Mitigation of voltage sag in a distribution system during start-up of water-pumping motors using superconducting magnetic energy storage: A case study

Voltage sag represents one of the most significant features of power quality in operation of distribution systems. The voltage sag throughout the distribution system caused by simultaneous start-up of water-pumping motors represents a problem, which negatively affects the power quality of the distribution system. The present research work investigates mitigation of voltage sag in a real Egyptian distribution system during simultaneous start-up of many connected water-pumping motors by using superconducting magnetic energy storage (SMES) unit. This calls for a transient analysis of the real distribution system using MATLAB package in order to follow up the temporal variation of the system voltage-profile during motors' start-up. A fuzzy-logic (FL) control strategy of SMES unit is adopted to compose of cascaded control a six-pulse pulse-width modulation (PWM) voltage source converter (VSC) and two-quadrant DC-DC chopper. The proposed fuzzy logic controller (FLC) of SMES unit employs the bus voltage variation and the variation of SMES current as input signals to control the power transfer between the distribution system and SMES. The effectiveness of the proposed FL-controlled SMES unit is vali-dated in a case study of a real distribution feeder named Karot distribution feeder loaded by 16 water-pumps driven by induction motors as well as residential loads. The feeder is part of a distribution system serving the Unified Egyptian Electrical Network. The obtained results indicate that the SMES unit successfully mitigated the voltage sag in Karot distribution feeder due to simultaneous start-up of connected water-pumping motors where the voltage never drops below 0.9 pu.