Matrix converter using MOS turn-off thyristors

MOS turn-off thyristors (MTOs) have been used to form the switches in a matrix converter. The MTO is a thyristor with a standard gate for turn-on and an additional MOS gate for turn-off. The matrix converter is an AC to AC converter with no intermediate DC link, which eliminates the need for large reactive components. This reduces converter size and weight and increases reliability. The converter discussed in this paper is a three phase to single phase converter, built as an intermediate step to a three phase to three phase converter intended for four quadrant operation of motor loads, specifically a motoring dynamometer. It has been operated at hundreds of volts and tens of amperes into a passive load, as well as for demonstration on driving single phase motor loads. A key operating factor has been the discharge of accumulated electrostatic charge on the MOS gate. Failure to properly do so, which can be traced to occasional manufacturing anomalies, forces the MTO into a constant open state, preventing it from closing. The MTO is therefore a thyristor than can fail open. The impact of minimum off time of the MTO on converter performance is examined. The benefits of applying MTO switch technology to the matrix converter circuit is fully explored. Auxiliary circuitry for the control of the converter is also discussed.