Development of uninterruptible secondary battery system using thyristor switches

In this paper, we present the control schemes of USBS (uninterruptible secondary battery system) with thyristor AC switches. When there is no fault in a commercial power network, it directly provides electrical power to the critical loads such as computer systems. If some fault such as a voltage interruption occurs on the network, USBS disconnects critical loads from it at instant, and supplies power to them as a UPS. We will discuss the method disconnecting the power network as quick as possible when any fault occurs on it, adopting nongate-turn-off devices such as thyristors to the AC switch, which connects the loads with the power network. Experimental operations are carried out to confirm feasibility of the proposed method, which demonstrate that it takes 1.7∼4.0 ms to restart supplying power to the loads in case of emergency by experiments.