Control system of an alternating-current motor

Electricity: motive power systems – Motor-reversing – Armature or primary circuit control

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318230, 318231, H02P 540

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active

040514196

ABSTRACT:
An alternating-current motor is used as an actuator of a positioning control system. The control variable to control the torque of the motor is the load angle .theta..sub.d of a synchronous motor or the slip frequency f.sub.s of an induction motor.
The highest and the lowest limit values of the control variable are respectively predetermined from the characteristics between the torque and the control variable and from other design considerations.
The preparatory value E for the control variable is synthesized in accordance with an equation E=G.sub.1 (.theta..sub.c -.theta..sub.a)-G.sub.2 p.theta..sub.a, where .theta..sub.c is the reference position, .theta..sub.a is the controlled position, G.sub.1 and G.sub.2 are respectively amplification constants, and p denotes the differential operator d/dt. When E is within the predetermined highest and the lowest limit values of the control variable, E is used as the control variable; when E is larger than the predetermined highest limit value, the highest limit value is used as the control variable; and when E is smaller than the predetermined lowest limit value, the lowest limit value is used as the control variable.
After the control variable is thus determined, the instantaneous phase angle signal is synthesized in accordance with an equation .theta..sub.p =.theta..sub.a + .theta..sub.d or .theta..sub.p =.theta..sub.a + 2 .pi.f.sub.s /p where the instantaneous electrical angular position of the rotor of the motor is also denoted by .theta..sub.a.
The instantaneous phase angle of the power supply to the motor is controlled with this synthesized .theta..sub.p as the reference signal.
The voltage amplitude V.sub.1 of the power supply is controlled as a constrained variable to control the torque of the motor. The reference signal of the voltage amplitude V.sub.1 is determined as a function of the frequency of the power supply, or in one embodiment for a synchronous motor, as a function of the frequency and the load angle.

REFERENCES:
patent: 3720863 (1973-03-01), Ringland et al.
patent: 3876918 (1975-04-01), Komuro et al.
patent: 3908130 (1975-09-01), Lafuze

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