双馈风电场的电网不对称故障穿越问题研究

Currently, the low voltage ride-through (LVRT) grid codes for wind energy conversion system (WECS) operated under asymmetrical grid fault conditions are not explicit. The LVRT strategy for the DFIG-based WECS with asymmetrical grid faults is still in development. This proposal intends to deal with such problems. The research issues include: (1) Analyze the characteristics of the real grid faults, and explore the control limit of the rotor side converter (RSC) to regulate the positive and negative sequence components of the rotor current under asymmetrical grid faults. The results are helpful to the improvement of the future grid codes, and can be the bias of the design of LVRT strategy for the DFIG. (2) Investigate the coordinated control strategy of the RSC and the grid side converter (GSC) based on the optimal control theory in order to improve the LVRT capability of the DFIG-based WECS under asymmetrical faults. (3) Improve the LVRT capability of the DFIG-based wind farm by installing the static var generator (SVG). The control strategy of the SVG to help the LVRT of the DFIG-based wind farm is addressed. The project will improve the capability of safe operation for the large DFIG-based wind farms and contribute to the improvement of the Chinese grid code.

目前，并网导则对于风电场在电网不对称故障下的低压穿越（LVRT）要求还不完善；对于双馈型发电系统（DFIG），在电网不对称故障下，其LVRT控制问题也未得到有效地解决。本课题将基于上述背景展开以下研究：（1）研究真实的电网故障特性，并定量分析典型故障下DFIG转子侧变流器正负序电流的控制能力，从而为相关并网导则的制定提供参考，同时为DFIG的LVRT控制策略的设计奠定基础；（2）基于最优控制等理论，设计DFIG的转子侧变流器和网侧变流器的协调控制策略，提高单机系统在不对称电网故障下的LVRT能力；（3）针对DFIG风电场，通过配备一定容量的静态无功发生器（SVG），并研究相应的SVG电压补偿策略，以提高风电场的不对称LVRT能力。通过本课题的研究，必将提高大型DFIG风电场的安全稳定运行能力，同时对我国风电并网导则的进一步完善也有十分重要的意义。

以提高电网不对称故障下双馈型风力发电系统的低压穿越（LVRT）能力为目标，项目取得了以下成果：（1）给出了典型的不对称电网电压的幅值和相位特征；分析了电网电压不对称跌落时双馈型（DFIG）风电机组模型、安全运行的约束条件及其控制要点，提出了DFIG机组正序无功电流输出能力的分析方法并给出了量化指标；（2）改进了用于电网电压不对称故障检测的数字锁相环子系统，提出了一种基于新并网导则草案的DFIG机组正负序有功、无功电流的控制方法；（3）提出了配置于DFIG风电场的静止无功发生器（STATCOM）容量配置方法及其不对称LVRT控制策略；（4）作为增加内容，分析了风电并网发电系统的高电压穿越能力，并提出了改进的控制策略。