基于SiC-MOSFET与Si-IGBT的电容开关型半全桥MMC子模块损耗优化与电容减小研究

In the future, VSC-HVDC technology makes more requirements on the volume and weight of modular multilevel converter (MMC), active defense capability of MMC and transmission efficiency. Light weight, DC fault ride through capability and low loss are the development directions of MMC sub-module. This project proposes a capacitor-switching semi-full bridge (CS-SFB) MMC sub-module structure combining SiC-MOSFETs and Si-IGBTs, and studies following three aspects. Firstly, based on the characteristic of circuit structure and SiC device, the internal advantage of conduction and switching loss optimization will be studied, and external loss reduction potential will be explored. Loss analysis method and loss reduction strategies will be proposed. Then, based on the variable equivalent capacitance of CS-SFB, the internal advantage of lower capacitor ripple will be studied, and external capacitance reduction potential will be explored. Capacitor voltage analysis method and capacitance reduction strategies will be proposed. At last, the auxiliary designing schemes for CS-SFB sub-module, such as drive, protection and cooling, will be developed, and the equivalent models of multi-physics field containing electric, magnetic thermal and stress analysis will be established. The design method of high-power density CS-SFB sub-module will be proposed. This project is of great significance for the basic theory and application in practical MMC project of CS-SFB sub-module.

未来柔性直流输电技术对模块化多电平换流器（MMC）体积与重量、主动防御能力、输电效率提出更高要求，轻型化、具备直流故障穿越能力、低损耗是MMC子模块的发展方向。本项目提出一种结合SiC-MOSFET与Si-IGBT的电容开关型半全桥（CS-SFB）子模块结构，展开以下三个方面的研究：基于电路结构及SiC器件的特点，挖掘CS-SFB开关损耗与导通损耗优化的内生性优势，探索降低损耗的外衍性潜能，提出CS-SFB损耗分析方法与降损措施；基于等效电容可变的特点，挖掘CS-SFB电容电压波动小的内生性优势，探索减小电容的外衍性潜能，提出CS-SFB电容电压波动分析方法与电容减小措施；开发CS-SFB子模块的驱动、保护、散热等辅助方案，建立子模块电磁热力多物理场等效模型，提出高功率密度CS-SFB子模块设计方案。本项目的研究将建立CS-SFB子模块的应用理论，并探明其在MMC工程中的应用前景。

未来柔性直流输电系统对换流阀体积与重量、电网安全性、输电效率提出新的要求，轻型化、具备直流故障穿越能力、低损耗是模块化多电平换流器（MMC）的发展方向。本项目研发了一种结合SiC-MOSFET与Si-IGBT的电容开关型半全桥（CS-SFB）MMC子模块结构，使用CS-SFB子模块结构的MMC在保留直流故障穿越能力的同时，在损耗优化方面具备一定的应用优势，具体研究结论如下：提出针对CS-SFB MMC器件、子模块、系统三个层级的损耗分析方法，CS-SFB MMC与传统混合型MMC相比导通损耗降低15%，必要开关损耗降低50%；提出适用于过调制比工况下的CS-SFB MMC先进载波移相调制策略，克服了传统载波移相调至策略造成的电容电压失稳、输出电压电流质量严重下降的问题；通过研究CS-SFB子模块中的缓冲电路、驱动保护、散热、取电方案，已搭建单桥臂两个CS-SFB子模块的三相MMC的物理实验平台，测试结果很好的验证了所提调制策略的先进性与CS-SFB MMC的低损耗特性。本项目基本建立了CS-SFB子模块结构的应用理论，在实际MMC工程中其具备一定的应用前景。