Analysis and suppression strategy for high-frequency oscillation in offshore wind power through MMC HVDC system
Da Yu, Ying Huang, Lin Xu, Weihua Wang, Jianze Li
Abstract
• In this paper, the high frequency oscillation problem of offshore wind power transmission through MMC HVDC system is studied. The main conclusions are as follows. • Considering the internal harmonic dynamics and complete control structure of MMC, the AC-side impedance model of MMC is derived by using the multi-harmonic linearization method. It is found that the voltage control proportional coefficient has an effect on the full-band impedance of MMC, and too small proportional coefficient will introduce negative damping characteristics in the sub-supersynchronous frequency band. • Based on the simplified high-frequency impedance model, the high-frequency impedance characteristics are studied, and the influence mechanism of voltage control is analyzed emphatically. It is concluded that the voltage disturbance through the control delay is the key factor for the negative resistance of MMC AC side impedance. • Considering the requirement of minimizing the negative damping region of the high-frequency impedance, an active damping control strategy based on the collaborative parameter design of the voltage control loop and the voltage feed-forward loop is proposed, which makes the disturbance components of the grid voltage feedforward path and the voltage control path cancel each other, ensures that the highfrequency output impedance is approximately passive, and improves the high-frequency damping. The offshore wind power transmission through MMC HVDC system is a typical power electronic equipment interconnection system, the interactive coupling effect of power electronic control in the system seriously restricts the transmission and consumption of wind power. This study established a small-signal impedance model incorporating the internal harmonic dynamics and complete control structure of Modular Multilevel Converter (MMC) using the multi-harmonic linearization method. A comprehensive analysis is performed to investigate the influence of control parameters on impedance characteristics across the full frequency range, thereby revealing the high-frequency oscillation mechanisms in offshore wind power transmission through MMC HVDC system. Building on these findings, it proposed an active damping control strategy based on coordinated parameter design of the voltage control loop and voltage feedforward loop. The effectiveness of the proposed high-frequency oscillation suppression strategy is validated through simulations on an electromagnetic transient model built on the PSCAD/EMTDC platform.