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The instantaneous output power of a two-stage single-phase inverter pulsates at twice the output voltage frequency, generating second harmonic current (SHC) in the frontend dc-dc converter. To reduce the SHC, this paper proposes a virtual impedance based control strategy. For the case of adopting a resistor as the virtual impedance, a closed-loop parameter design method is presented, revealing that the voltage loop crossover frequency is relatively low under such circumstance. To overcome this problem, a control strategy incorporating a bandpass filter (BPF) into the inductor current feedback path is put forward and a damping resistor is further added into the BPF for the purpose of improving the system stability margin. Hence, the proposed control scheme can not only reduce the SHC significantly, but also improve the dynamic performance of the front-end dc-dc converter effectively while guaranteeing the stability of the converter. Finally, a 1-kVA prototype is built and tested in the laboratory, and the experimental results are presented to verify the effectiveness of the proposed control strategy.Index Terms-Bandpass filter (BPF), second harmonic current (SHC), two-stage inverter, virtual impedance.

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