Design and implementation of solid-state transfer switches for power quality enhancement

Voltage sags have become one of the major power quality concerns in recent years. For manufacturers which have automated production lines, a few cycles of voltage sags can interrupt the entire production line and result in significant losses. For example, a typical semiconductor foundry in Taiwan loses US$ 100,000 to US$ 1,000,000 per sag event. As the high-tech manufacturers often gather closely in the industry park, the utility provides premium grid arrangement to the park, such as direct connection from the high-voltage transmission network, or independent power feeders. These approaches improve the reliability and quality of electric power. However, voltage sags still can not be eliminated. This paper discusses the use of thyristor-based solid-state transfer switches (STS) to provide ride-through during voltage sags for critical and sensitive industrial loads. A synchronous-reference-frame-based control method for identifying voltage sags is presented. Laboratory test results are presented to validate the effectiveness of the controller. Comparisons between the proposed controller and other control method proposed in previous literatures are also demonstrated to show the improvement.