高压大容量IGBT换流阀蒸发冷却换热机理及热电耦合特性研究

With the development of electrical electronics, flexible HVDC Transmission Technology based on the IGBT has been paid more attention. High voltage and large capacity become its main developing trend. IGBT converter valve, as the key device, must operate steady and reliable. The fault caused by the thermal problem and the decrease of equipment reliability become the bottleneck of the development of the flexible HVDC technology toward large capacity. Based on the operating characteristics of high voltage, large capacity and high heat flux of IGBT converter valve, this project proposes the self-circulation, fully-immersion evaporative cooling technology, carry on the research of heat-exchange mechanism and thermal electro feature. Experimentally analysis the characteristics of the voltage breakdown strength of evaporative cooling fluid in liquid phase, vapor liquid phase and all gas phase respectively. Reveal the heat exchange mechanism of the evaporative cooling of IGBT converter valve taking the environmental friendly organic working medium, refine Heat transfer correlation and guide the thermal design and simulation. Analysis the influence rules of the evaporative coolant on parasitic parameter of IGBT module, through building the thermal electro couple analysis model under the consideration of parasitic parameter, fixed junction temperature and variable junction temperature, carry on the research of thermal electro couple characteristics. Finally summarize the immersion evaporative cooling of IGBT valve design guidelines. The research results have important theoretical guiding significance and application value for perfecting theoretical system, extending technology application and improving the reliability of IGBT converter valve equipment

随着电力电子技术的发展，以IGBT为基础的柔性直流输电技术广受重视，且高压、大容量成为发展趋势。IGBT换流阀作为关键设备，因热问题引发故障继而导致设备可靠性降低成为柔直技术大容量发展的瓶颈问题。本项目围绕IGBT换流阀高电压、大容量、高热流密度的运行特征，提出主动式全浸蒸发冷却技术，开展蒸发冷却换热机理和热电耦合特性研究。实验分析蒸发冷却工质在液相、汽液两相和全汽相下电压击穿强度规律，掌握其全面的电气特性；揭示采用环保型有机工质的IGBT换流阀蒸发冷却换热机理，提炼换热关联式，用于指导热设计和仿真；分析蒸发冷却工质对IGBT模块寄生参数影响规律，通过建立考虑寄生参数变化和结温变化的蒸发冷却IGBT热电耦合模型，开展其热电耦合特性的研究；最后总结主动式全浸蒸发冷却ＩＧＢＴ换流阀优化设计指导原则。研究成果对完善理论体系，推广技术应用和提高IGBT换流阀设备可靠性具有重要的研究意义和应用价值。

柔性直流输电是我国大规模可再生能源远距离输送的重要发展方向，高电压、大容量是柔性直流输电技术的发展趋势。因IGBT换流阀结温过高引发故障继而导致设备可靠性降低成为柔直系统向大容量发展的瓶颈问题。因此强化换流阀散热、控制IGBT模块温度水平是提高柔直系统输电容量及提升系统运行可靠性的关键。围绕IGBT换流阀高电压、大容量、高热流密度的运行特征，本项目提出主动式全浸蒸发冷却技术，将IGBT模块直接浸没在蒸发冷却工质中，突破IGBT模块封装限制，为IGBT芯片提供双面散热条件，从而大幅度改善IGBT散热效果，降低模块温升。全浸蒸发冷却技术彻底改变了IGBT模块原有散热模式，IGBT芯片工作环境由硅胶变为绝缘冷却工质，两者在电气特性、换热原理、材料属性等方面有本质区别，可能会导致IGBT模块工作特性的变化。本项目围绕全浸蒸发冷却IGBT换流阀研制所涉及的关键科学问题开展以下创新研究工作：.（1）设计开发了蒸发冷却工质三相态、可调频绝缘特性测试平台及20kHz高频耐压测试源，解决了高频下介质的耐压测试问题。得到了冷却工质三相态、一定频率范围内击穿电压统计分布及变化规律，得到了冷却工质不同温度及频率下介电常数及介损变化规律，构建了蒸发冷却工质电气特性数据库。.（2）得到了IGBT芯片不同放置位置、不同系统压力下蒸发冷却工质与硅芯片表面配合时的芯片表面温度分布；开展光滑表面和强化换热表面结构下的沸腾换热可视化实验研究，揭示其换热规律，提出了适合蒸发冷却工质的对流换热系数实验关联式。.（3）从IGBT模块温度和介质环境两个角度，得到了冷却方式对IGBT模块寄生参数的影响规律。.（4）提出了一种全浸式蒸发冷却IGBT模块热电耦合建模方法，所建模型能够准确表征IGBT模块的电、热及其耦合特性，并且具有模型参数提取简单，准确性好，仿真效率高的优点。.（5）总结了主动式全浸蒸发冷却IGBT换流阀优化设计指导原则。.本项目研究成果论证了蒸发冷却技术应用于IGBT换流阀的可行性及技术优势，可为全浸蒸发冷却IGBT换流阀设计提供指导。