Efficiency improvement of ESS for DC transit system

This paper presents the design example and overall operation of an energy storage system (ESS) for applying to the urban railway cars. ESS prevents the line voltage from the voltage fluctuation during the motoring or breaking. It keeps the line voltage not to be increased in deceleration region by storing the regenerative braking energy in the energy storage unit or not to be decreased in acceleration region by reusing that stored energy. The control algorithm of a bidirectional DC-DC converter and the line voltage tracking algorithm to keep the DC line voltage fluctuation in 3 % is proposed. Through the test results of the real installation of ESS using super-capacitors at Daedong Substation in Daejeon Metro, the validity of proposed algorithm is verified.