Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1979-03-12
1981-09-29
Truhe, J. V.
Electricity: motive power systems
Induction motor systems
Primary circuit control
318723, 318799, 318807, 318811, H02P 528, H02P 534
Patent
active
042925770
ABSTRACT:
A tachometer is coupled to the rotor of an A.C. motor and generates an output voltage proportional to the rotor's speed. A VELOCITY COMMAND voltage is generated having an amplitude which specifies a desired rotor speed. The tachometer voltage is subtracted from the VELOCITY COMMAND voltage to produce a VELOCITY ERROR voltage. The output of a D.C. power source is chopped at a fixed frequency and variable pulse width, the pulse width being proportional at any time to the amplitude of the VELOCITY ERROR voltage. The chopped D.C. voltage is filtered to provide a variable D.C. voltage having an amplitude which is proportional to the amplitude of the VELOCITY ERROR voltage. The variable D.C. voltage is applied to an inverter which changes it into an A.C. voltage. The A.C. voltage is applied to the stator windings of the motor to drive the rotor thereof. The frequency of the A.C. voltage is variable and is proportional, at rotor speeds above 150 RPM, to the amplitude of the velocity command voltage. At rotor speeds below 150 RPM, the frequency of the A.C. voltage is held fixed at approximately 28 Hz. The amplitude of the A.C. voltage is proportional to the VELOCITY ERROR voltage at all speeds. The frequency of the A.C. voltage is determined by an oscillator which drives a ring counter whose counting direction is controlled by a direction flip-flop. The state of the direction flip-flop is changed whenever the polarity of the VELOCITY ERROR voltage changes so that deceleration of the motor always occurs in a plugging mode.
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Cesarz Michael R.
Stobbe Richard E.
Hajewski Cyril M.
Kearney & Trecker Corporation
Levy Robert B.
Moose Richard M.
Truhe J. V.
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