Analysis on controller of grid-connected inverter by using virtual circuit

Control of grid-connected inverter (GCI) directly affects the performance of inverter-interfaced distributed generators. In this paper, a circuit-based modeling method is proposed to combine the control algorithm in software and the topology configuration in hardware of a GCI. On the basis of the same mathematical model, control blocks are equivalently changed into circuit models. By using the proposed circuit model, the mathematical principles and physical natures of proportional-integral (PI) and proportional-resonant (PR) controllers for GCI applications are examined in depth. It concludes that the PI controller cannot track sinusoidal reference without error, because of the equivalent capacitor and ac leakage current in the circuit model obtained for the GCI. In contrast, due to the extra equivalent inductor and resonance circuit in series compared with PI, the equivalent capacitor in PI is opened. And as a result, the PR control can provide accurate current-following performance. Selected experimental results are also presented to validate the effectiveness of the proposed control modeling method.