Adaptive output impedance correction strategy for enhancing STATCOM grid-connected system’s adaptability to the weak grid condition

The dynamic interaction between the Static Synchronous Compensator (STATCOM) and the grid impedance may lead to harmonic distortion of the grid-connected current and even instability of the system under weak network conditions. In this paper, the output impedance characteristics and stability of STATCOM are analyzed first. In order to improve the adaptability of STATCOM to weak grid and ensure the stable operation of grid-connected system, an improved adaptive series and parallel integrated output impedance correction strategy based on grid impedance identification is proposed. This strategy can realize the adaptive adjustment of the virtual series impedance according to the expression of the fitting curve, so that STATCOM can operate stably when the impedance of the power grid changes (SCR=3-10), and improve the suppression ability of the background harmonics of the power grid voltage. Finally, the validity and correctness of the proposed strategy are verified by simulation.