Abstract
In the recent years, voltage sags have become a very important power quality issue. Voltage sags often interrupt the manufacturing process and result in significant losses. In the high-tech industry parks of Taiwan, Manufacturers can lose up to a million US dollars for each voltage sags. To improve the power quality and reliability, more and more utility companies provide dual power feeders to these high-tech manufacturers. The static 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 load condition. In this thesis, an improved STS with resonant commutator circuit is proposed. The proposed system can greatly shorten the transfer time and provide better protection against voltage sags. Computer simulations and laboratory test results are presented to validate the performance of the proposed STS system.