Circuit for controlling a brushless electric motor

Details Circuit for controlling a brushless electric motor Circuit for controlling a brushless electric motor

1986-11-04

1988-10-25

Ro, Bentsu

Electricity: motive power systems

Switched reluctance motor commutation control

318345H, H02P 600

Patent

active

047806524

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention concerns a circuit for controlling a brushless electric motor, especially a slow-running flat motor of the type appropriate for operating washing machines directly for example. In directly operating the drum of a washing machine the speed must be varied within extensive limits, specifically 40 to 70 rpm for the wash cycle and approximately 1000 rpm for the spin cycle. With synchronous motors this is completely impossible because the speed of a synchronous motor depends on the mains frequency, which is invariable.


SUMMARY OF THE INVENTION

The object of the invention is create a circuit for controlling a brushless electric motor that will allow the motor to run slowly independent of the mains frequency. A further development of the invention also attains the object of maintaining a symmetrical load on the mains in spite of unsymmetrical feeding of the stator winding.
There are several advantages to operating a motor with the circuit in accordance with the invention. The potential for varying the speed of the motor within extensive limits makes it possible to employ the motor in a washing machine for directly driving the drum both during the slow wash cycle and during the rapid spin cycle. The potential for controlling the currents supplied to the stator windings and to the brushless rotor eliminates the need for collectors and accordingly increases reliability. Since the reversal of direction that is so important with washing machines can be accomplished strictly electronically by controlling the stator winding, no output relay is necessary. Electronic controls can also lead to electric braking. For this purpose a torque can be generated, by reversing the polarities of the incoming voltages for instance, that is directly opposite the existing direction of rotation. The phase-trimming control also makes it possible to vary the torque because varying the phase-trimming angle will affect the electric power being supplied to the motor and hence the torque.
The control circuit for controlling a plurality of stator windings is preferably employed. It is, however, also possible to restrict the employment to only one stator winding. This is in particular possible at a high speed, at which the frequency of the magnetic field and that of the mains are approximately equal. The motor can then run like a synchronous motor, in which the torque that is generated can be controlled by varying the phase-trimming angle. The mains voltage can be simply the voltage obtained from one line. It can, however, also by derived by means of a voltage converter (inverse rectifier) from a direct-current voltage, from a battery for example, when the motor output is low and allows input from a battery. The torque generated by the motor is generally not constant, but varies periodically through the motor's angle of rotation. This torque, however, will be adequately integrated by the inertia of the rotor and of the components it drives.


BRIEF DESCRIPTION OF THE DRAWING

The invention will now be specified with reference to the drawings, wherein
FIG. 1 illustrates the principle behind the controls in accordance with the invention,
FIG. 2 shows curves that illustrate the operation of the embodiment illustrated in FIG. 1,
FIG. 3 illustrates a practical embodiment of the invention,
FIG. 4 shows curves that illustrate the operation of the embodiment illustrated in FIG. 3,
FIG. 5 illustrates a second embodiment of the invention, and
FIG. 6 shows curves that illustrate the operation of the embodiment illustrated in FIG. 5.


DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates the rotor 1, two stator windings S1 and S2, and two Hall components D1 and D2 of a motor. Rotor 1 has, diametrically opposed, a north pole N and a south pole S created by permanent magnets. Hall components D1 and D2 generate voltages eH1 and eH2 that represent the instantaneous angle of rotation of rotor 1. Voltages eH1 and eH2 control the currents iS1 and iS2 supplied to windings S1 and S2 in such a way that the windings

REFERENCES:
patent: 3333171 (1967-07-01), Platnick
patent: 3466519 (1969-09-01), Platnick
patent: 3529220 (1970-09-01), Kazutsugu Kobayashi et al.
patent: 3959709 (1976-05-01), Irish
patent: 4238719 (1980-12-01), Bourbeau
patent: 4431958 (1984-02-01), Schutten et al.

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