JP2011120337A - Single-phase ac synchronous motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single-phase AC synchronous motor, which surely makes a transition from its starting operation to its synchronous operation, regardless of its sensorless system, and is inexpensive and downsizable. <P>SOLUTION: The motor is started as a DC brushless motor by performing a preliminary operation and a starting operation. In the preliminary operation, a permanent magnet rotor is fixed in the position of a stator where either coil is wound, by letting a rectified current flow to an A coil L1 and a B coil L2 alternately, repeating it by the specified number of times for specified time when the permanent magnet rotor can start. In the starting operation, the number of revolutions is raised to the vicinity of the number of synchronous revolutions by letting the rectified current flow to the A coil L1 and the B coil L2 alternately by the specified number of times, narrowing time gradually, starting with the other coil wound in the position of the stator where the permanent magnet rotor is not fixed, after the preliminary operation. Then, the A coil L1 and the B coil L2 are connected in series to an AC power source, and an AC current is applied to the A coil L1 and the B coil L2 to let it operate synchronously as an AC synchronous motor. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a single-phase AC synchronous motor, and more particularly to a single-phase AC synchronous motor that drives a single-phase AC synchronous motor having a rotor structure using a magnet without a position sensor for detecting the rotor magnetic pole position.

  As a conventional single-phase AC synchronous motor, for example, a start-up operation as a DC brushless motor is performed, and the rotation of the rotor is started up to the synchronous rotation. Thereafter, an AC current is passed through the motor coil to switch to a synchronous operation as an AC synchronous motor. A phase AC synchronous motor has been proposed (see, for example, Patent Document 1).

  The single-phase AC synchronous motor of Patent Literature 1 rectifies an AC current supplied from the single-phase AC power supply to a motor coil connected to a single-phase AC power supply by a rectifier bridge circuit and smoothes the DC current by a filter circuit. A starting operation circuit for starting operation as a direct current brushless motor by switching the starting switching means by a detection signal from a detection sensor that detects the magnetic pole position of the permanent magnet rotor and switching the direction of the motor current to energize And a synchronous operation circuit that synchronously operates as an AC synchronous motor by supplying an alternating current to the motor coil and a single-phase alternating current power supply and the motor coil. The operation changeover switch and the operation changeover switch are switched from the start-up operation circuit to the synchronous operation circuit and shifted to synchronous operation. The control means switches the start-up switching means according to the detection signal of the detection sensor while the operation changeover switch is connected to the start-up operation circuit while the operation changeover switch is connected to the start-up operation circuit. When the rotational speed of the permanent magnet rotor reaches a predetermined rotational speed near the synchronous rotational speed, the motor current waveform whose phase is delayed from the output waveform of the detection sensor is changed so that the energization direction is switched at least at the zero cross point of the sensor output waveform. Since the start-up operation is performed while suppressing the energization range, it is possible to suppress the generation of reverse rotation torque in the start-up operation and increase the rotor rotation speed up to the synchronous rotation speed, and perform stable synchronous pull-in. It is said.

Japanese Patent No. 4030571

However, the single-phase AC synchronous motor of Patent Document 1 has the following problems.
That is, since the rectified current rectified by the rectifier bridge circuit is a large current, the capacitor of the filter circuit that smoothes the rectified current needs to use an expensive capacitor with a large rated capacity, and the lifetime is increased by flowing a large current. There is also a problem that leads to a decline. In addition, since six switching elements (transistors) are used to switch the direction of the motor current during start-up operation, the number of components is large, making it difficult to reduce the size and cost. There is. In addition, a Hall element is used as a detection sensor for detecting the number of rotations of the permanent magnet rotor, and this also causes a problem that becomes an obstacle to downsizing and cost reduction.

  The present invention has been made in view of the above problems, and while being a sensorless system, it is possible to reliably perform the transition from the start-up operation to the synchronous operation, and has a small number of parts and an expensive part. It is an object of the present invention to provide a single-phase AC synchronous motor that has high reliability, is inexpensive, and can be downsized by adopting a simple circuit configuration that eliminates the above.

  The following aspects of the present invention exemplify the configuration of the present invention, and will be described separately for easy understanding of various configurations of the present invention. Each section does not limit the technical scope of the present invention, and some of the components of each section are replaced, deleted, or further, while referring to the best mode for carrying out the invention. Those to which the above components are added can also be included in the technical scope of the present invention.

