Motor drive unit

Abstract

The present invention provides a motor drive device including a switch having mechanical opening and closing contacts, wherein the opening and closing contacts of the switch are connected between the other ends of each phase winding of a motor. The electrical path between each phase winding of the motor and the opening and closing contacts has an impedance value sufficient to suppress a sudden change in the voltage across each upper switching element and each lower switching element in a second inverter, thereby preventing damage to the upper switching element and each lower switching element.

Description

Technical Field

[0001] The present invention relates to a motor driving device for driving a motor having a plurality of phase windings that are not connected to each other. Background Art

[0002] As a drive motor for a compressor mounted in a refrigeration cycle apparatus such as an air conditioner, a permanent magnet synchronous motor having multiple phase windings is used. In addition, an open-winding motor is known in which the multiple phase windings are disconnected from each other.

[0003] A motor drive device for driving an open-winding motor (hereinafter referred to as a motor) includes a first inverter for controlling energization to one end of each phase winding of the motor, a second inverter for controlling energization to the other end of each phase winding of the motor, and switches connected between the other ends of each phase winding. The device selectively sets a star connection mode in which the phase windings are connected in a star pattern (also called a star connection) by closing the switches, causing the first inverter to switch independently, and an open-winding mode in which the phase windings are disconnected by opening the switches, causing the first and second inverters to switch in a coordinated manner. Setting the open-winding mode allows the motor to be driven at high speeds, while setting the star connection mode in a low-speed range allows the motor to be driven efficiently. This allows the motor to be driven as efficiently as possible over a wide operating range from high to low speeds. This is expected to achieve both an expanded operating range for the motor and improved efficiency for the motor drive device.

[0004] As a switch for switching between the star connection mode and the open winding mode, a relay having mechanical opening and closing contacts is preferably used in order to reduce resistance when a drive current flows in the star connection mode.

[0005] Furthermore, when a voltage is applied to the relay's open / close contacts during motor operation, surge voltage and arcing occur between the two ends of the open / close contacts, adversely affecting the life of the relay. Therefore, when switching the relay during motor operation, a pseudo-neutral point operation is performed by switching the first and second inverters to avoid a potential difference between the two ends of the relay's open / close contacts. The relay is then switched during this pseudo-neutral point operation. This allows the relay to be switched without a potential difference between the two ends of the open / close contacts, extending the life of the relay.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent No. 4804381

[0009] Patent Document 2: Japanese Patent Application Publication No. 2019-62726 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] However, the inventors of this application conducted various experiments and discovered that, although the probability is extremely low, when switching relays during the simulated neutral point operation, there is a risk that one of the inverter's switching elements may be damaged, depending on the combination of the opening and closing timing of the relay's open and close contacts and the timing of the inverter's switching operation. Mechanical relays involve mechanical operation, in which the open and close contacts are actuated by the attractive force of an electromagnetic coil. Therefore, strict control of the opening and closing timing of the open and close contacts is not possible. The inventors have been searching for appropriate solutions to this problem.

[0012] An object of an embodiment of the present invention is to provide a motor drive device that uses relays to prevent damage to switching elements of an inverter even when switching between a star connection mode and an open winding mode.

[0013] Means for solving problems

[0014] Technical solution 1 is a motor drive device, which has multiple phase windings that are in a non-connected state. The motor drive device comprises: a first inverter, including a series circuit of multiple upper switching elements and lower switching elements, and the mutual connection point of the upper switching elements and the lower switching elements in these series circuits is connected to one end of each of the above-mentioned phase windings; a second inverter, including a series circuit of multiple upper switching elements and lower switching elements, and the mutual connection point of the upper switching elements and the lower switching elements in these series circuits is connected to the other end of each of the above-mentioned phase windings; a switch, having mechanical opening and closing contacts connected between the other ends of each of the above-mentioned phase windings; an impedance element, inserted into the circuit connected to the above-mentioned opening and closing contacts; and a controller, which, when the above-mentioned switch is operated, performs a simulated neutral point operation of alternately connecting and disconnecting each of the above-mentioned upper switching elements and each of the above-mentioned lower switching elements in the above-mentioned second inverter. The conducting path between the other end of each phase winding and the switching contact has an impedance value that suppresses a sudden change in voltage across the switching elements in the first inverter and the second inverter to prevent damage to the switching elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a block diagram showing the configuration of the first embodiment.

[0016] Figure 2 This is a flowchart showing control in the first embodiment.

