模块化多电平换流器电容电压波动抑制技术研究

The modular multilevel converter (MMC) is receiving increasing attentions in recent years due to its very high efficiency and distinctive features, and has been regarded as the development trend of high-voltage power conversion technologies. Particularly, MMC has already achieved great success in the field of high voltage direct current (HVDC) power transmission. However, MMC suffers from the necessity of very large capacitances, which stops it from reducing cost, increasing reliability, and applying to high-voltage motor drive and high-voltage DC/DC power conversion. Therefore, this project proposes a novel capacitor voltage suppression scheme to significantly reduce the capacitance of required capacitors by means of simultaneously injecting multiple-frequency circulating currents into the legs of MMC. The research contents of this project includes: investigating the nature of the capacitor voltage ripple and the principle of the energy transmission between legs; designing the proposed capacitor voltage suppression scheme based on multiple-frequency circulating current injection and the corresponding closed-loop controller, including the fuzzy controller and the repetitive controller; proposing an optimization methodology to the proposed capacitor voltage suppression scheme from the perspectives of efficiency, semiconductor reliability, and the input/output harmonic features; filtering of the common mode voltage harmonics introduced by the proposed capacitor voltage suppression scheme; developing effective capacitor voltage balancing solutions and phase-shifted carrier PWM modulation techniques; constructing the experimental prototype and testing the proposed methods. In conclusion, the aim of this project is to provide the theoretical basis and application guides for improving the industrialization of the modular multilevel converter, which is very meaningful and promising.

模块化多电平换流器由于其极高的效率和优异的性能已成为高压大功率电力电子变换技术的发展方向，并已在高压柔性直流输电领域中得到了广泛应用。然而如何降低其所需电容器的容量是制约模块化多电平换流器降低成本、增强可靠性、以及推广其在高压电机变频调速、高压DC/DC变换器中应用的关键问题。本项目首次提出基于多频率环流混合注入技术的电容电压波动抑制方案，以大幅减少所需电容器的容量。项目主要研究：电容电压波动的本质与桥臂能量的传输机理分析；基于多频率环流混合注入的电容电压波动抑制方案及其闭环控制器设计，包括模糊控制器与重复控制器的参数设计；从效率、功率器件可靠性、输入输出谐波含量等角度综合优化所提波动抑制方法；电容电压波动抑制引入的共模电压(轴电压)滤除技术；电容电压平衡与载波移相调制技术；样机建设与实验调试。项目旨在为模块化多电平换流器的市场化提供理论依据和实践参考，具有重要的研究意义和巨大的应用前景。

模块化多电平换流器(MMC)由于其极高的效率和优异的性能已成为高压大功率电力电子变换技术的发展方向，并已在高压柔性直流输电领域中得到了广泛应用。然而如何降低其所需电容器的容量是制约模块化多电平换流器降低成本、增强可靠性、以及推广其在高压电机变频调速中应用的关键问题。本项目主要针对模块化多电平换流器电容电压波动抑制关键科学问题进行研究。.首先分析了电容电压波动的类型与成因，并推导出电容电压波动幅值的具体表达式，为后续波动抑制以及电容容量的选取提供了理论依据.针对传统高频注入的电容电压波动抑制方法存在的环流幅值过高问题，提出优化的高频环流注入方法，不再对电容电压波动进行全抑制，而是将其限制在合理的范围之内，从而显著减小注入环流的幅值，降低器件的开关损耗和电流应力，确保MMC全频率范围下稳定运行，更具有工程实践意义。.在拓扑改进方面，提出一种改进型的MMC拓扑结构，相比传统MMC，该结构展现出固有的波动降低性能，顶层、底层、中间子模块的电容电压波动得到了显著的降低，且相同功率等级下可节省三个子模块，尤其适用于中压电机驱动等子模块数目较少的场合。.提出一种含有直流开关的混合型模块化多电平变频器，不仅具有较低的电容电压波动，相比传统注入方法还避免了额外的桥臂电流应力和共模电压问题，在高压变频领域极具应用前景。在此基础上，本项目提出一系列的改进方案，在不显著增加电容容量的情况下实现MMC的恒转矩全频率运行，为MMC变频应用的推广提供有力支撑。.当变频器面临电机停机等制动的场合，为了提高节电效果、减少制动过程的能量损耗，需要将从电机侧回馈的能量反馈到电网，实现节能、环保效果。本项目提出了一种背靠背混合型MMC拓扑，该拓扑相比全桥子模块结构的MMC，可减少75%全桥子模块数量，并能实现四象限和低频运行，拓宽了MMC变频器的适用性。.建设了基于MMC的电机拖动实验平台，为技术理论的验证提供了有力的支撑。