JP2008182783A - Coil switching device and switching method of three-phase ac motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coil switching device and method that can solve a problem of efficiency deterioration by conduction loss, while achieving high-speed switching, which is a feature of a semiconductor switch. <P>SOLUTION: The coil switching portion comprises both the semiconductor switch and a mechanical switch. Switching is performed by the semiconductor switch at the transient time of the switching, and the mechanical switch is used in a continuous conduction period. As a result, advantages of both switches, the high-speed switching operation of the semiconductor switch and less loss of the mechanical switch, can be obtained. Furthermore, if any abnormality occurs in an inverter, the coil switching device system can be protected by turning off the coil switching portion and opening all motor coils. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a winding switching device for a three-phase AC motor that expands the speed control range by switching the windings of the three-phase AC motor, and includes industrial fields including vehicle drive, machine tool spindle drive, and servo device. It is intended for.

Conventionally, there has been a concept of winding switching using a semiconductor of an electric motor. As a conventional technology example, a rectification unit consisting of a three-phase rectifier diode bridge, a switch unit consisting of a semiconductor switch that short-circuits or opens a direct current created by the rectification unit, and surge energy generated by the switching operation of the switch unit are absorbed. There is an electronic switch consisting of a snubber. (For example, refer to Patent Document 1). In contrast to this, there are some which are realized by installing a switch unit on the AC side (see, for example, Patent Document 2).
In FIG. 4, 1 is an inverter, 2 is an AC motor, and 12 is a winding switching unit. The AC motor 2 has a low-speed operation winding and a high-speed operation winding. Taps are provided at the middle and the end of the winding and connected to the winding switching unit 12. By switching SW1 and SW2 of the winding switching unit 12 on or off, switching between the low speed operation winding and the high speed operation winding becomes possible.
In FIG. 5, 1 is an inverter, 2 is an AC motor, and 12 is a winding switching unit. The winding of the AC motor 2 includes a winding for low speed operation and a winding for high speed operation, taps are provided at the middle and the end of the winding, and a winding constituted by a bidirectional semiconductor switch between the inverter 1 and the AC motor 2. A line switching unit 12 is provided. The bidirectional semiconductor switch of the winding switching unit is connected to each phase of the inverter 1 and the AC motor 2. By turning on or off the three bidirectional semiconductor switches connected to the high-speed operation winding and the three bidirectional semiconductor switches connected to the low-speed operation winding, the low-speed operation winding and the high-speed operation winding Can be switched.
As described above, the conventional device realizes the switching of the winding of the AC motor using the semiconductor switch.
JP2003-111492A (FIG. 1) Japanese Patent Laid-Open No. 2-106197 (FIG. 1)

In the conventional winding switching device, the winding switching switch is formed of a semiconductor element, and high-speed switching is possible. However, the conduction loss of the semiconductor switch becomes a problem, and in particular, the efficiency reduction due to the loss when the capacity is increased.
The present invention has been made in view of such problems. By combining a semiconductor switch and a mechanical switch, high-speed switching, which is a feature of the semiconductor switch, is achieved, and efficiency due to conduction loss, which is a problem. An object of the present invention is to provide a winding switching device and method capable of solving the degradation. Further, the winding switching signal itself uses a signal generating means having the same configuration as the gate signal used for driving the IGBT used in the inverter main circuit, thereby unifying the gate drive circuit. It is another object of the present invention to prevent a permanent magnet synchronous motor from being in a restrained state instantaneously even when an abnormality is detected in an inverter device so as not to adversely affect a load machine.