[0017] Figure 3This is a timing chart showing the pseudo neutral point operation and the operation of each relay performed when switching from the open winding mode to the star connection mode in the first embodiment.

[0018] Figure 4 This is a timing chart showing the pseudo neutral point operation and the operation of each relay executed when switching from the star connection mode to the open winding mode in the first embodiment.

[0019] Figure 5 It will Figure 3 as well as Figure 4 A timing diagram showing the on / off state of each switching element in a simulated neutral point operation, with the on / off state of each switching element magnified in time.

[0020] Figure 6 This is a block diagram showing the configuration of the second embodiment.

[0021] Figure 7 This is a flowchart showing control in the second embodiment.

[0022] Figure 8 This is a timing chart showing the pseudo neutral point operation and the operation of each relay executed when switching from the open winding mode to the star connection mode in the second embodiment.

[0023] Figure 9 This is a timing chart showing the pseudo neutral point operation and the operation of each relay executed when switching from the star connection mode to the open winding mode in the second embodiment. DETAILED DESCRIPTION

[0024] [1] First embodiment

[0025] The first embodiment will be described with reference to the drawings.

[0026] like Figure 1 As shown, a motor drive circuit 2 is connected to a three-phase AC power supply 1 , and a motor 3 and a controller 4 are connected to the motor drive circuit 2 .

[0027] The motor 3 is a three-phase permanent magnet synchronous motor for driving a compressor having a plurality of mutually disconnected phase windings Lu, Lv, and Lw, and is a so-called open-winding motor having six terminals serving as both ends of each phase winding Lu, Lv, and Lw.

[0028] The motor drive circuit 2 includes a converter 10 connected to a three-phase AC power supply 1, converting the three-phase AC voltage into a DC voltage for output; an inverter (first inverter) 20 controlling the flow of current to the output of the converter 10 and three terminals, which constitute one end of each of the phase windings Lu, Lv, and Lw of the open-winding motor 1M; and an inverter (second inverter) 30 controlling the flow of current to the output of the converter 10 and three terminals, which constitute the other end of each of the phase windings Lu, Lv, and Lw of the open-winding motor 1M. A DC link sharing scheme is employed, in which the converter 10 serves as a common DC power supply for the inverters 20 and 30. The converter 10 is implemented as a full-wave rectifier, a PWM converter, or the like.

[0029] Inverter 20 is a three-phase inverter, comprising a U-phase series circuit, comprising an upper switching element Tu+ and a lower switching element Tu- connected in series, to which the output voltage of converter 10 is applied; a V-phase series circuit, comprising an upper switching element Tv+ and a lower switching element Tv- connected in series, to which the output voltage of converter 10 is applied; and a W-phase series circuit, comprising an upper switching element Tw+ and a lower switching element Tw- connected in series, to which the output voltage of converter 10 is applied. The interconnection points Au, Av, and Aw between the upper switching elements Tu+, Tv+, and Tw+ and the lower switching elements Tu-, Tv-, and Tw- in these series circuits are connected to one end of the phase windings Lu, Lv, and Lw, respectively. The upper switching elements Tu+, Tv+, and Tw+ and the lower switching elements Tu-, Tv-, and Tw- are IGBTs, each including a freewheeling diode (also called a freewheel diode) D connected in antiparallel with the main body of each switching element. In addition, the switching element may be another semiconductor switching element such as MOS-FET.

[0030] Similar to inverter 20, inverter 30 includes a U-phase series circuit, which connects an upper switching element Tu+ and a lower switching element Tu- in series and is applied with the output voltage of converter 10; a V-phase series circuit, which connects an upper switching element Tv+ and a lower switching element Tv- in series and is applied with the output voltage of converter 10; and a W-phase series circuit, which connects an upper switching element Tw+ and a lower switching element Tw- in series and is applied with the output voltage of converter 10. The interconnection points Bu, Bv, and Bw between the upper switching elements Tu+, Tv+, and Tw+ and the lower switching elements Tu-, Tv-, and Tw- in these series circuits are connected to the other ends of the phase windings Lu, Lv, and Lw, respectively. The upper switching elements Tu+, Tv+, and Tw+ and the lower switching elements Tu-, Tv-, and Tw- in inverter 30 are also, for example, IGBTs, and include freewheeling diodes D connected in antiparallel with the main bodies of each switching element.

