An improved virtual current method for single-phase converters under frequency variations

Few papers concern about the instantaneous current control (ICC) scheme for single-phase converters under frequency variations. The inherent relations between inaccurate virtual current and the relevant dynamic and static performances of converters are rarely reported. To address the issue, the inherent relations among the DC error, double-line frequency error and inaccurate virtual current are discussed in the paper. An improved virtual current method is proposed to eliminate the DC error and double-line frequency error, which are caused by frequency variations. Based on this method, a new ICC scheme, which is immune to frequency variations, is presented in steady-state scenarios. The improved virtual current method and the proposed ICC scheme are validated in a single-phase converter. Simulation and experimental results show that a unity power factor under frequency variations and a fast dynamic response under load change and voltage sag can be achieved with the proposed ICC scheme.