弱电网下双馈风电机组无锁相环自同步控制的基础理论和关键技术

As the weak grids gradually become more and more popular in the wind power generation, the conventional control strategies used in the strong grids would suffer the insufficient damping and the reduced stability due to the coupling interactions between the phase-locked loop (PLL) and the grid impedance. Thereby, it would lead to the potential instability of the generator. In our previous studies, the self-synchronized control strategy without PLL has been developed. It can realize the grid self-synchronization of the doubly fed induction generation (DFIG), which is independent of the PLL. Based on the pre-studies, this project is aimed to investigate the basic theory and the key technology of DFIG’s self-synchronized control strategy without PLL in the unbalanced and harmonic distorted weak grid and its faults. Firstly, taking the grid impedance into account, the entire mathematic model of the DFIG is developed to design the self-synchronized control strategy without PLL in the unbalanced and harmonic distorted weak grid and its faults. Secondly, the adaptive multi-frequency controller in the self-synchronized control strategy without PLL of the DFIG in the unbalanced and harmonic distorted weak grid is proposed. Finally, focused on DFIG’s enhanced operation in the weak grid and its faults, the self-synchronized control strategy without PLL is improved to achieve the voltage-coordinated management and the fault ride-through capability. The successful study of this project would solve the potential instability of the DFIG in the weak grids. It would also be one of the significant breakthroughs in the control system only for the strong grids. Besides, it is beneficial to the innovation and the development of the wind power generation technology.

在弱电网特征逐渐显现的风电并网新形势下，原以强电网为背景设计的风电机组控制系统由于锁相环与弱电网阻抗的耦合而出现阻尼不足、稳定裕度降低等现象，导致风电机组运行失稳的风险增加。在前期研究中，项目组有针对性地提出了无锁相环自同步控制，实现了双馈风电机组不依靠锁相环且与电网自动同步的并网运行。在此基础上，本项目主要研究在弱电网三相不平衡、谐波及故障环境下双馈风电机组无锁相环自同步控制的基础理论和关键技术，具体为：建立包括弱电网阻抗与三相不平衡、谐波及故障特征在内的双馈风电机组无锁相环自同步控制的数学模型；设计弱电网三相不平衡与谐波环境下无锁相环自同步控制的自适应多频控制器；改进无锁相环自同步控制以增强双馈风电机组在弱电网及故障环境下的电压协同治理和故障穿越能力。本项目的成功研究将解决弱电网下风电机组面临的控制失稳问题，突破风电机组控制系统仅面向强电网环境的限制，有助于我国风电技术研究的创新发展。

本项目紧扣弱电网下双馈（DFIG）风电机组运行控制的主题，针对弱电网网络阻抗显著、电压扰动频繁的特点，重点研究了双馈风电机组无锁相环自同步控制技术及其弱电网适应性增强技术，主要成果如下：第一，构建了涵盖机侧变流器和网侧变流器的并网端口电流无锁相环自同步控制方案，该控制方式可在无锁相环的条件下完成新能源并网端电流调控，同时增强了DFIG控制系统对电机参数偏差的鲁棒性；第二，提出基于降阶矢量积分器的直接谐振控制，该控制策略通过对二倍频扰动特征量的直接控制，在无需相序分离的条件下实现正负序电流的间接调控，增强了DFIG风电机组在弱电网下的运行适应性；第三，探究了DFIG网侧变流器在弱电网电压跌落下运行失稳机制，并指出控制系统中同步环节的阻尼不足是导致弱电网电压跌落下DFIG网侧变流器失稳的关键因素，进一步提出了应弱电网故障的DFIG网侧变流器暂态阻尼增强方案，拓展了弱电网故障下DFIG网侧变流器稳定运行区间。本项目发表录用SCI/EI期刊论文10篇、会议论文3篇，授权国家发明专利4项、受理2项，相关成果获2020年中国产学研合作创新成果奖一等奖（5/10）。