Electricity: motive power systems – Switched reluctance motor commutation control
Patent
1991-04-26
1993-01-26
Ro, Bentsu
Electricity: motive power systems
Switched reluctance motor commutation control
318138, H02P 602
Patent
active
051825007
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a brushless motor control circuit for controlling rotation of a brushless motor.
DESCRIPTION OF RELATED ART
FIG. 1 shows an example of a conventional drive circuit of a brushless motor. Signals H.sub.a, H.sub.b, and H.sub.c of three Hall elements used as rotor position detecting elements of a three-phase brushless motor are amplified by amplifiers 1.sub.1, 1.sub.2, and 1.sub.3. To reduce third harmonic component, a difference "H.sub.a -H.sub.b ", a difference "H.sub.c -H.sub.a ", and a difference "H.sub.c -H.sub.a " are obtained respectively by amplifiers 2.sub.1, 2.sub.2, and 2.sub.3. Output signals from the amplifiers 2.sub.1, 2.sub.2, and 2.sub.3 are amplified by amplifiers 3.sub.1, 3.sub.2, and 3.sub.3 to obtain output signals L.sub.a, L.sub.b, and L.sub.c, thereby driving a motor coil (stationary) 4.
Another circuit example is also conventionally employed as shown in FIG. 2 in which the output signals from two Hall elements are synthesized by an amplifier 5 to obtain a signal H.sub.c ' which is equivalent to the third output signal of FIG. 1. Signals H.sub.a and H.sub.b, and the signal H.sub.c ' are processed in the same manner as in FIG. 1, thereby driving a motor coil 4 (not shown in FIG. 2).
However, with the drive circuit shown in FIGS. 1 or 2, when the motor position detecting elements, i.e., the Hall elements, are incorporated in a motor, a variation in the Hall elements or imbalance during motor assembly may occur. Hence, it is difficult to obtain three or two Hall element signals that are amplified in a similar manner.
This leads to the following problem. The outputs L.sub.a, L.sub.b, and L.sub.c that finally drive the motor coil 4 are adversely influenced by variations in Hall element output signals, amplifiers, and motor coils and become unbalanced with respect to ideal output signals (motor coil drive signals in which only the phases are shifted from each other by 120.degree. and which have no imbalance regarding other conditions, e.g., amplitudes.) Then, the motor coil windings of the respective phases are driven in an unbalanced manner to increase a torque ripple, thus, reducing rotational precision.
It is, therefore, an object of the present invention to perform well-balanced motor driving which is free from an adverse influence caused by variation in Hall elements as the position detecting elements or in motor assembly.
SUMMARY OF THE INVENTION
A brushless motor control circuit according to the present invention is characterized by comprising a three-phase brushless motor, amplifiers, commonly provided to three-phase input lines of the motor, for receiving rotor position detection signals of the motor, and a control circuit for comparing, with a constant value, one of a difference and a sum of a product of two phase signals, among three phase outputs of the amplifiers, and a signal as a square of the remaining phase signal, and feeding back a comparison result signal to the amplifiers of common stages of the three-phase input lines, thereby controlling rotation of the motor.
More specifically, three Hall elements as rotor position detecting elements are used, and are arranged on the rotor side such that their phases are shifted from each other by 120.degree.. Then, the signals input to the three-phase motor coil are shifted from each other by 120.degree.. Similarly, when two Hall elements are used, they are also arranged such that their phases are shifted from each other by 120.degree.. Therefore, the third signal formed by using the two signals is also phase-shifted from the two signals by 120.degree.. Assuming that signals whose phases are shifted from each other by 120.degree. are "H.sub.a =K.times.sin.alpha., H.sub.b =K.times.sin(.alpha.+120.degree.), H.sub.c =K.times.sin(.alpha.+240.degree.)", it is possible to prove that the following relation: =H.sub.a.sup.2 =H.sub.c .times.H.sub.a -H.sub.b.sup.2 =constant (1) +H.sub.a.sup.2 =H.sub.c .times.H.sub.a +H.sub.b.sup.2 =constant (2) Ideally, since the outputs L.sub.a, L.sub
REFERENCES:
patent: 4658190 (1987-04-01), Miyazaki et al.
Kabushiki Kaisha Toshiba
Ro Bentsu
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