Motor drive device and refrigeration cycle device

Abstract

A motor drive device includes a first inverter, a second inverter, a plurality of on-off contacts, a plurality of semiconductor switching elements, and a controller. The controller performs a virtual neutral point operation in advance and turns on the semiconductor switching elements when the opening and closing contacts are opened and closed. 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 the third inductance is smaller than the sum of the value of the first inductance and the value of the second inductance.

Description

Technical Field

[0001] The present invention relates to a motor drive device of a motor having a plurality of phase windings that are not connected to each other, and a refrigeration cycle device equipped with the motor drive device. Background Art

[0002] As drive motors for compressors mounted in refrigeration cycle devices such as air conditioners, there are known permanent magnet synchronous motors having multiple phase windings and open-winding motors having multiple, for example, three phase windings that are not connected to each other.

[0003] A motor drive device for driving an open-circuit winding motor (referred to as a motor for short) comprises: a first inverter for controlling the energization of one end of each phase winding of the motor; a second inverter for controlling the energization of the other end of each phase winding of the motor; and one or more switches for connecting the other ends of each phase winding to each other. The motor drive device selectively sets a star connection mode and an open-circuit winding mode. In the star connection mode, the other ends of each phase winding are connected to each other by closing the switch, that is, set to a so-called star connection (also called a star connection) to switch the first inverter alone, thereby driving the motor. In the open-circuit winding mode, the other ends of each phase winding are set to a non-connected state separated from each other by opening the above-mentioned switch to switch the first and second inverters in a linked manner, thereby driving the motor.

[0004] By setting the open-circuit winding mode, the voltage applied to each phase winding can be increased, the back electromotive force generated in the permanent magnet synchronous motor can be overcome, and the motor can be driven at a high speed. By setting the star connection mode in the low speed area, the motor can be driven with high efficiency. That is, the motor can be driven as efficiently as possible in a wide operating range from high speed to low speed. In this way, the expansion of the operating range of the motor and the improvement of the efficiency of the motor drive device can be taken into account.

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

[0006] However, during motor driving, a potential difference is generated between the two ends of the above-mentioned opening and closing contacts, that is, between the other ends of each phase winding. If the opening and closing contacts are opened and closed in a state where such a potential difference is generated, a surge voltage and an arc are generated between the two ends of the opening and closing contacts, which have an adverse effect on the life of the opening and closing contacts. Furthermore, due to these surge voltages and arcs, the switching elements of each inverter may also be damaged.

[0007] Therefore, as a countermeasure, a virtual neutral point operation is performed by the switch of the second inverter so that no potential difference is generated between both ends of the opening and closing contacts, and the opening and closing relay contacts are controlled during this operation.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent No. 4804381

[0011] Patent Document 2: Japanese Patent Application Publication No. 2019-62726 Summary of the invention

[0012] Technical problem to be solved by the invention

[0013] However, various test results show that even during execution of the virtual neutral point operation, a potential difference is generated between both ends of the open and close contacts due to the relationship between the switching timing of the second inverter and the operation timing of the relay contacts.

[0014] Therefore, an object of an embodiment of the present invention is to provide a motor drive device and a refrigeration cycle device that are capable of suppressing the potential difference between both ends of a switching contact to be as small as possible and that are excellent in safety and reliability.

[0015] Solutions for solving the above technical problems

[0016] The motor drive device of the embodiment is a motor drive device for a motor having multiple phase windings that are in a non-connected state with each other, and comprises: a first inverter, which includes a series circuit of multiple upper switching elements and lower switching elements, the two ends of these series circuits are connected to a DC power supply, and the mutual connection point of the upper switching elements and the lower switching elements of each series circuit is connected to one end of each phase winding; a second inverter, which includes a series circuit of multiple upper switching elements and lower switching elements, the two ends of these series circuits are connected to the DC power supply, and the mutual connection point of the upper switching elements and the lower switching elements of each series circuit is connected to the other end of each phase winding through each first wiring; a plurality of opening and closing contacts are connected to each other at the other end of each phase winding through each second wiring; a plurality of semiconductor switching elements are connected in parallel with respect to each opening and closing contact through each third wiring; a controller controls the driving of the first inverter, the driving of the second inverter, and the opening and closing of each opening and closing contact. The controller performs a virtual neutral point operation in advance to alternately turn on and off all the upper switching elements and all the lower switching elements in the second inverter when the opening and closing contacts are opened and closed, and turns on the semiconductor switching elements. The first wirings each have a first inductance, the second wirings each have a second inductance, and the third wirings each have a third inductance. 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.

[0017] The refrigeration cycle apparatus according to the embodiment includes a compressor driven by the above-mentioned motor drive device. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a block diagram showing the structure of the first embodiment.

[0019] Figure 2 This is a flowchart showing control in the first embodiment.

[0020] Figure 3 This is a timing chart showing a virtual neutral point operation and a closing operation of each switching contact point executed when switching from the open winding mode to the star connection mode in the first embodiment.

[0021] Figure 4 This is a timing chart showing a virtual neutral point operation and an opening operation of each switching contact performed when switching from the star connection mode to the open winding mode in the first embodiment.

[0022] Figure 5 is shown magnified in time Figure 3 as well as Figure 4 The timing diagram of the conduction and disconnection of each switching element in the virtual neutral point operation.

[0023] Figure 6 This is a diagram showing the flow of current during the dead time in the first embodiment.

[0024] Figure 7 It is shown Figure 6 A diagram showing changes in voltage and potential difference of each part when current flows.

[0025] Figure 8 It is shown Figure 6 A diagram showing other changes in the voltage and potential difference of each part when current flows.

[0026] Fig. 9 This is a block diagram showing the structure of the second embodiment.

[0027] Fig.10 This is a block diagram showing a main part of the configuration of the third embodiment.

[0028] Fig.11 This is a block diagram showing a main part of the configuration of the fourth embodiment. DETAILED DESCRIPTION

[0029] [1] First Embodiment

[0030] The first embodiment will be described with reference to the drawings.

[0031] like Figure 1 As shown, a three-phase AC power supply 1 is connected to a motor drive circuit 2, and an output end of the motor drive circuit 2 is connected to a motor 3 and a controller 4. In this embodiment, the motor 3 is a compressor drive motor for driving a compressor of an air conditioner as a refrigeration cycle device.

