Electricity: motive power systems – Synchronous motor systems – Hysteresis or reluctance motor systems
Patent
1994-06-06
1996-08-06
Martin, David S.
Electricity: motive power systems
Synchronous motor systems
Hysteresis or reluctance motor systems
318254, H02D 146
Patent
active
055437001
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a driver circuit and a driving method for a variable-reluctance motor (VR motor). More specifically, the invention relates to a driver circuit and a driving method, in which drive control is effected by means of a circuit for motor current control including switching devices one more in number than the phases of the motor.
BACKGROUND ART
A VR motor is a motor in which excitation current is supplied to exciting coils of a stator so that salient-pole teeth of the stator are excited, a salient-pole tooth of a rotor is attracted by means of a magnetic force of attraction generated in the salient-pole teeth of the stator, and the rotor is rotated by means of the resulting rotatory force. This motor is provided with switching devices for supplying excitation current to the exciting coils for individual phases, and the switching devices are opened and closed in response to the rotational angle of the motor, whereby the exciting coils for the individual phases are excited to rotate the rotor.
In the case of a three-phase VR motor with A-, B- and C-phases, for example, an A-phase switching device is closed to connect an A-phase exciting coil and a DC power source, thereby starting to supply current. When an A-phase salient-pole tooth attracts the salient-pole tooth of the rotor so that the rotor rotates through a predetermined angle, the A-phase switching device is opened to suspend current supplying. Then, a B-phase switching device is closed to excite a B-phase exciting coil. The motor is rotated in one direction by successively exciting the A-, B-, and C-phase coils in a like manner, thereafter. In reversing the motor, the motor can be reversed by exciting the A-, C-, and B- phase coils in the order named.
In controlling the current flowing through each exciting coil of this VR motor according to the pulse-width modulation system (PWM system), driver circuits must be formed independently for the individual phases. Therefore, each phase requires four switching devices or a combination of two switching devices and two diodes. Thus, a driver circuit of the conventional VR motor requires use of a number of switching devices and diodes, so that the driver circuit itself is increased greatly in cost, and requires two cables for each phase. Accordingly, the driver circuit becomes more expensive, and its wiring entails more man-hours.
An arrangement improving this point has been disclosed in a patent application in Japan (Jpn. Pat. Appln. No. 4-84966). According to this patent application, there is provided a driver circuit which requires use of only (N+1) switching devices where N is the number of phases of the VR motor.
The circuit diagram of FIG. 2 shows an example of the driver circuit of the three-phase VR motor in which the number of switching devices-is equal to "phase number+1."
In FIG. 2, reference numeral 1 denotes a rectifier circuit which rectifies three-phase alternating currents R, S and T to generate a DC voltage (main voltage) V. C1 designates a smoothing capacitor. In this driver circuit, a common series circuit is formed such that one end of a common switching device Q1 for pulse width modulation (PWM) operation is connected to a positive terminal of the rectifier circuit 1, and the cathode of a diode D1 is connected to the other end of the device Q1, the anode of the diode D1 being connected to a negative terminal of the rectifier circuit 1.
Moreover, this driver circuit is provided with series circuits for the individual phases, that is, the A-, B-, and C-phases, such that one end of each of switching devices (transistors) Q2, Q3 and Q4 for alternatively exciting the A-, B-, and C-phase coils is connected to the negative terminal of the rectifier circuit 1, the other ends are connected individually to the respective anodes of diodes D2, D3 and D4. The respective cathodes of the diodes D2, D3 and D4 are connected to the positive terminal of the rectifier circuit 1.
The junctions of the switching devices Q2, Q3 and Q4 and the diodes D2, D3 and D4 of
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Arimoto Kohei
Sakano Tetsuro
Fanuc Ltd.
Martin David S.
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