Full Feedforward of Grid Voltage for Discrete State Feedback Controlled Grid-Connected Inverter With LCL Filter

Due to multifeedback of state variables, a discrete state-space controller offers outstanding control bandwidth as well as control stability for popular LCL-type grid-connected inverters, while the grid current is still vulnerable to the grid-voltage harmonics. The feedforward of grid voltage, usually employed in continuous controllers to solve such a problem, is too complicated to be applied for the discrete state-space controller. By means of continuous transformation, a full grid-voltage feedforward (GVFF) decoupling strategy is successfully proposed in this paper to make the feedforward possible for the discrete state-space controller. Based on the transfer function analysis and comparison of discretized and continuous system, comprehensive verification is also provided to verify the effectiveness of the derivation of the GVFF path. Subsequently, the robustness analysis of the proposed strategy to the grid impedance is also performed. Moreover, a grid-voltage estimator instead of the measured voltage is employed for the full GVFF, which not only retains the important information of grid voltage but also eliminates the influence of accompanied noises. The distinct features of the proposed feedforward controller plus implementation strategy are the super steady waveform, dynamic response, and robustness to the variation of grid impedance. Besides, the complexity of the algorithm is moderate and the computational burden is not significantly increased. Finally, simulation and experimental results are provided to verify the feasibility and validity of the proposed strategy.