模块级联型多电平固态变压器及其关键控制技术的研究

With the increased concerns on environment and cost of energy, the power industry is experiencing fundamental changes with more distributed renewable energy resources or micro-sources such as photovoltaic cells and small wind turbines being integrated into the power grid in the form of distributed generation. In this proposal project, as a novel power distributed transformer, a solid state transformer (SST) will be presented as a novel solution towards integrating distributed renewable energy generation into power grid. This project aims at research on a modular multilevel cascaded SST and its control schemes, solving or realizing the following tasks:(1) The problem of voltage and current unbalancing in each power module will be overcomed, so that the voltage or current stress on switching devices in each module is equal or same, which facilicate the development of the SST with high voltage and high power; (2) automatically bidirectional power transmission between power grid and the SST will be achieved, which is very suitable for integrating distributed renewable energy resources into power grid; (3) the fundamental current in the single-phase SST will be in phase with the grid voltage, achieving unity power factor and supplying high quality electrical energy for user' electrical equipment; (4) the control strategy for single-phase SST can be extended to SST consisting of more than three converter modules or SST with more complicated construction, and the three-phase SST system can be easily achieved by using and connecting three separate single-phase SSTs.

通过电力变压器既能有效可靠地将分布式可再生新能源融入电网，以解决电力能源的短缺，又能提供较好的电能质量，确保用户电气设备安全经济运行，这些已成为现代电力系统中亟待解决的关键问题之一。本申请项目拟研究高频固态变压器（SST）作为电力配电变压器，以研究模块级联型多电平SST及其关键控制技术为主要内容，拟提出SST的控制策略方法与技术：①研究解决模块级联型SST功率模块间电压、电流不平衡问题，以突破因高频功率开关器件容量及耐压过低而制约高压大功率SST发展的瓶颈；②研究实现SST与电网间能量双向自动传输，以及通过SST实现分布式新能源的直流并网功能；③研究实现单相SST电网侧的单位功率因数，提高电网的电能质量；④研究实现单相SST的控制技术可扩展到更多模块级联型的多电平单相SST，以及研究实现由三个独立单相SST灵活方便地构成一个三相SST系统。

本申请项目主要研究三端口模块级联型高频固态变压器（SST）作为电力配电变压器，通过该SST既能有效可靠地将分布式光伏电池组直接接入电网，同时又能为当地交流负荷提供较好的电能质量，确保电气设备等交流负载安全经济运行。本申请项目以研究三端口模块级联型SST及其关键控制技术为主要内容，主要研究内容和研究目标包括：①解决模块级联型SST功率模块间串联电压与并联电流不平衡问题，以突破因高频功率开关器件容量及耐压不足而制约高压大功率SST发展的瓶颈；②通过SST实现各类分布式光伏电池组的直接直流并网功能，并且实现分布式新能源、电网及本地用户负荷三者之间能量自然“和谐”共处或自动“无缝”切换；③实现单相SST电网侧的单位功率因数，以提高电网的电能质量；④实现单相SST的控制技术可扩展到更多模块级联型单相SST，以及实现由三个独立单相SST方便灵活地构成一个三相SST系统。三端口模块级联型固态变压器可方便地整合交、直流微网以及分布式新能源，是未来智能电网的关键设备之一，因此，本项目有着广阔的应用前景。