Study on uninterrupted switching topology and its control strategy of voltage sag protection

Voltage sag triggered by thunderstrike or short circuit could result in false tripping of AC contactor. Serious consequences, such as unintended shutdown in consecutive industrial manufacturing, would be caused subsequently. Thus, an uninterrupted switching topology of voltage sag protection for AC contactor is proposed in this paper. The proposed topology utilizes the reverse external voltage turn-off characteristic of the thyristors. Therefore the exciting current is consecutive, which ensures the energy source of the contactor to be with enough energy to maintain it closed during the switching procedure between the main control circuit and the alternate control circuit. Accordingly, steady state analysis of AC and DC power supply and the control strategy of dynamic switching process are addressed. Simulations and experiments are conducted simultaneously. The results of the simulations and experiments validate the correctness and feasibility of the proposed topology and its control strategy. The results also provide theoretical and practical references for uninterrupted operation of highly sensitive electrical equipment during continuous manufacturing.