  (1) A permanent magnet rotor provided in a housing so as to be rotatable around an output shaft, and a stator having an armature coil in which an A coil and a B coil are wound around a stator core in series via an intermediate tap. In a synchronous motor comprising: a rectifying circuit for rectifying an alternating current supplied from an alternating current power supply; and a rectified current connected between the rectifying circuit and the intermediate tap and rectified by the rectifying circuit to the armature coil. A first operation changeover switch for flowing, a first switching element connected in series to the A coil, and a second switching element connected in series to the B coil; In addition, the permanent magnet rotor is caused to flow through the B coil repeatedly for a predetermined number of times at a predetermined time during which the permanent magnet rotor can be activated. Preliminary operation for fixing at the position of the wound stator, and after the preliminary operation, the other coil wound at the position of the stator where the permanent magnet rotor is not fixed is used as a starting point for the rectified current to be the A coil and the coil A start-up operation circuit that starts as a DC brushless motor by performing a start-up operation in which the time is gradually narrowed alternately in the B coil and flowed a predetermined number of times to increase the rotation speed to the vicinity of the synchronous rotation speed, the AC power supply, and the A A second operation changeover switch connected between the coil and a third operation changeover switch connected between the AC power source and the B coil, wherein the first operation changeover switch is turned off. As a result, the rectified current from the rectifier circuit is cut off, and the second operation changeover switch and the third operation changeover switch are turned on. A synchronous operation circuit in which the A coil and the B coil are connected in series to the AC power source, and an AC current is supplied to the A coil and the B coil to operate synchronously as an AC synchronous motor, and the startup operation circuit In preliminary operation and start-up operation, the first operation changeover switch is turned on to allow the rectified current to flow through the intermediate tap, and the first switching element and the second switching element are turned on alternately to turn the A coil And the rectified current flowing alternately to the B coil, and when the rotational speed of the permanent magnet rotor reaches the vicinity of the synchronous rotational speed, the first operation changeover switch is turned off and the rectified current is Blocking the flow to the intermediate tap, turning on the second operation changeover switch and the third operation changeover switch to turn on the synchronous operation circuit And a control means for controlling to shift to the synchronous operation according to claim 1 (Claim 1).

(2) In the single-phase AC synchronous motor described in (1), a filter circuit that smoothes the rectified current to generate a DC current between the rectifier circuit and the control means, and the DC current is input. And a low voltage source that outputs a DC power supply to be supplied to the control means (Claim 2).

  (3) The single-phase AC synchronous motor according to (2), wherein the drive voltage of the first operation changeover switch is a smoothed voltage supplied from the filter circuit. A motor (claim 3).

  (4) In the single-phase AC synchronous motor according to (2) or (3), the motor is disposed between the first operation changeover switch and the control means, and according to a control signal from the control means. A single-phase AC synchronous motor, further comprising a switch drive circuit that outputs an ON / OFF operation switching signal to the first operation changeover switch (Claim 4).

  Since the single-phase AC synchronous motor according to the present invention is configured as described above, it is possible to surely perform the transition from the start operation to the synchronous operation while being a sensorless system, and the number of parts is small, and By adopting a simple circuit configuration that eliminates expensive parts, it is possible to provide a single-phase AC synchronous motor that is highly reliable, inexpensive, and capable of being downsized.

It is an axial sectional view explaining the structure of a single phase AC synchronous motor in one embodiment of the present invention. It is a circuit block diagram which shows the drive circuit of the single phase alternating current synchronous motor in one Embodiment of this invention. It is a circuit block diagram explaining operation | movement of the starting operation circuit of the single phase alternating current synchronous motor in one Embodiment of this invention. It is a circuit block diagram explaining operation | movement of the synchronous operation circuit of the single phase alternating current synchronous motor in one Embodiment of this invention. It is a timing chart figure which shows the output waveform of the principal part of the drive circuit of the single phase alternating current synchronous motor in one Embodiment of this invention.

(Motor configuration)
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is an axial sectional view showing an outline of a motor equipped with a drive circuit using the present invention. FIG. 1 shows a motor 21. The motor 21 is an AC fan motor as an example of a single-phase AC motor, and includes a shaft 22 serving as a rotating shaft. The shaft 22 is supported by bearings 23 and 24. The bearing 23 is attached to the lower part of the lower housing 25, and the bearing 24 is attached to the upper part of the lower housing 25. With this structure, the shaft 22 is attached to the lower housing 25 in a rotatable state. A permanent magnet rotor 26 is attached to the shaft 22. The permanent magnet rotor 26 includes a rotor yoke 28 to which a permanent magnet 27 having a structure magnetized by a plurality of magnetic poles is fixed on the inner peripheral side, and an impeller 29 having a plurality of blades 29 a and fixed to the outer peripheral side of the rotor yoke 28. And.

