JP7338071B2 - motor drive - Google Patents

Description

The present invention relates to a motor drive device for driving a motor having a plurality of phase windings that are not connected to each other.

A permanent magnet synchronous motor having a plurality of phase windings is used as a drive motor for a compressor mounted in a refrigeration cycle apparatus such as an air conditioner. Also known is an open-winding motor in which a plurality of phase windings are disconnected from each other.

A motor driving device for driving this open-winding motor (abbreviated as a motor) includes a first inverter that controls energization to one end of each phase winding of the motor, and a first inverter that controls energization to the other end of each phase winding of the motor. A second inverter to be controlled has a switch connected between the other ends of the windings of each phase. A star connection mode in which the inverter is switched independently, and an open winding mode in which the first and second inverters are switched in conjunction with each other with each phase winding disconnected by opening the switch are selectively set. By setting the open winding mode, the motor can be driven at a high rotation speed, and by setting the star connection mode in the low rotation speed range, the motor can be driven with high efficiency, so that the motor can be driven from high rotation speed to low rotation speed. It is possible to drive the motor as efficiently as possible over a wide operating range. As a result, it is expected that both the expansion of the operating range of the motor and the improvement of the efficiency of the motor driving device can be achieved.

As a switch for switching between the star connection mode and the open winding mode, it is desirable to use a relay having a mechanical open/close contact in order to reduce the resistance when the drive current flows in the star connection mode.

In addition, if the switching contact of the relay is opened and closed while voltage is applied to the switching contact while the motor is being driven, a surge voltage or an arc is generated across the switching contact, adversely affecting the life of the relay. Therefore, when the relay is switched while the motor is running, a quasi-neutral point operation is performed by switching the first and second inverters so as not to generate a potential difference across the open/close contacts of the relay, and the quasi-neutral point Switch relays during operation. As a result, the relay can be switched in a state where there is no potential difference between both ends of the open/close contact, and the service life of the relay can be extended.

Patent No. 4804381 Japanese Patent Application Laid-Open No. 2019-62726

However, as a result of various tests conducted by the inventors of the present application, when switching the relay during the execution of the pseudo neutral point operation, although the probability is extremely low, the opening/closing timing of the opening/closing contact of the relay and the switching operation of the inverter It has been found that there is a problem that one of the switching elements of the inverter is destroyed due to the combination with the timing of . Mechanical relays are accompanied by mechanical movement that moves the opening and closing contacts by the attractive force of the electromagnetic coil, so it is not possible to strictly control the opening and closing timing of the opening and closing contacts, and the appropriate solution to the above problem is explored.

An object of embodiments of the present invention is to provide a motor drive device that can prevent damage to switching elements of an inverter even when switching between a star connection mode and an open winding mode using a relay.

According to a first aspect of the present invention, there is provided a motor driving device for a motor having a plurality of phase windings that are not connected to each other, comprising a plurality of series circuits of an upper switching element and a lower switching element. a first inverter in which the interconnection point of the side switch elements is connected to one end of each phase winding; and a plurality of series circuits of the upper switch elements and the lower switch elements, wherein the upper switch elements and the lower switch elements in the series circuits. a second inverter in which an element interconnection point is connected to the other end of each phase winding; a switch having a mechanical switching contact connected between the other ends of each phase winding; an impedance element inserted and connected to a current-carrying path to the switching contact; and a quasi-neutral element that alternately turns on and off each of the upper switching elements and the lower switching elements in the second inverter when the switch operates. a controller for performing point operations; The current path between the other end of each phase winding and the switching contact suppresses abrupt changes in the voltage across the switch element in the first and second inverters, thereby suppressing destruction of the switch element. has an impedance value that

