Compensation of Voltage Sag and Swell by Unit Vector Template Generation Technique and Synchronous Reference Frame Theory for Dynamic Voltage Restorer

This paper includes development of voltage control scheme that can compensate voltage sag and swell in three-phase power systems. Faults occurring in power distribution systems cause the voltage sag or swell. If a fault occurs or Heavy inductive loads are switched then the system experiences voltage sag and voltage swell problems. For sensitive loads, even voltage sags of short duration can cause serious problems in the entire system. Normally, a voltage interruption triggers a protection device, which causes shutdown of the entire system. In order to mitigate voltage sag and voltage swell, this research proposes a scheme called "DYNAMIC VOLTAGE RESTORER (DVR)". The proposed scheme is able to quickly recognize the voltage sag and swell, and it can correct the voltage by either boosting the input voltage during voltage sag events or reducing the input voltage during voltage swell events. Among existing methods, the scheme based on the inverter system requires an inverter, a transformer, a liner control scheme. The proposed scheme can be applied at any voltage and provides cost and size advantages over existing methods. Simulations have been carried out to verify the validity of the proposed scheme.