Abstract
In recent years, voltage sags have become a very important power quality issue. Voltage sags often interrupt manufacturing processes and result in significant losses. To improve the quality and reliability of electric power, more and more utility companies provide dual power feeders to high-tech manufacturers. The solid-state transfer switch (STS) based on thyristors can utilize the dual power feeders to protect sensitive loads against voltage sags. Conventional STS may require more than a quarter cycle to complete the transfer process depending on the operating condition of its loads. In this paper, an improved STS with resonant impulse commutation circuit is proposed. The proposed system can greatly reduce the transfer time and provide better protection against voltage sags. Laboratory test results are presented to validate the performance of the proposed STS system.