Analytical Calculation Method of Outer Loop Controller Parameters of HVDC Converter Station Connected to Weak AC Grid and Analysis of Limiting Factors

The dynamic response speed of AC voltage of flexible high voltage direct current (HVDC) converter connected to weak AC grid is manly related to the parameters of AC voltage controller, SCR, steady state operating points and equivalent capacitance paralleled at point of common coupling (PCC). Firstly, due to the lack of analytical calculation of the parameters of AC voltage controller and analysis of their limiting factors, the key influence variables and participations of eigenvalues related to dynamic response and stability have been analyzed according to the distribution of zeros and poles based on the detailed analytical model of whole system. Secondly, based on the quasi steady state model of AC system, the analytical calculation expressions of outer loop controller parameters are derived, and their selection ranges are preliminarily analyzed. Thirdly, the effects of outer loop controller parameters, bandwidth of current inner loop, PLL parameters and SCR on stability are studied. The results show that bandwidth of PLL closed to that of AC voltage loop may not be the factor inducing resonance of system. Reducing the parameters of AC voltage controller and PLL can improve the stability of converter station running in inverter mode. Finally, the correctness of parameter calculation and stability analysis is verified by electromagnetic transient simulations.