Mitigation of Voltage Sag/Swell Using Peak Detector Based Pulse Width Modulation Switched Autotransformer

This article presents the fast detection of voltage sag/swell events by employing peak estimation of the signal. The algorithm used is very fast compared to event detection using root mean square calculation. A mitigation device with a pulse width modulation controlled autotransformer is employed for compensation of voltage sags/swells in a distribution system. This device does not require any energy storage device unlike mitigation devices employing DC-to-AC converter topology. Simulation results for mitigation of voltage sag due to faults/induction motor start and voltage swell due to capacitor switching show that nominal load voltage is achieved with a pulse width modulation switched autotransformer employing the peak estimation technique. The transient response of the device is about one cycle, and the total harmonic distortion of the load voltage is found to be within limits. A prototype model of a 230-V 2.5-kVA pulse width modulation switched autotransformer device is tested for mitigation of voltage sag/swell in an artificial transmission line system, and experimental results show that the device performance is satisfactory.