A power conditioning system (PCS) with a single-phase power supply requires a large-capacity electrolytic capacitor in the DC link to keep the input current of the PV panel constant. In addition, the PCS requires an isolated transformer for system safety because of the stray capacitance of PV panels. This paper describes an active power decoupling method using a small-capacity film capacitor. The proposed 3-leg circuit does not require a transformer for isolation, because the input terminal can be connected the output terminal. The experimental results show that twice the grid-frequency components of the input current, which is a power pulsation, is reduced by 91.2%.