  A stator core 30 is disposed facing the permanent magnet rotor 26 in the radial direction. The stator core 30 is made of a magnetic material such as silicon steel and is fixed to the lower housing 25. The stator core 30 has a structure having salient poles corresponding to the number of magnetic poles, and is arranged so that a plurality of salient poles are surrounded by the permanent magnet rotor 26 from the periphery. In the motor 21, the stable point of the permanent magnet rotor 26 is fixed so as to deviate in the rotation direction, and the rotation direction is determined. Since this area is the same as that of a normal DC fan motor, detailed description is omitted. To do.

  The stator core 30 is provided with an insulator member 31 that covers a part of the stator core 30 and an armature coil 32 wound around the insulator member 31. The end of the armature coil 32 is connected to the drive circuit board 33, and the external connection line 34 connected to the starting circuit board 33 is a wiring lead hole provided in the housing body 34 arranged on the outer periphery so as to surround the impeller 29. Through the housing.

(Configuration of drive circuit)
Next, in order to explain the driving method of the above-described single-phase AC synchronous motor in the embodiment of the present invention, an example of a driving circuit suitable for implementing the driving method is shown in FIG.
The drive circuit 1 shown in FIG. 2 includes a rectifier circuit 2 that rectifies an alternating current supplied from the alternating current power supply Vac, and an intermediate tap between the A coil L1 and the B coil L2 that constitute the armature coil 32 and the rectifier circuit 2. And a control means (microcomputer) 5. The control switch (microcomputer) 5 includes a first operation changeover switch SW <b> 1 that flows the rectified current rectified by the rectifier circuit 2 to the armature coil 32. The rectifier circuit 2 is a full-wave rectifier circuit formed by a diode bridge circuit including diodes D1 to D4. The first operation changeover switch SW1 is a MOS
It includes a switching element Q1 made of an FET and a diode D5 connected between the drain terminal and the gate terminal of the switching element Q1. The diode D5 can be a parasitic diode of the switching element Q1 or an external rectifier element.

  Between the rectifier circuit 2 and the microcomputer 5, a filter circuit 3 for smoothing the rectified current output from the rectifier circuit 2 to generate a direct current, and a direct current output from the filter circuit 3 are input. A low voltage source 4 for supplying a predetermined DC voltage to the input terminal IN1 of the microcomputer 5 is disposed. As shown in FIG. 2, the filter circuit 3 includes a resistor R1 and a capacitor C1 connected in series, and one end of the capacitor C1 is connected to GND. Since the capacitor C1 is arranged at the subsequent stage of the smoothing resistor R1, a capacitor having a small capacity and a long life (for example, a film capacitor) can be used.

The connection point between the resistor R1 and the capacitor C1 is connected to the gate terminal of the switching element Q1 via the resistor R2. Thus, by connecting the connection point of the resistor R1 and the capacitor C1 to the gate terminal of the switching element Q1, the drive voltage of the first operation changeover switch SW1 is a smoothed voltage supplied from the filter circuit 3. Is used. As described above, since the smoothed current after smoothing the rectified current with unstable voltage by the resistor R1 is applied to the gate terminal of the switching element Q1, the first operation changeover switch SW1 can be stably turned on. It becomes possible.

The gate terminal of the switching element Q1 is connected to the switch drive circuit 6. The switch drive circuit 6 includes a resistor R3 and a switching element Q4. The switching element Q4 has a base terminal connected to the output terminal OUT1 of the microcomputer 5 via a resistance element, and a collector terminal connected to the gate terminal of the switching element Q1 via a resistance R3. Based on the control signal from the output terminal OUT1 of the microcomputer 5, the switch drive circuit 6 outputs an ON / OFF operation switching signal to the first operation switch SW1. The switch drive circuit 6 is arranged between the first operation changeover switch SW1 and the microcomputer 5 so as to prevent a large rectified current flowing through the first operation changeover switch SW1 from flowing into the microcomputer 5. Playing a role.