1 is a block diagram showing the configuration of a first embodiment; FIG. FIG. 2 is a flowchart showing control in the first embodiment; FIG. 3 is a time chart showing quasi-neutral point operation and operation of each relay executed when switching from the open winding mode to the star connection mode in the first embodiment; FIG. 4 is a time chart showing quasi-neutral point operation and operation of each relay executed when switching from the star connection mode to the open winding mode in the first embodiment; FIG. 5 is a time chart showing ON/OFF of each switching element in the quasi-neutral point operation of FIGS. FIG. 6 is a block diagram showing the configuration of the second embodiment; FIG. 7 is a flowchart showing control of the second embodiment; FIG. 8 is a time chart showing quasi-neutral point operation and operation of each relay executed when switching from the open winding mode to the star connection mode in the second embodiment; FIG. 9 is a time chart showing quasi-neutral point operation and operation of each relay executed when switching from the star connection mode to the open winding mode in the second embodiment;

[1] First embodiment
A first embodiment will be described with reference to the drawings.
As shown in FIG. 1, 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. As shown in FIG.

The motor 3 is a compressor-driving three-phase permanent magnet synchronous motor having a plurality of phase windings Lu, Lv, and Lw that are not connected to each other. It is a so-called open-winding motor with terminals.

A motor drive circuit 2 is connected to a three-phase AC power supply 1, and includes a converter 10 that converts the three-phase AC voltage into a DC voltage and outputs the DC voltage. , Lw, and the output end of the converter 10 and the other ends of the phase windings Lu, Lv, Lw of the open winding motor 1M. includes an inverter (second inverter) 30 that controls energization to the three terminals. A DC link common system in which the converter 10 is used as a common DC power supply for the inverters 20 and 30 is adopted. Converter 10 is a full-wave rectifier, a PWM converter, or the like.

The inverter 20 is a U-phase series circuit to which the output voltage of the converter 10 is applied by connecting the upper switching element Tu+ and the lower switching element Tu- in series, and the upper switching element Tv+ and the lower switching element Tv- are connected in series. The three-phase inverter includes a V-phase series circuit to which the output voltage of the converter 10 is applied and a W-phase series circuit to which the output voltage of the converter 10 is applied by connecting the upper switching element Tw+ and the lower switching element Tw- in series. . Interconnection points Au, Av, and Aw of upper switching elements Tu+, Tv+, Tw+ and lower switching elements Tu-, Tv-, Tw- in these series circuits are connected to one ends of phase windings Lu, Lv, Lw, respectively. . The upper switching elements Tu+, Tv+, Tw+ and the lower switching elements Tu−, Tv−, Tw− are IGBTs, and free wheel diodes (also called free wheel diodes) D connected in anti-parallel to the respective switching element bodies. including. Note that the switch element may be another semiconductor switch element such as a MOS-FET.

Like the inverter 20, the inverter 30 is a U-phase series circuit to which the output voltage of the converter 10 is applied by connecting the upper switching element Tu+ and the lower switching element Tu- in series, the upper switching element Tv+ and the lower switching element Tv-. are connected in series to receive the output voltage of the converter 10, and a W-phase series circuit to which the output voltage of the converter 10 is applied by connecting the upper switching element Tw+ and the lower switching element Tw− in series. . Interconnection points Bu, Bv, and Bw of upper switching elements Tu+, Tv+, Tw+ and lower switching elements Tu-, Tv-, Tw- in these series circuits are connected to the other ends of phase windings Lu, Lv, Lw, respectively. be. The upper switch elements Tu+, Tv+, Tw+ and the lower switch elements Tu-, Tv-, Tw- in the inverter 30 are also IGBTs, for example, and include free wheel diodes D connected in anti-parallel to the respective switch element bodies.

Note that the inverters 20 and 30 are actually composed of a main circuit in which a U-phase series circuit, a V-phase series circuit, and a W-phase series circuit are bridge-connected, and peripheral circuits such as a drive circuit for driving each switch element of the main circuit. and are housed in a single package, i.e., a so-called IPM (Intelligent Power Module), but all the switch elements and drive circuits may be configured as discrete parts. Moreover, although each of the inverters 20 and 30 is a three-phase inverter, each of the inverters 20 and 30 may be configured using three single-phase inverters.

