H - Electricity – 02 – M
Patent
H - Electricity
02
M
318/103, 321/42
H02M 1/08 (2006.01) H02M 7/527 (2006.01) H02M 7/48 (2006.01)
Patent
CA 1084582
ABSTRACT OF THE DISCLOSURE Alternating voltage for energizing an adjustable speed a-c motor is derived from unipolarity input voltage by means of electric power inverting apparatus comprising at least one pair of alternately conducting controllable electric valves. The conducting states of these valves are periodically switched by a control which is responsive to frequency and amplitude command signals, whereby the frequency and the amplitude of the fundamental component of the alternating voltage are varied as functions of the respective command signals. The control provides a triangular wave for obtaining interception points for deriving pulse width modulation (PWM) of the alternating voltage so long as the amplitude command signal does not exceed a predetermined reference value (which is less than 1.0 per unit) and the speed of the motor does not exceed a predetermined reference speed. The control additionally pro- vides a "transition" PWM mode of operation whenever the amplitude command signal exceeds its reference value or the motor speed exceeds said reference speed. As disclosed herein the transition PWM mode is provided by a dual a-c level set scheme in which the lower level is varied as a function of the higher level so as to minimize selected harmonics of the alternating voltage and the higher level is varied as a function of the amplitude command signal thereby to vary the amplitude of the fundamental voltage component. A smooth transitioning to a square wave mode of operation is made as the amplitude command signal approaches 1.0 per unit.
272283
Company General Electric
Eckersley Raymond A.
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