The drive circuit 1 further includes a first switching element Q2 connected in series to the A coil L1 and a second switching element Q3 connected in series to the B coil L2. The first switching element Q2 and the second switching element Q3 are composed of transistors, and diodes D6 and D7 are connected between the emitter terminal and the collector terminal, respectively. The base terminal of the first switching element Q2 is connected to the output terminal OUT4 of the microcomputer 5 via a resistance element, and the base terminal of the second switching element Q3 is connected to the output terminal OUT3 of the microcomputer 5 via a resistance element. Has been. A second operation changeover switch SW2 made of triac is disposed between a connection point between the A coil L1 and the first switching element Q2 and one end of the AC power supply Vac, and the B coil L2 and the second switching element. Between the connection point with Q3 and the other end of the AC power supply Vac, a third operation changeover switch SW3 made of triac is arranged, and each of the second operation changeover switch SW2 and the third operation changeover switch SW3. The gate terminal of the microcomputer 5 is connected to the output terminal OUT2 of the microcomputer 5 through the triac gate voltage generation circuit 7. The triac gate voltage generation circuit 7 has a function of generating a gate voltage necessary for operating the second operation changeover switch SW2 and the third operation changeover switch SW3 according to a command from the microcomputer 5.

In the drive circuit 1, a counter electromotive force detection circuit 8 is disposed between the intermediate tap between the A coil L 1 and the B coil L 2 and the input terminal IN 2 of the microcomputer 5. The back electromotive force detection circuit 8 can confirm that the permanent magnet rotor is rotating normally by detecting a pulse signal output by the back electromotive force generated during the rotation, if necessary. .

  Here, an example of the start-up operation and the synchronous operation of the drive circuit 1 will be described with reference to the drawings. FIG. 3 is a circuit configuration diagram for explaining the operation of the start-up operation circuit 1 a configured in the preliminary operation period and the start-up operation period in the drive circuit 1. FIG. 4 is a circuit configuration diagram for explaining the operation of the synchronous operation circuit 1b configured during the synchronous operation in the drive circuit 1. FIG. 5 is a timing chart showing output waveforms of main parts of the drive circuit 1 during the preliminary operation period, the startup operation period, and the synchronous operation.

First, the circuit operation of the startup operation circuit 1a will be described.
In the preliminary operation period, as shown in FIG. 3, the alternating current of the alternating current power supply Vac is rectified through the rectifier circuit 2, the rectified current is smoothed through the filter circuit 3, and the smoothed direct current is a low voltage. Input to source 4. Then, a predetermined DC voltage is applied from the low voltage source 4 to the microcomputer 5 as a drive voltage. In other words, the drive voltage of the microcomputer 5 is such that a predetermined voltage stepped down by the low voltage source 4 is used after rectifying / smoothing the AC current of the AC power supply Vac, so that the microcomputer 5 is driven from the external DC power supply. There is no need to take in a voltage, and the circuit can be simplified.

The first operation change-over switch SW1 is turned on by a High level signal output from the output terminal OUT1 of the microcomputer 5 via the switch drive circuit 6 (the switching element Q1 is turned on by the gate signal; FIG. c)), the rectified current (see FIG. 5 (b)) obtained by rectifying the alternating current (see FIG. 5 (a)) of the alternating current power supply Vac through the rectifier circuit 2 causes the first operation changeover switch SW1. It passes through and flows into the intermediate tap of the armature coil 32. Since the output signal of the output terminal OUT2 of the microcomputer 5 is at the low level, both the second operation switch SW2 and the third operation switch SW3 are in the off state (FIG. 5 (d), In addition, since a high level signal for a predetermined period is alternately output from the output terminals OUT4 and OUT3 of the microcomputer 5, the rectified current flows into the armature coil 32, and the first switching element Q2 and the first switching element Q2 2 switching elements Q3 are alternately turned on for a predetermined period (see FIGS. 5 (f) and 5 (g)), and the A coil L1 and the B coil L2 are alternately energized (open circle 1 in FIG. 3, outlined white). The path indicated by the circled arrow 2), the motor rotates as a DC brushless motor. In accordance with output signals from the output terminals OUT4 and OUT3 of the microcomputer 5, a rectified current flows alternately through the A coil L1 and the B coil L1 for a predetermined time (= predetermined number of pulses; for example, 20 pulses of 5 mS). After repeating this a predetermined number of times, the output signals of the output terminals OUT4 and OUT3 of the microcomputer 5 are set to the low level to stop energization to the A coil L1 and the B coil L2, and the permanent magnet rotor is moved to a predetermined position (in FIG. L2 is initially fixed at the position of the wound stator core. Since the permanent magnet rotor is stably fixed at a predetermined position, it is preferable that the energization time of the last energized coil is slightly longer than the energization time until then.

