A global robust output regulation method for grid-connected inverter with LCL filter in weak grid condition

Grid-connected inverters with LCL passive filters have been wildly utilized in renewable energy community. The high order filter helps to suppress harmonic current in high frequency range and inject the power of high quality into the utility grid. However, due to long distance transmission line and penetration of transformers, the point of common coupling (PCC) voltage may present variant grid impedances which could induce filter system instability. In addition, the harmonic current caused by nonlinear load flowing through grid impedance possibly distorts the voltage of PCC and even results in unbalanced grid voltage. These salient defects of weak grid challenge the regulation of LCL output current. A robust current control method by integrating backstepping with global output regulation approach (BGOR) is proposed in this paper to realize the enhanced performances of LCL filter. The proposed method ensures internal stability by choosing a proper Lyapunov function for the entire system. Inverter system robustness is also ensured against uncertainties of grid impedance, PCC voltage distortion and unbalanced grid voltage. Exhaustive derivation of BGOR is presented in this paper and simulation results verify the effectiveness of the proposed method.