[0032] Motor 3 is a three-phase permanent magnet synchronous motor for driving a compressor having three phase windings Lu, Lv, Lw that are in a non-connected state. Specifically, it is a so-called open-winding motor having three terminals 31u, 31v, 31w which are one end of each phase winding Lu, Lv, Lw and three terminals 32u, 32v, 32w which are the other end of each phase winding Lu, Lv, Lw.

[0033] 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 side power line C1 and a negative side power line C2 connected to the output end of the converter 10, an inverter (first inverter) 20 and an inverter (second inverter) 30 connected between the positive side power line C1 and the negative side power line C2.

[0034] 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 of each of the phase windings Lu, Lv, and Lw of the open-winding motor 3, namely, the terminals 31u, 31v, and 31w. The inverter 30 controls the energization of each of the phase windings Lu, Lv, and Lw of the open-winding motor 3, namely, the terminals 32u, 32v, and 32w. The converter 10 adopts a DC link sharing method as a DC power supply shared by the inverters 20 and 30.

[0035] The inverter 20 is a so-called three-phase inverter, and includes a U-phase series circuit in which an upper switching element Tu and a lower switching element Tx are connected in series, a V-phase series circuit in which an upper switching element Tv and a lower switching element Ty are connected in series, and a W-phase series circuit in which an upper switching element Tw and a lower switching element Tz are connected 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 a positive-side 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 a negative-side power supply line C2.

[0036] The mutual connection point Au of the upper switching element Tu and the lower switching element Tx is connected to the terminal 31u, which is one end of the phase winding Lu, through a wiring 51u such as a lead wire or a conductive pattern. The mutual connection point Av of the upper switching element Tv and the lower switching element Ty is connected to the terminal 31v, which is one end of the phase winding Lv, through a wiring 51v such as a lead wire or a conductive pattern. The mutual connection point Az of the upper switching element Tw and the lower switching element Tz is connected to the terminal 31w, which is one end of the phase winding Lz, through a wiring 51w such as a lead wire or a conductive pattern.

[0037] The inverter 30 is a so-called three-phase inverter having the same circuit configuration as the inverter 20, and includes a U-phase series circuit in which an upper switching element Tu and a lower switching element Tx are connected in series, a V-phase series circuit in which an upper switching element Tv and a lower switching element Ty are connected in series, and a W-phase series circuit in which an upper switching element Tw and a lower switching element Tz are connected 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 a positive-side 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 a negative-side power supply line C2.

[0038] The mutual connection point Bu of the upper switching element Tu and the lower switching element Tx is connected to the terminal 32u, which is the other end of the phase winding Lu, through a wiring (first wiring) 52u such as a lead wire or a conductive pattern. The mutual connection point Bv of the upper switching element Tv and the lower switching element Ty is connected to the terminal 32v, which is the other end of the phase winding Lv, through a wiring (first wiring) 52v such as a lead wire or a conductive pattern. The mutual connection point Bw of the upper switching element Tw and the lower switching element Tz is connected to the terminal 32w, which is the other end of the phase winding Lz, through a wiring (first wiring) 52w such as a lead wire or a conductive pattern.

[0039] All the switching elements Tu to Tz of the inverters 20 and 30 are IGBTs in which a freewheeling diode (also called a commutation diode) D is connected in antiparallel to the switching element body. Not limited to IGBTs, MOS-FETs and the like may be used as the switching elements Tu to Tz.

[0040] Inverter 20 is actually a module that houses a main circuit formed by bridging 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 switching element of the main circuit in a single package, namely, a so-called IPM (Intelligent Power Module). Inverter 30 is also an IPM. Not limited to IPM, inverters 20 and 30 in which all switching elements Tu~Tz and drive circuits are constructed as discrete components can also be used. Not limited to three-phase inverters, as long as it can perform six corresponding switches, two three-phase inverters 20 and 30 can also be constructed by three single-phase inverters.

[0041] A switch having a mechanical opening and closing contact, such as a normally open first opening and closing contact (referred to as a relay contact) 12a of the relay 12, is connected between the other end (terminal 32u) of the phase winding Lu of the motor 1M and the other end (terminal 32v) of the phase winding Lv through wiring (second wiring) 53u, 53v such as a lead wire or a conductive pattern. A switch having a mechanical opening and closing contact, such as a normally open second opening and closing contact (referred to as a relay contact) 13a of the relay 13, is connected between the other end (terminal 32v) of the phase winding Lv of the motor 1M and the other end (terminal 32w) of the phase winding Lw through wiring (second wiring) 53v, 53w such as a lead wire or a conductive pattern. The relays 12 and 13 are controlled by the controller 4 to be turned on (excited) by supply of an excitation current and turned off (de-excited) by cutoff of the excitation current in synchronization with each other. Therefore, a configuration may be adopted in which one relay including two relay contacts is used instead of the two relays 12 and 13 .

[0042] By turning on (excitation) the relays 12 and 13, 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 to each other via the relay contact 12a, and the other end of the phase winding Lv and the other end of the phase winding Lw are connected to each other via the relay contact 13a. That is, the phase windings Lu, Lv, and Lw are in a star connection state (also called a star connection state). By turning off (de-excitation) the relays 12 and 13, the relay contacts 12a and 13a are disconnected, and the phase windings Lu, Lv, and Lw are in a non-connected state separated from each other, that is, an open-circuit winding state electrically separated.

[0043] Furthermore, the series circuit of auxiliary switches SW1 and SW2 is connected in parallel to the relay contact 12a via wiring (third wiring) 54u and 54v such as lead wires or conductive patterns. The series circuit of auxiliary switches SW3 and SW4 is connected in parallel to the relay contact 13a via wiring (third wiring) 54v and 54w such as lead wires or conductive patterns.

[0044] Specifically, at the connection point N1 between the wiring 53u and one end of the relay contact 12a, one end of the series circuit of the auxiliary switches SW1 and SW2 is connected via the wiring 54u. At the connection point N2 between the wiring 53v and the other end of the relay contact 12a (and one end of the relay contact 12b), the other end of the series circuit of the auxiliary switches SW1 and SW2 is connected via the wiring 54v, and one end of the series circuit of the auxiliary switches SW3 and SW4 is connected via the same wiring 54v. At the connection point N3 between the wiring 53w and the other end of the relay contact 12b, the other end of the series circuit of the auxiliary switches SW3 and SW4 is connected via the wiring 54w. The connection points N1, N2, and N3 become branch points from the wiring 53u, 53v, and 53w to the wiring 54u, 54v, and 54w. Hereinafter, the connection points N1, N2, and N3 are referred to as branch points N1, N2, and N3.

