A New PWM Strategy for High Efficiency Drive of DC Servo Motors


IEICE TRANSACTIONS (1976-1990)   Vol.E71   No.12   pp.1298-1302
Publication Date: 1988/12/25
Online ISSN: 
Print ISSN: 0000-0000
Type of Manuscript: PAPER
Category: Electroic Circuits

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A new pulse-width-modulation (PWM) circuit is developed for high efficiency, bidirectional drive of dc servo motors. The circuit generates the positive- and negative-going sweeps shifted each other in time by a half period of the repetition frequency. Compared with these sweeps, a control input is converted into the PWM signal which drives a motor in a push-pull manner. This method of driving a motor consumes no power when it is at rest and reduces the switching loss of power stage to a half that of a conventional PWM scheme. An efficiency higher than 90% is achieved by a prototype PWM driver using power MOSFET's for the switching frequency lower then 60 kHz. Simultaneous conduction of two complementary power transistors in each leg of a power bridge, and thus the short-circuit current, never occurs because of the phase-shift in the two sweeps. Besides the high efficiency, the new scheme features wide dynamic range made possible by nonlinear PWM process.