[0031] Inverters 20 and 30 are actually modules, known as IPMs (Intelligent Power Modules), that house a main circuit consisting of a U-phase series circuit, a V-phase series circuit, and a W-phase series circuit connected in a bridge configuration, along with peripheral circuits such as a driver circuit for each switching element in the main circuit. However, all switching elements and driver circuits can also be constructed as discrete components. Furthermore, while inverters 20 and 30 are each three-phase inverters, they can also be constructed using three single-phase inverters.

[0032] A normally open switch contact (referred to as a relay contact) 12a of a relay 12, a switch having mechanical opening and closing contacts, is connected between the other ends of the phase winding Lu and Lv of the motor 1M via electrical paths 14u and 14v. Electrical path 14u includes an impedance component Zu of a predetermined impedance value and exists between the other end of the phase winding Lu and one end of the relay contact 12a. Electrical path 14v includes an impedance component Zv of a predetermined impedance value and exists between the other end of the phase winding Lv and the other end of the relay contact 12a.

[0033] Between the other end of the phase winding Lv of the motor 1M and the other end of the phase winding Lw, a switch having a mechanical opening and closing contact, such as a normally open opening and closing contact (referred to as a relay contact) 13a of the relay 13, is connected via the above-mentioned circuit 14v and circuit 14w. The circuit 14v exists between the other end of the phase winding Lv and one end of the relay contact 13a. The circuit 14w includes an impedance component Zw of a predetermined impedance value and exists between the other end of the phase winding Lw and the other end of the relay contact 13a. In addition, Figure 1 Although two relays, the relay 12 and the relay 13, are described, since the relays 12 and 13 are switched synchronously, a single relay having two contacts may also be used.

[0034] The impedance components Zu, Zv, and Zw of the conductive paths 14u, 14v, and 14w are primarily composed of inductance and resistance, and their impedance values ​​vary proportionally with the frequency of the flowing current. The conductive paths 14u, 14v, and 14w can be any conductive component that exhibits the specified impedance components Zu, Zv, and Zw. For example, they can be wiring components (electrical wires) of a certain length or air-core coils formed by winding electric wires into a circular shape without a core.

[0035] The switching on (loading) of relays 12 and 13 by supplying excitation current and their disconnection (unloading) by shutting off excitation current are synchronously controlled by controller 4. When relays 12 and 13 are switched on, relay contacts 12a and 13a close, connecting the other ends of phase windings Lu and Lv via relay contact 12a and impedance components Zu and Zv of electrical paths 14u and 14v. Furthermore, the other ends of phase windings Lv and Lw are connected via relay contact 13a and impedance components Zv and Zw of electrical paths 14v and 14w, creating a star connection between the phase windings Lu, Lv, and Lw. When relays 12 and 13 are switched off, relay contacts 12a and 13a open, disconnecting the phase windings Lu, Lv, and Lw, or creating an open winding state where they are electrically separated.

[0036] Current sensors 11u, 11v, and 11w are arranged on three conducting lines between the inverter 20 and one end of the phase windings Lu, Lv, and Lw, and their output signals are sent to the controller 4. The current sensors 11u, 11v, and 11w detect the currents Iu, Iv, and Iw (referred to as motor currents) flowing through the phase windings Lu, Lv, and Lw.

[0037] Controller 4 performs PWM control on the opening and closing of relay contacts 12a and 13a and the switching of inverters 20 and 30 so that the rotational speed N of motor 3 reaches the target rotational speed Nt instructed by a higher-level external device, such as an air conditioner control device. Controller 4 includes a main control unit 40, a current detection unit 41, and a relay driver 42. Current detection unit 41 detects the instantaneous values ​​of motor currents Iu, Iv, and Iw detected by current sensors 11u, 11v, and 11w, respectively. Relay driver 42 drives relays 12 and 13 based on instructions from main control unit 40.

[0038] The main control unit 40, comprised of a microcomputer and its peripheral circuits, selectively sets, based on the values ​​of motor currents Iu, Iv, and Iw, an open winding mode (in which the other ends of phase windings Lu, Lv, and Lw are disconnected by opening relay contacts 12a and 13a, switching inverters 20 and 30 in a coordinated manner) and a star connection mode (in which the other ends of phase windings Lu, Lv, and Lw are connected by closing relay contacts 12a and 13a, switching inverter 20 independently). For example, the star connection mode is set during low-load conditions, when the motor speed N is low and motor currents Iu, Iv, and Iw are less than a specified value. The open winding mode is set during high-load conditions, when the motor speed N increases and motor currents Iu, Iv, and Iw exceed a specified value. This ensures high efficiency across the entire motor operating range.

