Soft Switched AC-Link AC/AC and AC/DC Buck-Boost Converter

A novel soft switched ac-link buck-boost converter for medium and high power ac-ac and ac-do applications is proposed. The proposed configuration uses two bi-directional switches per leg of the converter resulting in 12 bi-directional switches for a three-phase to three-phase topology. Power transfer from input to output is accomplished via a link inductor which is first charged from the input phases, then discharged to the output phases with a precisely controllable current PWM technique. Capacitance in parallel with the link inductor produces low turn-off losses. Turn-on is always at zero voltage as each switch swings from reverse to forward bias. Reverse recovery is with low di/dt and also is buffered due to the link capacitance. The soft switching nature of the converter permits use of slower switches with high link frequencies. Converter operation is bi-directional and supports any input or output power factor or voltage, within the current and voltage capacity of the switches. Simulation results showing converter operation under different conditions are presented along with loss calculations. The topology is expected to offer relatively low weight, compact and efficient power converters and motor drives.