Motor drive device and refrigeration cycle device

Abstract

This motor driving device comprises a first inverter, a second inverter, a plurality of opening and closing connections, a plurality of semiconductor switch elements, and a controller. The controller, at the opening or closing of the opening and closing connections, executes a pseudo neutral point operation and turns on the semiconductor switch elements in advance. First wirings each have a first inductance, second wirings each have a second inductance, and third wirings each have a third inductance. The third inductance value is smaller than the total of the first inductance value and the second inductance value.

Description

Technical Field

[0001] The present invention relates to a motor drive device for a motor having a plurality of phase windings in a non-connected state with each other, and a refrigeration cycle device equipped with the motor drive device.

Background Art

[0002] As a drive motor for a compressor mounted on a refrigeration cycle device such as an air conditioner, a permanent magnet synchronous motor having a plurality of phase windings, and an open-winding motor (for example, three phase windings in a non-connected state with each other) are known.

[0003] A motor drive device for driving an open-winding motor (abbreviated as a motor) includes a first inverter that controls energization to one end of each phase winding of the motor, a second inverter that controls energization to the other end of each phase winding of the motor, and one or a plurality of switches for interconnecting the other ends of each phase winding. By closing this switch, the other ends of each phase winding are interconnected, so-called star connection (also called star connection), and the first inverter is switched alone to drive the motor in the star connection mode. And an open winding mode in which the other ends of each phase winding are separated from each other by opening the switch, and the first and second inverters are switched in cooperation with each other to drive the motor, are selectively set.

[0004] By setting the open winding mode, the applied voltage to each phase winding can be increased to overcome the back electromotive force generated in the permanent magnet synchronous motor, and the motor can be driven at a high rotational speed. In the low rotational speed range, the motor can be driven with high efficiency by setting the star connection mode. That is, the motor can be driven as efficiently as possible over a wide operating range from high rotational speed to low rotational speed. Therefore, it is possible to achieve both an expansion of the operating range of the motor and an improvement in the efficiency of the motor drive device.

[0005] In motor drive in star connection mode, the current (motor current) flowing between the first inverter and each phase winding passes through the switch. By using a mechanical switch contact with a small resistance value, for example, a relay contact, as the switch, power loss in the switch can be reduced, and motor efficiency can be improved.

[0006] However, during motor drive, a potential difference occurs between both ends of the switch contact, that is, between the other ends of each phase winding. When the switch contact opens and closes in a state where such a potential difference occurs, a surge voltage or an arc is generated between both ends of the switch contact, which has an adverse effect on the life of the switch contact. Furthermore, these surge voltages and arcs may cause the switching elements of each inverter to be damaged. Therefore, as a countermeasure, a virtual neutral point operation that does not generate a potential difference between both ends of the switch contact is executed by switching of the second inverter, and control is performed to open and close the relay contact during the execution.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, as a result of various tests, it has been found that even during the execution of the virtual neutral point operation, depending on the relationship between the switching timing of the second inverter and the operating timing of the relay contact, a potential difference may occur between both ends of the switch contact.

[0009] Therefore, an object of an embodiment of the present invention is to provide a motor drive device and a refrigeration cycle device with excellent safety and reliability that can suppress the potential difference between both ends of the switch contact to be as small as possible.

Means for Solving the Problems

[0010] The motor drive device of the embodiment is a motor drive device for a motor having a plurality of phase windings that are not connected to each other, including a plurality of series circuits of an upper switch element and a lower switch element, with both ends of these series circuits connected to a DC power supply, and the interconnection point of the upper switch element and the lower switch element of each series circuit being connected to one end of each phase winding; a first inverter; a second inverter including a plurality of series circuits of an upper switch element and a lower switch element, with both ends of these series circuits connected to the DC power supply, and the interconnection point of the upper switch element and the lower switch element of each series circuit being connected to the other end of each phase winding by each first wiring; a plurality of open / close contacts connected to each other between the other ends of each phase winding by each second wiring; a plurality of semiconductor switch elements connected in parallel to each open / close contact by each third wiring; and a controller for controlling the drive of the first inverter, the drive of the second inverter, and the opening and closing of each open / close contact. When opening and closing each open / close contact, the controller executes a virtual neutral point operation of alternately turning on and off all of the upper switch elements and all of the lower switch elements in the second inverter in advance and turns on each semiconductor switch element. Each of the first wirings has a first inductance, each of the second wirings has a second inductance, and each of the third wirings has a third inductance. The value of this third inductance is smaller than the total value of the value of the first inductance and the value of the second inductance.

[0011] The refrigeration cycle device of the embodiment includes a compressor driven by the above motor drive device.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0013] [1] First Embodiment The 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 output end of the motor drive circuit 2. In this embodiment, the motor 3 is a compressor drive motor that drives the compressor of an air conditioner, which is a refrigeration cycle device.

[0014] The motor 3 is a three-phase permanent magnet synchronous motor for driving a compressor, which has three phase windings Lu, Lv, and Lw that are not connected to each other. Specifically, it is a so-called open-winding motor that includes three terminals 31u, 31v, and 31w that are the respective one ends of the phase windings Lu, Lv, and Lw, and three terminals 32u, 32v, and 32w that are the respective other ends of the phase windings Lu, Lv, and Lw.

[0015] The motor drive circuit 2 includes a DC power supply such as a converter 10 connected to a three-phase AC power supply 1, a positive power supply line C1 and a negative power supply line C2 connected to the output terminal of this converter 10, and an inverter (first inverter) 20 and an inverter (second inverter) 30 connected between the positive power supply line C1 and the negative power supply line C2.

[0016] The converter 10 is, for example, a full-wave rectifier or a PWM converter, and converts the AC voltage of the three-phase AC power supply 1 into a DC voltage. The inverter 20 controls the energization to the terminals 31u, 31v, and 31w that are the respective one ends of the phase windings Lu, Lv, and Lw of the open-winding motor 3. The inverter 30 controls the energization to the terminals 32u, 32v, and 32w that are the respective other ends of the phase windings Lu, Lv, and Lw of the open-winding motor 3. A DC link common method configuration is adopted in which the converter 10 serves as a common DC power supply for the inverters 20 and 30.

[0017] The inverter 20 is a so-called three-phase inverter that includes a U-phase series circuit formed by connecting an upper-side switch element Tu and a lower-side switch element Tx in series, a V-phase series circuit formed by connecting an upper-side switch element Tv and a lower-side switch element Ty in series, and a W-phase series circuit formed by connecting an upper-side switch element Tw and a lower-side switch element Tz in series. One end of each of the U-phase series circuit, the V-phase series circuit, and the W-phase series circuit is connected to the positive power supply line C1, and the other end of each of the U-phase series circuit, the V-phase series circuit, and the W-phase series circuit is connected to the negative power supply line C2.

