Performance improvement of Adjustable Speed Drives (ASD´s) using supercapacitors during voltage sag

Voltage unbalance or sag conditions generated by the power system faults can have a significant negative impact on the ASD´s (Adjustable Speed Drives) performance. Significant input current unbalances, injection of second harmonics voltage component on the DC-Link and torque pulsations of double the fundamental frequency are the major effects, which may be overcome by injecting energy at the DC-Link. A practical ride-through topology for ASD´s is presented in this paper based on supercapacitor as an energy storage device. The performance of ASD´s under different power system faults is first simulated in MATLab Simulink and then experimentally verified.