Series-Parallel Active Damping to Improve the Robustness of Inverter in Weak Grid

Since weak grid introduces non-negligible inductive line impedance, the parameters of grid connected inverter will change, which may lead to system collapse in serious cases. This paper proposes to add series-parallel active damping at Point of Common Coupling (PCC) that equivalents resistance characteristics in specific frequency band to suppress harmonic components. Compared with independent parallel active damping, series-parallel active damping introduces extra positive real part in correcting the equivalent output impedance of inverter. It can completely decouple the grid connected inverter and grid impedance within the control bandwidth. This method ensures the high modularity and passivity of output impedance and suppresses harmonics in a wide range. Finally, the effectiveness of the proposed strategy is verified by simulation and experimental results.