In order to solve the above problem, the present invention is configured as follows.
Each phase winding is composed of a plurality of windings, and a connecting terminal that connects the plurality of windings to each other and an AC motor that has both terminals of each phase winding provided outside the motor, and a winding that switches the connecting terminals as appropriate. A line switching unit, an inverter for supplying a variable voltage of a variable frequency to the AC motor, and the winding switching unit connects one end of each phase winding to the inverter, and connects the other end and the connection terminal to each other. A plurality of three-phase rectifiers each connected to an AC-side input terminal of a three-phase rectifier for each phase; a semiconductor switch provided to open and close both ends on the DC output side of the plurality of three-phase rectifiers; and the semiconductor A current that flows from the three-phase rectifier when the semiconductor switch is off flows to a snubber circuit at one end on the DC output side of each of the drive circuit that drives the switch and the plurality of three-phase rectifiers, When on, said snubber times In winding switching device of the three-phase AC motor connected to the DC output side of the three-phase rectifier unit in the snubber circuit via a diode which is provided in a direction which does not flow back to the semiconductor switch from,
Mechanical switches (MSW1, MSW2) connected in parallel with the three-phase rectifier input so that the connection terminals can be opened and closed, respectively;
And a drive signal generator (114) for opening and closing the mechanical switches (MSW1, MSW2).
Further, in the present invention, the mechanical switches (MSW1, MSW2) are built in the casing of the inverter unit.
The mechanical switch is characterized in that the electromagnetic contact terminal portion is sealed with gas.
Further, in claim 1, when switching the connection terminal, the drive signal generation unit (114) first turns on a semiconductor switch that opens and closes the connection terminal when the connection terminal is on, and turns on the connection terminal after a certain period of time. A mechanical switch that opens and closes is turned on. When the mechanical switch is turned off, the mechanical switch is turned off first, and a function of generating an operation sequence for turning off the semiconductor switch after a certain period of time is provided.
Further, in claim 1, the drive signal generator (114) turns on the semiconductor switch (SSW1) when switching from the low-speed winding for low-speed operation of the three-phase AC motor to the high-speed winding for high-speed operation, After a certain delay, the mechanical switch (MSW1) provided at the same connection terminal as the semiconductor switch (SSW1) is turned on, and then the semiconductor switch (SSW1) is turned off to perform high-speed operation of the three-phase AC motor. When switching from low speed winding to low speed winding, turn off the mechanical switch (MSW1) that was energized, turn on the semiconductor switch (SSW2) at the same time, turn on the mechanical switch (MSW2) after a certain delay, Thereafter, a signal for turning off the semiconductor switch (SSW2) is generated.
The snubber circuit may be a parallel circuit of a resistor and a capacitor.
Further, in claim 1, the AC motor is a synchronous motor in which a field magnet is embedded in a rotor core.
Further, in claim 1, when the connection terminal is switched from the low-speed winding to the high-speed winding, the drive signal generation unit (114) turns on the semiconductor switch (SSW2) on the low-speed winding that has been turned off. At that time, both the semiconductor switch (SSW2) and the mechanical switch (MSW2) are in the on state, and then the mechanical switch (MSW2) is turned off, and only the semiconductor switch (SSW2) is in a conductive state. Thereafter, the semiconductor switch (SSW2) is turned off and at the same time the semiconductor switch (SSW1) is turned on, then the mechanical switch (MSW1) is turned on, and then the semiconductor switch (SSW1) is turned off.
Further, in claim 1, when the connection terminal is switched from the high-speed winding to the low-speed winding, the drive signal generation unit (114) turns on the semiconductor switch (SSW1) on the high-speed winding that has been turned off. At that time, both the semiconductor switch (SSW1) and the mechanical switch (MSW1) are turned on, then the mechanical switch (MSW1) is turned off, and the semiconductor switch (SSW1) is once turned on. Thereafter, the semiconductor switch (SSW1) is turned off, and at the same time, the semiconductor switch (SSW2) is turned on, then the mechanical switch (MSW2) is turned on, and then the semiconductor switch (SSW2) is turned off.
Further, in claim 1, when the AC motor is a permanent magnet type synchronous motor, the semiconductor switch (SSW1, SSW2) and the mechanical switch (MSW1) that open and close the connection terminal as soon as the winding switching device detects an abnormal state. , MSW2) are all opened.
In addition, in claim 10, the abnormal state is any one of a vertical short circuit of a switching element of the inverter main circuit, a ground fault, and a commercial power failure.
Further, each phase winding is composed of a plurality of windings, and a connection terminal that connects the plurality of windings to each other and both terminals of each phase winding are provided outside the motor, and the connection terminal is appropriately connected A winding switching unit that switches, an inverter that supplies a variable voltage of a variable frequency to the AC motor, and the winding switching unit connects one end of each phase winding to the inverter, and the other end and the connection terminal A plurality of three-phase rectification units connected to the AC side input terminals of the three-phase rectification units for each phase, and a semiconductor switch provided so as to open and close both ends on the DC output side of the plurality of three-phase rectification units, A current that flows from the three-phase rectifier when the semiconductor switch is off flows to a snubber circuit at one end on the DC output side of each of the drive circuit that drives the semiconductor switch and the plurality of three-phase rectifiers, and the semiconductor When the switch is on, In the winding switching method of the winding switching unit of the three-phase AC motor connected to the DC output side of the three-phase rectifier unit in the snubber circuit via a diode provided from bus circuit in a direction that does not flow back to the semiconductor switch,
Mechanical switches (MSW1, MSW2) are connected in parallel with the three-phase rectifier input so that the connection terminals can be opened and closed,
A drive signal for opening and closing the mechanical switch (MSW1, MSW2) is output from the drive signal generation unit (114).

