High speed silicon controlled rectifier static transfer switch

This thesis presents new fault/disturbance detection and thyristor-gating schemes for a Silicon Controlled Rectifier (SCR) Static Transfer Switch (STS) to achieve fast load-switching between two sources of ac power. STSs have been used in Uninterruptible Power Supply (UPS) systems. They have also attracted interests in medium-voltage applications for fast load-switching between two distribution feeders. However, the performance evaluation of the STSs from a detection/transfer time point of view has not been reported in the literature. In this thesis, a detailed analysis of both voltage-detection and transfer-and-gating logics is given under various operating conditions. The voltage-detection method results in a short detection time and is not susceptible to capacitor-switching voltage transients. The designed transfer-and-gating strategy can operate at different operating conditions while optimizing the transfer time.; A detailed description of the power circuit and the control circuit of the STS is given. For the voltage-detection, analytical expressions are derived to estimate its response time to different faults/disturbances in the system. The principles of operation of the transfer-and-gating circuit are described, and it is shown that the gating logic can meet the thyristor-gating requirements. The performance of the STS is evaluated for RL loads and regenerative loads under some simplifying assumptions. A systematic design procedure is proposed for the design of the thyristor modules and the control circuit of the STS. An experimental set-up is also prepared to verify the performance of the designed detection and gating methods and the theoretical results derived in the thesis.