Voltage distribution and design for lightning surge of A PWM-switched autotransformer-based sag supporter

This paper discusses the design of a voltage sag supporter (VSS) device for lightning surge protection. This novel distribution-level voltage control device can compensate voltage sag and swell conditions in three-phase power systems. It is based on a pulse width modulated (PWM) autotransformer. The proposed scheme is able to quickly recognize the voltage sag or swell condition, and it can correct the voltage by either boosting the input voltage during voltage sag events or reducing the voltage during swell events. There exist two possible configurations, series and shunt types. Since the majority of voltage sag events occur under severe weather conditions, the voltage distribution of the system under lightning surge must be investigated. The distribution of voltage across the switches during normal conditions as well as lightning surge conditions is evaluated for both the series and shunt type of VSS circuits. Based on these results, the shunt type VSS is preferred.