[0045] That is, the wirings 53u, 53v, 53w start from the terminals 32u, 32v, 32w which are the other ends of the motor windings Lu, Lv, Lw, and end at the branch points N1, N2, N3. The first and second wirings 54u, 54v start from the branch points N1, N2, and end at both ends of the series circuit of the auxiliary switches Sw1, Sw2. The second and third wirings 54v, 54w start from the branch points N2, N3, and end at both ends of the series circuit of the auxiliary switches Sw3, Sw4.

[0046] Auxiliary switches SW1 to SW4 are semiconductor switch elements in which a freewheeling diode D is connected to each element body in an anti-parallel direction. The series circuit of auxiliary switches SW1 and SW2 is connected in a state where the auxiliary switches SW1 and SW2 are in opposite directions to each other. That is, the outputs (current outflow sides) of both auxiliary switches SW1 and SW2 are connected to each other. Similarly, the series circuit of auxiliary switches SW3 and SW4 is also connected in a state where the auxiliary switches SW3 and SW4 are in opposite directions to each other. Therefore, when the auxiliary switches SW1 and SW2 are turned on, the series circuit of auxiliary switches SW1 and SW2 flows current in both directions through the freewheeling diode D of one of the auxiliary switches, and does not flow current in any direction when the auxiliary switches SW1 and SW2 are turned off. Similarly, when the auxiliary switches SW3 and SW4 are turned on, the series circuit of auxiliary switches SW3 and SW4 flows current in both directions through the freewheeling diode D of one of the auxiliary switches, and does not flow current in any direction when the auxiliary switches SW3 and SW4 are turned off.

[0047] 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 inductors Lsu1, Lsv1, and Lsw1 have substantially the same value, but may have slightly different values ​​depending on the arrangement of the wirings 52u, 52v, and 52w, respectively. Similarly, the second inductors Lsu2, Lsv2, and Lsw2 have substantially the same value, but may have slightly different values ​​depending on the arrangement of the wirings 53u, 53v, and 53w, respectively.

[0048] The wiring 54u between the branch point N1 and one end of the series circuit of the auxiliary switches SW1 and 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 and SW2, and also has the same third inductance Lsv3 between the branch point N2 and one end of the auxiliary switches SW3 and SW4. In addition, the wiring of the connection portion between the collector of the auxiliary switch SW2 and the collector of the auxiliary switch SW3 only needs to be extremely short, so in the third inductance Lsv3 of the wiring 54v, the inductance of the wiring from the branch point N2 to the connection point between the auxiliary switches SW2 and SW3 is dominant. The wiring 54w between the branch point N3 and the other end of the series circuit of the auxiliary switches SW3 and SW4 has a third inductance Lsw3.

[0049] In summary, the relay contact 12a is connected between the branch points N1 and N2, and the series circuit of the auxiliary switches SW1 and SW2 is connected between the branch points N1 and N2. The relay contact 13a is connected between the branch points N2 and N3, and the series circuit of the auxiliary switches SW3 and SW4 is connected between the branch points N2 and N3.

[0050] Current sensors 11u, 11v, 11w are arranged in wirings 51, 51v, 51z between interconnection points Au, Av, Az of the inverter 20 and respective ends (terminals 31u, 31v, 31z) of the phase windings Lu, Lv, Lw, and 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.

[0051] 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, which controls the opening and closing of the relay contacts 12a, 13a and the drive (switching) of the inverters 20, 30 so that the rotational speed N of the motor 3 becomes the target rotational speed Nt instructed by a higher-level external device (such as a control device of an air conditioner) and performs high-efficiency operation.

[0052] The current detection unit 41 detects the instantaneous value of each of the motor currents Iu, Iv, Iw detected by the current sensors 11u, 11v, 11w. The relay driver 42 drives the relays 12, 13 according to the command from the main control unit 40. The auxiliary SW driver 43 drives the auxiliary switches SW1 to SW4 according to the command from the main control unit 40.

[0053] The main control unit 40 is composed of a microcomputer and its peripheral circuits, and selectively sets the star connection mode and the open winding mode according to the values ​​of the motor currents Iu, Iv, Iw corresponding to the size of the load. In the star connection mode, the other ends of the phase windings Lu, Lv, Lw are connected to each other by closing the relay contacts 12a and 13a, and the inverter 20 is driven independently. In the open winding mode, the other ends of the phase windings Lu, Lv, Lw are set to a mutually disconnected state by opening the relay contacts 12a and 13a, and the inverters 20 and 30 are driven in a mutually linked manner. For example, the star connection mode is set when the motor speed N is low and the motor currents Iu, Iv, Iw are low loads less than a specified value, and the open winding mode is set when the motor speed N increases and the motor currents Iu, Iv, Iw are high loads greater than a specified value. As a result, high efficiency can be obtained over the entire operating range of the motor. In addition, the selection of the star connection mode and the open winding mode can be switched by judging various parameters related to the motor, such as the combination of the motor speed and the weak magnetic amount, in addition to the above. In addition, in abnormal conditions such as when the motor currents Iu, Iv, and Iw are in an overcurrent state, it can also be considered to switch to either the star connection mode or the open winding mode first.

[0054] When switching from the open winding mode to the star connection mode and from the star connection mode to the open winding mode, the main control unit 40 performs a virtual neutral point action in which all the upper switching elements Tu, Tv, Tw and all the lower switching elements Tx, Ty, Tz in the inverter 30 are alternately turned on and off with an on / off duty ratio of 50%, so that the potential difference between the two ends of the relay contact 12a and the potential difference between the two ends of the relay contact 13a are zero.

[0055] In particular, in 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 in a state where the auxiliary switches SW1 to SW4 are turned on in advance, and after a certain time t1 longer than the time required for the relay contacts 12a and 13a to actually close, the auxiliary switches SW1 to SW4 are turned off. Similarly, in 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 in a state where the auxiliary switches SW1 to SW4 are turned on in advance, and after a certain time t2 longer than the time required for the relay contacts 12a and 13a to actually open, the auxiliary switches SW1 to SW4 are turned off.

