基于Floquet定理的构网型柔直系统稳定性分析及附加阻尼策略OA

The grid-forming flexible direct current(DC)converter stations possess the capabilities of dynamic frequency and voltage regulation and active support,as well as favorable resonance stability under weak grid conditions.However,there is still a gap in the research on their small-signal stability under various non-fault and short-circuit fault conditions.This paper focuses on the analysis of linear periodic time-varying modeling and small-signal stability of grid-forming flexible DC transmission systems.Firstly,a nonlinear state space model of the grid-forming flexible DC transmission system is established,and a linear periodic model suitable for small-signal stability analysis is derived through linearization.Then,based on this model and using Floquet theorem,the small-signal stability of the system under various operating conditions with different short-circuit ratios is investigated.Aiming at the resonance risk of the system under low grid impedance,an additional damping strategy is proposed to improve the stability margin of the system.Finally,simulation verification is carried out on the PSCAD/EMTDC platform.The results show that short-circuit faults in the AC grid significantly affect the stability boundary of the differential-mode control parameters,and the impact of three-phase faults is more significant than that of single-phase faults.When the grid-forming flexible DC transmission system is connected to an AC grid with low impedance,there is an obvious resonance risk.Moreover,under fault conditions,the stability deteriorates as the fault severity increases.