[0018] The connection point Au between the upper switch element Tu and the lower switch element Tx is connected to the terminal 31u, which is one end of the phase winding Lu, by a wiring 51u such as a lead wire or a conductive pattern. The connection point Av between the upper switch element Tv and the lower switch element Ty is connected to the terminal 31v, which is one end of the phase winding Lv, by a wiring 51v such as a lead wire or a conductive pattern. The connection point Aw between the upper switch element Tw and the lower switch element Tz is connected to the terminal 31w, which is one end of the phase winding Lz, by a wiring 51w such as a lead wire or a conductive pattern.

[0019] The inverter 30 has the same circuit configuration as the inverter 20 and is a so-called three-phase inverter including a U-phase series circuit formed by connecting the upper switch element Tu and the lower switch element Tx in series, a V-phase series circuit formed by connecting the upper switch element Tv and the lower switch element Ty in series, and a W-phase series circuit formed by connecting the upper switch element Tw and the lower switch element Tz in series. One end of each of the U-phase series circuit, the V-phase series circuit, and the W-phase series circuit is connected to the positive power supply line C1, and the other end of each of the U-phase series circuit, the V-phase series circuit, and the W-phase series circuit is connected to the negative power supply line C2.

[0020] The connection point Bu between the upper switch element Tu and the lower switch element Tx is connected to the terminal 32u, which is the other end of the phase winding Lu, by a wiring (first wiring) 52u such as a lead wire or a conductive pattern. The connection point Bv between the upper switch element Tv and the lower switch element Ty is connected to the terminal 32v, which is the other end of the phase winding Lv, by a wiring (first wiring) 52v such as a lead wire or a conductive pattern. The connection point Bw between the upper switch element Tw and the lower switch element Tz is connected to the terminal 32w, which is the other end of the phase winding Lz, by a wiring (first wiring) 52w such as a lead wire or a conductive pattern.

[0021] All the switch elements Tu to Tz of the inverters 20 and 30 are IGBTs with a free-wheeling diode D (also called a free-wheel diode) connected in reverse parallel to the switch element body. Not limited to IGBTs, MOS-FETs or the like may be used as each of the switch elements Tu to Tz.

[0022] Inverter 20 is actually a module, so-called IPM (Intelligent Power Module), which houses in a single package a main circuit formed by bridge-connecting a U-phase series circuit, a V-phase series circuit, and a W-phase series circuit, and peripheral circuits such as a drive circuit for driving each switch element of this main circuit. Inverter 30 is also an IPM. Not limited to IPMs, inverters 20 and 30 configured with all switch elements Tu to Tz and drive circuits as discrete components may also be used. Not limited to three-phase inverters, as long as six-phase switching is possible, two three-phase inverters 20 and 30 may be configured with three single-phase inverters.

[0023] Between the other ends (terminals 32u) of the phase winding Lu and the other ends (terminals 32v) of the phase winding Lv of the motor 1M, a switch having a mechanical opening and closing contact, for example, a normally open first opening and closing contact (referred to as a relay contact) 12a of a relay 12, is connected by wirings (second wirings) 53u and 53v such as lead wires and conductive patterns. Between the other ends (terminals 32v) of the phase winding Lv and the other ends (terminals 32w) of the phase winding Lw of the motor 1M, a switch having a mechanical opening and closing contact, for example, a normally open second opening and closing contact (referred to as a relay contact) 13a of a relay 13, is connected by wirings (second wirings) 53v and 53w such as lead wires and conductive patterns. For relays 12 and 13, turning on (energizing) by supplying an exciting current and turning off (de-energizing) by cutting off the exciting current are controlled in synchronization with each other by the controller 4. Therefore, instead of the two relays 12 and 13, a configuration using one relay including two relay contacts may be adopted.

[0024] When relays 12 and 13 are turned on (energized), 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 via the relay contact 12a, and the other end of the phase winding Lv and the other end of the phase winding Lw are interconnected via the relay contact 13a. That is, the phase windings Lu, Lv, and Lw are in a star connection state (also referred to as a wye connection state). When relays 12 and 13 are turned off (de-energized), relay contacts 12a and 13a are opened, and the phase windings Lu, Lv, and Lw are in a non-connected state where they are separated from each other, that is, an open winding state where they are electrically separated.

[0025] Furthermore, a series circuit of auxiliary switches SW1 and SW2 is connected in parallel to relay contact 12a by wirings (third wirings) 54u and 54v such as lead wires and conductive patterns. A series circuit of auxiliary switches SW3 and SW4 is connected in parallel to relay contact 13a by wirings (third wirings) 54v and 54w such as lead wires and conductive patterns.

[0026] Specifically, one end of the series circuit of auxiliary switches SW1 and SW2 is connected to connection point N1 between wiring 53u and one end of relay contact 12a via wiring 54u. The other end of the series circuit of auxiliary switches SW1 and SW2 is connected to connection point N2 between wiring 53v and the other end of relay contact 12a (and one end of relay contact 12b) via wiring 54v, and one end of the series circuit of auxiliary switches SW3 and SW4 is connected via the same wiring 54v. The other end of the series circuit of auxiliary switches SW3 and SW4 is connected to connection point N3 between wiring 53w and the other end of relay contact 12b via wiring 54w. Connection points N1, N2, and N3 are branching points from wirings 53u, 53v, and 53w to wirings 54u, 54v, and 54w. Hereinafter, connection points N1, N2, and N3 are referred to as branching points N1, N2, and N3.

[0027] That is, wirings 53u, 53v, and 53w start from terminals 32u, 32v, and 32w which are the other ends of motor windings Lu, Lv, and Lw, and end at branching points N1, N2, and N3. The first and second wirings 54u and 54v start from branching points N1 and N2, and end at both ends of the series circuit of auxiliary switches Sw1 and Sw2. The second and third wirings 54v and 54w start from branching points N2 and N3, and end at both ends of the series circuit of auxiliary switches Sw3 and Sw4.

[0028] The auxiliary switches SW1 to SW4 are semiconductor switch elements each having a freewheeling diode D connected in the reverse parallel direction to the respective element body. The series circuit of the auxiliary switches SW1 and SW2 is connected in a state where the auxiliary switches SW1 and SW2 are in opposite directions. That is, the outputs (current outflow sides) of both of the auxiliary switches SW1 and SW2 are connected to each other. Similarly, the series circuit of the auxiliary switches SW3 and SW4 is also connected in a state where the auxiliary switches SW3 and SW4 are in opposite directions. For this reason, in the series circuit of the auxiliary switches SW1 and SW2, when the auxiliary switches SW1 and SW2 are on, current flows bidirectionally through the freewheeling diode D of one of the auxiliary switches, and when the auxiliary switches SW1 and SW2 are off, no current flows in either direction. Similarly, in the series circuit of the auxiliary switches SW3 and SW4, when the auxiliary switches SW3 and SW4 are on, current flows bidirectionally through the freewheeling diode D of one of the auxiliary switches, and when the auxiliary switches SW3 and SW4 are off, no current flows in either direction.