[0039] In addition, when switching from the open winding mode to the star connection mode and vice versa, the main control unit 40 performs a simulated neutral point operation in which each upper switching element and each lower switching element in the inverter 30 are alternately connected and disconnected with an on-off duty ratio of 50%, so that the line-to-line voltages Euv and Evw applied to the relay contacts 12a and 13a become zero.

[0040] Furthermore, the main control unit 40 performs the following complementary operation when turning on and off the upper and lower switching elements in each series circuit of inverters 20 and 30: when one switching element is turned on, the other switching element is subsequently turned off. During this operation, a dead time td is maintained during which both the upper and lower switching elements are turned off to prevent them from being turned on simultaneously.

[0041] Next, refer to Figure 2 The flowchart of FIG. 1 illustrates the main control executed by the main control unit 40 of the controller 4. Steps S1, S2, ... in the flowchart are simply referred to as S1, S2, ...

[0042] In the open winding mode ("YES" in S1), the main control unit 40 monitors whether switching to the star connection mode is necessary (S2). If switching to the star connection mode is not necessary ("NO" in S2), the main control unit 40 returns to the determination in S1 and continues operation in the open winding mode.

[0043] When a request to switch to the star connection mode is generated from an upper external device and switching to the star connection mode is required ("Yes" in S2), the main control unit 40 executes the operation of switching the upper switching elements Tu+, Tv+, and Tw+ of the inverter 30 and the lower switching elements Tu-, Tv-, and Tw- as shown in FIG. Figure 3 As shown, a pseudo neutral point operation of alternately turning on and off is performed with an on / off duty ratio of 50% so that the line voltages Euv and Evw applied to the relay contacts 12a and 13a become zero (S3).

[0044] Figure 5For ease of understanding, this diagram shows the on / off operation of the upper switching elements Tu+, Tv+, and Tw+, and the on / off operation of the lower switching elements Tu-, Tv-, and Tw- during this simulated neutral point operation, magnified in time. Specifically, the main control unit 40 maintains a dead time td during which both the upper switching elements Tu+, Tv+, and Tw+ and the lower switching elements Tu-, Tv-, and Tw- are off. This prevents a short circuit from forming at the output of the converter 10 when the upper switching elements Tu+, Tv+, and Tw+ are turned on and the lower switching elements Tu-, Tv-, and Tw- are turned off. Furthermore, the main control unit 40 maintains a dead time td during which both the lower switching elements Tu-, Tv-, and Tw-, and the upper switching elements Tu+, Tv+, and Tw+ are off. This prevents a short circuit from forming at the output of the converter 10 even when the lower switching elements Tu-, Tv-, and Tw- are turned on and the upper switching elements Tu+, Tv+, and Tw+ are turned off. While various methods exist for creating dead time td, generally, the switching elements to be turned off are turned off at the commanded timing, while the switching elements to be turned on are delayed by a delay, i.e., dead time td, to delay the turn-on timing. While this dead time td is preferably as short as possible for efficiency and waveform shaping purposes, the minimum required time is determined based on the on-off transient characteristics of the switching elements.

[0045] During this simulated neutral point operation, the main control unit 40 turns on relays 12 and 13 (S4). After a certain time t1, which is longer than the time required from turning on relays 12 and 13 until relay contacts 12a and 13a actually close, has elapsed ("YES" in S5), the main control unit 40 terminates the simulated neutral point operation and transitions to star connection mode control (individual switching of inverter 20) (S6). After this transition, the main control unit 40 returns to the determination in S1 described above.

[0046] However, in this simulated neutral point operation, e.g. Figure 1As shown by the arrows, when motor currents Iu and Iv flow from phase windings Lu and Lv toward interconnection points Bu and Bv of inverter 30, and motor current Iw flows from interconnection point Bw of inverter 30 toward phase winding Lw, line voltage Euv applied to relay contact 12a becomes zero, but line voltage Evw applied to relay contact 13a does not become zero. This is because the directions of motor currents Iu and Iv flow differently from those of motor current Iw, and because a current path is formed through freewheeling diodes D in either upper switching elements Tu+, Tv+, and Tw+ or lower switching elements Tu-, Tv-, and Tw-, the potential at interconnection point Bw and the potential at interconnection points Bu and Bv become different values ​​during dead time td.