[0056] In addition, the main control unit 40 performs the following complementary actions when the upper switch elements and the lower switch elements of the inverters 20 and 30 are turned on and off during the virtual neutral point operation: when the upper switch element in each series circuit is turned on, the lower switch element is turned off, and when the lower switch element in each series circuit is turned on, the upper switch element is turned off. In this complementary action, the main control unit 40 ensures that the upper switch element and the lower switch element are both turned off during the on and off drive, so that the upper switch element and the lower switch element of each series circuit will not be turned on at the same time to form a short circuit. In addition, the dead time td is not limited to setting in the virtual neutral point operation. In the PWM control during normal operation, the dead time td must be set to prevent the short circuit of the upper and lower switch elements.

[0057] Next, refer to Figure 2 The flowchart of FIG. 1 illustrates the main control executed by the main control unit 40 of the controller 4. Steps S1, S2, ... in the flowchart are simply referred to as S1, S2, ...

[0058] When the motor is driven in the open winding mode (S1: Yes), the main control unit 40 monitors whether it is necessary to switch to the star connection mode according to the reduction of the load (S2). If it is not necessary to switch to the star connection mode (S2: No), the main control unit 40 repeats the determination of S1.

[0059] When switching to the star connection mode is required (“Yes” in S2), the main control unit 40 executes switching of all upper switching elements Tu, Tv, Tw and all lower switching elements Tx, Ty, Tz in the inverter 30 as follows: Figure 3 As shown, a virtual neutral point operation is performed which is alternately turned on and off at an on / off duty ratio of 50% so that the potential difference between both ends of the relay contacts 12a and 13a becomes zero (S3).

[0060] Figure 5This is a diagram that is enlarged in time to facilitate understanding of the relationship between the on / off of the upper switching elements Tu, Tv, Tw and the on / off of the lower switching elements Tx, Ty, Tz in the virtual neutral point operation. When the upper switching elements Tu, Tv, Tw are turned on and the lower switching elements Tx, Ty, Tz are turned off, the main control unit 40 ensures a dead time td in which the upper switching elements Tu, Tv, Tw and the lower switching elements Tx, Ty, Tz are both turned off, so as to prevent a short circuit from being formed with respect to the output end of the converter 10. Similarly, when the lower switching elements Tx, Ty, Tz are turned on and the upper switching elements Tu, Tv, Tw are turned off, the main control unit 40 ensures that the lower switching elements Tx, Ty, Tz and the upper switching elements Tu, Tv, Tw are all in the disconnected state for a dead time td to prevent a short circuit from being formed relative to the output end of the converter 10.

[0061] There are various ways to generate the dead time td, but generally speaking, the most common method is to turn off the switching element on the side that should be turned off and then turn on the switching element on the side that should be turned on after the dead time td has passed. From the perspective of efficiency and waveform shaping, it is desirable that the dead time td is as short as possible, and in practice, the minimum time based on the on / off transition characteristics of the switching element is allocated.

[0062] However, as described later, due to the existence of the dead time td, even if the virtual neutral point operation is performed, when 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 sometimes occur between the respective ends of the relay contacts 12a and 13a.

[0063] In 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 the two ends of the relay contacts 12a and 13a, and turns on the relays 12 and 13 after the short circuit (S5). Then, after a certain time t1 longer than the time required for the relay contacts 12a and 13a to actually close ("Yes" in S6), the main control unit 40 turns off the auxiliary switches SW1 to SW4 (S7). Then, the main control unit 40 ends the virtual neutral point operation and shifts to the motor drive in the star connection mode (S8).

[0064] After the transfer, the main control unit 40 returns to the determination of S1. From the viewpoint of circuit simplification, it is desirable to synchronize the turning on and off of the auxiliary switches SW1 to SW4 in step S4 and the turning off of the auxiliary switches SW1 to SW4 in step S7, but it is not necessary to turn on and off completely synchronously. The key is that all the auxiliary switches SW1 to SW4 can be turned on before the relay contacts 12a and 13a are actually closed, and all the auxiliary switches SW1 to SW4 can be turned off after the relay contacts 12a and 13a are actually closed.

[0065] Through the above processing, execution Figure 3 By this operation, when the auxiliary switches SW1 to SW4 are in 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, energy saving is achieved, and the heat generation of the auxiliary switches SW1 to SW4 is eliminated, and there is no need to take measures against the temperature rise of these semiconductor switches.

[0066] When the motor is driven 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 load (S9). If it is not necessary to switch to the open winding mode (No in S9), the main control unit 40 returns to the determination of S1 above.

[0067] When the open winding mode is required (Yes in S9), the main control unit 40 executes the operation of switching the upper switching elements Tu, Tv, Tw and the lower switching elements Tx, Ty, Tz in the inverter 30 as follows: Figure 4 As shown in FIG. 1 , a virtual neutral point operation is performed by alternately turning on and off at a duty ratio of 50% so that the potential difference between the two ends of each of the relay contacts 12a and 13a is zero (S10). This virtual neutral point operation is the same as the virtual neutral point operation when switching from the open winding mode to the star connection mode. In addition, in this state, the operation is performed in the star connection mode, so the relay contacts 12a and 13a are turned on.

[0068] In the execution of the virtual neutral point operation, the main control unit 40 first turns on the auxiliary switches SW1 to SW4 (S11), thereby short-circuiting the two ends of the relay contacts 12a and 13a, and disconnects the relays 12 and 13 after the short circuit (S12). Then, after a certain time t2 longer than the time required for the relay contacts 12a and 13a to actually disconnect has passed ("Yes" in S13), the main control unit 40 disconnects the auxiliary switches SW1 to SW4 (S14). Then, the main control unit 40 ends the virtual neutral point operation and shifts to the open winding mode (S15).

[0069] After the transfer, the main control unit 40 returns to the judgment of the above S1. It is expected that all the auxiliary switches SW1 to SW4 are turned on and off synchronously for the conduction of the auxiliary switches SW1 to SW4 in step S11 and the disconnection of the auxiliary switches SW1 to SW4 in step S14, but it is not necessary to turn on / off completely synchronously. It is sufficient as long as all the auxiliary switches SW1 to SW4 can be turned on before the relay contacts 12a and 13a are actually disconnected, and all the auxiliary switches SW1 to SW4 can be turned off after the relay contacts 12a and 13a are actually disconnected. Through the above processing, execution Figure 4 Action shown.

