DC injection control for grid-connected inverters based on virtual capacitor concept

DC injection is a critical issue in the distributed generation systems according to IEEE Std. 1547-2003. Unfortunately, few literatures discuss this problem. In this paper, a novel control strategy is proposed to achieve zero steady-state DC injection. The proposed idea stems from a well-known fact that a capacitor can block DC component naturally. Generally, this capacitor should be large enough to avoid excessive losses of the grid-connected inverter system. In this paper, this large and costly capacitor is replaced with the proposed control strategy. So it is called virtual capacitor. Theoretical analysis and simulation results confirm the concept.