A 7.5 kW ultrasonic inverter motor drive employing MOS-controlled thyristors

The design and performance of an inverter induction motor drive that employs an ultrasonic switching frequency to minimize audible noise is described. The MOS-controlled thyristor (MCT) is a high-speed power semiconductor with the potential for high voltage and current ratings. Distinctive features of the device are discussed relative to inverter topology, gate drive requirements, and fault protection. Since MCT devices of sufficient rating were not available, insulated-gate-bipolar-transistor (GBT) devices were used in the experimental model. MCT and IGBT devices have comparable switching times. The design of a 7.5 kW and 20 kHz inverter is discussed, including a modified pulsewidth modulation (PWM) switching algorithm conducive to microprocessor implementation. The algorithm requires reduced computational and storage requirements over previous PWM methods. Implementation of the algorithm is accomplished by a digital signal processor using the efficient C language. Experimental waveforms are presented