase current Ix of the fourth current path, in which current flow is completely cut off, becomes “0” as shown in FIG. 11 .

[0038] Next, the controller 30 selects the phase current Iz as the maximum value Imax and the phase current Ix as the minimum value Imin (S14), and calculates the ratio α (=Imax / Imin) between the maximum value Imax and the minimum value Imin (S15). In this case, since the minimum value Imin is "0", the ratio α is infinite.

[0039] If the calculated ratio α is infinite, α>αs (=2) (NO in S16), so the controller 30 determines that an abnormality has occurred (S19), and does not start the motor M, keeping it stopped (S20). Then, since the calculated ratio α is infinite, the controller 30 determines that the cause of the abnormality is an open fault in the switch element Tx corresponding to the phase current Ix with the minimum value Imin="0", stores this information in its internal memory, and notifies an external maintenance person or the like of the details of the abnormality by displaying the information on the display or communicating via network (S21).

[0040] As described above, by turning on a predetermined number of switch elements Tu to Tz of switching circuit 20, a plurality of current paths (first to sixth current paths) through which current flows in a predetermined direction in phase windings Lu, Lv, Lw are sequentially formed, and for each current path formed, a U-phase check operation through a Z-phase check operation are performed to sequentially detect the values ​​of phase currents Iw, Iv, Iu, Ix, Iz, Iy flowing between switching circuit 20 and motor M. Of the values ​​of phase currents Iw to Iy detected in these check operations, a maximum value Imax and a minimum value Imin are selected, and an abnormality in switch elements Tu to Tz and an abnormality in motor M are determined based on the ratio α (=Imax / Imin) between the selected maximum value Imax and minimum value Imin, thereby enabling accurate and quick detection of an abnormality in switch elements Tu to Tz and an abnormality in motor M. Regarding the phase check operation, in the U-phase, V-phase, and W-phase check operation, current paths (first to third current paths) are formed in which current flows from one phase winding to two phase windings, and in the X-phase, Y-phase, and Z-phase check operation, current paths (fourth to sixth current paths) are formed in which current flows from two phase windings to one phase winding.

[0041] Furthermore, since the predetermined period t, which is the on period of each switch element during the check operation of each phase, is variably set according to the value of the AC voltage Vc, the values ​​of the phase currents Iw, Iv, Iu, Ix, Iz, and Iy during the check operation of each phase can be accurately detected regardless of fluctuations in the AC voltage Vc.

[0042] Because the phase current value during each phase check operation is detected based on the voltage generated across a single shunt resistor Rs arranged in the negative-side current path Ln of the switching circuit 20, costs can be reduced compared to, for example, providing a current sensor for each of the phase windings Lu, Lv, and Lw. Even if a current sensor is provided for each phase winding as in the conventional method so that the phase currents of all three phases can be detected at all times, it is still effective to select a maximum value Imax and a minimum value Imin of the phase currents Iu to Iz detected in a series of phase check operations and determine whether there is an abnormality in the switch elements Tu to Tz or the motor M based on the ratio α (= Imax / Imin) between the selected maximum value Imax and minimum value Imin.

[0043] As a modified example, as described in Patent Document 2, during the W-phase check operation in which the switch elements Tw, Tx, and Ty are turned on for a predetermined period t while the switch elements Tu, Tv, and Tz are maintained in an off state, after the switch elements Tw, Tx, and Ty have finished being turned on, as shown by the dashed lines in FIG. 3 , a pulsed gate signal Po is supplied to turn on the switch elements Tu, Tv, and Tz, which had been in an off state until then, for a period substantially equal to the predetermined period t, so that a negative-phase voltage is applied to the phase windings Lu, Lv, and Lw to cancel out the current that flowed between the switching circuit and the motor M when the switch elements Tw, Tx, and Ty were initially turned on.

[0044] In this way, by applying a negative-phase voltage before proceeding to the next V-phase check operation, the phase current Iw during the W-phase check operation can be quickly attenuated without affecting the phase current Iv during the next V-phase check operation, thereby enabling the phase current Iv during the next V-phase check operation to be accurately detected.

[0045] Similarly, during the V-phase check operation in which the switch elements Tv, Tx, and Tz are turned on for a predetermined period t while the switch elements Tu, Tw, and Ty are maintained in an off state, after the switch elements Tu, Tw, and Ty have finished being turned on, as shown by the dashed lines in FIG. 3 , a pulsed gate signal Po is supplied to turn on the switch elements Tu, Tw, and Ty, which had been in an off state until then, for a period substantially equal to the predetermined period t, so that a negative-phase voltage is applied to the phase windings Lu, Lv, and Lw to cancel out the current that flowed between the switching circuit and the motor M when the switch elements Tv, Tx, and Tz were initially turned on.

[0046] In this way, by applying a negative-phase voltage before proceeding to the next U-phase check operation, the phase current Iv during the V-phase check operation can be quickly attenuated without affecting the phase current Iu during the next U-phase check operation, thereby enabling the phase current Iu to be accurately detected during the next U-phase check operation.

