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It is well known that there exist second-order harmonic current and corresponding ripple voltage on dc bus for single phase PWM rectifiers. The low frequency harmonic current is normally filtered using a bulk capacitor in the bus which results in low power density. This paper studies the energy storage capacitor reduction methods for single phase rectifiers. The minimum ripple energy storage requirement is derived independent of a specific topology. Based on the minimum ripple energy requirement, the feasibility of the active capacitor's reduction schemes is verified. Then, we propose a bidirectional buck-boost converter as our ripple energy storage circuit that can effectively reduce the energy storage capacitance. Simulation and experimental results are provided for verification purposes.