[0047] In this way, if the timing of line voltage Evw not reaching zero coincides with the closing of relay contact 13a, discharge occurs between the two terminals of relay contact 13a, or a steep high-frequency current flows through the tiny capacitance component existing between relay contacts 13a, causing line voltage Evw to drop rapidly to zero. This, along with the output capacitance (output capacitance) of the IGBTs (high-side switching element Tv+) and low-side switching element Tw-) in inverter 30, i.e., the collector-emitter capacitance, charges. Consequently, even though high-side switching element Tv+ and low-side switching element Tw- are off, the voltage across each terminal, i.e., the collector-emitter voltage Vce, of each of these elements increases rapidly at a rate several times higher than during normal switching operation. At this time, a high-frequency current flows through the parasitic collector-gate capacitance of each of these elements. This high-frequency current flows toward the emitter side of each of the upper switching element Tv+ and the lower switching element Tw- through the parasitic capacitance between the gate and emitter. At this point, high-frequency noise is superimposed on the gate-emitter voltage Vge of each of the upper switching element Tv+ and the lower switching element Tw-. Meanwhile, in the lower switching element Tv- and the upper switching element Tw+, the collector-emitter voltage drops rapidly at a rate several times higher than during normal switching operation. This, based on the same principle as described above, superimposes high-frequency noise on the gate portion of the IGBT. When the level of this high-frequency noise increases or the frequency of this high-frequency noise generation is high, it can cause malfunction of the drive circuits driving the upper and lower switching elements, thermal damage due to oscillation of the drive circuits, or overvoltage damage to the gate portion. While the above description uses the line-to-line voltage Evw as an example, this phenomenon can occur between any phases.

[0048] Furthermore, when semiconductor switching elements are used instead of mechanical relay contacts 12a and 13a, the on-time of the semiconductor switching elements can be controlled in μsec units. This eliminates the aforementioned problem, but semiconductor switching elements have a larger on-resistance than relays. Furthermore, when connected in a star configuration, current constantly flows through the semiconductor switching elements, increasing losses and necessitating heat dissipation measures.

[0049] In the present embodiment, since mechanical relay contacts 12 a and 13 a having very low resistance are used, almost no loss occurs and no heat dissipation measures are required.

[0050] Furthermore, by providing impedance components Zu, Zv, and Zw of predetermined impedance values ​​between the other ends of the phase windings Lu, Lv, and Lw and the relay contacts 12a and 13a, the conduction paths 14u, 14v, and 14w are configured. Therefore, even if relay contacts 12a and 13a close at a timing when neither line voltage Euv or Evw reaches zero during pseudo-neutral point operation, allowing a high-frequency current to flow through either relay contact 12a or 13a, the di / dt of the current charging the output capacitance (output capacitance) of the IGBTs serving as the upper and lower switching elements can be suppressed. Consequently, abrupt changes in the collector-emitter voltage Vce, the voltage across each switching element, can be suppressed, preventing damage to the switching elements caused by high-frequency noise passing through the collector-gate capacitance and gate-emitter capacitance.

[0051] In other words, the impedance components Zu, Zv, and Zw of the through-circuits 14u, 14v, and 14w are such that even when the timing relay contacts 12a and 13a close, where neither the line voltages Euv or Evw reaches zero during simulated neutral point operation, a sudden change in the collector-emitter voltage Vce, which could damage the switching elements, does not occur. For outputs comparable to those of motor drive devices for compressors in typical air conditioners, the impedance value is preferably set at 2.0 mΩ or greater. Furthermore, the impedance value is preferably as low as possible to minimize the reduction in motor efficiency during operation. On the other hand, to minimize the reduction in efficiency caused by the impedance components Zu, Zv, and Zw during motor operation, the impedance values ​​of the impedance components Zu, Zv, and Zw are preferably set at 5.0 mΩ or less. Naturally, this impedance value is significantly lower than the impedance value when the semiconductor switch is turned on, if the relay is replaced with a semiconductor switching element. Therefore, the impedance values ​​of the impedance components Zu, Zv, and Zw of the through-current paths 14u, 14v, and 14w are appropriately within a range of 2.0 mΩ to 5.0 mΩ.

