基于模型预测控制的模块化多电平变换器可靠性及主动热管理研究

The modular multilevel converter (MMC) with power semiconductor devices as its core component has become the key power conversion devices in the fields of flexible DC transmission, medium and high voltage power transmission and power quality regulation with the new trend of the power electronics dominated power systems. However, the low reliability of power converter is contradict to the requirement of the high voltage high power conversion technology, which is the key problem and technical bottleneck that seriously restricts the application of flexible HVDC transmission and other technologies. Thus, some key scientific and technical issues existing in the safe and reliable operation of MMC system under complicated operating conditions will be researched. A multiphysics coupling model of power device with consideration of the electronics, thermal and mechanical stress will be established to illuminate the nature of thermal fatigue failure. And based on the above research, the basic theory and method of reliability evaluation based on internal and external factors will be explored. The active thermal control strategy combining the advantages of the improved model predictive control will be put forward to increase the reliability and lifetime of the MMC system based on analysis of the thermal behavior and selection of control parameters. And then, the multi-parameter combined thermal coordinated control scheme will be explored. This research project can lay a solid scientific basis for the MMC widely used in the medium/high voltage and high power systems.

电力系统电子化新趋势下，以功率半导体器件为核心部件的模块化多电平变换器以其独特优势已成为实现柔性直流输电、中高压电力传动及电能质量调节等领域的关键功率变换装置。然而，功率变换器低可靠性现状与高压大功率变流技术高可靠性的要求构成了矛盾，成为严重制约柔性直流输电等技术应用的关键问题和技术瓶颈。本项目围绕复杂运行工况下模块化多电平变换器系统安全可靠运行中存在的关键科学问题展开研究。通过建立功率器件电-热-机械应力多物理场耦合模型，阐明功率模块热失效本质，提出实时精确的结温在线提取方法；基于解析寿命预测模型与线性累积损伤理论，探索兼顾内外部因素的可靠性评估基本理论与方法；通过热行为分析及控制参量选取，结合改进模型预测控制的优势，提出兼顾功率控制的主动热管理控制策略，并探索多参量联合调节的综合热管理协调控制方案。本项目的研究成果将为MMC在中高压大功率电力系统电子化领域的广泛应用奠定坚实的科学基础。

本项目针对新能源并网发电中电力电子变换器系统复杂运行工况及可靠性需求，对并网系统运行安全可靠性中的关键问题进行深入研究。本项目经过研究得出，相较于基于晶闸管的电网换相换流器和基于电压源的模块化多电平变换器，电流源型模块化多电平变换器具有结构简单、造价低、损耗小、直流短路故障穿越能力强、不存在换相失败等优点，其在高压直流输电系统中具有广阔的应用前景。因此，项目针对电流源型变换器，通过仿真与实验相结合的技术手段对并网系统运行安全可靠性中的关键问题展开研究。提出了一种优化开关序列的新型混合调制策略，能降低减小直流链路电流纹波；提出了一种基于有效开关法的叠流效应抑制策略，抑制了叠流效应，提高了电能质量；提出了一种基于矢量提前筛选的电流源型变换器多步模型预测控制方法，解决了传统多步预测控制计算量大的问题，实现了准定频控制以便于滤波器设计，因此具有较好的动、稳态性能，网侧电流THD更低，方案简单，易于实现。该项目研究中结合理论分析、仿真和实验进行，较好地改进了电力电子变换器系统复杂运行工况下的可靠性，具有重大的理论价值和广泛的应用前景。