[0070] The certain time t1 and t2 may be the same time, but are preferably 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 conduction (excitation) and disconnection (de-excitation) based on the excitation current to the actual opening and closing of the relay contacts 12a and 13a. Considering this delay, it is desirable to set the certain time t1 and t2 to about 50 msec to 100 msec obtained by adding a margin to the delay time of the opening and closing of the relay contacts 12a and 13a.

[0071] As described above, when the relay contacts 12a and 13a are opened and closed, the virtual neutral point operation is performed in advance and the auxiliary switches SW1 to SW4 are turned on so that the potential difference between the two ends of each of the relay contacts 12a and 13a becomes zero.

[0072] However, even if the virtual neutral point operation is performed, as long as the dead time td in which the upper switching elements Tu, Tv, Tw and the lower switching elements Tx, Ty, Tz of the inverter 30 are all turned off, the current flows through the path of the freewheeling diode D of any one of the upper switching elements Tu, Tv, Tw and the lower switching elements Tx, Ty, Tz. Figure 6 As shown by the solid arrows, the motor currents I v and I w flow in a path from the phase windings Lv and Lw through the interconnection points Bv and Bw of the inverter 30 and the freewheeling diodes D of the upper switching elements Tv and Tw, respectively, and the motor current I u flows in a path from the freewheeling diode D of the lower switching element Tx through the interconnection point Bu toward the phase winding Lu.

[0073] Figure 7 Shows Figure 6The relationship between the collector-emitter voltage Vcex of the lower switch element Tx in the current path, the collector-emitter voltage Vcey of the lower switch element Ty, the potential difference Vuv1 of the interconnection points Bu and Bv, the potential difference Vuv2 between the two ends of the relay contact 12a, and the potential difference Vuv3 between the two ends of the series circuit of the auxiliary switches Sw1 and Sw2. That is, when the collector-emitter voltage Vcex of the lower switch element Tx is zero, the collector-emitter voltage Vcey of the lower switch element Ty rises, and the potential difference Vuv1 of the interconnection points Bu and Bv becomes non-zero. If the potential difference Vuv1 is generated, then Figure 6 As shown by the dotted arrow in the middle, the current flows from the interconnection point Bv through the auxiliary switch Sw2 and the auxiliary switch Sw1 toward the interconnection point Bu, and voltages are generated in the first inductor Lsu1, Lsv1 and the second inductor Lsu2, Lsv2, and the potential difference Vuv2 between the two ends of the relay contact 12a becomes non-zero. After that, the collector-emitter voltage Vcex of the lower switching element Tx and the collector-emitter voltage Vcey of the lower switching element Ty become the same value, and the potential difference Vuv1 between the interconnection points Bu and Bv becomes zero. The same phenomenon also occurs at the relay contact 13a.

[0074] In the mechanical opening and closing contact, i.e., the relay contact 12a, it is impossible to strictly control the opening and closing period as described above, so there is a situation where the relay contact 12a opens and closes when the potential difference Vuv2 between the two ends of the relay contact 12a is not zero. If the relay contact 12a opens and closes when the potential difference Vuv2 between the two ends of the relay contact 12a is not zero, there is a possibility that a surge voltage or an arc will be generated between the two ends of the relay contact 12a. The dead time td is a very short time compared to the regular on and off period of the inverter 30, so the possibility of the relay contact 12a actually opening and closing when the potential difference between the two ends of the relay contact 12a is not zero is extremely low. However, since the probability of its occurrence is not zero, it is necessary to take corresponding countermeasures.

[0075] Here, the potential difference Vuv2 between the two ends of the relay contact 12a changes according to the relationship between the following values: the total value "Lsu1+Lsu2" of the value of the first inductance Lsu1 possessed by the wiring 52u from the interconnection point Bu to the branch point N1 and the value of the second inductance Lsu2 possessed by the wiring 53u, the total value "=Lsv1+Lsv2" of the value of the first inductance Lsv1 possessed by the wiring 52v from the interconnection point Bv to the branch point N2 and the value of the second inductance Lsv2 possessed by the wiring 53v, the value of the third inductance Lsu3 possessed by 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 possessed by the wiring 54v between the branch point N2 and the other end of the series circuit of the auxiliary switches SW1 and SW2.

[0076] For example, when the sum of the values ​​of the first inductance Lsu1 and the second inductance Lsu2, "Lsu1+Lsu2", is smaller than the value of the third inductance Lsu3 ("Lsu1+Lsu2"<Lsu3), and the sum of the values ​​of the first inductance Lsv1 and the second inductance Lsv2, "Lsv1+Lsv2", is smaller than the value of the third inductance Lsv3 ("Lsv1+Lsv2"<Lsv3), a Figure 7 On the other hand, when the value of the third inductor Lsu3 is smaller than the above-mentioned total value "Lsu1+Lsu2" (Lsu3<"Lsu1+Lsu2"), and the value of the third inductor Lsv3 is smaller than the above-mentioned total value "Lsv1+Lsv2" (Lsv3<"Lsv1+Lsv2"), as shown in FIG. Figure 8 As shown, the potential difference Vuv2 can be suppressed to Figure 7 The situation is small.

[0077] Similarly, the potential difference Vvw2 between the two ends of the relay contact 13a also changes according to the relationship between the following values: the total value "Lsv1+Lsv2" of the value of the first inductance Lsv1 possessed by the wiring 52v from the interconnection point Bv to the branch point N2 and the value of the second inductance Lsv2 possessed by the wiring 53v, the total value "=Lsw1+Lsw2" of the value of the first inductance Lsw1 possessed by the wiring 52w from the interconnection point Bw to the branch point N3 and the value of the second inductance Lsw2 possessed by the wiring 53w, the value of the third inductance Lsv3 possessed by 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 possessed by the wiring 54w between the branch point N3 and the other end of the series circuit of the auxiliary switches SW3 and SW4.