[0029] The wiring 52u between the interconnection point Bu of the inverter 30 and the other end (terminal 32u) of the phase winding Lu has a first inductance (parasitic inductance) Lsu1. The wiring 53u between the other end (terminal 32u) of the phase winding Lu and the branch point N1 has a second inductance (parasitic inductance) Lsu2. The wiring 52v between the interconnection point Bv of the inverter 30 and the other end (terminal 32v) of the phase winding Lv has a first inductance (parasitic inductance) Lsv1. The wiring 53v between the other end (terminal 32v) of the phase winding Lv and the branch point N2 has a second inductance Lsv2. The wiring 52w between the interconnection point Bw of the inverter 30 and the other end (terminal 32w) of the phase winding Lw has a first inductance (parasitic inductance) Lsw1. The wiring 52w between the other end (terminal 32w) of the phase winding Lw and the branch point N3 has a second inductance Lsw2. The first inductances Lsu1, Lsv1, Lsw1 are generally of the same value as each other, but may vary slightly in magnitude depending on the routing situation of each of the wirings 52u, 52v, 52w. Similarly, the second inductances Lsu2, Lsv2, Lsw2 are generally of the same value as each other, but may vary slightly in magnitude depending on the routing situation of each of the wirings 53u, 53v, 53w.

[0030] The wiring 54u between the branch point N1 and one end of the series circuit of the auxiliary switches SW1, SW2 has a third inductance (parasitic inductance) Lsu3. The wiring 54v has a third inductance Lsv3 between the branch point N2 and the other end of the auxiliary switches SW1, SW2, and also has the same third inductance Lsv3 between the branch point N2 and one end of the auxiliary switches SW3, SW4. Since the wiring at the connection portion between the collector of the auxiliary switch SW2 and the collector of the auxiliary switch SW3 can be extremely short, the third inductance Lsv3 of the wiring 54v is generally dominated by the inductance of the wiring between the branch point N2 and the connection point between the auxiliary switch SW2 and the auxiliary switch SW3. The wiring 54w between the branch point N3 and the other end of the series circuit of the auxiliary switches SW3, SW4 has a third inductance Lsw3.

[0031] To summarize, a relay contact 12a is connected between branch points N1 and N2, and a series circuit of auxiliary switches SW1 and SW2 is connected between branch points N1 and N2. A relay contact 13a is connected between branch points N2 and N3, and a series circuit of auxiliary switches SW3 and SW4 is connected between branch points N2 and N3.

[0032] Current sensors 11u, 11v, and 11w are arranged in wirings 51, 51v, and 51z between the interconnection points Au, Av, Az of the inverter 20 and one ends (terminals 31u, 31v, 31z) of the phase windings Lu, Lv, Lw, respectively, and output signals of these current sensors are sent to the controller 4. The current sensors 11u, 11v, and 11w detect currents (referred to as motor currents) Iu, Iv, and Iw flowing through the phase windings Lu, Lv, and Lw.

[0033] The controller 4 includes a main control unit 40, a current detection unit 41, a relay drive unit 42, and an auxiliary SW drive unit 43, and controls the opening and closing of the relay contacts 12a and 13a and the driving (switching) of the inverters 20 and 30 so that the rotational speed N of the motor 3 becomes the target rotational speed Nt commanded from a higher-level external device (for example, a control device of an air conditioner) and so that highly efficient operation is achieved.

[0034] 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. The relay drive unit 42 drives the relays 12 and 13 in response to a command from the main control unit 40. The auxiliary SW drive unit 43 drives the auxiliary switches SW1 to SW4 in response to a command from the main control unit 40.

[0035] The main control unit 40 is composed of a microcomputer and its peripheral circuits, and selectively sets a star connection mode in which the other ends of the phase windings Lu, Lv, and Lw are interconnected by closing the relay contacts 12a and 13a to drive the inverter 20 alone, and an open winding mode in which the other ends of the phase windings Lu, Lv, and Lw are disconnected from each other by opening the relay contacts 12a and 13a to drive the inverters 20 and 30 in association with each other, according to values such as the values of the motor currents Iu, Iv, and Iw corresponding to the load magnitude. For example, in the case of a low load where the motor speed N is low and the motor currents Iu, Iv, and Iw are less than a predetermined value, the star connection mode is set, and in the case of a high load where the motor speed N increases and the motor currents Iu, Iv, and Iw are equal to or greater than the predetermined value, the open winding mode is set. Thereby, high efficiency can be obtained throughout the entire operating range of the motor. Note that the selection between the star connection mode and the open winding mode can be switched by determining using various parameters related to the motor, such as the combination of the motor speed and the field weakening amount, in addition to the above. In an abnormal state such as when the motor currents Iu, Iv, and Iw are in an overcurrent state, it is also conceivable to preferentially switch to either one of the star connection mode and the open winding mode.

[0036] When the main control unit 40 switches from the open winding mode to the star connection mode and from the star connection mode to the open winding mode, a virtual neutral point operation is executed in which all the upper side switch elements Tu, Tv, and Tw and all the lower side switch elements Tx, Ty, and Tz in the inverter 30 are alternately turned on and off at an on / off duty of 50% so that the potential difference between both ends of the relay contact 12a and the potential difference between both ends of the relay contact 13a become zero.

[0037] In particular, during the execution of the virtual neutral point operation when switching from the open winding mode to the star connection mode, the main control unit 40 turns on the relays 12 and 13 with the auxiliary switches SW1 to SW4 turned on in advance, and after a fixed time t1 longer than the time required for the relay contacts 12a and 13a to actually close, turns off the auxiliary switches SW1 to SW4. Similarly, during the execution of the virtual neutral point operation when switching 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 turned on in advance, and after a fixed time t2 longer than the time required for the relay contacts 12a and 13a to actually open, turns off the auxiliary switches SW1 to SW4.

[0038] Note that when driving the upper and lower switch elements of the inverters 20 and 30 during the virtual neutral point operation, the main control unit 40 performs complementary operations such that when the upper switch element turns on in each series circuit, the lower switch element turns off, and when the lower switch element turns on in each series circuit, the upper switch element turns off. In this complementary operation, the main control unit 40 ensures a dead time td during which both the upper and lower switch elements are in the off state so that a short circuit is not formed due to the upper and lower switch elements being simultaneously in the on state. Note that the dead time td is provided not only during the virtual neutral point operation but also during normal PWM control during operation to prevent short circuits of the upper and lower switch elements.

[0039] Next, the main control performed by the main control unit 40 of the controller 4 will be described with reference to the flowchart of FIG. 2. Steps S1, S2,... in the flowchart will be simply abbreviated as S1, S2,.... When driving the motor in the open winding mode (YES in S1), the main control unit 40 monitors whether it is necessary to switch to the star connection mode in response to a decrease in the load (S2). If switching to the star connection mode is not necessary (NO in S2), the main control unit 40 repeats the determination in S1 above.

[0040] When switching to the star connection mode (YES in S2), the main control unit 40 alternately turns on and off all the upper side switch elements Tu, Tv, Tw and all the lower side switch elements Tx, Ty, Tz in the inverter 30 at an on / off duty of 50% as shown in FIG. 3 so that the potential difference between both ends of each of the relay contacts 12a and 13a becomes zero, and executes a pseudo-neutral point operation (S3).

