The methods to stabilize power sources, which are the measures against voltage drop, power-loading fluctuation, and regenerative power lapse, have been important issues in DC railway feeding circuits. Therefore, an energy storage medium that uses power efficiently and reduces the above-mentioned problems is much concerned about. Electric double-layer capacitors (EDLS) can be charged and discharged rapidly in a short time with large power. On the other hand, a battery has a high energy density so that it is proper to be charged and discharged for a long time. Therefore, in view of load pattern for electric railway, a hybrid energy-storage system combining both energy storage media may be effective. This paper introduces two methods for hybrid energy system theoretically, and describes the results of the fundamental tests.

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