According to the present invention, the switching of the AC motor having the high-speed operation winding and the low-speed operation winding can be set inside the inverter according to the speed, and the switching signal itself is used for the inverter main circuit. Signal generating means having the same configuration as the gate signal used for driving the IGBT can be used, and the circuit can be unified.
In addition, by combining a semiconductor switch and a mechanical switch, a three-phase AC motor equipped with a winding switching device that can solve the problem of reduced efficiency due to conduction loss while realizing high-speed switching, which is a feature of the semiconductor switch. Can be realized.
In addition, when the AC motor is a synchronous motor, an abnormal state in which the synchronous motor becomes in a restrained state due to some malfunction of the inverter can be avoided by opening all the winding switching units.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a configuration diagram when an AC motor having a low-speed operation winding and a high-speed operation winding is driven by the inverter device of the present invention. In the figure, 1 is an inverter unit, 2 is an AC motor, and 12 is a winding switching unit. P is a positive input terminal of the inverter unit 1, N is a negative input terminal, and a DC power source is connected between PN. The AC motor 2 has a low-speed operation winding and a high-speed operation winding. Intermediate terminals (TU2, TV2, TW2) and terminals (TU1, TV1, TW1, TU3, TV3, TW3) are provided at both ends of the winding, and intermediate terminals (TU2, TV2, TW2) and one end of the AC motor winding (TU3) , TV3, TW3) are connected to the AC side of each of the three-phase rectification units (3, 4) of the winding switching unit 12. The case where all the windings between the terminals U1-U3, V1-V3, W1-W3 are used is the low-speed operation winding. On the other hand, when only the windings between the terminals U1-U2, V1-V2, and W1-W2 are used, the winding for high-speed operation is used. This is because the induced voltage of the permanent magnet type synchronous motor increases in proportion to the speed, so that it is necessary to reduce the induced voltage for high speed operation. In the case of a low-speed operation winding, all intermediate terminals (TU2, TV2, TW2) are opened and all terminals (TU3, TV3, TW3) are connected to form a Y connection. On the other hand, in the case of a winding for high speed operation, all terminals (TU3, TV3, TW3) are opened and all intermediate terminals (TU2, TV2, TW2) are connected to form a Y connection.

The control circuit unit 100 for driving the inverter unit 1 and the winding switching unit 12 includes a CPU 110, a winding switching signal generation unit 111, a PWM signal generation unit 112, a gate drive circuit 113, and drive signals for the mechanical switches MSW1 and MSW2. It is comprised from the drive signal production | generation part 114 which produces | generates. The mechanical switches MSW1 and MSW2 are, for example, electromagnetic contactors that simultaneously open and close the three phases. It is also possible to use a gas-sealed electromagnetic contact terminal portion that prevents deterioration of the contact terminal portion and improves reliability. The configuration of the mechanical switches (MSW1, MSW2) is built in the casing of the inverter unit, and the entire winding switching device can be configured more compactly.
The gate drive circuit 113 generates drive signals for the IGBTs that are the main circuit switching elements of the inverter unit 1 and the semiconductor switches SSW1 and SSW2 of the winding switching unit 12, and the semiconductor switches SSW1 of the main circuit switching element and the winding switching unit 12 And output to the gate of SSW2. The drive signal generator 114 that generates drive signals for the mechanical switches MSW1 and MSW2 generates drive signals for the mechanical switches MSW1 and MSW2 of the winding switching unit 12, and outputs the drive signals to the mechanical switches MSW1 and MSW2. To do.
Note that the CPU 100 outputs a winding switching signal to the winding switching signal generation unit 111 in accordance with commands from the host controller of the inverter device according to various applications. When the inverter device itself includes application program software, the inverter device outputs a winding switching signal to the winding switching signal generation unit 111 based on the position and speed information of the AC motor without having a host controller.