Between the other end of the phase winding Lu and the other end of the phase winding Lv of the motor 1M, a normally open switching contact (referred to as a relay contact) 12a of a relay 12, which is a switch having a mechanical switching contact. are connected via electric paths 14u and 14v. The conducting path 14u includes an impedance component Zu having a predetermined impedance value, and exists between the other end of the phase winding Lu and one end of the relay contact 12a. The conducting path 14v includes an impedance component Zv having a predetermined impedance value, and exists between the other end of the phase winding Lv and the other end of the relay contact 12a.

Between the other end of the phase winding Lv and the other end of the phase winding Lw of the motor 1M, there is a normally open switching contact (referred to as a relay contact) 13a of a switch having a mechanical switching contact, such as a relay 13. They are connected via the electric path 14v and the electric path 14w. The current-carrying path 14v exists between the other end of the phase winding Lv and one end of the relay contact 13a. The conducting path 14w includes an impedance component Zw having a predetermined impedance value, and exists between the other end of the phase winding Lw and the other end of the relay contact 13a. Although two relays, the relay 12 and the relay 13, are shown in FIG. 1, the relays 12 and 13 are synchronously switched, so a single relay having two contacts may be used.

The impedance components Zu, Zv, and Zw of the current-carrying paths 14u, 14v, and 14w mainly consist of an inductance component and a resistance component, and the impedance values change in proportion to the frequency of the flowing current. Any conductive member containing predetermined impedance components Zu, Zv, and Zw may be used as the current-carrying paths 14u, 14v, and 14w. An air-core coil wound in a circle may be used.

The relays 12 and 13 are synchronously controlled by the controller 4 so as to be turned on (energized) by supplying an exciting current and turned off (deenergized) by cutting off the exciting current. When the relays 12 and 13 are turned on, the relay contacts 12a and 13a are closed, and the other end of the phase winding Lu and the other end of the phase winding Lv are connected through the relay contact 12a and the impedance components Zu and Zv of the energization paths 14u and 14v. The other end of the phase winding Lv and the other end of the phase winding Lw are interconnected via the relay contact 13a and the impedance components Zv, Zw of the current paths 14v, 14w, and the phase windings Lu, Lv and Lw are in a star connection state. When the relays 12 and 13 are turned off, the relay contacts 12a and 13a are opened, and the phase windings Lu, Lv and Lw are in a non-connected state, that is, an electrically separated open winding state.

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

The controller 4 performs PWM switching of the relay contacts 12a and 13a and the switching of the inverters 20 and 30 so that the rotation speed N of the motor 3 becomes the target rotation speed Nt commanded by a higher-level external device such as an air conditioner control device. It controls, and includes a main control section 40 , a current detection section 41 and a relay drive section 42 . The current detection unit 41 detects instantaneous values of the motor currents Iu, Iv and Iw detected by the current sensors 11u, 11v and 11w. A relay drive unit 42 drives the relays 12 and 13 according to commands from the main control unit 40 .

The main control unit 40 is composed of a microcomputer and its peripheral circuits, and disconnects the other ends of the phase windings Lu, Lv, and Lw by opening the relay contacts 12a and 13a to link the inverters 20 and 30 for switching. and a star connection mode in which the other ends of the phase windings Lu, Lv, Lw are interconnected by closing the relay contacts 12a, 13a to switch the inverter 20 alone. It is selectively set according to the value of Iw. For example, when the motor speed N is low and the motor currents Iu, Iv, Iw are less than a predetermined value, the star connection mode is set, and the motor currents Iu, Iv, Iw values increase as the motor speed N increases. The open winding mode is set when the load is higher than a predetermined value. This provides high efficiency over the entire operating range of the motor.

In addition, the main control unit 40 causes the line voltages Euv and Evw applied to the relay contacts 12a and 13a to become zero when switching from the open winding mode to the star connection mode and from the star connection mode to the open winding mode. Thus, a quasi-neutral point operation is performed in which each upper switching element and each lower switching element in the inverter 30 are alternately turned on and off with an on/off duty of 50%.