[0041] FIG. 5 shows an enlarged view in time of the on / off relationship between the upper side switch elements Tu, Tv, Tw and the on / off relationship between the lower side switch elements Tx, Ty, Tz in this pseudo-neutral point operation for easy understanding. When turning on the upper side switch elements Tu, Tv, Tw and turning off the lower side switch elements Tx, Ty, Tz, the main control unit 40 secures a dead time td during which both the upper side switch elements Tu, Tv, Tw and the lower side switch elements Tx, Ty, Tz are in the off state in order to prevent the formation of a short circuit with respect to the output terminal of the converter 10. Similarly, when turning on the lower side switch elements Tx, Ty, Tz and turning off the upper side switch elements Tu, Tv, Tw, the main control unit 40 secures a dead time td during which both the lower side switch elements Tx, Ty, Tz and the upper side switch elements Tu, Tv, Tw are in the off state in order to prevent the formation of a short circuit with respect to the output terminal of the converter 10.

[0042] There are various methods for generating the dead time td. Generally, after turning off the switch element on the side to be turned off, the switch element on the side to be turned on is turned on after the elapse of the dead time td. It is desirable that the dead time td be as short as possible from the viewpoints of efficiency and waveform shaping. In practice, the minimum time based on the on / off transient characteristics of the switch element is allocated.

[0043] However, as will be described later, even if the pseudo-neutral point operation is executed due to the existence of this dead time td, if the switching timing of the inverter 30 and the operation timing of the relay contacts 12a and 13a overlap with the dead time td, a potential difference may occur between both ends of each of the relay contacts 12a and 13a.

[0044] During the execution of the virtual neutral point operation, the main control unit 40 first turns on the auxiliary switches SW1 to SW4 (S4), thereby short-circuiting both ends of each of the relay contacts 12a and 13a, and then turns on the relays 12 and 13 after the short-circuit (S5). Subsequently, after a certain time t1 longer than the time required for the relay contacts 12a and 13a to actually close has elapsed (YES in S6), the main control unit 40 turns off the auxiliary switches SW1 to SW4 (S7). After this, the main control unit 40 ends the virtual neutral point operation and shifts to the motor drive in the star connection mode (S8).

[0045] After this transition, the main control unit 40 returns to the determination in S1 above. Turning on the auxiliary switches SW1 to SW4 in step S4 and turning off the auxiliary switches SW1 to SW4 in step S7 are desirably performed by driving all the auxiliary switches to turn on and off synchronously from the viewpoint of circuit simplification and the like, but it is not necessary to turn on and off completely synchronously. The key is that all the auxiliary switches SW1 to SW4 are turned on before the relay contacts 12a and 13a actually close, and all the auxiliary switches SW1 to SW4 can be turned off after the relay contacts 12a and 13a actually close.

[0046] By the above processing, the operation shown in FIG. 3 is executed. By this operation, during the stable operation in the star connection mode, the auxiliary switches SW1 to SW4 are turned off, so the power consumption when the auxiliary switches SW1 to SW4 are turned on is eliminated, resulting in energy saving, and the heat generation of the auxiliary switches SW1 to SW4 is also eliminated, eliminating the need to take measures against the temperature rise of these semiconductor switches.

[0047] When driving the motor 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 according to the increase in the load (S9). When it is not necessary to switch to the open winding mode (NO in S9), the main control unit 40 returns to the determination in S1 above.

[0048] When a switch to the open winding mode is necessary (YES in S9), the main control unit 40 performs a pseudo-neutral point operation (S10) in which the upper side switch elements Tu, Tv, Tw and the lower side switch elements Tx, Ty, Tz in the inverter 30 are alternately turned on and off at an on / off duty of 50% so that the potential difference between both ends of each of the relay contacts 12a and 13a becomes zero, as shown in FIG. 4. This pseudo-neutral point operation is the same as the pseudo-neutral point operation at the time of switching from the open winding mode to the star connection mode. Note that in this state, since the operation is being performed in the star connection mode, the relay contacts 12a and 13a are on.

[0049] During the execution of this pseudo-neutral point operation, the main control unit 40 first turns on the auxiliary switches SW1 to SW4 (S11), thereby short-circuiting between both ends of each of the relay contacts 12a and 13a, and then turns off the relays 12 and 13 after the short circuit (S12). Subsequently, after a fixed time t2 longer than the time required for the relay contacts 12a and 13a to actually open has elapsed (YES in S13), the main control unit 40 turns off the auxiliary switches SW1 to SW4 (S14). After this, the main control unit 40 ends the pseudo-neutral point operation and shifts to the open winding mode (S15).

[0050] After this transition, the main control unit 40 returns to the determination in S1 above. It is desirable that the turning on of the auxiliary switches SW1 to SW4 in step S11 and the turning off of the auxiliary switches SW1 to SW4 in step S14 drive all the auxiliary switches SW1 to SW4 to be turned on and off synchronously, but it is not necessary to turn them on / off completely synchronously. It is sufficient that all the auxiliary switches SW1 to SW4 are turned on before the relay contacts 12a and 13a actually open and that all the auxiliary switches SW1 to SW4 are turned off after the relay contacts 12a and 13a actually open. By the above processing, the operation shown in FIG. 4 is executed.

[0051] The certain times t1 and t2 may be the same time as each other, and it is desirable to make them as short as possible from the perspective of efficiency. In the mechanical relays 12 and 13, there is a delay of 10 to 30 msec from the energization (actuation) and de-energization (de-actuation) by the exciting current until the relay contacts 12a and 13a actually open and close. Considering this delay, it is desirable to set the certain times t1 and t2 to about 50 msec to 100 msec by adding a margin to the delay time for the relay contacts 12a and 13a to open and close.

[0052] As described above, when the relay contacts 12a and 13a open and close, the virtual neutral point operation is executed in advance and the auxiliary switches SW1 to SW4 are turned on so that the potential difference between both ends of each of the relay contacts 12a and 13a becomes zero.

[0053] However, even when the virtual neutral point operation is executed, current flows through the path of any of the freewheeling diodes D of the upper switch elements Tu, Tv, Tw and the lower switch elements Tx, Ty, Tz of the inverter 30 only during the dead time td when both the upper switch elements Tu, Tv, Tw and the lower switch elements Tx, Ty, Tz are turned off. For example, as shown by the solid arrows in FIG. 6, the motor currents Iv and Iw flow through the paths from the phase windings Lv and Lw through the freewheeling diodes D of the interconnection points Bv and Bw of the inverter 30 and the upper switch elements Tv and Tw, respectively, and the motor current Iu flows through the path from the freewheeling diode D of the lower switch element Tx through the interconnection point Bu and toward the phase winding Lu.

