In an
electric power storage
system according to the present invention, in the case of charging, a plurality of capacitors of each circuit block of the
electric power storage
system are switched to a serial connection to initiate the charging. When the output
voltage of
power storage means reaches the maximum input
voltage of DC-AC conversion means, each
capacitor of a number j of circuit blocks is switched to a parallel connection in order of higher block
voltage. Also up to the time when the maximum input voltage is reached again, each
capacitor of a number j of circuit blocks is switched to a parallel connection in order of higher block voltage. In the case of discharging, pluralities of capacitors of each circuit block of the
electric power storage
system are switched to a parallel connection to initiate the discharging. When the output voltage of
power storage means reaches the minimum input voltage of DC-AC conversion means, each
capacitor of a number k of circuit blocks is switched to a serial connection in order of higher block voltage. Also up to the time when the minimum input voltage is reached
gain, each capacitor of a number k of circuit blocks is switched to a serial connection in order of higher block voltage. Accordingly, the electric
power storage system is hardly affected by the
capacitance error of the capacitors, and charging / discharging efficiency can be improved.