[0052] In practice, when circuits 14u, 14v, and 14w consist solely of wiring, in order to achieve the aforementioned impedance values, the length of each wiring is preferably within the range of 15 cm to 60 cm. In particular, the wiring length is more preferably within the range of 25 cm to 45 cm. To achieve this, relay contacts 12a and 13a are located separately from the circuit board on which inverters 20 and 30 are mounted, and inverter 30 is connected to relay contacts 12a and 13a via wiring having the impedance components Zu, Zv, and Zw. Specifically, relay contacts 12a and 13a are located at a location separate from the circuit board on which inverter 30 is mounted. Furthermore, wiring of the aforementioned length is used to connect the inverter output terminals of the circuit board on which inverter 30 is mounted to the connection terminals of relay contacts 12a and 13a. In general, from the perspective of efficiency, it is usually desirable to minimize the wiring length of the through-circuit. If only switches are inserted into the wiring to the phase windings Lu, Lv, and Lw, a maximum of approximately 10 cm is sufficient, and wastefully extending the wiring length to over 15 cm is not considered desirable. Furthermore, in a typical motor drive device for a compressor such as an air conditioner, if the wiring length of each through-circuit 14u, 14v, and 14w is 60 cm, the impedance value is approximately 5.0 mΩ.

[0053] On the other hand, when air-core coils are used as the conducting paths, the sizes of the conducting paths 14u, 14v, and 14w can be reduced, and thus the inverters 20 and 30 and the relays 12a and 13a can be mounted on the same circuit board for miniaturization.

[0054] Return to Figure 2 , in the star connection mode ("No" in S1), the main control unit 40 monitors whether it is necessary to switch to the open winding mode (S7). If it is not necessary to switch to the open winding mode ("No" in S7), the main control unit 40 returns to the determination of S1 above.

[0055] When the open winding mode is required (Yes in S7), the main control unit 40 controls the upper switching elements Tu+, Tv+, and Tw+ of the inverter 30 and the lower switching elements Tu-, Tv-, and Tw- as shown in FIG. Figure 4 As shown, a simulated neutral point operation is performed alternately with an on / off duty ratio of 50% to reduce the line voltages Euv and Evw applied to the relay contacts 12a and 13a to zero (S8). This simulated neutral point operation is similar to the switching from the open winding mode to the star connection mode described above.

[0056] During the execution of this simulated neutral point operation, the main control unit 40 disconnects the relays 12 and 13 (S9). Then, after a certain time t2, which is longer than the time required from disconnecting the relays 12 and 13 to the actual opening of the relay contacts 12a and 13a, has passed ("Yes" in S10), the main control unit 40 ends the simulated neutral point operation and transfers to the control of the open winding mode (interlocking switching of the inverters 20 and 30) (S11). After this transfer, the main control unit 40 returns to the judgment of the above-mentioned S1. In addition, the certain times t1 and t2 of S5 and S10 can be the same time, but are preferably set to as short a time as possible. In the case of mechanical relays 12 and 13, there is a delay of 10 to 30 msec from the loading and unloading based on the excitation current to the actual opening and closing of the relay contacts 12a and 13a. Taking this into account, the above-mentioned certain times t1 and t2 are preferably about 50 msec to 100 msec.

[0057] [2] Second embodiment

[0058] Figure 6 The configuration of the second embodiment is shown.

[0059] A relay contact 12a is connected between the other ends of the phase winding Lu and the other ends of the phase winding Lv of the motor 1M. A series circuit of semiconductor-type auxiliary switches SW1 and SW2 is connected in parallel with this relay contact 12a, allowing current to flow in both directions when the elements are switched on. A relay contact 13a is connected between the other ends of the phase winding Lv and the other ends of the phase winding Lw of the motor 1M. A series circuit of semiconductor-type auxiliary switches SW3 and SW4 is connected in parallel with this relay contact 13a, allowing current to flow in both directions when the elements are switched on, similar to the relay contact 12a. Furthermore, the impedance of the circuit between the relay contacts 12a and 13a and the phase windings Lu, Lv, and Lw can be lower than the impedance of the circuits 14u, 14v, and 14w of the first embodiment. Therefore, a relatively short wiring, for example, about 10 cm in length, can be used as a conducting path between the relay contacts 12 a and 13 a and the phase windings Lu, Lv, and Lw, and the motor drive device can be miniaturized.

[0060] The auxiliary switches SW1 and SW2 and the switching elements SW3 and SW4 may have any circuit configuration as long as they allow current to flow in both directions when on and prevent current from flowing in either direction when off. For example, a single switching element may be provided between the output terminals of the full-wave rectifier.

[0061] Relays 12 and 13 are controlled by controller 4 to switch on (load) and off (unload) in a synchronized state. When relays 12 and 13 are switched on, relay contacts 12a and 13a close, connecting the other end of phase winding Lu and the other end of phase winding Lv via relay contact 12a. Furthermore, the other end of phase winding Lv and the other end of phase winding Lw are connected via relay contact 13a, creating a star connection for the phase windings Lu, Lv, and Lw. When relays 12 and 13 are switched off, relay contacts 12a and 13a open, disconnecting the phase windings Lu, Lv, and Lw, or creating an open winding state where they are electrically separated.

