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.