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This paper proposes a ripple reduction method in current without using any additional switching devices. The current ripple that has double frequency component of the power supply is generated in the DC part when a single-phase PWM inverter is used for a grid connection. The current ripple causes short lifetime for electrolytic capacitors, batteries and fuel cells. The proposed circuit realizes a DC active filter function without increasing the number of the switching device because the energy buffer capacitor is connected to the center tap of the isolation transformer. In addition, the buffer capacitor voltage is controlled by the common mode voltage of the inverter. This paper describes the features of the proposed circuit, control strategy and experimental results. As a result, about 1/5 times of the ripple can be reduced.