Variable Frequency AC Motor Controller Using MCTs

The use of MCTs in a high-frequency, high-power motor controller requires soft switching. While MCTs are known to possess significant forward drop advantages over IGBTs or MOSFETs, their switching behavior is much more complex. Conventional PWM switching of MCTs at high frequency leads to significant switching losses due mostly to a current tailing problem during device turn-off. Zero-voltage switching or zero-current switching can be achieved with a resonant link inverter. This can greatly reduce the switching losses. However, this approach leads to higher voltage and/or current stresses on the devices. A novel fixed-frequency, soft-switching, PWM, bidirectional, inverter/rectifier circuit employing state vector modulation is proposed for use as an MCT, four quadrant, AC induction motor controller for an electric vehicle. This new circuit topology combines the low stress advantages of the PWM circuit. Digitally controlled state vector modulation provides for low torque ripple over a wide range of motor speeds with fixed-frequency PWM control. ANTICIPATE BENEFITS: Significant potential exists with electric vehicle for the government. In the defense sector EVs can be used military utility vehicles. In the civilian sector EVs are ideally suited for post office vehicles. Virginia Power Technologies is particularly interested in using this SBIR funding to generate a product for commercial use. We feel that the commerical uses could be unlimited if an MCT based motor controller shows cost and performance advangates over an IGBT-based motor controller.