STATION BUILDING POWER SUPPLY DEVICE

To provide a station-building power supply device that can effectively use surplus regenerative power while suppressing fluctuations in the amount of power of an AC system that supplies AC power to station loads. The station-building power supply device includes a capacitor unit 9 that stores therein surplus regenerative power in an electrical transformation zone, a first power conversion unit 11 that performs DC/DC power conversion in both directions between a feeder 6 and the capacitor unit 9, and a second power conversion unit 12 that converts DC power supplied from the capacitor unit 9 to AC power to be supplied to the station loads 4. A first voltage threshold for detecting the occurrence of surplus regenerative power generated in the electrical transformation zone is set for a feeding voltage and a first SOC threshold for detecting whether the capacitor unit 9 can discharge is set for an SOC of the capacitor unit 9. The first power conversion unit 11 is controlled such that power is supplied from the feeder 6 to the capacitor unit 9 to charge the capacitor unit 9 when the feeding voltage exceeds the first voltage threshold, and the second power conversion unit 12 is controlled such that power is supplied from the capacitor unit 9 to the station loads 4 when the SOC of the capacitor unit 9 exceeds the first SOC threshold.