Further, when the upper switching element and the lower switching element in each series circuit of the inverters 20 and 30 are turned on and off, the main control unit 40 turns off the other switching element when one switching element turns on. Complementary action. At this time, a dead time td is ensured during which both the upper switching element and the lower switching element are turned off so that the upper switching element and the lower switching element are not turned on at the same time.

Next, main control executed by the main control section 40 of the controller 4 will be described with reference to the flowchart of FIG. Steps S1, S2, . . . in the flowchart are abbreviated as S1, S2, .

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 unnecessary (NO in S2), the main control unit 40 returns to the determination in S1, and continues the operation in the open winding mode.

When a request to switch to the star connection mode is generated from a higher-level external device and it becomes necessary to switch to the star connection mode (YES in S2), the main control unit 40 controls the line voltage applied to the relay contacts 12a and 13a. The upper switching elements Tu+, Tv+, Tw+ and the lower switching elements Tu-, Tv-, Tw- in the inverter 30 are alternately turned on and off with an on/off duty of 50% as shown in FIG. 3 so that Euv and Evw become zero. A pseudo-neutral point operation of turning on and off is executed (S3).

The on/off operations of the upper switching elements Tu+, Tv+, and Tw+ and the on/off operations of the lower switching elements Tu-, Tv-, and Tw- in this pseudo-neutral point operation are enlarged temporally for easy understanding. FIG. 5 shows this. That is, when the upper switching elements Tu+, Tv+, and Tw+ are turned on and the lower switching elements Tu−, Tv−, and Tw− are turned off, the main control unit 40 avoids forming a short circuit to the output terminal of the converter 10. A dead time td in which the upper switching elements Tu+, Tv+, Tw+ and the lower switching elements Tu-, Tv-, Tw- are turned off is ensured. Furthermore, the main control unit 40 avoids formation of a short circuit to the output end of the converter 10 even when the lower switching elements Tu−, Tv−, Tw− are turned on and the upper switching elements Tu+, Tv+, Tw+ are turned off. , lower switch elements Tu-, Tv-, Tw- and upper switch elements Tu+, Tv+, Tw+ are all turned off to ensure dead time td. There are various methods for creating the dead time td, but in general, the switch element on the side to be turned off is turned off at the timing as instructed, and the switch element on the side to be turned on is generally turned off. It is common to provide a delay time for delaying the ON timing of , that is, a dead time td. This dead time td is desirably as short as possible from the viewpoint of efficiency and waveform shaping, but the minimum required time is determined from the ON/OFF transient characteristics of the switching element.

During execution of this pseudo neutral point operation, the main control unit 40 turns on the relays 12 and 13 (S4). Then, after a certain time t1 longer than the time required for the relay contacts 12a and 13a to actually close after turning on the relays 12 and 13 (YES in S5), the main control unit 40 switches to the pseudo-neutral state. After finishing the point operation, the control shifts to the star connection mode control (single switching of the inverter 20) (S6). After this transition, the main control unit 40 returns to the determination of S1.

However, in this pseudo neutral point operation, motor currents Iu and Iv flow from the phase windings Lu and Lv to the interconnection points Bu and Bv of the inverter 30 as indicated by arrows in FIG. When the motor current Iw flows from the interconnection point Bw toward the phase winding Lw, the line voltage Euv applied to the relay contact 12a becomes zero, but the line voltage Evw applied to the relay contact 13a does not become zero. This is because the direction of flow of the motor currents Iu and Iv is different from the direction of flow of the motor current Iw; This is because a current path is formed through the free wheel diode D, so that the potential of the interconnection point Bw and the potentials of the interconnection points Bu and Bv have different values for the period of the dead time td.

