复杂Z源功率变换器理论及其在海上直流风电传输中的应用基础

In future, for off-shore DC wind farms, the random variation of output power will result in a large variation range of the DC transmission voltage and cause the problem of low wind energy conversion efficiency. This feature requests high boost inversion capability of on-shore DC-AC converter station. With a very strong boost inversion capability, advanced Z-source inverters might be a good solution. So far, the study on the topology theory of Z-source inverter family cannot establish a research system. Therefore, the project re-examines the topology theory of Z-source inverters and build a theoretical basis for those advanced Z-source topologies that can be used for the on-shore converter station. Several dynamic models are derived for small-time scale and large-time scale, respectively. Those models pave a way to understanding dynamics of Z-source topologies. On the basis of theoretical analysis, a candidate Z-source topology for high-voltage-high-capacity on-shore converter station wil be presented. The coupling between the DC wind farm and on-shore converter station are explored, by which a power decoupling control method is proposed to solve the problem of wind curtailment. With the considerations of virtual synchronous generator and low frequency oscillation suppression, the improvement of control methods is studied. The research work will enrich the knowledge of Zsource inverters, and will help us establish the theoretical system of Z-source topologies. Furthermore, the application potential of Z-source topologies in the area of wind energy will be significantly promoted.

未来海上直流型风电场，其风场变化将引起直流输出电压在大范围内波动，并导致弃风现象。这对DC-AC换流站产生了较高技术要求。先进Z源变换器，具备较强升压逆变能力，对于海上直流风电并网，是一种理想解决方案。目前，国内外尚没有对Z源变换器建立完整的拓扑体系。本申请书提出从多角度出发，重新阐述Z源变换器拓扑家族的演变规律，为探索适合高压大容量DC-AC换流站的先进Z源变换器拓扑，奠定理论基础。针对先进Z源变换器，分别研究建立了多种动态模型，为全面理解Z源变换器提供思路。在此基础上，给出高压大容量Z源DC-AC换流站的拓扑设计，研究其与直流风电场之间的耦合机理，提出风电功率解耦控制策略，从而解决海上直流风电输出电压波动而带来的弃风问题。同时结合虚拟同步概念与低频震荡问题，对所提出的解耦控制策略进行了相应改进。此项研究，将建立完整的Z源变换器拓扑理论体系，提升其在未来风电领域中的应用价值。

各类直流汇集型可再生能源场站具备输出电压与功率宽范围波动特性，并导致系统发电效率问题。这对承担功率变换与并网功能的电力电子装置的特性提出较高要求。先进Z源阻抗型变换器，具备灵活的电压增益调整能力，对于各类集中或分布式的可再生能源场站直流并网，是一种理想解决方案。.本项目从电路拓扑，建模控制与系统应用三个层面着手，探索Z源变换器应用于可再生能源场站直流并网的理论技术基础。在拓扑层面，提出具备强升压能力的开关抽头电感型Z源网络与独立输入串联输出型多模块Z源变换器，可分别用于分布式光伏并网与可再生能源场站直流并网；在建模控制层面，实现对于多种使用型Z源变换器拓扑的动态建模并针对SZIBDC拓扑提出多种电压增益控制策略，同时提出基于模糊逻辑控制器的Z源变换器控制方案；在系统应用层面结合可再生能源场站直流汇集并网系统实际技术需求，提出稳态功率条件与故障隔离控保与暂态穿越控制策略，并完成针对特定Z源变换器的运行适应性分析。