开关频率与谐波电流协同控制的柔性直流换流阀降损方法研究

With the increasing voltage level and transmission capacity, the number of cascaded sub-module and power semiconductor devices of VSC-HVDC converter valve grows rapidly, resulting in high valve losses, which reduced the transmission efficiency and reliability of power transmission system. In order to solve this problem, this project mainly studies the loss characteristics, loss modeling and calculation method, and the control strategies. This research is intended to reduce the switching frequency and the average device current, combining with the energy balancing requirements of the flying capacitors. This project researches on the physical law of the energy fluctuation, conversion and dissipation of the HVDC converter valve, and also studies on the control methods. On this basis of the theories above all, the experimental verification is carried out through transformation and upgrading of the existing experimental platform. The preliminary research has demonstrated the feasibility of this method to reduce the valve losses. This research mainly focuses on the two key scientific issues, those are the influence of the steady-state energy fluctuation of the converter valve on the sub-module switching, as well as the mapping function between the transient energy conversion among the converter arms and the distribution characteristic of the device harmonic current. The analytical loss model and the loss reduction control strategies are expected to be proposed, which can not only enrich and perfect the theoretical system of intelligent transmission and distribution power system, but also provide a theoretical reference for the practical application of the efficient operation technology for VSC-HVDC transmission systems.

由于电压等级和传输容量不断提升，柔性直流输电换流阀的级联子模块和功率半导体器件数量快速增长，导致换流阀损耗过高，降低了输电系统传输效率和可靠性。针对这一问题，本课题主要研究柔性直流输电换流阀的损耗特性、损耗建模及其计算方法、降损控制策略。本课题拟以降低换流阀开关频率和器件平均电流为目标，结合对于悬浮电容能量的均衡要求，研究换流阀能量波动、转换和耗散的物理规律与控制方法，并通过已有实验平台的升级和改造来进行实验验证。申请人已有初步研究结果表明该降损控制方法具有可行性。课题重点解决悬浮电容稳态能量波动对于子模块投切的影响规律、桥臂间暂态能量转换与器件谐波电流分布的数理关系两个关键科学问题，预期提出适用于大容量柔性直流输电换流阀的损耗解析模型及其降损控制策略，丰富和完善智能输配电理论体系，为柔性直流输电高效运行技术的工程实用化提供理论参考。

随着电压等级和传输容量不断提升，柔性直流输电换流阀的级联子模块和功率半导体器件数量快速增长，导致换流阀损耗过高，降低了输电系统传输效率和可靠性。针对这一问题，本课题主要研究柔性直流输电换流阀的损耗特性、损耗建模及其计算方法、降损控制策略。本项目主要研究内容包括高压大容量柔性直流输电换流阀损耗理论、换流阀内部能量波动转换和耗散的物理意义，并提出了谐波电流与开关频率协同控制的新型降损运行策略。此外，本项目构建了8电平±375Vdc-380Vac/30kW MMC物理实验平台，完成了课题主要理论研究内容的实验验证。.课题主要研究成果包括：1、MMC拓扑结构的柔性直流输电换流阀损耗特性分析，包括换流阀电路元件损耗特性、基于子模块投切规律的开关频率计算、环流谐波分量与换流阀损耗分布特征等；2、提出了一种高压大容量MMC换流阀损耗精确计算方法，为MMC的参数设计、运行控制优化等提供了理论支撑；3、建立了MMC换流阀损耗模型，明确了电容稳态能量波动对开关频率的影响机理、桥臂暂态能量差异与器件谐波电流映射函数等基础理论问题；4、提出开关频率及谐波电流协同控制的新型降损运行策略，并成功应用于云南鲁西柔直工程中的±350kV/1000MW 广西侧换流站，取得了良好的经济效益。综上，本项目研究成果丰富和完善了柔性直流输电理论体系，为柔性直流输电高效运行技术的工程实用化提供了理论参考，并创造了较好的工程应用价值。