[0054] Fig. 7 shows the relationships between the collector-emitter voltage Vcex of the lower switch element Tx, the collector-emitter voltage Vcey of the lower switch element Ty, the potential difference Vuv1 between the interconnection points Bu and Bv, the potential difference Vuv2 across the relay contact 12a, and the potential difference Vuv3 across the series circuit of the auxiliary switches Sw1 and Sw2 in the current path of Fig. 6. That is, with the collector-emitter voltage Vcex of the lower switch element Tx being zero, the collector-emitter voltage Vcey of the lower switch element Ty rises, and accordingly, the potential difference Vuv1 between the interconnection points Bu and Bv becomes non-zero. When the potential difference Vuv1 occurs, as indicated by the dashed arrow in Fig. 6, a current flows from the interconnection point Bv through the auxiliary switch Sw2 and the auxiliary switch Sw1 towards the interconnection point Bu, voltages are generated across the first inductances Lsu1, Lsv1 and the second inductances Lsu2, Lsv2, and the potential difference Vuv2 across the relay contact 12a becomes non-zero. Thereafter, the collector-emitter voltage Vcex of the lower switch element Tx and the collector-emitter voltage Vcey of the lower switch element Ty become the same value, and accordingly, the potential difference Vuv1 between the interconnection points Bu and Bv becomes zero. A similar phenomenon also occurs at the relay contact 13a.

[0055] In the relay contact 12a which is a mechanical make-and-break contact, since the exact opening and closing times cannot be controlled as described above, the relay contact 12a may open and close at a timing when the potential difference Vuv2 across the relay contact 12a is non-zero. If the relay contact 12a opens and closes while the potential difference Vuv2 across the relay contact 12a is non-zero, there is a possibility that a surge voltage or an arc may be generated across the relay contact 12a. Since the dead time td is an extremely short time compared to the normal on and off periods of the inverter 30, the possibility that the relay contact 12a actually opens and closes while the potential difference across the relay contact 12a is non-zero is extremely low. However, since the occurrence probability is not zero, some countermeasures are necessary.

[0056] Here, the potential difference Vuv2 between both ends of the relay contact 12a varies according to the relationship of the sum value "Lsu1 + Lsu2" of the value of the first inductance Lsu1 of the wiring 52u from the interconnection point Bu to the branch point N1 and the value of the second inductance Lsu2 of the wiring 53u, the sum value "=Lsv1 + Lsv2" of the value of the first inductance Lsv1 of the wiring 52v from the interconnection point Bv to the branch point N2 and the value of the second inductance Lsv2 of the wiring 53v, the value of the third inductance Lsu3 of the wiring 54u between the branch point N1 and one end of the series circuit of the auxiliary switches SW1 and SW2, and the value of the third inductance Lsv3 of the wiring 54v between the branch point N2 and the other end of the series circuit of the auxiliary switches SW1 and SW2.

[0057] For example, when the sum value "Lsu1 + Lsu2" of the value of the first inductance Lsu1 and the value of the second inductance Lsu2 is smaller than the value of the third inductance Lsu3 ("Lsu1 + Lsu2" < Lsu3), and when the sum value "Lsv1 + Lsv2" of the value of the first inductance Lsv1 and the value of the second inductance Lsv2 is smaller than the value of the third inductance Lsv3 ("Lsv1 + Lsv2" < Lsv3), a potential difference Vuv2 of the magnitude shown in FIG. 7 occurs. On the contrary, when the value of the third inductance Lsu3 is smaller than the above "sum value "Lsu1 + Lsu2" (Lsu3 < "Lsu1 + Lsu2"), and when the value of the third inductance Lsv3 is smaller than the above sum value "Lsv1 + Lsv2" (Lsv3 < "Lsv1 + Lsv2"), as shown in FIG. 8, the potential difference Vuv2 can be suppressed to be smaller than that in the case of FIG. 7.

[0058] Similarly, the potential difference Vvw2 between both ends of the relay contact 13a also changes according to the relationship between the total value “Lsv1 + Lsv2” of the value of the first inductance Lsv1 of the wiring 52v from the interconnection point Bv to the branch point N2 and the value of the second inductance Lsv2 of the wiring 53v, the total value “Lsw1 + Lsw2” of the value of the first inductance Lsw1 of the wiring 52w from the interconnection point Bw to the branch point N3 and the value of the second inductance Lsw2 of the wiring 53w, the value of the third inductance Lsv3 of the wiring 54v between the branch point N2 and one end of the series circuit of the auxiliary switches SW3 and SW4, and the value of the third inductance Lsw3 of the wiring 54w between the branch point N3 and the other end of the series circuit of the auxiliary switches SW3 and SW4.

[0059] That is, when the value of the third inductance Lsv3 is smaller than the above “total value “Lsv1 + Lsv2” (Lsv3 < “Lsv1 + Lsv2”) and the value of the third inductance Lsw3 is smaller than the above total value “Lsw1 + Lsw2” (Lsw3 < “Lsw1 + Lsw2”), the potential difference Vvw2 between both ends of the relay contact 13a can be kept small. By setting such inductance values, the adverse effects on the relay contacts 12a and 13a can be reduced to a level without problems.

[0060] Focusing on these points, in this embodiment, the value of the third inductance Lsu2 is smaller than the sum value "Lsu1 + Lsu2" of the value of the first inductance Lsu1 and the value of the second inductance Lsu2 (Lsu1 < "Lsu1 + Lsu2"), the value of the third inductance Lsv2 is smaller than the sum value "Lsv1 + Lsv2" of the value of the first inductance Lsv1 and the value of the second inductance Lsv2 (Lsv1 < "Lsv1 + Lsv2"), and the value of the third inductance Lsw2 is smaller than the sum value "Lsw1 + Lsw2" of the value of the first inductance Lsw1 and the value of the second inductance Lsw2 (Lsw1 < "Lsw1 + Lsw2"), and thus, in order to make the potential differences Vuv2 and Vvw2 smaller, the lengths of the respective wirings (third wirings) 54u, 54v, 54w are set to be as short as possible compared to the sum value of the lengths of the respective wirings (first wirings) 52u, 52v, 52w and the lengths of the respective wirings (second wirings) 53u, 53v, 53w. For example, by bringing the arrangement positions of the relay contacts 12a and 13a as close as possible to the arrangement positions of the auxiliary switches SW1 to SW4, the lengths of the wirings 54u, 54v, 54w can be shortened.

[0061] The values of the parasitic inductances generated in the wirings such as the first inductances Lsu1, Lsv1, Lsw1, the second inductances Lsu2, Lsv2, Lsw2, and the third inductances Lsu3, Lsv3, Lsw3 are generally proportional to the wiring lengths. The shorter the lengths of the wirings 54u, 54v, 54w, the smaller the values of the third inductances Lsu3, Lsv3, Lsw3 can be. Therefore, in this embodiment, it is set that "the length of the wiring 54u + the length of the wiring 52u" > "the length of the wiring 53u", "the length of the wiring 54v + the length of the wiring 52v" > "the length of the wiring 53v", and "the length of the wiring 54w + the length of the wiring 52w" > "the length of the wiring 53w".

