Kyoung-Min Kwon

Line voltage regulation of urban transit systems using supercapacitors

In DC electric railway system, when the railcar starts, the electric power is absorbed from the line, and then the line voltage is instantaneously collapsed to provide a large accelerating torque. On the other hand, when the railcar brakes, the regenerative power is created and it increases the line voltage at the pantograph of the railcar. If it is possible to install an energy storage system near the train, the regenerated power can be saved to this system. This paper describes the control of energy storage system which consists of a supercapacitor bank and a bidirectional DC-DC converter. Supercapacitor can be used for storing the regenerative energy and for peak power requirement to increase the efficiency and life cycle of the system. This paper presents a method to identify the parameters of supercapacitor equivalent circuit by using the experimental results. In order to verify the validity of this method, parameters of a Maxwell BCAP 3000F are extracted through the experiments and then the equivalent circuit model using these parameters is implemented for PSiM simulation. And the control strategy of a bidirectional DC-DC converter is described to meet the performance for the initial charging mode and power control mode. Finally the experimental data in laboratory and at Kyoungsan test site for urban light rail road system are provided in detail. From the simulation and experimental results, the validity of this energy storage system using capacitor is verified.

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.

Enhanced operating scheme of ESS for DC transit system

The energy storage system (ESS) used in the DC feeding urban railway system is an equipment that recycles the regenerated energy produced by the railway vehicles as well stabilizing the catenary voltage. This paper proposes an operation algorithm of ESS that allows a more effective use of the equipment. The proposed algorithm includes an advanced line voltage tracker (ALVT), which responds to the fluctuating catenary voltage by tracking it and the supercapacitor voltage tracker (SCVT), which modifies the operating voltage of the supercapacitors to increase the receptivity of power constrained by the rated current of supercapacitors. The feasibility of this algorithm has been tested and verified at the Seocho substation in Seoul Metropolitan Rapid Transit (SMRT) Line.