A flexible micro-controller based chopper driving a permanent magnet DC motor

Microcontrollers are used more and more in motor drives, most commonly to turn on and off the motor, or to control the conduction angle of a triac, associated with a universal motor. In this paper, the universal motor is replaced by a permanent magnet DC motor, which offers the advantage of yielding a high power in a small volume. The variable speed drive is supplied from the rectified mains voltage, and consists of a chopper driven by a PWM signal generated by the microcontroller. The microcontroller measures the DC power supply voltage and adjusts the PWM duty cycle accordingly, which has the primary effect of regulating the motor voltage against mains and load variations, which in turn adjusts the motor speed, and the secondary effect of reducing the motor current ripple, thus improving motor efficiency and copper losses. This drive also implements a software power limitation, which avoids motor overheating in case of excessive loading and costs only a few discrete components. Software flexibility allows to easily modify drive parameters such as maximum power, time constants, etc. The drive principle and practical results are given