If the timing at which the line voltage Evw does not become zero coincides with the timing at which the relay contact 13a is closed, a discharge may occur across the relay contact 13a, or a very small capacitance may exist between the relay contacts 13a. A steep high-frequency current flows through the component, and the line voltage Evw drops sharply to zero. Accordingly, the output capacitance of the IGBT, which is the upper switching element Tv+ and the lower switching element Tw− in the inverter 30, that is, the capacitance between the collector and the emitter is charged, so that the upper switching element Tv+ and the lower switching element Tw are charged. - is off, the collector-emitter voltage Vce, which is the voltage across each of the upper switching element Tv+ and the lower switching element Tw-, rapidly increases many times faster than the normal switching operation. At this time, a high-frequency current flows through the collector-gate parasitic capacitance of each of the upper switching element Tv+ and the lower switching element Tw-. This high-frequency current flows through the gate-emitter parasitic capacitances of the upper switching element Tv+ and the lower switching element Tw- to the respective emitter sides. At that time, 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-. On the other hand, in the lower switching element Tv- and the upper switching element Tw+, the voltage between the collector and the emitter rapidly decreases at a rate many times faster than in normal switching operation, and high-frequency noise is generated at the gate of the IGBT based on the same principle as above. superimpose. If the level of these high-frequency noises is high or the frequency of occurrence of such high-frequency noises is high, the driving circuits that drive the upper switching elements and lower switching elements may malfunction, and the oscillation of the driving circuits may cause thermal damage or gate damage. It may lead to overvoltage breakdown of the part. Although the line voltage Evw has been described above as an example, this phenomenon occurs between any phases.

Incidentally, when a semiconductor switch element is used instead of the mechanical relay contacts 12a and 13a, it is possible to control the ON timing of the semiconductor switch element in microsecond units. For this reason, the above-mentioned problem does not occur, but the on-resistance of the semiconductor switch element is higher than that of the relay, and moreover, current always flows through the semiconductor switch element during star connection, so the loss increases, and heat dissipation measures must be taken. There are problems such as disappearance.

In this embodiment, since the mechanical relay contacts 12a and 13a with very low resistance are used, there is almost no loss and heat dissipation measures are not required.

Current paths 14u, 14v and 14w between the other ends of the phase windings Lu, Lv and Lw and the relay contacts 12a and 13a are provided with impedance components Zu, Zv and Zw of predetermined impedance values. Therefore, even if the relay contacts 12a and 13a are closed at a timing at which one of the line voltages Euv and Evw does not become zero during pseudo neutral point operation and a high frequency current flows through either of the relay contacts 12a and 13a, each upper side It is possible to suppress the di/dt of the current charging the output capacitance of the IGBT, which is the switch element and each lower switch element. Therefore, a sharp change in the collector-emitter voltage Vce, which is the voltage across each switch element, is suppressed, and destruction of each switch element due to high-frequency noise via the collector-gate capacitance and the gate-emitter capacitance is suppressed. be able to.

In other words, the impedance components Zu, Zv, and Zw of the current-carrying paths 14u, 14v, and 14w are the same even if the relay contacts 12a and 13a are closed at the timing when either of the line voltages Euv and Evw does not become zero during the pseudo-neutral point operation. , is an impedance value that does not cause a sharp change in the collector-emitter voltage Vce that may cause destruction of each switch element. An impedance value of 2.0 mΩ or more is appropriate for the output of a motor driving device for a compressor of a general air conditioner or the like. Furthermore, it is desirable to have the impedance value as small as possible so as not to degrade efficiency as much as possible during motor operation. On the other hand, in order to suppress a decrease in efficiency due to the impedance components Zu, Zv, and Zw during motor operation, it is desirable to set the impedance values of the impedance components Zu, Zv, and Zw to 5.0 mΩ or less. Naturally, this impedance value is extremely small compared to the impedance value when the semiconductor switch is turned on when the relay is replaced with a semiconductor switch element. Therefore, the proper range of the impedance values of the impedance components Zu, Zv, Zw of the current-carrying paths 14u, 14v, 14w is 2.0 mΩ or more and 5.0 mΩ or less.

