Apparatus for controlling firing of thyristors relative to a cur

Details Apparatus for controlling firing of thyristors relative to a cur Apparatus for controlling firing of thyristors relative to a cur

1986-10-16

1990-03-27

Shoop, Jr., William M.

Electricity: motive power systems

Induction motor systems

Primary circuit control

318729, H02P 318

Patent

active

049123904

ABSTRACT:
Timing the firing of thyristors in a motor controller is done by using a microprocessor for timing relative to the event of current reaching zero, and by using hardware that generates firing signals in response to the voltage crossing zero. A motor controller has: thyristors for connecting the motor to a source of AC electrical energy; motor voltage zero crossing circuitry and motor current zero crossing circuitry for measuring a LAG TIME indicative of the time interval between the event of voltage applied; to the motor crossing zero and current flow to the motor reaching zero; a microprocessor generating a desired OFF TIME indicative of a desired time interval between the event of current flow to the motor reaching zero and firing of the thyristors; phase angle controller circuitry for firing the thyristors at a firing time after the event that the voltage applied to the motor crosses zero, the firing time being computed by adding the LAG TIME and the OFF TIME. The desired OFF TIME may be computed from an energy saving apparatus for adjusting the voltage applied to the motor to provide efficient operation for a highly loaded motor.

REFERENCES:
patent: 3728557 (1973-04-01), Pelly et al.
patent: 4426609 (1984-01-01), Nagy et al.
patent: 4470092 (1984-09-01), Lombardi
patent: 4581568 (1986-04-01), Fitzpatrick et al.
patent: 4710692 (1987-12-01), Libert et al.

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