[0062] Note that since the magnitudes of the potential differences Vuv2 and Vvw2 across both ends of each of the relay contacts 12a and 13a are determined by the relative relationship between the above total values “Lsu1 + Lsu2”, “Lsv1 + Lsv2”, “Lsw1 + Lsw2” and the values of the third inductances Lsu3, Lsv3, and Lsw3, even if the total values “Lsu1 + Lsu2”, “Lsv1 + Lsv2”, “Lsw1 + Lsw2” are made larger than the values of the third inductances Lsu3, Lsv3, and Lsw3, it is possible to keep the potential differences Vuv2 and Vvw2 small. To make the total values “Lsu1 + Lsu2”, “Lsv1 + Lsv2”, “Lsw1 + Lsw2” larger than the values of the third inductances Lsu3, Lsv3, and Lsw3, it is only necessary to increase the total length of the lengths of the wirings 52u, 52v, 52w and the lengths of the wirings 53u, 53v, 53w. Also, in order to make the total values “Lsu1 + Lsu2”, “Lsv1 + Lsv2”, “Lsw1 + Lsw2” larger than the values of the third inductances Lsu3, Lsv3, and Lsw3, inductance elements such as small coils may be inserted respectively in the middle parts of the wirings 52u, 52v, 52w or the wirings 53u, 53v, 53w. However, in these countermeasures, since the resistance value increases accordingly with the extension of the wiring length or the addition of the coils, resulting in power loss, it is more preferable to take the measure of making the lengths of the wirings 54u, 54v, 54w as short as possible as described above.

[0063] In this way, by suppressing the potential differences Vuv2 and Vvw2 generated across both ends of each of the relay contacts 12a and 13a, even if the relay contacts 12a and 13a open and close in a state where the potential differences Vuv2 and Vvw2 are generated, it is possible to eliminate the problem of the occurrence of a surge voltage or an arc of a size that causes problems across both ends of the relay contacts 12a and 13a. As a result, it is possible to avoid an adverse effect on the life of the relays 12 and 13 and prevent the destruction of each switching element of the inverters 20 and 30 due to the surge voltage or the arc.

[0064] [2] Second Embodiment The configuration of the second embodiment is shown in FIG. 9. Between the branch points N1 and N2 at the tips of the wirings (second wirings) 53u and 53v connected to the other ends (terminals 32u and 32v) of the phase windings Lu and Lv of the motor 1M, a series circuit of auxiliary switches SW1 and SW2 is connected via the wirings (third wirings) 54u and 54v1. Between the branch points N2 and N3 at the tips of the wirings (second wirings) 53v and 53w connected to the other ends (terminals 32v and 32w) of the phase windings Lv and Lw of the motor 1M, a series circuit of auxiliary switches SW3 and SW4 is connected via the wirings (third wirings) 54v2 and 54w.

[0065] And, a relay contact 12a is connected between the branch points N1 and N2 via the wirings (fourth wirings) 55u and 55v. A relay contact 13a is connected between the branch points N2 and N3 via the wirings (fourth wirings) 55v and 55w.

[0066] That is, the tip of the wiring 53u branches into the wiring 54u and the wiring 55u at the branch point N1, and the tip of the wiring 53v branches into three, the wirings 54v1, 54v2, and the wiring 55v at the branch point N2. Similarly, the tip of the wiring 53w branches into the wiring 54w and the wiring 55w at the branch point N3. The wiring 54u is connected to the auxiliary switch SW1 side in the series circuit of the auxiliary switches SW1 and SW2, and the wiring 54v1 is connected to the auxiliary switch SW2 side in the series circuit of the auxiliary switches SW1 and SW2. The wiring 54v2 is connected to the auxiliary switch SW3 side in the series circuit of the auxiliary switches SW3 and SW4, and the wiring 54w is connected to the auxiliary switch SW4 side in the series circuit of the auxiliary switches SW3 and SW4. The auxiliary switches SW2 and SW3 are in a state of being connected in series with each other via the branch point N2 and the wirings 54v1 and 54v2.

[0067] The wirings 54u and 54v1 start from the branch points N1 and N2 and end at both ends of the series circuit of the auxiliary switches SW1 and SW2. The wirings 54v2 and 54w start from the branch points N2 and N3 and end at both ends of the series circuit of the auxiliary switches SW2 and SW3.

[0068] The relay contact 12a is connected in parallel to the series circuit of the auxiliary switches SW1 and SW2 by the wirings 55u and 55v. The relay contact 13a is connected in parallel to the series circuit of the auxiliary switches SW3 and SW4 by the wirings 55v and 55w. The wiring 55u is electrically connected to the wiring 53u via the branch point N1, the wiring 55v is electrically connected to the wiring 53v via the branch point N2, and the wiring 55w is electrically connected to the wiring 53w via the branch point N2. The other end of the relay contact 12a and one end of the relay contact 13a are electrically connected via a common connection point P1 connected to the wiring 55v. The wirings 55u and 55v start from the branch points N1 and N2 and end at both ends of the relay contact 12a. The wirings 55v and 55w start from the branch points N2 and N3 and end at both ends of the relay contact 12a.

[0069] Also in this second embodiment, similar to the first embodiment, the relationships of the values of the first inductances Lsu1, Lsv1, Lsw1, the values of the second inductances Lsu2, Lsv2, Lsw2, and the values of the third inductances Lsu3, Lsv3, Lsw3 need to satisfy the above conditions of (Lsu1 < “Lsu1+Lsu2”), (Lsv1 < “Lsv1+Lsv2”), (Lsw1 < “Lsw1+Lsw2”). Therefore, by using the circuit configuration of this second embodiment, the lengths of the wirings 54u to 54w can be made extremely short due to the circuit configuration, so that the above conditions can be satisfied without performing a troublesome wiring routing design. Other configurations are the same as those of the first embodiment.

[0070] [3] Third Embodiment The main part of the configuration of the third embodiment is shown in FIG. 10. A relay contact 12a is connected between the branch points N1 and N2 at the tips of the wirings 53u and 53v connected to the other ends (terminals 32u and 32v) of the phase windings Lu and Lv of the motor 1M. A relay contact 13a is connected between the branch points N2 and N3 at the tips of the wirings 53v and 53w connected to the other ends (terminals 32v and 32w) of the phase windings Lv and Lw of the motor 1M.

[0071] And a series circuit of auxiliary switches SW1 and SW2 is connected in parallel to relay contact 12a by wirings 54u and 54v connected to branch points N1 and N2. A series circuit of auxiliary switches SW2 and SW3 is connected in parallel to relay contact 13a by wirings 54v and 54w connected to branch points N2 and N3. The auxiliary switches SW1 to SW3 are semiconductor switch elements, such as IGBTs or MOS-FETs, to which a freewheeling diode D is connected in the reverse parallel direction to each element body. Emitters of the three auxiliary switches SW1, SW2, and SW3 are commonly connected at a common connection point (virtual neutral point) P2 in the figure.

