This paper proposes a universal large-capacity capacitor simulator consisting of a chemical capacitor and three-leg converter. One of three legs performs a bi-directional dc-to-dc converter. The others are used for a single-phase PWM rectifier. In the charging operation of the proposed large-capacity simulator, one-leg is used as a boost converter. Most power, which is stored in the proposed simulator, is injected to the utility through the PWM rectifier. In the discharging operation, the one-leg performs a buck converter. Most power, which is supplied to the load, is from the utility through the PWM rectifier. Thus the proposed simulator performs a large-capacity capacitor in both charging and discharging operations. The basic principle of the proposed simulator is discussed in detail. For an EDLC simulator operation, series resistors should be considered. A new control method, which performs the series resistor, is also proposed. The validity and excellent practicability of the proposed large-capacity capacitor simulator are confirmed using the PSIM software.