In practice, when the current-carrying paths 14u, 14v, and 14w are simple wires, it is desirable that the length of each wire is in the range of 15 cm to 60 cm in order to provide the above impedance value in each wire. In particular, the wiring length is more preferably in the range of 25 to 45 cm. In order to realize this, the relay contacts 12a and 13a are arranged in places different from the circuit board on which the inverters 20 and 30 are mounted, and the inverter 30 and the relay contacts 12a and 13a are connected to the impedance components Zu, Zv and Zw. It is sufficient to connect with a wiring having a length of . Specifically, the relay contacts 12a and 13a are provided at positions separated from the circuit board on which the inverter 30 is mounted. After that, the inverter output terminals of the circuit board on which the inverter 30 is mounted and the connection terminals of the relay contacts 12a and 13a are connected by wires having the length described above. In general, from the viewpoint of efficiency, it is common to shorten the wiring of the energizing path as much as possible. is sufficient, and it is unthinkable to wastefully extend the wiring length beyond 15 cm. Incidentally, in a general motor drive device for a compressor such as an air conditioner, when the wiring length of each of the electric paths 14u, 14v, and 14w is 60 cm, the impedance value is close to 5.0 mΩ.

On the other hand, when air-core coils are used as current paths, the dimensions of the current paths 14u, 14v, and 14w can be reduced. , can also be miniaturized.

Returning to the flowchart of FIG. 2, in the star connection mode (NO in S1), the main control unit 40 monitors whether switching to the open winding mode is necessary (S7). If switching to the open winding mode is unnecessary (NO in S7), the main control unit 40 returns to the determination in S1.

If it is necessary to switch to the open winding mode (YES in S7), the main control unit 40 switches the upper switch elements Tu+, Tv+, Tw+ and the lower switching elements Tu-, Tv-, Tw- are alternately turned on and off at an on/off duty of 50% as shown in FIG. 4 (S8). This pseudo-neutral point operation is the same as switching from the open winding mode to the star connection mode described above.

During execution of this pseudo neutral point operation, the main control unit 40 turns off the relays 12 and 13 (S9). Then, after a certain period of time t2 longer than the time required for the relay contacts 12a and 13a to actually open after the relays 12 and 13 are turned off (YES in S10), the main control unit 40 switches to the pseudo neutral point. After finishing the operation, the control shifts to the open winding mode control (linked switching of the inverters 20 and 30) (S11). After this transition, the main control unit 40 returns to the determination of S1. The fixed times t1 and t2 of S5 and S10 may be the same, and it is desirable to set them as short as possible. In the case of the mechanical relays 12, 13, there is a delay of 10 to 30 msec from the activation and deactivation of the excitation current to the actual opening and closing of the relay contacts 12a, 13a. About 50msec to 100msec is desirable.

[2] Second Embodiment FIG. 6 shows the configuration of the second embodiment.
A relay contact 12a is connected between the other end of the phase winding Lu and the other end of the phase winding Lv of the motor 1M, and current can flow bidirectionally through the relay contact 12a when the element is turned on. A series circuit of semiconductor element type auxiliary switches SW1 and SW2 is connected in parallel. A relay contact 13a is connected between the other end of the phase winding Lv of the motor 1M and the other end of the phase winding Lw. A series circuit of semiconductor element type auxiliary switches SW3 and SW4 are connected in parallel to allow current to flow. Conducting paths between the relay contacts 12a, 13a and the phase windings Lu, Lv, Lw may have smaller impedance values than the conducting paths 14u, 14v, 14w of the first embodiment. Therefore, it is possible to use a short wire, for example, about 10 cm long, as the conducting path between the relay contacts 12a, 13a and the phase windings Lu, Lv, Lw, and the size of the motor driving device can be reduced.