The present invention is different from the prior art in a winding switching unit 12 in which not only the semiconductor switches SSW1 and SSW2 but also mechanical switches MSW1 and MSW2 are connected to intermediate terminals (TU2, TV2, TW2) of the winding and one end of the winding (TU3). , TV3, TW3) are connected in parallel with the input of the three-phase rectifier so that they can be directly short-circuited, and are provided with MSW1, MSW2 drive signal generator 114 for driving these mechanical switches MSW1, MSW2.
The winding switching unit 12 includes a three-phase rectification unit (3, 4), a semiconductor switch (SSW1, SSW2) that opens and closes the output terminal of the three-phase rectification unit, a snubber circuit (5, 6), and a snubber circuit (5, 6). It comprises a diode (7-10) for preventing a backflow current to the semiconductor switches (SSW1, SSW2) and mechanical switches (MSW1, MSW2). The snubber circuit (5, 6) is composed of a parallel circuit of a resistor and a capacitor.

  FIG. 1 shows a case where the winding of the AC motor is divided into two. However, when the number of divisions increases, it can be dealt with by adding a corresponding number of winding switching units. However, the present invention is not limited to the two-divided configuration. In addition, the present invention can be applied to either an induction motor or a synchronous motor using a permanent magnet (a type in which a magnet is embedded in a rotor core, or a type in which a magnet is arranged on a rotor surface).

FIG. 2 shows a sequence during the coil switching operation in the inverter device of the present invention. In general, the semiconductor switches (SSW1, SSW2) operate in the order of several μs by inputting gate (base) signals, whereas mechanical switches cause an operation delay of several ms to several hundred ms. The semiconductor switch corresponding to the power winding is turned on, and the mechanical switch is turned on after a certain delay. In the example shown in the figure, when switching from the low-speed winding to the high-speed winding, first, the semiconductor switch SSW1 is turned on at time t1, and MSW1 is turned on at time t2 after a certain delay. After the mechanical switch MSW1 is turned on at time t2, the semiconductor switch SSW1 is turned off at time t3, so that conduction loss generated in the semiconductor switch SSW1 can be eliminated.
Next, when switching from the high-speed winding to the low-speed winding, first, the mechanical switch MSW1 that has been energized so far is turned off at time t4. At time t4, the semiconductor switch SSW2 is turned on at the same time, and after a certain delay, the mechanical switch MSW2 is turned on at time t5. After the mechanical switch MSW2 is turned on at time t5, the semiconductor switch SSW2 is turned off at time t6, so that the conduction loss generated in the semiconductor switch SSW2 can be eliminated.

  FIG. 3 shows another sequence during the winding switching operation in the inverter device of the present invention. The operation of FIG. 2 is a basic operation. However, when considering the operation delay when turning off the mechanical switches MSW1 and MSW2, the sequence shown in FIG. 3 is used to turn off the mechanical switches MSW1 and MSW2. Can solve the problem of operation delay. In the example of the figure, when switching from the low-speed winding to the high-speed winding, the semiconductor switch SSW2 on the low-speed winding side that was turned off is turned on at time t1, and at this time (time t1), the semiconductor switch SSW2 and the mechanical switch MSW2 Are both turned on. Here, the mechanical switch MSW2 is first turned off at the time t2, and the semiconductor switch SSW2 alone is once in a conductive state (section [t2, t3]). Thereafter, the semiconductor switch SSW2 is turned off at the time t3 and at the same time the semiconductor switch SSW1 is turned on, so that the switching can be performed only by the semiconductor switch, and the problem of the operation delay of the mechanical switch at the time of turning off can be solved. Thereafter, the mechanical switch MSW1 is turned on at time t4, and then the semiconductor switch SSW1 is turned off at time t5.

Similarly, when switching from the high-speed winding to the low-speed winding, the switching operation can be performed only by the semiconductor switch as shown in FIG. That is, when switching from the high-speed winding to the low-speed winding, the semiconductor switch SSW1 on the high-speed winding side that was turned off is turned on at time t6, and at this time (time t6), both the semiconductor switch SSW1 and the mechanical switch MSW1 are It will be on. Here, at time t7, the mechanical switch MSW1 is first turned off, and the semiconductor switch SSW1 alone is once in a conductive state (section [t7, t8]). Thereafter, the semiconductor switch SSW1 is turned off at the time t8 and at the same time the semiconductor switch SSW2 is turned on, so that switching by only the semiconductor switch becomes possible, and the problem of the operation delay of the mechanical switch at the time of turning off can be solved. At time t9, the mechanical switch MSW2 is turned on, and then at time t10, the semiconductor switch SSW2 is turned off.
As described above, according to the present invention, in the inverter device for driving an AC motor that requires winding switching, the winding switching unit includes both the semiconductor switch and the mechanical switch, so that the high-speed switching operation of the semiconductor switch is performed. And the advantages of both low loss and mechanical switch.

