Controller for induction motors

Electricity: motive power systems – Induction motor systems – Power-factor control

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318434, H02P 540

Patent

active

047679751

ABSTRACT:
Many induction motor controllers employ a reference angle relative to the supply voltage which is a target for the phase lag of current behind voltage but the choice of the optimum reference angle for energy saving varies from motor to motor. In the present invention firing signals for thyristors connected between a supply and a motor to be controlled are generated by firing circuits under the control of a microprocessor 18. The firing angle for the thyristors is continuously adjusted according to the phase lag as indicated by supply voltage zero crossings and current sensing circuits, load on the motor, and a signal indicating the tendency of the motor to stall obtained from the back e.m.f. of the motor. Using the said signal can be regarded as equivalent to adjusting the reference angle for the optimum value mentioned above. A procedure for starting a motor and setting the initial value of the reference angle is also described.

REFERENCES:
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patent: 4276505 (1981-06-01), Bose
patent: 4307325 (1981-12-01), Saar
patent: 4361792 (1982-11-01), Davis, Jr. et al.
patent: 4384243 (1983-05-01), Muskovac
patent: 4408149 (1983-10-01), Collins et al.
patent: 4454462 (1984-06-01), Spann
patent: 4468603 (1984-08-01), Vander Meer
Toth, A., "Energy Savings in an Induction Motor Using the 8022 Microcontroller", Intel. Application Note AP. 94, May 1980.
Chan et al., "A Microprocessor-Based Current Controller for SCR-DC Motor Drives", IEEE Transactions on Industrial Electronics and Control Instrumentation, vol. IECI-27, No. 3, Aug. 1980, pp. 169-176.

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