[0072] The first wiring 54u and the second wiring 54v start from branch points N1 and N2 and end at both ends of the series circuit of auxiliary switches SW1 and SW2. The second wiring 54v and the third wiring 54w start from branch points N2 and N3 and end at both ends of the series circuit of auxiliary switches SW2 and SW3. Other configurations are the same as those in the first embodiment, including the relationships of the values of the first inductances Lsu1, Lsv1, Lsw1, the values of the second inductances Lsu2, Lsv2, Lsw2, and the values of the third inductances Lsu3, Lsv3, Lsw3. The three auxiliary switches SW1, SW2, and SW3 are turned on and off simultaneously in the same manner as the four auxiliary switches SW1 to SW4 in the first embodiment.

[0073] When the auxiliary switches SW1, SW2, and SW3 are turned off with the relay contacts 12a and 13a open, the phase windings Lu, Lv, and Lw of the motor 1M are in an open winding state where they are separated from each other. When the auxiliary switches SW1, SW2, and SW3 are turned on with the relay contacts 12a and 13a open, the other ends of the phase windings Lu, Lv, and Lw of the motor 1M are short-circuited through the auxiliary switches SW1, SW2, SW3 and the common connection point P2, resulting in a star connection mode. When the relay contacts 12a and 13a are closed with the auxiliary switches SW1, SW2, and SW3 off, the other ends of the phase windings Lu, Lv, and Lw of the motor 1M are short-circuited through the relay contacts 12a, 13a, and the branch point N2, resulting in a star connection mode. According to the configuration of this embodiment, the number of auxiliary switches SW1, SW2, and SW3, that is, the number of semiconductor switch elements, is only three, which is less than that in the first and second embodiments, and the circuit can be simplified.

[0074] [4] Fourth Embodiment The main part of the configuration of the fourth embodiment is shown in FIG. 11. Between the branch points N1 and N2 at the tips of the wirings (second wirings) 53u and 53v connected to the other ends (terminals 32u and 32v) of the phase windings Lu and Lv of the motor 1M, a series circuit of the auxiliary switches SW1 and SW2 is connected by the wirings (third wirings) 54u and 54v. Between the branch points N2 and N3 at the tips of the wirings (second wirings) 53v and 53w connected to the other ends (terminals 32v and 32w) of the phase windings Lv and Lw of the motor 1M, a series circuit of the auxiliary switches SW2 and SW3 is connected by the wirings (third wirings) 54v and 54w.

[0075] And the relay contact 12a is connected in parallel to the series circuit of the auxiliary switches SW1 and SW2 by the wirings (fourth wirings) 55u and 55v connected to the branch points N1 and N2. The relay contact 13a is connected in parallel to the series circuit of the auxiliary switches SW2 and SW3 by the wirings (fourth wirings) 55v and 55w connected to the branch points N2 and N3. The other end of the relay 12a connected to the wiring 55v and one end of the relay 13a connected to the wiring 55v are connected at the common connection point P1.

[0076] The first wiring 54u and the second wiring 54v start from the branch points N1 and N2 and end at both ends of the series circuit of the auxiliary switches SW1 and SW2. The above-mentioned second wiring 54v and the third wiring 54w start from the branch points N2 and N3 and end at both ends of the series circuit of the auxiliary switches SW2 and SW3.

[0077] The first wiring 55u and the second wiring 55v start from the branch points N1 and N2 and end at both ends of the relay contact 12a. The second wiring 55v and the third wiring 55w start from the branch points N2 and N3 and end at both ends of the relay contact 13a. Other configurations are the same as those of the first embodiment, including the relationships of the values of the first inductances Lsu1, Lsv1, Lsw1, the values of the second inductances Lsu2, Lsv2, Lsw2, and the values of the third inductances Lsu3, Lsv3, Lsw3. The three auxiliary switches SW1, SW2, and SW3 are simultaneously turned on and off in the same manner as the four auxiliary switches SW1 to SW4 of the first embodiment.

[0078] When the auxiliary switches SW1, SW2, and SW3 are turned off with the relay contacts 12a and 13a open, the phase windings Lu, Lv, and Lw of the motor 1M are in an open winding state separated from each other. When the auxiliary switches SW1, SW2, and SW3 are turned on with the relay contacts 12a and 13a open, the other ends of the phase windings Lu, Lv, and Lw of the motor 1M are short-circuited through the auxiliary switches SW1, SW2, and SW3 and the common connection point P2, resulting in a star connection mode. When the relay contacts 12a and 13a are closed with the auxiliary switches SW1, SW2, and SW3 off, the other ends of the phase windings Lu, Lv, and Lw of the motor 1M are short-circuited through the relay contacts 12a and 13a and the branch point N2, resulting in a star connection mode. According to the configuration of this embodiment, the number of auxiliary switches SW1, SW2, and SW3, that is, the number of semiconductor switch elements, is only three, and the number of semiconductor switch elements is less than that of the first and second embodiments, enabling circuit simplification.

[0079] [5] Modification The above-described embodiments are presented as examples and are not intended to limit the scope of the invention. This novel embodiment and its variations can be implemented in various other forms, and various omissions, rewritings, and changes can be made without departing from the gist of the invention. These embodiments and variations are included in the scope of the invention as well as in the scope of the invention described in the claims and its equivalents.

Description of Reference Numerals

[0080] 2... drive circuit, 3... open-winding motor, Lu, Lv, Lw... phase windings, 4... controller, 12, 13... relays (switches), 12a, 13a... switch contacts (relay contacts), SW1 to SW4... semiconductor switch elements, Lsu1, Lsv1, Lsw1... first inductances, Lsu2, Lsv2, Lsw2... second inductances, 20... inverter (first inverter), 30... inverter (second inverter), 40... main control unit

Claims

1. A motor drive device for a motor having a plurality of phase windings that are not connected to each other, including a plurality of series circuits of an upper switch element and a lower switch element, both ends of these series circuits being connected to a DC power supply, and the interconnection points of the upper switch element and the lower switch element of each series circuit being connected to one end of each phase winding; a first inverter, including a plurality of series circuits of an upper switch element and a lower switch element, both ends of these series circuits being connected to the DC power supply, and the interconnection points of the upper switch element and the lower switch element of each series circuit being connected to the other end of each phase winding by each first wiring; a second inverter, a plurality of open / close contacts connected to each other between the other ends of each phase winding by each second wiring, a plurality of semiconductor switch elements connected in parallel to each open / close contact by each third wiring, a controller for controlling the driving of the first inverter, the driving of the second inverter, and the opening and closing of each open / close contact, comprising: when opening and closing each open / close contact, the controller executes a pseudo neutral point operation of alternately turning on and off all of the upper switch elements and all of the lower switch elements in the second inverter in advance and turns on each semiconductor switch element, each first wiring has a first inductance respectively, each second wiring has a second inductance respectively, each third wiring has a third inductance respectively, wherein the value of the third inductance is smaller than the sum of the value of the first inductance and the value of the second inductance, a motor drive device.