  Further, in the inverter device of the present invention, the winding switching unit can be operated as a motor protection device. Many of the problems that occur in the inverter device are failures of the main circuit power semiconductor element (IGBT). For example, when a vertical short circuit of an IGBT of a certain phase occurs, the AC motor 2 is a synchronous motor in which a permanent magnet is incorporated. Then, the electric motor is instantly locked and adversely affects the machine side to which the electric motor is connected. In this inverter device, as soon as an IGBT vertical short circuit prevention function that is generally put into practical use in the inverter device operates, the semiconductor switches SSW1 and SSW2 and mechanical switches MSW1 and MSW2 in the winding switching unit 12 are connected via the CPU 110. Can be put into a free-run state (a so-called coasting state in which the motor is rotated by repulsion due to the inertial moment of the rotor), and the motor is naturally decelerated safely without locking. be able to. This protection function is not limited to when the IGBT is short-circuited up and down, and the protection function in the winding switching unit 12 can always be validated via the CPU 110 when any abnormality occurs in the inverter device. For example, in the case of a normal inverter device, the IGBT of the inverter unit performs a gate block operation due to some abnormality, and all the energy stored in the motor winding is instantaneously regenerated in the inverter unit at the moment when all the elements are opened. A rapid rise in the DC bus voltage occurs in the inverter unit. As in the inverter device of the present invention, if the inverter device includes a winding switching unit, the winding switching unit can be turned off at the moment of abnormality so that the motor windings can be opened. There is no problem. As an abnormality of the inverter device when the motor is put into a free-run state, the main circuit power semiconductor element (IGBT) of the inverter unit 1 is short-circuited, ground fault, commercial power failure, and other inverters that cannot continue the operation of the motor. Various protection operations provided in the apparatus are assumed.

  The present invention relates to an inverter device that drives an AC motor that requires winding switching, and more particularly to a winding switching unit. This is not limited to a rotary AC motor, and can also be applied to switching of a winding of a linear motor.

The block diagram of the inverter apparatus which shows 1st Example of this invention Operation sequence diagram of winding switching unit of inverter device of present invention Operation sequence diagram of winding switching unit of inverter device of present invention Configuration diagram of a conventional winding switching device Configuration diagram of a conventional winding switching device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inverter part 2 AC motor 3, 4 Three-phase rectification part 5, 6 Snubber circuit 7-10 Diode 12 Winding switching part 100 Control circuit part 110 CPU
111 Winding Switching Signal Generator 112 PWM Signal Generator 113 Gate Drive Circuit 114 MSW1, MSW2 Drive Signal Generator
SSW1, SSW2 Semiconductor switch MSW1, MSW2 Mechanical switch P Inverter positive input terminal N Inverter negative input terminal P1 Snubber circuit positive terminal N1 Snubber circuit negative terminal P2 Snubber circuit positive terminal N2 Snubber circuit positive terminal Negative terminal

Claims (12)