[0078] That is, when the value of the third inductance Lsv3 is smaller than the above-mentioned total value "Lsv1+Lsv2" (Lsv3<"Lsv1+Lsv2"), and the value of the third inductance Lsw3 is smaller than the above-mentioned total value "Lsw1+Lsw2" (Lsw3<"Lsw1+Lsw2"), the potential difference Vvw2 between the two ends of the relay contact 13a can be suppressed to a small level. By setting such an inductance value, the adverse effects on the relay contacts 12a and 13a can be reduced to a level where there is no problem.

[0079] In view of these points, in the present embodiment, the length of each wiring (third wiring) 54u, 54v, 54w is set to be as short as possible compared to the total value of the length of each wiring (first wiring) 52u, 52v, 52w and the length of each wiring (second wiring) 53u, 53v, 53w, so that the value of the third inductance Lsu2 is smaller than the total value "Lsu1+Lsu2" of the value of the first inductance Lsu1 and the value of the second inductance Lsu2 (Lsu1<"Lsu1 1+Lsu2”), the value of the third inductor Lsv2 is smaller than the total value “Lsv1+Lsv2” of the value of the first inductor Lsv1 and the value of the second inductor Lsv2 (Lsv1<“Lsv1+Lsv2”), and the value of the third inductor Lsw2 is smaller than the total value “Lsw1+Lsw2” of the value of the first inductor Lsw1 and the value of the second inductor Lsw2 (Lsw1<“Lsw1+Lsw2”), thereby reducing the potential differences Vuv2 and Vvw2. For example, by making the configuration positions of the relay contacts 12a and 13a as close as possible to the configuration positions of the auxiliary switches SW1 to SW4, the lengths of the wirings 54u, 54v, and 54w can be shortened.

[0080] The values ​​of parasitic inductances generated in wirings such as the first inductance Lsu1, Lsv1, Lsw1, the second inductance Lsu2, Lsv2, Lsw2, and the third inductance Lsu3, Lsv3, Lsw3 are generally proportional to the length of the wirings. The shorter the lengths of the wirings 54u, 54v, and 54w are, the smaller the values ​​of the third inductances Lsu3, Lsv3, and Lsw3 can be. Therefore, in the present 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".

[0081] In addition, the magnitude of the potential difference Vuv2, Vvw2 between the two ends of each of the relay contacts 12a, 13a is determined by the relative relationship between the above-mentioned total value "Lsu1+Lsu2", "Lsv1+Lsv2", "Lsw1+Lsw2" and the value of the third inductance Lsu3, Lsv3, Lsw3. Therefore, even if the total value "Lsu1+Lsu2", "Lsv1+Lsv2", "Lsw1+Lsw2" is made larger than the value of the third inductance Lsu3, Lsv3, Lsw3, the potential difference Vuv2, Vvw2 can be suppressed to be small. In order to make the total value "Lsu1+Lsu2", "Lsv1+Lsv2", "Lsw1+Lsw2" larger than the value of the third inductance Lsu3, Lsv3, Lsw3, it is sufficient to extend the total value of the length of the wiring 52u, 52v, 52w and the length of the wiring 53u, 53v, 53w. In addition, in order to make the total value "Lsu1+Lsu2", "Lsv1+Lsv2", "Lsw1+Lsw2" greater than the value of the third inductance Lsu3, Lsv3, Lsw3, inductance elements such as small coils may be inserted in the middle of the wirings 52u, 52v, 52w or the wirings 53u, 53v, 53w. However, in these measures, as the wiring length is extended and the coil is added, the resistance value increases accordingly, resulting in power loss, so it is preferable to shorten the length of the wirings 54u, 54v, 54w as much as possible as described above.

[0082] In this way, by suppressing the potential differences Vuv2 and Vvw2 generated between the two ends of the relay contacts 12a and 13a to be small, even if the relay contacts 12a and 13a are opened and closed in a state where the potential differences Vuv2 and Vvw2 are generated, it is possible to eliminate the generation of a surge voltage or arc of a size that may cause a problem between the two ends of the relay contacts 12a and 13a. In addition, it is possible to avoid adverse effects on the life of the relays 12 and 13, and prevent the destruction of the switching elements of the inverters 20 and 30 by surge voltage and arc.

[0083] [2] Second Embodiment

[0084] exist Fig. 9 The configuration of the second embodiment is shown.

[0085] A series circuit of auxiliary switches SW1 and SW2 is connected between branch points N1 and N2 at the front end of wiring (second wiring) 53u and 53v connected to the other ends (terminals 32u and 32v) of the phase windings Lu and Lv of the motor 1M via wiring (third wiring) 54u and 54v1. A series circuit of auxiliary switches SW3 and SW4 is connected between branch points N2 and N3 at the front end of wiring (second wiring) 53v and 53w connected to the other ends (terminals 32v and 32w) of the phase windings Lv and Lw of the motor 1M via wiring (third wiring) 54v2 and 54w.

[0086] The relay contact 12a is connected between the branch points N1 and N2 via wirings (fourth wirings) 55u and 55v. The relay contact 13a is connected between the branch points N2 and N3 via wirings (fourth wirings) 55v and 55w.

[0087] That is, the front end of the wiring 53u branches into the wiring 54u and the wiring 55u at the branch point N1, and the front end of the wiring 53v branches into the wirings 54v1, 54v2 and the wiring 55v at the branch point N2. Similarly, the front end 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 of the series circuit of the auxiliary switches SW1 and SW2, and the wiring 54v1 is connected to the auxiliary switch SW2 side of the series circuit of the auxiliary switches SW1 and SW2. The wiring 54v2 is connected to the auxiliary switch SW3 side of the series circuit of the auxiliary switches SW3 and SW4, and the wiring 54w is connected to the auxiliary switch SW4 side of the series circuit of the auxiliary switches SW3 and SW4. The auxiliary switches SW2 and SW3 are connected in series with each other via the branch point N2 and the wirings 54v1 and 54v2.

[0088] 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.

[0089] The relay contact 12a is in a state of being connected in parallel with the series circuit of the auxiliary switches SW1 and SW2 through the wirings 55u and 55v. The relay contact 13a is in a state of being connected in parallel with the series circuit of the auxiliary switches SW3 and SW4 through the wirings 55v and 55w. The wiring 55u is connected to the wiring 53u via the branch point N1, the wiring 55v is connected to the wiring 53v via the branch point N2, and the wiring 55w is 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 connected via the 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.

