海上风电-柔直送端系统频率控制研究现状及建议

Frequency control of VSC-HVDC transmission system for offshore wind farms: research status and suggestions

海上风电通过柔性直流远距离输送是大规模开发远海风资源的重要手段,然而风电的低惯性、波动性及电力电子化系统动态易对送端系统及其接入电网的频率稳定产生重大挑战。为应对海上风电并网频率稳定问题,提升海上新能源电源频率支撑能力,本文对海上风电-柔直送端系统的频率控制研究进行系统论述。首先,明确了该系统的基本结构和频率控制要求;其次,从风电机组侧、柔直换流站侧和风电-柔直双侧协调控制三方面,总结已有基于下垂控制及虚拟惯量控制的跟网型控制策略或基于虚拟同步机控制的构网型控制策略,比较有储能或无储能情况下海上风电场控制方式,介绍基于通信或直流电容电压控制、辅助直流电压控制等非通信手段的换流站控制策略和风电-柔直协调控制策略,分析了各控制策略的特点;最后,从参数设计、协调控制及储能配置等方面探讨了已有控制策略面临的问题及挑战,并给出了综合自适应参数体系、多时间尺度分区协调控制和分散式储能等潜在改进思路及建议。

The long-distance transmission of offshore wind power via VSC-HVDC(voltage source converter based high voltage direct current) is an important way to develop large-scale offshore wind resources. However, the low inertia and volatility of wind power, as well as the dynamics of power electronics-dominated system, are likely to threaten the frequency stability of the transmission system and the power grid it connects to. Aiming to improve the frequency support ability of offshore wind power and solve the frequency stability problem it caused, this paper comprehensively discusses the frequency control strategies of the VSC-HVDC transmission system for offshore wind farms. Firstly, the basic structure of the system and its frequency control requirements are clarified. Secondly, from the aspects of wind turbines, converter stations and their coordination, the control strategies for wind turbines including the grid-following strategies based on droop control and virtual inertia control and the grid-forming strategies based on virtual synchronous generator control are summarized. And the control methods of offshore wind farms with or without energy storage are compared. The converter station and coordinated control strategies based on communication means or other non-communication means like DC capacitance voltage control and auxiliary DC voltage control are introduced, and the characteristics of each control strategy are analyzed. Finally, from the aspects of parameter design problems, coordinated control problems, and energy storage configuration challenges, some potential improvement ideas and suggestions are given, such as the comprehensive adaptive parameter system, the multi-time scale coordinated control, and the distributed energy storage system.