MY118330A - Soft switching, pwm controller and method for reducing torque ripple in multiphase dc motor - Google Patents

Abstract

A PWM CONTROLLED MULTIPHASE DC MOTOR APPARATUS HAS A MULTIPHASE DC MOTOR (20), A CURRENT SENSOR (26), AND A PWM CONTROLLER (28). THE DC MOTOR (20) HAS MULTIPLE WINDINGS (42,43,44) WHICH TURN ON AND OFF DURING COMMUTATION AT A COMMUTATION FREQUENCY. THE CURRENT SENSOR (26) IS COUPLED TO SENSE POWER SUPPLY CURRENT FLOWING IN ALL WINDINGS OF THE DC MOTOR. THE PWM CONTROLLER (28) IS COUPLED TO CONTROL THE DC MOTOR (20) USING A PWM SIGNAL (PWM1, PWM2) AT SELECTED PWM FREQUENCY WITH VARIABLE DUTY CYCLE. USING THE FEEDBACK FROM THE CURRENT SENSOR (26), THE PWM CONTROLLER (28) MAINTAINS APPROXIMATELY CONSTANT TORQUE IN THE DC MOTOR BY ADJUSTING THE DUTY CYCLE OF THE PWM SIGNAL (PWM1, PWM2). THE PWM CONTROLLER INCLUDES A SOFT SWITCHING CIRCUIT WHICH MANIPULATES A VOLTAGE (V30, V32) USED TO GENERATE THE CONTROLLING PWM SIGNAL (PWM1, PWM2) IN A MANNER WHICH CAUSES LINEAR SLEWING OF CURRENTS IN THE WINDINGS DURING COMMUTATION. THE LINEAR CURRENT SLEWING 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. (FIG.1)