Each phase winding is composed of a plurality of windings, and a connecting terminal that connects the plurality of windings to each other and an AC motor that has both terminals of each phase winding provided outside the motor, and a winding that switches the connecting terminals as appropriate. A line switching unit, an inverter for supplying a variable voltage of a variable frequency to the AC motor, and the winding switching unit connects one end of each phase winding to the inverter, and connects the other end and the connection terminal to each other. A plurality of three-phase rectifiers each connected to an AC-side input terminal of a three-phase rectifier for each phase; a semiconductor switch provided to open and close both ends on the DC output side of the plurality of three-phase rectifiers; and the semiconductor A current that flows from the three-phase rectifier when the semiconductor switch is off flows to a snubber circuit at one end on the DC output side of each of the drive circuit that drives the switch and the plurality of three-phase rectifiers, When on, said snubber times In winding switching device of the three-phase AC motor connected to the DC output side of the three-phase rectifier unit in the snubber circuit via a diode which is provided in a direction which does not flow back to the semiconductor switch from,
Mechanical switches (MSW1, MSW2) connected in parallel with the three-phase rectifier input so that the connection terminals can be opened and closed, respectively;
A winding switching device for a three-phase AC motor, comprising a drive signal generator (114) for opening and closing the mechanical switches (MSW1, MSW2).   The winding switching device for a three-phase AC motor according to claim 1, wherein the mechanical switches (MSW1, MSW2) are built in a casing of an inverter unit.   2. The winding switching device for a three-phase AC motor according to claim 1, wherein the mechanical switch has an electromagnetic contact terminal portion sealed with gas.   When switching the connection terminal, the drive signal generation unit (114) first turns on a semiconductor switch that opens and closes the connection terminal when turned on, and sets a mechanical switch that opens and closes the connection terminal after a certain time. 2. The three-phase AC motor according to claim 1, wherein the three-phase AC motor has a function of generating an operation sequence in which the mechanical switch is turned off when the power is turned on and the semiconductor switch is turned off after a predetermined time. Winding switching device.   The drive signal generator (114) turns on a semiconductor switch (SSW1) when switching from a low-speed winding for low-speed operation of a three-phase AC motor to a high-speed winding for high-speed operation. The mechanical switch (MSW1) provided at the same connection terminal as the switch (SSW1) is turned on, then the semiconductor switch (SSW1) is turned off, and the low-speed operation is performed from the high-speed winding for high-speed operation of the three-phase AC motor. When switching to the winding, the mechanical switch (MSW1) that was energized is turned off and the semiconductor switch (SSW2) is turned on at the same time. After a certain delay, the mechanical switch (MSW2) is turned on, and then the semiconductor switch (SSW2) The winding switching device for a three-phase AC motor according to claim 1, wherein a signal for turning off is generated.   The winding switching device for a three-phase AC motor according to claim 1, wherein the snubber circuit is a parallel circuit of a resistor and a capacitor.   The winding switching device for a three-phase AC motor according to claim 1, wherein the AC motor is a synchronous motor in which a field magnet is embedded in a rotor core.   When switching the connection terminal from the low-speed winding to the high-speed winding, the drive signal generation unit (114) turns on the semiconductor switch (SSW2) on the low-speed winding side that has been turned off, and at this time, the semiconductor switch (SSW2) ) And the mechanical switch (MSW2) are both turned on, then the mechanical switch (MSW2) is turned off, and only the semiconductor switch (SSW2) is turned on, and then the semiconductor switch (SSW2) 2. The winding of the three-phase AC motor according to claim 1, wherein the semiconductor switch (SSW1) is turned on at the same time, the mechanical switch (MSW1) is turned on, and then the semiconductor switch (SSW1) is turned off. Line switching device.   The drive signal generator (114) turns on the semiconductor switch (SSW1) on the high-speed winding side that has been turned off when switching the connection terminal from the high-speed winding to the low-speed winding, and at this time, the semiconductor switch (SSW1) ) And the mechanical switch (MSW1) are both turned on, then the mechanical switch (MSW1) is turned off, and only the semiconductor switch (SSW1) is turned on, and then the semiconductor switch (SSW1) The semiconductor switch (SSW2) is turned on at the same time as turning off, and then the mechanical switch (MSW2) is turned on, and then the semiconductor switch (SSW2) is turned off. Line switching device.   When the AC motor is a permanent magnet type synchronous motor, all of the semiconductor switches (SSW1, SSW2) and the mechanical switches (MSW1, MSW2) that open and close the connection terminals are opened as soon as the winding switching device detects an abnormal state. The winding switching device for a three-phase AC motor according to claim 1.   The winding switching device for a three-phase AC motor according to claim 10, wherein the abnormal state is any one of a vertical short circuit of a switching element of the inverter main circuit, a ground fault, and a power failure of a commercial power source. Each phase winding is composed of a plurality of windings, and a connecting terminal that connects the plurality of windings to each other and an AC motor that has both terminals of each phase winding provided outside the motor, and a winding that switches the connecting terminals as appropriate. A line switching unit, an inverter for supplying a variable voltage of a variable frequency to the AC motor, and the winding switching unit connects one end of each phase winding to the inverter, and connects the other end and the connection terminal to each other. A plurality of three-phase rectifiers each connected to an AC-side input terminal of a three-phase rectifier for each phase; a semiconductor switch provided to open and close both ends on the DC output side of the plurality of three-phase rectifiers; and the semiconductor A current that flows from the three-phase rectifier when the semiconductor switch is off flows to a snubber circuit at one end on the DC output side of each of the drive circuit that drives the switch and the plurality of three-phase rectifiers, When on, said snubber times In the winding switching method of the winding switching unit of the three-phase AC motor via a provided a diode in a direction that does not flow back to connect the DC output side of the three-phase rectifier unit in the snubber circuit to the semiconductor switch from,
Mechanical switches (MSW1, MSW2) are connected in parallel with the three-phase rectifier input so that the connection terminals can be opened and closed,
A winding switching method for a three-phase AC motor, wherein a driving signal for opening and closing is output from the driving signal generation unit (114) to the mechanical switches (MSW1, MSW2).

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