[0062] Controller 4 performs PWM control on the opening and closing of relay contacts 12a and 13a and the switching of inverters 20 and 30 so that the rotational speed N of motor 3 reaches the target rotational speed Nt instructed by a higher-level external device. Controller 4 includes a main control unit 40, a current detection unit 41, a relay driver 42, relays 12 and 13, and an auxiliary switch driver 43. Auxiliary switch driver 43 drives auxiliary switches SW1 to SW4 based on instructions from main control unit 40.

[0063] Similar to the first embodiment, the main control unit 40 selectively sets the open winding mode and the star connection mode based on the values ​​of the motor currents Iu, Iv, and Iw, and when switching from the open winding mode to the star connection mode and from the star connection mode to the open winding mode, performs a simulated neutral point action in which each upper switching element and each lower switching element in the inverter 30 are alternately connected and disconnected with an on-off duty ratio of 50%, so that the line-to-line voltages Euv and Evw applied to the relay contacts 12a and 13a become zero.

[0064] Furthermore, similarly to the first embodiment, the main control unit 40 ensures a dead time td in which both the upper switching element and the lower switching element in each series circuit of the inverters 20 and 30 are turned off.

[0065] In particular, as a feature of the second embodiment, the main control unit 40 turns on the auxiliary switches SW1 to SW4 during the pseudo-neutral point operation when transitioning from the open winding mode to the star connection mode. Subsequently, with the auxiliary switches SW1 to SW4 still on, the main control unit 40 turns on the relays 12 and 13, and after a certain time t1, which is longer than the time required from the time the auxiliary switches SW1 to SW4 are turned on until the relay contacts 12a and 13a close, the main control unit 40 turns off the auxiliary switches SW1 to SW4. Furthermore, during the pseudo-neutral point operation when transitioning from the star connection mode to the open winding mode, the main control unit 40 turns off the relays 12 and 13 with the auxiliary switches SW1 to SW4 already turned on, and after a certain time t2, which is longer than the time required from the time the auxiliary switches SW1 to SW4 are turned off until the relay contacts 12a and 13a open, the main control unit 40 turns off the auxiliary switches SW1 to SW4.

[0066] Next, refer to Figure 7 The flowchart of FIG. 1 illustrates the main control executed by the main control unit 40 of the controller 4.

[0067] In the open winding mode (YES in S21 ), the main control unit 40 monitors whether switching to the star connection mode is necessary ( S22 ). If switching to the star connection mode is not necessary (NO in S22 ), the main control unit 40 returns to the determination in S21 .

[0068] When it is necessary to switch to the star connection mode ("Yes" in S22), the main control unit 40 performs a simulated neutral point action in which the upper switching elements Tu+, Tv+, Tw+ and the lower switching elements Tu-, Tv-, Tw- in the inverter 30 are alternately connected and disconnected with an on-off duty cycle of 50%, so that the line-to-line voltages Euv, Evw applied to the relay contacts 12a, 13a become zero (S23).

[0069] In the execution of this simulated neutral point action, if Figure 8 As shown, the main control unit 40 first turns on the auxiliary switches SW1 to SW4 (S24), then turns on the relays 12 and 13 (S25). After a certain time t1, which is longer than the time required from the turning on of the relays 12 and 13 until the relay contacts 12a and 13a close ("YES" in S26), the main control unit 40 turns off the auxiliary switches SW1 to SW4 (S27). After this turning off, the pseudo-neutral point operation is terminated and control is switched to the star connection mode (individual switching of the inverter 20) (S28). After this transition, the main control unit 40 returns to the determination in S21 described above.

[0070] During the pseudo-neutral point operation, before relay contacts 12a and 13a close, auxiliary switches SW1 to SW4 are turned on, short-circuiting both ends of relay contacts 12a and 13a. Therefore, when relay contacts 12a and 13a close, no line voltages Euv and Evw are applied to relay contacts 12a and 13a. Therefore, even in this embodiment, abrupt changes in the voltage across both ends of each upper switching element and each lower switching element, i.e., the collector-emitter voltage Vce, can be suppressed, preventing damage to the switching elements in inverter 20 or inverter 30 caused by high-frequency noise passing through the collector-gate capacitance and the gate-emitter capacitance.

