HIGH-TURNDOWN DC MOTOR CONTROLLER AND METHOD

摘要

A hybrid DC motor controller is provided for driving a DC motor. A switch is connected in series with the DC motor, and a capacitor is coupled in parallel with the DC motor and the switch. The speed of the DC motor is controlled by the capacitor voltage and the duty cycle of a pulse-width modulated (PWM) signal supplied to the switch. The hybrid controller combines a motor speed control loop with a PWM optimization loop. The motor speed control loop generates a PWM signal in response to the speed of the DC motor and conducts that PWM signal to the switch to control the DC motor. The PWM optimization loop includes a controller that is responsive to the PWM signal and an AC voltage signal. This controller compares the PWM signal wiht a PWM signal setpoint, and drives the PWM signal toward the PWM signal setpoint by adjusting the capacitor voltage in response to the comparison between the PWM signal and the PWM signal setpoint. The speed of the DC motor changes in response to the adjusted capacitor voltage, and the motor speed control loop changes the PWM signal in response to the changed motor speed. These adjustments have the cumulative effect of driving the PWM signal toward the PWM signal setpoint. The controller included in the PWM optimization loop controls a rectifier for selectively supplying a rectified voltage to the capacitor.