DC drive for universal motor

Universal motors are usually operated in AC mode and are controlled by means of triacs. This conventional solution is characterized by a cheap control hardware. On the other hand, it has some drawbacks. In particular the high peak to peak current gives poor motor efficiency and the consequential high brush temperature leads to limited motor lifetime. Significant improvements are obtained when using a more exacting converter. This paper presents the results obtained by using a diode rectifier and PWM controlled IGBT chopper. The RMS and peak-to-peak current of the motor are reduced, as well as electric losses and brush temperature. In addition, this operation mode enables increasing the motor output power or the motor lifetime. In order to reduce switching losses and electromagnetic interference of the converter, the assumed switching frequency is not higher than 1000 Hz.