SOFT SWITCHING PWM CONTROLLER AND METHOD FOR REDUCING TORQUE RIPPLE IN MULTIPHASE DC MOTOR

摘要

The PWM controlled multiphase DC motor arrangement of the present invention includes a multiphase DC motor 22, a current sensor 26 and a PWM controller 28. The DC motor 22 includes multiple windings 42-44 that turn on and off at the commutating frequency during commutation. The current sensor 26 is connected to sense a power supply current flowing in all the windings 42-44 of the DC motor 22. [ The PWM controller 28 is connected to control the DC motor 22 using a PWM signal at a selected PWM frequency having a variable duty cycle. The PWM controller 28 uses feedback from the current sensor 26 and then adjusts the duty cycle of the PWM signal to cause the DC motor 22 to maintain a substantially constant torque. The PWM controller 28 includes a soft switching circuit that adjusts the voltage in such a way that the current in the windings 42-44 is slewed linearly during rectification so that the control PWM signal is generated . Linear current slewing occurs at a slower slew rate relative to the PWM frequency, which reduces torque ripple during commutation. If continuous PWM duty cycle control and linear current slewing are combined during rectification, the torque ripple is greatly reduced in the first few harmonics as well as the fundamental commutation frequency. Further, a method for PWM control of a multi-phase DC motor is described.