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

The relays 12 and 13 are synchronously controlled to be on (energized) and off (deenergized) by the controller 4 . When the relays 12 and 13 are turned on, the relay contacts 12a and 13a are closed, the other end of the phase winding Lu and the other end of the phase winding Lv are interconnected through the relay contact 12a, and the phase winding The other end of Lv and the other end of phase winding Lw are interconnected via relay contact 13a, and phase windings Lu, Lv, and Lw are in a star connection state. When the relays 12, 13 are deenergized, the relay contacts 12a, 13a are opened, and the phase windings Lu, Lv, Lw are in a non-connected state, that is, an electrically separated open winding state.

The controller 4 PWM-controls the opening and closing of the relay contacts 12a and 13a and the switching of the inverters 20 and 30 so that the rotational speed N of the motor 3 becomes the target rotational speed Nt commanded by the external device of the higher order. 40 , current detector 41 , relay driver 42 , relays 12 and 13 , and auxiliary SW driver 43 . The auxiliary SW driving section 43 drives the auxiliary switches SW1 to SW4 according to commands from the main control section 40. FIG.

As in the first embodiment, the main control unit 40 selectively sets the open winding mode and the star connection mode according to the values of the motor currents Iu, Iv, and Iw, and switches from the open winding mode to the star connection mode. When switching from the star connection mode to the open winding mode, each upper switch element and each lower switch element in the inverter 30 are arranged so that the line voltages Euv and Evw applied to the relay contacts 12a and 13a are zero. is turned on and off alternately with a 50% duty cycle.

Further, the main control unit 40 ensures the 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, as in the first embodiment.

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 shifting from the open winding mode to the star connection mode. After that, the main control unit 40 turns on the relays 12 and 13 with the auxiliary switches SW1 to SW4 turned on, and a fixed time t1 longer than the time required from turning on until the relay contacts 12a and 13a are closed elapses. After that, the auxiliary switches SW1 to SW4 are turned off. Further, the main control unit 40 turns off the relays 12 and 13 while the auxiliary switches SW1 to SW4 are turned on in advance during the pseudo-neutral point operation when shifting from the star connection mode to the open winding mode. After a certain time t2 longer than the time required for the relay contacts 12a and 13a to open after turning off, the auxiliary switches SW1 to SW4 are turned off.

Next, main control executed by the main control section 40 of the controller 4 will be described with reference to the flowchart of FIG.

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 unnecessary (NO in S22), the main control unit 40 returns to the determination of S21.

If switching to the star connection mode is required (YES in S22), the main control unit 40 switches the upper switch elements Tu+, Tv+ in the inverter 30 so that the line voltages Euv, Evw applied to the relay contacts 12a, 13a become zero. , Tw+ and the lower switch elements Tu−, Tv−, Tw− are alternately turned on and off at an on/off duty of 50% (S23).

During execution of this pseudo neutral point operation, as shown in FIG. 8, the main control unit 40 first turns on the auxiliary switches SW1 to SW4 (S24) and then turns on the relays 12 and 13 (S25). After a certain time t1 longer than the time required for the relay contacts 12a and 13a to close after turning on the relays 12 and 13 (YES in S26), the main control unit 40 turns off the auxiliary switches SW1 to SW4. (S27) After this turn-off, the quasi-neutral point operation is ended, and control of the star connection mode (single switching of the inverter 20) is shifted to (S28). After this transition, the main control unit 40 returns to the determination of S21.

Since both ends of the relay contacts 12a and 13a are short-circuited by turning on the auxiliary switches SW1 to SW4 before the relay contacts 12a and 13a are closed during execution of the quasi-neutral point operation, the relay contacts 12a and 13a are closed. At this time, the line voltages Euv and Evw are not applied to the relay contacts 12a and 13a. Therefore, in this embodiment as well, a sharp change in the collector-emitter voltage Vce, which is the voltage across each upper switching element and each lower switching element, is suppressed, and the collector-gate capacitance and the gate-emitter capacitance Therefore, it is possible to prevent the switching elements of the inverter 20 or the inverter 30 from being destroyed by the high-frequency noise.