In order to ensure the stable operation of the synchronous motor, it is preferable to provide a stop period of a predetermined time during the transition from the preliminary operation period to the start operation period as shown in FIG.
In the start-up operation period, energization is started from a coil (A coil L1 in FIG. 5) at a position opposite to a predetermined position of the permanent magnet rotor initially fixed in the preliminary operation period. Thereafter, similarly to the preliminary operation period, the A coil L1 and the B coil L2 are alternately energized a predetermined number of times alternately. Thus, it is possible to reliably start in a desired rotation direction. The time during which each is energized is controlled by the microcomputer 5 so as to gradually decrease with the number of energizations, and is set so that the rotation speed of the permanent magnet rotor increases to the vicinity of the synchronous rotation speed at the end of the startup operation period ( (See FIG. 5).

Next, the circuit operation of the synchronous operation circuit 1b will be described.
In the synchronous operation, as shown in FIG. 4, when the rotational speed of the permanent magnet rotor reaches a predetermined rotational speed in the vicinity of the synchronous rotational speed, the signal output from the output terminal OUT1 of the microcomputer 5 is changed from High level to Low. The level is switched, the switch drive circuit 6 is turned off, and the first operation switch SW1 is also turned off (the switching element Q1 is turned off). For this reason, the rectified current from the rectifier circuit 2 does not flow into the armature coil 32, is smoothed through the filter circuit 3, and the smoothed direct current is input to the low voltage source 4. Then, a predetermined DC voltage is applied from the low voltage power source 4 to the microcomputer 5 as a drive voltage.
After the first operation changeover switch SW1 is turned off by the microcomputer 5, the output signal of the output terminal OUT2 of the microcomputer 5 is switched from the Low level to the High level, so that the second signal is output via the triac gate voltage generation circuit 7. A high level signal is applied to the respective gate terminals of the operation changeover switch SW2 and the third operation changeover switch SW3, and both the second operation changeover switch SW2 and the third operation changeover switch SW3 are turned on. When the output signals of the output terminals OUT4 and OUT3 of the computer 5 are switched from the High level to the Low level, both the first switching element Q2 and the second switching element Q3 are turned off. As described above, the A coil L1 is connected to the AC power source Vac via the second operation changeover switch SW2, and the B coil L2 is connected to the AC power source Vac via the third operation changeover switch SW3. The AC current supplied from the AC power supply Vac flows through a circuit in which the A coil L1 and the B coil L2 are connected in series (path indicated by the white circle 3 in FIG. 4), and is predetermined as a single-phase AC synchronous motor. Synchronous operation is started at the synchronous rotational speed. In addition, since it takes some time until the second operation changeover switch SW2 and the third operation changeover switch SW3 start the on operation from the off state, a short idling is required during the transition from the start operation to the synchronous operation. A period occurs (see FIG. 5 (h)).

  As described above, the single-phase AC synchronous motor according to the present embodiment determines the initial fixed position of the permanent magnet rotor with respect to the stator, and performs the preliminary operation for reliably starting in the desired rotation direction and the vicinity of the rotation speed near the synchronization. By providing a drive circuit that constitutes a startup operation circuit that performs startup operation that increases the number of revolutions, it is possible to perform stable synchronous pull-in even though it is a sensorless system, and reliably shift from startup operation to synchronous operation Can be done.

In the drive circuit 1, the rectified current that has been full-wave rectified by the rectifier circuit 2 is directly passed through the armature coil 32 without being smoothed, so that the rectified current as in the prior art (synchronous motor according to Patent Document 1). Since a capacitor having a large rated capacity for smoothing is not required, the component cost can be reduced.

  Further, since the rectified current flowing through the armature coil 32 is cut off only by turning the first operation switch SW1 to the OFF state, the transition from the start operation to the synchronous operation can be performed with a simple circuit configuration with a small number of parts. It can be carried out.

As described above, by using the drive circuit according to the present embodiment, it is possible to simplify the drive circuit with a sensorless method, and thus provide a single-phase AC synchronous motor that is highly reliable, inexpensive, and can be downsized. can do.