[0071] In the star connection mode (No in S21), the main control unit 40 monitors whether switching to the open winding mode is necessary (S29). If switching to the open winding mode is not necessary (No in S29), the main control unit 40 returns to the determination of S21.

[0072] When it is necessary to switch to the open winding mode ("Yes" in S29), the main control unit 40 performs a simulated neutral point action in which the upper switching elements Tu+, Tv+, Tw+ and the lower switching elements Tu-, Tv-, Tw- in the inverter 30 are alternately connected and disconnected with an on-off duty cycle of 50%, so that the line-to-line voltages Euv, Evw applied to the relay contacts 12a, 13a become zero (S30).

[0073] In the execution of this simulated neutral point action, if Figure 9 As shown, the main control unit 40 first turns on the auxiliary switches SW1 to SW4 (S31), then turns off the relays 12 and 13 (S32). After a certain time t2, which is longer than the time required from the turning off of the relays 12 and 13 to the opening of the relay contacts 12a and 13a, has elapsed ("YES" in S33), the main control unit 40 turns off the auxiliary switches SW1 to SW4 at a timing where none of the switching elements of the inverters 20 and 30 are within the dead time period (S34). After this turning off, the pseudo-neutral point operation is terminated and control transitions to the open winding mode (interlocked switching of the inverters 20 and 30) (S35). After this transition, the main control unit 40 returns to the determination in S21 described above.

[0074] As described above, the motor current flows temporarily through the semiconductor auxiliary switch. After the switch to the star connection mode is complete, during subsequent stable operation, the motor current flows only through relays 12 and 13, thereby maintaining high efficiency during operation. Furthermore, heat generation from the auxiliary switch can be minimized, eliminating the need for a large heat sink or the like for heat dissipation.

[0075] The above embodiments are provided as examples and are not intended to limit the scope of the invention. The new embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. These embodiments and their variations are included in the scope and spirit of the invention and are included in the invention described in the patent claims and their equivalents.

[0076] Explanation of symbols

[0077] 2: Drive circuit; 3: Open-winding motor; Lu, Lv, Lw: Phase winding; 4: Controller; 12, 13: Relay (switch); 12a, 13a: Relay contacts (open and close contacts); 14u, 14v, 14w: Through circuit; Zu, Zv, Zw: Impedance component; 20: Inverter (1st inverter); 30: Inverter (2nd inverter); 40: Main control unit.

Claims

1. A motor drive device, wherein the motor has a plurality of phase windings that are not connected to each other, characterized in that: have: The first inverter includes a plurality of series circuits of upper switching elements and lower switching elements, wherein a connection point between the upper switching elements and the lower switching elements in the series circuits is connected to one end of each of the phase windings; a second inverter including a plurality of series circuits of upper switching elements and lower switching elements, wherein a connection point between the upper switching elements and the lower switching elements in the series circuits is connected to the other end of each of the phase windings; a switch having mechanical opening and closing contacts connected between the other ends of the phase windings; and The controller performs a pseudo neutral point operation for alternately turning on and off each of the upper switching elements and each of the lower switching elements in the second inverter when the switch is actuated. The conducting path between the other end of each phase winding and the switching contact has an impedance value that suppresses a sudden change in voltage across the switching elements in the first inverter and the second inverter, thereby preventing the switching elements from being destroyed.

2. The motor drive device according to claim 1, wherein: Each of the upper switching elements and each of the lower switching elements includes a freewheeling diode connected in antiparallel to each switching element body.

3. The motor drive device according to claim 1, wherein: The controller ensures a dead time in which both the upper switching element and the lower switching element in the series circuits of the first inverter and the second inverter are turned off.

4. The motor drive device according to claim 1, wherein: The through-circuit is a wiring having a length corresponding to the above-mentioned impedance value.

5. The motor drive device according to claim 4, characterized in that: The length of the wiring is 15 cm to 60 cm.

6. The motor drive device according to any one of claims 1 to 5, characterized in that: The impedance value is greater than or equal to 2.0 mΩ and less than or equal to 5.0 mΩ.

7. The motor drive device according to claim 1, wherein: The conducting path is an electric wire or an air-core coil whose impedance value changes in proportion to the frequency of the flowing current.

8. The motor drive device according to claim 1, wherein: The controller selectively sets: an open winding mode, in which the other end of each of the phase windings is disconnected by opening the switching contacts, so that the first inverter and the second inverter are switched in conjunction with each other; and a star connection mode, in which the other end of each of the phase windings is connected to each other by closing the switching contacts, so that the first inverter is switched.

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