[0047] Similarly, during the remaining U-phase check operation, X-phase check operation, Z-phase check operation, and Y-phase check operation, a reverse-phase voltage for canceling the current flowing between the switching circuit and the motor M may be applied to the phase windings Lu, Lv, and Lw.

[0048] In other words, by applying a negative-sequence voltage to quickly attenuate each phase current during each phase check operation, the period of each phase check operation can be shortened and the phase current during the next phase check operation can be accurately detected. Note that in the last phase check operation, there is no need to apply a negative-sequence voltage because there will be no further current flow due to a phase check operation thereafter.

[0049] In the above embodiment, the phase check operation is performed in the order of W phase, V phase, U phase, X phase, Z phase, and Y phase, but the order is not limited thereto.

[0050] An application example of the above embodiments is a refrigeration cycle apparatus in which a compressor is driven by an inverter device 10. As an example of this refrigeration cycle apparatus, FIG. 12 shows an air conditioner 40 equipped with a heat pump refrigeration cycle. The air conditioner 40 is composed of an outdoor unit 41 and an indoor unit 42. The outdoor unit 41 includes a compressor 51, a four-way valve 52, an outdoor heat exchanger 53, an expansion valve 54, an outdoor fan 56, and the inverter device 10 of each of the above embodiments. The indoor unit 42 includes an indoor heat exchanger 55 and an indoor fan 57. The compressor 51 includes a motor M driven by the inverter device 10 and a compression mechanism 51a driven by the motor M.

[0051] During cooling operation, the refrigerant discharged from the compression mechanism 51a flows through the four-way valve 52 to the outdoor heat exchanger 53, where it condenses by heat exchange with air (outdoor air) drawn in by the outdoor fan 56. The refrigerant condensed in the outdoor heat exchanger 53 is decompressed by the expansion valve 54 and flows to the indoor heat exchanger 55, where it evaporates by heat exchange with air (indoor air) drawn in by the indoor fan 57. The refrigerant evaporated in the indoor heat exchanger 55 passes through the four-way valve 52 and is drawn into the compression mechanism 51a. During heating operation, the flow path of the four-way valve 52 is switched, and the refrigerant discharged from the compression mechanism 51a flows through the four-way valve 52 to the indoor heat exchanger 55, where it condenses by heat exchange with air (indoor air) drawn in by the indoor fan 57. The refrigerant condensed in the indoor heat exchanger 55 is decompressed by the expansion valve 54 and flows to the outdoor heat exchanger 53, where it evaporates through heat exchange with air (outdoor air) drawn in by the outdoor fan 56. The refrigerant evaporated in the outdoor heat exchanger 53 passes through the four-way valve 52 and is sucked into the compression mechanism 51a.

[0052] Furthermore, the above-described embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. These embodiments and modifications can be embodied in various other forms, and various omissions, rewritings, and modifications can be made without departing from the spirit of the invention. These embodiments and modifications are included within the spirit of the invention, and are also included in the scope of the inventions and their equivalents as defined in the claims.

[0053] 1...AC power supply, 2...full-wave rectifier circuit, 3...smoothing capacitor, 10...inverter device, 20...switching circuit, Tu to Tz...switch elements, Rs...shunt resistor, M...motor, Lu, Lv, Lw...phase winding, 30...controller, 30a...current detection unit, 30b...voltage detection unit, 30c...determination unit, 30d...first control unit, 30e...second control unit.

Claims

1. An inverter device connected to a motor having a plurality of phase windings, comprising: a switching circuit including a plurality of series circuits of a switch element on the upstream side and a switch element on the downstream side along the application direction of a DC voltage, and each phase winding is connected to an interconnection point of the switch elements of these series circuits; and a controller for controlling the switching circuit, wherein the controller sequentially forms a plurality of energization paths through which current flows in a predetermined direction of each phase winding through each switch element, and performs a phase check operation for detecting a value of a phase current flowing between the switching circuit and each phase winding for each formation, and determines an abnormality of the motor and an abnormality of each switch element based on a ratio between a maximum value and a minimum value among the values of the phase currents detected by these phase check operations. Inverter device.

2. The inverter device according to claim 1, further comprising a shunt resistor disposed in a DC power supply path to the switching circuit, wherein the controller detects a value of each phase current during each phase check operation based on a voltage generated in the shunt resistor.

3. The inverter device according to claim 1, wherein the controller executes the determination before starting the motor, starts the motor when the result of the determination is normal, and stops starting the motor when the result of the determination is abnormal.

4. The inverter device according to claim 1, further comprising a DC circuit that converts an AC voltage into a DC voltage and supplies the DC voltage to the switching circuit, wherein the controller variably sets an on period of each switch element during each phase check operation according to a value of the AC voltage.

5. The inverter device according to claim 1, wherein the controller applies a cancelling reverse voltage to the current flowing between the switching circuit and the motor through each switch element to each phase winding before shifting to each phase check operation.

6. A refrigeration cycle device that drives a compressor by the inverter device according to any one of claims 1 to 5.

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