  The representative embodiment of the present invention has been described above, but the present invention is not limited to the circuit configuration of the above embodiment, and various modifications can be made without departing from the spirit of the present invention. .

  For example, in the drive circuit 1 according to the above-described embodiment, the control unit 5 is a microcomputer. However, the control unit 5 is not limited to this, and a programmable device such as a DSP or FPGA can be used.

  In the drive circuit 1, triacs are used as the first operation changeover switch SW2 and the second operation changeover switch SW3. However, these may be bidirectional elements and can be replaced with components such as a relay switch. is there.

1: drive device, 2: rectifier circuit (full-wave rectifier circuit), 3: filter circuit, 4: low voltage source, 5: control means (microcomputer), 6: switch drive circuit, 7: triac gate voltage generation circuit, 8: Back electromotive force detection circuit, 21: Motor, 22: Shaft, 23, 24: Bearing, 25: Lower housing, 26: Permanent magnet rotor 26, 27: Permanent magnet, 28: Rotor yoke, 29: Impeller, 29a: Blade , 30: Stator core, 31: Insulator member, 32: Armature coil, 33: Drive circuit board, 34: External connection line, Vac: AC power supply, L1: A coil, L2: B coil, SW1: First operation switching Switch, SW2: second operation changeover switch (triac), SW3: third operation changeover switch (triac), Q1: switching element (MOS
FET), Q2: first switching element (transistor), Q3: second switching element (transistor), Q4: switching element (transistor), D1 to D4, D5, D6, D7: diode, R1, R2, R3 : Resistance, C1: Capacitor

Claims (4)

A permanent magnet rotor provided rotatably in the housing around an output shaft, and a stator having an armature coil in which an A coil and a B coil are wound around a stator core in series via an intermediate tap. In phase AC synchronous motor,
A rectifying circuit that rectifies an alternating current supplied from an alternating current power source, and a first operation switching that is connected between the rectifying circuit and the intermediate tap and that flows the rectified current rectified by the rectifying circuit to the armature coil. A switch, a first switching element connected in series to the A coil, and a second switching element connected in series to the B coil, wherein the rectified current is alternately supplied to the A coil and the B coil. The permanent magnet rotor is activated at a predetermined time during which the permanent magnet rotor can be activated a predetermined number of times, and the permanent magnet rotor is fixed at the position of the stator around which one of the coils is wound. The rectified current is gradually and alternately applied to the A coil and the B coil, starting with the other coil wound around the stator where the magnet rotor is not fixed. By performing a starting operation to raise the rotational speed to the synchronous speed near to flow a predetermined number of times by narrowing and a starting operation circuit for starting a brushless DC motor,
A second operation changeover switch connected between the AC power supply and the A coil; and a third operation changeover switch connected between the AC power supply and the B coil. When the operation switch is turned off, the rectified current from the rectifier circuit is cut off, and when the second operation switch and the third operation switch are turned on, the AC power supply is turned off. A synchronous operation circuit in which the A coil and the B coil are connected in series, and an alternating current is passed through the A coil and the B coil to synchronously operate as an AC synchronous motor;
In the preliminary operation and the start-up operation by the start-up operation circuit, the first operation changeover switch is turned on to flow the rectified current to the intermediate tap, and the first switching element and the second switching element are turned on alternately. And controlling the rectified current flowing alternately to the A coil and the B coil, and turning off the first operation changeover switch when the rotational speed of the permanent magnet rotor reaches the vicinity of the synchronous rotational speed. Control means for preventing the rectified current from flowing into the intermediate tap, and controlling the second operation changeover switch and the third operation changeover switch to shift to the synchronous operation by the synchronous operation circuit;
A single-phase AC synchronous motor comprising:   A filter circuit for smoothing the rectified current between the rectifier circuit and the control means to generate a direct current; and a low voltage source for inputting the direct current and supplying a direct current power supply to the control means. The single-phase AC synchronous motor according to claim 1, further comprising:   3. The single-phase AC synchronous motor according to claim 2, wherein the driving voltage of the first operation changeover switch is a smoothed voltage supplied by the filter circuit.   A switch drive that is disposed between the first operation changeover switch and the control means, and outputs an on / off operation changeover signal to the first operation changeover switch in response to a control signal from the control means. 4. The single-phase AC synchronous motor according to claim 2, further comprising a circuit.

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