6. Power Storage System Using Electric Double-Layer Capacitors

      There has been a growing demand for the introduction of power storage media to level out power load and increase efficiency by charging power during regenerative braking of DC electric rolling stock and discharging during power running. The Railway Technical Research Institute (RTRI) is developing a power storage system using an electric double layer capacitor (Fig. 1), a kind of capacitor with long life characteristics that can charge and discharge power quickly. To check system performance, a mini-model (DC 400-V system) was introduced, in which a three-phase bridge diode rectifier simulated a substation, and a PWM converter corresponding to rolling stock was simulated by a DC power supply operated by arbitrary current patterns. Power running was simulated by returning power from the DC to the AC side, and regeneration was simulated by supplying power from the AC to the DC side (Fig. 2).
      It was verified that the voltage at point A for the simulated rolling stock (corresponding to pantograph point voltage) when the capacitor charges/discharges drops sharply when the car load is large, and the voltage drop is mitigated by capacitor discharge (Fig. 3). It was also shown that an electric double layer capacitor is effective for load leveling of the substation and as a countermeasure against regenerative power loss.
      Plans are underway to study applications in the field and evaluate further factors such as storage capacities.

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