复杂电网条件下并网系统谐波谐振机制及优化控制研究

Distributed grid-connected power generation has gained continuing and wide attentions and the grid-connected system is one of its key interfaces. However, in the practical applications, many non-ideal factors of grid-connected system, including the resonance of high-order filters, discrete features of digital control system, grid voltage harmonics at the point of common coupling (PCC), inter-harmonics and complex grid impedance, have non-negligible impacts on the performance. The grid current can be highly-distorted or even resonated under these non-ideal conditions. Therefore, this project aims at researching the mechanisms of harmonics generations and proposing the improved approaches for grid-connected inverters under non-ideal conditions. The high-performance current control methods with single current sampling for high-order filter based grid-connected inverters are studied, and the robustness and improved current control with single current sampling are investigated. By considering the above non-ideal factors of grid-connected system, an analytical model for analyzing harmonics of grid-connected system is established so that the mechanisms of harmonics and resonance of grid-connected system are clearly identified. For the sake of high robustness and high performance under complex grid conditions (especially for unknown grid impedance), this project researches the easily-implemented adaptive and robust control techniques. Consequently, based on the outcomes of the above studies, the grid-connected system can achieve a high robustness under those non-ideal conditions while being cost-effective and easy to implement.

分布式并网发电获得了持续且广泛的关注，并网逆变系统是其关键环节之一。然而，实际应用中并网逆变系统的非理想因素，如高阶滤波器谐振现象、数字控制离散特性、公共耦合点电压谐波、系统间谐波以及复杂电网阻抗等，往往使得进网电流严重失真甚至发生振荡，对系统有着不可忽视的影响。为此，本课题研究非理想状况下并网逆变器系统谐波产生机制及优化控制技术，包括：研究适用于高阶滤波并网逆变器的单电流采样、高性能电流控制方法，研究单电流采样电流控制的并网逆变器系统鲁棒性及优化手段；综合考虑前述非理想因素，建立并网逆变系统谐波分析模型，明晰并网系统谐波及谐振产生机制；针对实际电网状况尤其是电网阻抗特性未知场合，研究适用于复杂电网状况的简单高效的并网逆变器自适应/鲁棒控制技术。基于上述研究，可在提高非理想状况下系统鲁棒性的同时又兼顾良好的经济性以及易用性。

分布式并网发电获得了持续且广泛的关注，并网逆变系统是其关键环节之一。然而，实际应用中并网逆变系统的非理想因素，如高阶滤波器谐振、电网电压谐波与波动以及复杂电网阻抗等，往往使得进网电流严重失真甚至发生振荡。为此，项目组深入研究并网逆变器系统谐波产生机制及优化控制技术，包括：基于单电流采样的并网逆变器控制与设计、弱电网下并网逆变器系统模型及谐波振荡机制、适应复杂电网状况的并网逆变器自适应与鲁棒控制技术、电网波动下并网逆变器稳定性分析与优化。.首先，项目组深入讨论了适用于高阶滤波并网逆变器的有源阻尼及电流控制技术。数字控制下,高阶LCL-LC滤波器的谐振频率折叠现象可能导致系统发生不稳定。综合考虑LCL-LC滤波器性能和控制器性能，提出了LCL-LC滤波器和控制器参数协调优化设计准则及优化设计方法，在仅采用单电流反馈控制下并网逆变器实现了参数波动下较好的鲁棒性。.其次，项目组建立了考虑锁相环非线性频率耦合作用的输出阻抗模型，并基于输出阻抗的级联系统稳定性判据，明晰了锁相环影响逆变系统稳定性及谐波谐振（含整数次以及分数次谐波）的机制。基于此，项目组提出并深入研究了多种并网逆变器的优化控制技术，包括：基于进网电流前馈的改进锁相环、基于附加低通滤波器的改进锁相环及其优化设计以及基于扰动观测器的并网逆变器电流控制技术等，提高了弱电网下并网逆变系统鲁棒性。.最后，针对电网电压波动严重威胁系统稳定运行的问题，项目组分析研究了电网电压波动对系统大扰动稳定性的影响，揭示了电网电压波动下并网逆变器失稳机制。进而，针对电网电压波动和高电网阻抗同时存在的复杂电网情形，提出了兼顾小扰动稳定性以及大扰动稳定性的锁相环参数优化方法，有效改善了系统在复杂电网状况下的鲁棒运行能力。.上述关键技术的突破有助于提高并网逆变系统的综合性能，有助于推动分布式并网发电技术的发展，促进新能源发电的规模化应用。