[0090] In the second embodiment, as in the first embodiment, the relationship between the values ​​of the first inductors Lsu1, Lsv1, and Lsw1, the values ​​of the second inductors Lsu2, Lsv2, and Lsw2, and the values ​​of the third inductors Lsu3, Lsv3, and Lsw3 needs to satisfy the above-mentioned conditions of (Lsu1<"Lsu1+Lsu2"), (Lsv1<"Lsv1+Lsv2"), and (Lsw1<"Lsw1+Lsw2"). Therefore, if the circuit configuration of the second embodiment is used, the length of the wirings 54u to 54w can be made extremely short in terms of the circuit configuration, so that the above-mentioned conditions can be satisfied without performing a complicated wiring layout design.

[0091] The other configurations are the same as those of the first embodiment.

[0092] [3] Third Embodiment

[0093] exist Fig.10 The main part of the structure of the third embodiment is shown.

[0094] A relay contact 12a is connected between branch points N1 and N2 at the front ends of 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 branch points N2 and N3 at the front ends of wirings 53v and 53w connected to the other ends (terminals 32v and 32w) of the phase windings Lv and Lw of the motor 1M.

[0095] Furthermore, the series circuit of the auxiliary switches SW1 and SW2 is connected in parallel with the relay contact 12a via the wirings 54u and 54v connected to the branch points N1 and N2. The series circuit of the auxiliary switches SW2 and SW3 is connected in parallel with the relay contact 13a via the wirings 54v and 54w connected to the branch points N2 and N3. The auxiliary switches SW1 to SW3 are semiconductor switch elements in which a freewheeling diode D is connected to each element body in an anti-parallel direction, such as an IGBT or a MOS-FET. The emitters of the three auxiliary switches SW1, SW2, and SW3 are connected in common to the common connection point (virtual neutral point) P2 in the figure.

[0096] 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 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.

[0097] The other configuration including the relationship between the values ​​of the first inductors Lsu1, Lsv1, Lsw1, the values ​​of the second inductors Lsu2, Lsv2, Lsw2, and the values ​​of the third inductors Lsu3, Lsv3, Lsw3 is the same as that of the first embodiment. The three auxiliary switches SW1, SW2, SW3 are simultaneously turned on and off similarly to the four auxiliary switches SW1 to SW4 of the first embodiment.

[0098] When the relay contacts 12a and 13a are disconnected, the auxiliary switches SW1, SW2, and SW3 are disconnected, and the phase windings Lu, Lv, and Lw of the motor 1M are in an open winding state separated from each other. When the relay contacts 12a and 13a are disconnected, the auxiliary switches SW1, SW2, and SW3 are turned on, and 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, and a star connection mode is formed. When the auxiliary switches SW1, SW2, and SW3 are disconnected, the relay contacts 12a and 13a are closed, and 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, and a star connection mode is formed.

[0099] 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. Compared with the first and second embodiments, the number of semiconductor switch elements is reduced, thereby simplifying the circuit.

[0100] [4] Fourth Embodiment

[0101] exist Fig.11 The main part of the structure of the fourth embodiment is shown.

[0102] A series circuit of auxiliary switches SW1 and SW2 is connected between branch points N1 and N2 at the front end of wiring (second wiring) 53u and 53v connected to the other ends (terminals 32u and 32v) of the phase windings Lu and Lv of the motor 1M via wiring (third wiring) 54u and 54v. A series circuit of auxiliary switches SW2 and SW3 is connected between branch points N2 and N3 at the front end of wiring (second wiring) 53v and 53w connected to the other ends (terminals 32v and 32w) of the phase windings Lv and Lw of the motor 1M via wiring (third wiring) 54v and 54w.

[0103] Furthermore, the relay contact 12a is connected in parallel to the series circuit of the auxiliary switches SW1 and SW2 via the wiring (fourth wiring) 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 via the wiring (fourth wiring) 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 via a common connection point P1.

[0104] 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 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.

[0105] 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.

[0106] The other configuration including the relationship between the values ​​of the first inductors Lsu1, Lsv1, Lsw1, the values ​​of the second inductors Lsu2, Lsv2, Lsw2, and the values ​​of the third inductors Lsu3, Lsv3, Lsw3 is the same as that of the first embodiment. The three auxiliary switches SW1, SW2, SW3 are simultaneously turned on and off similarly to the four auxiliary switches SW1 to SW4 of the first embodiment.

[0107] When the relay contacts 12a and 13a are disconnected, the auxiliary switches SW1, SW2, and SW3 are disconnected, and the phase windings Lu, Lv, and Lw of the motor 1M are in an open winding state separated from each other. When the relay contacts 12a and 13a are disconnected, the auxiliary switches SW1, SW2, and SW3 are turned on, and 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, and a star connection mode is formed. When the auxiliary switches SW1, SW2, and SW3 are disconnected, the relay contacts 12a and 13a are closed, and 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, and a star connection mode is formed.

[0108] 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. Compared with the first and second embodiments, the number of semiconductor switch elements is reduced, thereby simplifying the circuit.

[0109] [5] Modifications

[0110] The above-mentioned embodiments are proposed as examples and are not intended to limit the scope of the invention. The new embodiments and modifications can be implemented in various other ways, and various omissions, rewrites, and changes can be made without departing from the scope of the main purpose of the invention. These embodiments and their modifications are all included in the scope or main purpose of the invention, and are included in the schemes described in the claims and their equivalents.

[0111] Description of Reference Numerals

[0112] 2. Driving Circuit

[0113] 3 Open winding motor

[0114] Lu, Lv, Lw phase windings

[0115] 4 Controller

[0116] 12, 13 Relay (Switch)

[0117] 12a, 13a opening and closing contacts (relay contacts)

[0118] SW1~SW4 semiconductor switch elements

[0119] Lsu1, Lsv1, Lsw1 first inductor

[0120] Lsu2, Lsv2, Lsw2 second inductor

[0121] 20 Inverter (1st inverter)

[0122] 30 Inverter (2nd inverter)

[0123] 40 Main control unit.

