Design of an Impulse Commutation Bridge for the Solid-State Transfer Switch

Voltage sags have become a very critical power quality issue in recent years. In particular, in the high-tech industry parks of Taiwan, manufacturers can lose up to one million U.S. dollars for each voltage sag event. Some utility companies provide dual power feeders to these high-tech manufacturers to enhance power quality and reliability. The solid-state transfer switch (STS) based on thyristors can thus utilize the dual power feeders to protect sensitive loads against voltage sags. Conventional STS often requires more than a quarter cycle to complete the transfer process because its commutation is load dependent. An improved STS with impulse commutated circuit can greatly reduce the transfer time and provide better ride-through capability against voltage sags. In this paper, an impulse commutation bridge STS (ICBSTS) system is proposed to further simplify the forced-commutation circuitry. This paper also discusses the in-rush phenomenon of the transformer due to the line transfer. A flux estimator is developed with the ICBSTS system to reduce the in-rush current.