Development of a novel hybrid switch device and application to a solid-state transfer switch

Numerous industrial and commercial operations suffer from various types of outages and service interruptions which can cost significant financial loss per incident based on process down-time, lost production, idle work forces, and other factors. The types of interruptions which are experienced can generally be classified as power quality related problems caused by voltage sags and swells, lightning strikes, and other system related disturbances. In many instances, the use of a solid-state transfer switch can be one of the most cost-effective solutions for these power quality problems. The SSTS, which essentially consists of a pair of thyristor switch devices, enables seamless transfer of energy from a primary source to an alternate source in order to avoid service interruption upon a deficiency in power quality. As a result, power quality problems become transparent to the critical or sensitive customer loads that the SSTS protects. However, a thyristor is not a pure conductor and raises some issues in terms of loss consumption and cooling. In a conventional SSTS, line current flows in the thyristors continuously, causing a great deal of loss consumption and element heating during normal operation. As a result, relatively large cooling equipment is required which imposes additional operating costs on the user in order to maintain thyristor cooling. It also results in reduced efficiency and lower reliability in the device.