2. The controller selectively sets a star connection mode in which the other ends of each phase winding are interconnected by closing each open / close contact and the switch elements of the first inverter are driven to be turned on and off, and an open winding mode in which the other ends of each phase winding are disconnected by opening each open / close contact and the switch elements of the first inverter and the switch elements of the second inverter are driven to be turned on and off in relation to each other. The motor drive device according to Claim 1. The motor drive device according to claim 1.

3. When driving the upper and lower switch elements in the first inverter to be on and off, the controller ensures a dead time during which both the upper and lower switch elements in each series circuit in the first inverter are off, and when driving the upper and lower switch elements in the second inverter to be on and off, the controller ensures a dead time during which both the upper and lower switch elements in each series circuit in the second inverter are off. The motor drive device according to claim 1.

4. 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 switch element and a lower switch element, both ends of these series circuits being connected to a DC power supply, and the interconnection point of the upper and lower switch elements in each series circuit being connected to one end of each phase winding; a second inverter including a plurality of series circuits of an upper switch element and a lower switch element, both ends of these series circuits being connected to the DC power supply, and the interconnection point of the upper and lower switch elements in each series circuit being connected to the other end of each phase winding by each first wiring; a plurality of semiconductor switch elements connected by each second wiring and each third wiring between the other ends of the respective phase windings; a plurality of open / close contacts connected in parallel to each semiconductor switch element by each fourth wiring; a controller for controlling the driving of the first inverter, the driving of the second inverter, and the opening and closing of each open / close contact; comprising When opening and closing each open / close contact, the controller executes a pseudo-neutral point operation in which all of the upper switch elements and all of the lower switch elements in the second inverter are alternately turned on and off in advance and turns on each semiconductor switch element. Each of the first wirings has a first inductance respectively. Each of the second wirings has a second inductance respectively. Each of the third wirings has a third inductance respectively. The value of the third inductance is smaller than the sum of the value of the first inductance and the value of the second inductance. Motor drive device.

5. The controller selectively sets a star connection mode in which the other ends of the respective phase windings are interconnected by closing of the respective opening / closing contacts and the respective switch elements of the first inverter are driven on and off, and an open winding mode in which the other ends of the respective phase windings are disconnected by opening of the respective opening / closing contacts and the respective switch elements of the first inverter and the respective switch elements of the second inverter are driven on and off in association with each other. The motor drive device according to claim 4.

6. When driving the upper switch element and the lower switch element in the first inverter on and off, the controller ensures a dead time during which the upper switch element and the lower switch element in each series circuit in the first inverter are both off, and when driving the upper switch element and the lower switch element in the second inverter on and off, the controller ensures a dead time during which the upper switch element and the lower switch element in each series circuit in the second inverter are both off. The motor drive device according to claim 4.

7. 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 switch element and a lower switch element, both ends of these series circuits being connected to a DC power supply, and the interconnection points of the upper switch element and the lower switch element in each series circuit being connected to one end of each phase winding, A second inverter including a plurality of series circuits of an upper switch element and a lower switch element, both ends of these series circuits being connected to the DC power supply, and the interconnection points of the upper switch element and the lower switch element in each series circuit being connected to the other end of each phase winding by each first wiring, A plurality of opening / closing contacts connected to each other between the other ends of the respective phase windings by each second wiring, A plurality of semiconductor switch elements connected in parallel to each of the opening / closing contacts by each third wiring, A controller for controlling the driving of the first inverter, the driving of the second inverter, and the opening and closing of the respective opening / closing contacts, comprising: When opening and closing the respective opening / closing contacts, the controller executes a pseudo neutral point operation of alternately turning on and off all of the upper switch elements and all of the lower switch elements in the second inverter in advance and turns on the respective semiconductor switch elements. Each of the first wirings has a length. Each of the second wirings has a length, Each of the third wirings has a length, In all of the third wirings, the length of the third wiring is shorter than the total value of the length of the first wiring and the length of the second wiring connected to the third wiring, Motor drive device.

8. Each of the phase windings is three phase windings Lu, Lv, Lw, Each of the first wirings is three first wirings connected to the other ends of the Lu, Lv, Lw, Each of the second wirings is three second wirings starting from the other ends of the Lu, Lv, Lw and ending at three branch points N1, N2, N3, Each of the opening and closing contacts is a first opening and closing contact connected between the branch points N1 and N2 and a second opening and closing contact connected between the branch points N2 and N3, Each of the semiconductor switch elements is three semiconductor switch elements Sw1, Sw2, Sw3, Each of the third wirings is such that the first third wiring and the second third wiring start from the branch points N1 and N2 respectively and end at both ends of the series circuit of the semiconductor switch elements Sw1 and Sw2, and the second third wiring and the third third wiring start from the branch points N2 and N3 respectively and end at both ends of the series circuit of the semiconductor switch elements Sw2 and Sw3, The motor drive device according to claim 1 or claim 7.

9. Each of the phase windings is three phase windings Lu, Lv, Lw, Each of the first wirings is three first wirings connected to the other ends of the Lu, Lv, Lw, Each of the second wirings is three second wirings starting from the other ends of the Lu, Lv, Lw and ending at three branch points N1, N2, N3, Each of the opening and closing contacts is a first opening and closing contact connected between the branch points N1 and N2 and a second opening and closing contact connected between the branch points N2 and N3, Each of the semiconductor switch elements is three semiconductor switch elements Sw1, Sw2, Sw3, One ends of the three semiconductor switch elements Sw1, Sw2, Sw3 are commonly connected, Each of the third wirings is such that the first third wiring starts from the branch point N1 and ends at the other end of the semiconductor switch element Sw1, the second third wiring starts from the branch point N2 and ends at the other end of the semiconductor switch element Sw2, and the third third wiring starts from the branch point N3 and ends at the other end of the semiconductor switch element Sw2, The motor drive device according to claim 1 or claim 7.

10. Each of the phase windings is three phase windings Lu, Lv, Lw, Each of the first wirings is three first wirings connected to the other ends of the Lu, Lv, Lw, Each of the second wirings is three second wirings starting from the other ends of the Lu, Lv, Lw and ending at three branch points N1, N2, N3, Each of the semiconductor switch elements is three semiconductor switch elements Sw1, Sw2, Sw3, Each of the third wirings is such that the first third wiring and the second third wiring start from the branch points N1, N2 respectively and end at both ends of the series circuit of the semiconductor switch elements Sw1, Sw2, and the second third wiring and the third third wiring start from the branch points N2, N3 respectively and end at both ends of the series circuit of the semiconductor switch elements Sw2, Sw3, which are three third wirings, Each of the fourth wirings is such that the first fourth wiring and the second fourth wiring start from the branch points N1, N2 and end at both ends of the first on-off contact, and the second fourth wiring and the third fourth wiring end at both ends of the second on-off contact, which are three fourth wirings, The motor drive device according to claim 4 or claim 7.

11. Each of the semiconductor switch elements has a freewheeling diode connected in the reverse parallel direction to its respective element body The motor drive device according to any one of claims 1, 4, and 7.

12. A refrigeration cycle device including a compressor driven by the motor drive device according to any one of claims 1, 4, and 7.

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