经 DRU-HVDC 送出的海上风电场汇集网电气调节特性分析及集群构网控制策略

The low-cost high voltage direct current (HVDC) transmission scheme based on diode rectifier unit (DRU) and grid-forming (GFM) offshore wind farms (OWFs) is a hot topic in the development of large-scale distant offshore wind power. The GFM control strategy of wind turbines is the critical point of this scheme. However, there are still challenges, including the incomplete control law design mechanism, the difficulties in modifying the control structure, and the lack of synchronization mechanism analysis. To solve these problems, the voltage/power factor (U/PF) node model is proposed in this paper to describe the fundamental-frequency power characteristics of the DRU, and the backpropagation (BP) neural network method is utilized to fit the commutation process and multi-pulse topology features. Based on the equivalent load characteristics of the offshore AC system, the mechanism for the voltage/frequency formation, and the control law design requirements of wind turbines are revealed through the node-power flow relation. Furthermore, a clustered GFM control strategy is proposed for grid-side converters of offshore wind turbines based on phase-locked loop (PLL) and frequency-reactive power droop to realize self-synchronization. The design of frequency-reactive droop gain and synchronization mechanism is also elaborated. The wideband interactive stability of the system with the proposed GFM strategy under different operating conditions is analyzed using the impedance method. Finally, simulations are conducted in PSCAD/EMTDC to validate the accuracy of the modeling and analysis, and the effectiveness of the proposed GFM control strategy.