A Single-Stage Solid-State Transformer for PWM AC Drive With Source-Based Commutation of Leakage Energy

A solid-state transformer is a three-phase ac/ac converter with a high-frequency transformer. Due to advanced features like high power density, on demand var support and frequency regulation, solid-state transformer is an enabling technology for the modern power distribution system. It can also find application in high-power-density motor drives. The single-stage solid-state transformer considered in this paper is capable of bidirectional power flow and open loop power factor correction. This topology uses a minimum amount of copper and has relatively few semiconductor switches. One major problem in this converter is the commutation of leakage energy which results in power loss, reduction in switching frequency, loss of output voltage, and additional common-mode voltage switching. This paper presents a source-based commutation strategy along with a novel modulation technique resulting in 1) elimination of additional snubber circuits, 2) minimization of the frequency of leakage inductance commutation, 3) recovery of the leakage energy, and 4) soft switching of the output converter. The topology and its proposed control have been analyzed. Simulation and experimental results confirm the operation.