含全桥子模块的模块化多电平换流器优化运行与控制策略研究

Along with voltage-source-converter (VSC)-based HVDC applied for high voltage and large capability transmission field, full-bridge sub-module (FBSM) involved modular multilevel converter (MMC) has received worldwide attention due to its active dc fault handling capability. FBSM can generate a negative voltage to increase transmission capacity under steady state, which has not been fully utilized. In addition, FBSM involved MMC has been widely dismissed on the ground of high semiconductor losses and cost. This project utilizes FBSM’s negative voltage output capability, further optimizes the operation and control strategy for the FBSM involved MMC. The principle of increasing transmission capability for FBSM involved MMC with AC voltage boosting will be analyzed, and optimization design for converter topologies with consideration of comprehensive factors will be proposed. Moreover, key factors affecting sub-module’s capacitance requirement and converter losses will be explored. And optimal control strategy in favor of reducing submodule capacitance and converter losses will be studied. Finally, dynamics of sub-modules’ voltage and current stress during the pre-charging and DC fault ride through process will be explored, and a corresponding optimal control strategy will be proposed. This project is of great significance for the design and application of FBSM involved MMC.

随着柔性直流输电向着高压大容量的方向发展，含全桥子模块的模块化多电平换流器（MMC）因其具有直流故障处理能力而获得了广泛关注。然而其通过利用负电平输出获得稳态传输功率提升的潜力尚未被充分挖掘，且存在成本偏高、损耗偏大的问题，严重影响了其在实际工程中的应用。本项目拟针对含全桥子模块的MMC利用负电平输出能力带来的新机遇和新挑战，对其优化运行和控制策略进行研究：分析换流器容量提升机理，提出综合考虑多因素的换流器拓扑优化设计原则；归纳负电平输出情况下决定子模块电容需求和换流器稳态运行损耗的关键因素，提出可减小子模块电容、降低换流器损耗的稳态控制策略；揭示换流器启动、故障穿越等暂态过程中的电压、电流应力变化规律，提出可优化电压、电流应力的启动控制策略和直流故障穿越方案。通过本项目研究，为含全桥子模块的MMC换流器拓扑结构设计提供理论指导，并为其应用于实际工程提供技术支撑。

随着柔性直流输电向着高压大容量的方向发展，含全桥子模块的模块化多电平换流器（MMC）因其具有直流故障处理能力而获得了广泛关注。然而其通过利用负电平输出获得稳态传输功率提升的潜力尚未被充分挖掘，且存在成本偏高、损耗偏大的问题，严重影响了其在实际工程中的应用。本项目严格按照计划书，针对含全桥子模块的MMC工程应用中的实际问题提供了一系列的方案。第一部分针对含全桥子模块的MMC利用负电平输出能力带来的新机遇和新挑战，对其优化运行和控制策略进行了研究，分析了换流器容量提升机理，提出了综合考虑多因素的换流器拓扑优化设计原则；第二部分归纳了负电平输出情况下决定子模块电容需求和换流器稳态运行损耗的关键因素，提出了可减小子模块电容、降低换流器损耗的稳态控制策略；第三部分揭示了含全桥子模块的MMC在启动、故障穿越过程中的特性，针对性地提出了优化的启动控制策略和直流故障穿越方案。最后，本项目还搭建了实物平台，对上述研究进行了实验验证。通过本项目研究，为含全桥子模块的MMC换流器拓扑结构设计提供理论指导，并为其应用于实际工程提供技术支撑。