Induction motor drive apparatus

Electricity: motive power systems – Induction motor systems – Primary circuit control

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Details

318811, 318801, H02P 540

Patent

active

043226710

ABSTRACT:
An induction motor drive apparatus brings the actual speed of an induction motor into coincidence with a command speed by varying the frequency and effective value of a three-phase AC voltage applied to the induction motor and limits the torque of the induction motor in the low speed region by controlling an amplitude of a speed deviation signal below a prescribed value. The apparatus includes an inverter for generating three-phase AC voltage, a speed deviation signal generator, a torque limit signal generator, an amplitude controller for controlling the amplitude of the speed deviation signal based on the presence of the torque limit signal, a slip signal generator which generates a slip signal having a positive or negative constant voltage conforming to the rotational direction of the induction motor, an adder for adding together a voltage signal which conforms to the actual speed and the slip signal, a rectangular waveform signal generator, a multiplier for multiplying an output of the amplitude controller by an output of the adder and a pulse width modulator. The rectangular waveform signal generator is adapted to produce a three-phase rectangular signal whose frequency is proportional to the output voltage value of the adder. The rectangular signal of each phase is modulated in pulse width on the basis of the speed deviation, the inverter being controlled by each resulting pulse-width modulated rectangular signal to thereby vary the effective value of the three-phase AC voltage and to make the speed of the induction motor constant.

REFERENCES:
patent: 3819992 (1974-06-01), Opal
patent: 4160940 (1979-07-01), Wolf

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