Claims

1. A motor drive device, comprising a motor having a plurality of phase windings which are not connected to each other, characterized in that: have: a first inverter comprising a plurality of series circuits of upper switching elements and lower switching elements, wherein both ends of the series circuits are connected to a DC power source, and a mutual connection point between the upper switching elements and the lower switching elements of each series circuit is connected to one end of each phase winding; a second inverter comprising a plurality of series circuits of upper switching elements and lower switching elements, wherein both ends of the series circuits are connected to the DC power supply, and a mutual connection point between the upper switching elements and the lower switching elements of each series circuit is connected to the other end of each phase winding through each first wiring; A plurality of switch contacts are connected to each other at the other ends of the respective phase windings through respective second wirings; A plurality of semiconductor switch elements are connected in parallel with respect to the respective opening and closing contacts through respective third wirings; a controller for controlling the driving of the first inverter, the driving of the second inverter, and the opening and closing of each of the switch contacts, The controller performs a virtual neutral point operation in advance to alternately turn on and off all the upper switching elements and all the lower switching elements in the second inverter when the opening and closing contacts are opened and closed, and turns on the semiconductor switching elements. Each of the first wirings has a first inductance. Each of the second wirings has a second inductance. Each of the third wirings has a third inductance. The third inductance has a value smaller than a total value of the first inductance and the second inductance.

2. The motor drive device according to claim 1, characterized in that: The controller selectively sets a star connection mode and an open winding mode. In the star connection mode, the other ends of the phase windings are connected to each other by closing the opening and closing contacts, and the switching elements of the first inverter are driven on and off. In the open winding mode, the other ends of the phase windings are set to a non-connected state by opening the opening and closing contacts, and the switching elements of the first inverter and the second inverter are driven on and off in a linked manner.

3. The motor drive device according to claim 1, characterized in that: When the upper switch element and the lower switch element in the first inverter are driven on and off, the controller ensures a dead time in which the upper switch element and the lower switch element of each series circuit in the first inverter are both disconnected, and when the upper switch element and the lower switch element in the second inverter are driven on and off, the controller ensures a dead time in which the upper switch element and the lower switch element of each series circuit in the second inverter are both disconnected.

4. A motor drive device, comprising a motor having a plurality of phase windings which are not connected to each other, characterized in that: have: a first inverter comprising a plurality of series circuits of upper switching elements and lower switching elements, wherein both ends of the series circuits are connected to a DC power source, and a mutual connection point between the upper switching elements and the lower switching elements of each series circuit is connected to one end of each phase winding; a second inverter comprising a plurality of series circuits of upper switching elements and lower switching elements, wherein both ends of the series circuits are connected to the DC power supply, and a mutual connection point between the upper switching elements and the lower switching elements of each series circuit is connected to the other end of each phase winding through each first wiring; A plurality of semiconductor switch elements are connected to each other at the other ends of the respective phase windings through respective second wirings and respective third wirings; A plurality of opening and closing contacts are connected in parallel with respect to each of the semiconductor switch elements through 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 of the switch contacts, The controller performs a virtual neutral point operation in advance to alternately turn on and off all the upper switching elements and all the lower switching elements in the second inverter when the opening and closing contacts are opened and closed, and turns on the semiconductor switching elements. Each of the first wirings has a first inductance. Each of the second wirings has a second inductance. Each of the third wirings has a third inductance. The third inductance has a value smaller than a total value of the first inductance and the second inductance.

5. The motor drive device according to claim 4, characterized in that: The controller selectively sets a star connection mode and an open winding mode. In the star connection mode, the other ends of the phase windings are connected to each other by closing the opening and closing contacts, and the switching elements of the first inverter are driven on and off. In the open winding mode, the other ends of the phase windings are set to a non-connected state by opening the opening and closing contacts, and the switching elements of the first inverter and the second inverter are driven on and off in a linked manner.

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

7. A motor drive device, comprising a motor having a plurality of phase windings which are not connected to each other, characterized in that: have: a first inverter comprising a plurality of series circuits of upper switching elements and lower switching elements, wherein both ends of the series circuits are connected to a DC power source, and a mutual connection point between the upper switching elements and the lower switching elements of each series circuit is connected to one end of each phase winding; a second inverter comprising a plurality of series circuits of upper switching elements and lower switching elements, wherein both ends of the series circuits are connected to the DC power supply, and a mutual connection point between the upper switching elements and the lower switching elements of each series circuit is connected to the other end of each phase winding through each first wiring; A plurality of switch contacts are connected to each other at the other ends of the respective phase windings through respective second wirings; A plurality of semiconductor switch elements are connected in parallel with respect to the respective opening and closing contacts through respective third wirings; a controller for controlling the driving of the first inverter, the driving of the second inverter, and the opening and closing of each of the switch contacts, The controller performs a virtual neutral point operation in advance to alternately turn on and off all the upper switching elements and all the lower switching elements in the second inverter when the opening and closing contacts are opened and closed, and turns on the semiconductor switching 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 length of the first wiring connected to the third wiring and the length of the second wiring.

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

9. The motor drive device according to claim 1 or 7, characterized in that: The phase windings are three phase windings Lu, Lv, and Lw. The first wirings are three first wirings connected to the other ends of Lu, Lv, and Lw. The second wirings are three second wirings starting from the other ends of Lu, Lv, and Lw and ending at three branch points N1, N2, and N3. The switch contacts are a first switch contact connected between the branch points N1 and N2 and a second switch contact connected between the branch points N2 and N3. The semiconductor switch elements are three semiconductor switch elements Sw1, Sw2, and Sw3. One ends of the three semiconductor switch elements Sw1, Sw2, and Sw3 are connected in common. Among the third wirings, 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.

10. The motor drive device according to claim 4 or 7, characterized in that: The phase windings are three phase windings Lu, Lv, and Lw. The first wirings are three first wirings connected to the other ends of Lu, Lv, and Lw. The second wirings are three second wirings starting from the other ends of Lu, Lv, and Lw and ending at three branch points N1, N2, and N3. The semiconductor switch elements are three semiconductor switch elements Sw1, Sw2, and Sw3. The third wirings are the following three third wirings: 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, 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 fourth wirings are the following three fourth wirings: the first and second fourth wirings start from the branch points N1 and N2 and end at both ends of the first opening and closing contact, and the second and third fourth wirings end at both ends of the second opening and closing contact.

11. The motor drive device according to any one of claims 1, 4 and 7, characterized in that: Each of the semiconductor switch elements has a freewheeling diode connected to each element body in an anti-parallel direction.

12. A refrigeration cycle device, characterized in that: A compressor driven by the motor drive device according to any one of claims 1, 4, and 7.

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