During 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 unnecessary (NO in S29), the main control unit 40 returns to the determination of S21.

If switching to the open winding mode is required (YES in S29), the main control unit 40 switches the upper switch elements Tu+, A quasi-neutral point operation is executed in which Tv+, Tw+ and the lower switching elements Tu-, Tv-, Tw- are alternately turned on and off at an on/off duty of 50% (S30).

During execution of this pseudo neutral point operation, as shown in FIG. 9, the main control section 40 first turns on the auxiliary switches SW1 to SW4 (S31) and then turns off the relays 12 and 13 (S32). After a certain time t2, which is longer than the time required for the relay contacts 12a and 13a to open after the relays 12 and 13 are turned off (YES in S33), the main control unit 40 switches the switch elements of the inverters 20 and 30. Also, the auxiliary switches SW1 to SW4 are turned off at a timing that is not during the dead time period (S34). (S35). After this transition, the main control unit 40 returns to the determination of S21.

As described above, the motor current flows through the semiconductor auxiliary switch only temporarily, and after the switching to the star connection mode is completed, the motor current flows only through the relays 12 and 13 during stable operation. , high efficiency can be maintained during operation. Furthermore, the heat generated by the auxiliary switch can be suppressed to a low level, and a large heat sink for heat dissipation is not required.

The above embodiments are presented as examples and are not intended to limit the scope of the invention. The novel embodiments and modifications can be implemented in various other forms, and various omissions, rewrites, and modifications can be made without departing from the scope of the invention. These embodiments and modifications are included in the scope of the invention, and are included in the scope of the invention described in the claims and their equivalents.

2 Drive circuit 3 Open winding motor Lu, Lv, Lw Phase winding 4 Controller 12, 13 Relay (switch) 12a, 13a Relay contact (switching contact) 14u, 14v , 14w... energizing path, Zu, Zv, Zw... impedance component, 20... inverter (first inverter), 30... inverter (second inverter), 40... main control section

Claims (8)

A motor drive device for a motor having a plurality of phase windings that are not connected to each other,
a first inverter including a plurality of series circuits of an upper switching element and a lower switching element, wherein an interconnection point of the upper switching element and the lower switching element in the series circuit is connected to one end of each phase winding;
a second inverter including a plurality of series circuits of an upper switching element and a lower switching element, wherein an interconnection point of the upper switching element and the lower switching element in the series circuit is connected to the other end of each phase winding;
a switch having a mechanical switching contact connected between the other ends of the windings of each phase;
a controller for executing a quasi-neutral point operation of alternately turning on and off each of the upper switching elements and the lower switching elements in the second inverter when the switch is operated;
with
The current path between the other end of each phase winding and the switching contact suppresses abrupt changes in the voltage across the switch element in the first and second inverters, thereby suppressing destruction of the switch element. having an impedance value of
A motor drive device characterized by: each of the upper switch elements and each of the lower switch elements includes a freewheeling diode connected in anti-parallel to the respective switch element body,
2. The motor driving 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 and second inverters are turned off.
2. The motor driving device according to claim 1, wherein: The conducting path is a wire having a length having the impedance value,
2. The motor driving device according to claim 1, wherein: The wire has a length of 15 cm to 60 cm,
5. The motor driving device according to claim 4, characterized in that: the impedance value is 2.0 mΩ or more and 5.0 mΩ or less;
6. The motor driving device according to any one of claims 1 to 5, characterized in that: The conducting path is an electric wire or an air-core coil in which the impedance value changes in proportion to the frequency of the flowing current,
2. The motor driving device according to claim 1, wherein: The controller operates in an open winding mode in which the other end of each phase winding is disconnected by opening the switching contacts to switch the first and second inverters in cooperation with each other, and by closing the switching contacts. selectively setting a star connection mode in which the other ends of the phase windings are interconnected to switch the first inverter;
2. The motor driving device according to claim 1, wherein:

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