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. Especially in the high-tech industry parks of Taiwan, manufacturers can lose up to a million US dollars for each voltage sag events. 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 require more than quarter cycle to complete the transfer process because its commutation is load dependent. An improved STS with impulse commutated circuit (ICSTS) 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 reduce the number of the passive components required for forced-commutation. This paper will also discuss the in-rush phenomenon of the transformer due to the line transfer. A flux estimator is developed with the ICBSTS system to reduce the inrush current