Electricity: motive power systems – Constant motor current – load and/or torque control
Patent
1996-09-20
1998-07-14
Cabeca, John W.
Electricity: motive power systems
Constant motor current, load and/or torque control
318439, 388811, 388812, 363 41, G05B 500
Patent
active
057809860
ABSTRACT:
A PWM controlled multiphase DC motor apparatus has a multiphase DC motor, a current sensor, and a PWM controller. The DC motor has multiple windings which turn on and off during commutation at a commutation frequency. The current sensor is coupled to sense power supply current flowing in all windings of the DC motor. The PWM controller is coupled to control the DC motor using a PWM signal at selected PWM frequency with variable duty cycle. Using the feedback from the current sensor, the PWM controller maintains approximately constant torque in the DC motor by adjusting the duty cycle of the PWM signal. The PWM controller includes a soft switching circuit which manipulates a voltage used to generate the controlling PWM signal in a manner which causes linear stewing of currents in the windings during commutation. The linear current stewing occurs at a slew rate that is slow relative to the PWM frequency to thereby reduce torque ripple during commutation. The combined features of continuous PWM duty cycle control and linear current slewing during commutation significantly reduces torque ripple at the fundamental commutation frequency, as well as at the first few harmonics. A method for PWM control of a multiphase DC motor is also described.
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Buthker Henricus C. J.
Shelton Boyd N.
Cabeca John W.
Hewlett--Packard Company
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