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We developed novel energy-storage equipment that is series-connected to DC side of traction inverter of DC electric railway vehicle. When a train is powering and braking at a high-speed and the equipment boosts an input voltage of the traction inverter, the motor torque increases. Consequently, the mechanical brake force, compensating the electric brake force, becomes less. That leads to less energy dissipation. During the powering period, the acceleration of the train becomes larger due to the boosting operation of the equipment. The equipment charges a part of regenerated energy when it boosts the voltage during braking period, and discharges the stored energy when it boosts the voltage during accelerating period. In this paper, we selected electric double layer capacitor (EDLC) for the energy storage device of the equipment. Firstly, we explain the operational principle of the energy storage equipment: how to boost voltage at a desired level; how to charge and discharges the energy of the EDLC. Next, we described the circuit configuration and the control algorithm. Finally, we present simulation results to evaluate the performance of the energy storage equipment. According to the simulation results, the equipment charged/discharged the regenerated energy smoothly, and controlled the input voltage of the traction inverter at a desired level.