混合式限流技术中大电流转移及开关绝缘恢复机理的研究

To resolve the difficulties of fault current limiting in medium voltage DC system, after the basis process research of naturally current commutating and forced current commutating, a novel hybrid current limiting topology structure is proposed. Based on the topology structure, the internal mechanism of current commutating and its control methods and strategies are researched in the project. First, the dynamic characteristics of mechanical switches and power electronic switches at current zero-crossing instant and insulation recovery characteristics are studied. The nonlinear model of the current commutating process in the new hybrid current limiter are established to find out the internal mechanism during current commutating, influence factors and patterns of current limiting characteristics.The control strategies and methods of components and branchs are proposed according them. Next, combined with the transient analysis of power system, the effect on system stability of hybrid current limiter are studied to get the matching relationship between current limiting characteristics and other equipments, then the specific application of current limiter in the system are determined. On this basis, an experimental apparatus of hybrid current limiting for DC 5kV and below voltage system are set up, and the related experimental tests are made. Finally, the theoretical basis and method for design of new type hybrid current limiter are formed based on the experiments and simulations. It can provide a new solution for short circuit current limit in medium voltage DC system.

针对中压直流系统短路电流限制所面临的困难，本项目在自然换流和强制换流基本过程研究基础上，提出一种综合电流自然和强制转移的新型混合式限流拓扑结构，开展中压直流系统混合式限流过程电流转移内在机理及其控制方法和策略的研究。首先，研究机械开关和电力电子开关在电流过零瞬间的动态特性及过零后的绝缘恢复特性，建立新型混合式限流器电流转移过程的非线性模型，探求混合式限流器电流转移的内在机理、限流特性的影响因素及规律，提出限流器元器件及各支路间的控制策略和方法；其次，结合系统的暂态分析，研究混合式限流器对系统稳定性的影响，获得其限流特性与其它设备之间的匹配关系，确定限流器在系统中的具体应用方案；在此基础上，搭建适合于直流5kV及以下系统电压等级的混合式限流实验装置，并进行实验测试。最后，基于实验和仿真分析归纳形成新型混合式限流器设计的理论依据和方法，为中压直流系统短路电流的限制提供新的解决思路。

直流供电系统具有输送电能功率密度高、线路损耗小、系统稳定性高等优点，近年来在民用和国防领域得到越来越多的应用，也受到国内外的广泛关注。然而，随着直流供电容量的提升，短路故障电流的水平也急剧增加，短路电流成为困扰当前直流供电系统发展的难点问题。在系统串接故障限流器限制系统短路电流，是保证系统安全运行的有效措施。结合机械开关和电力电子开关各自优势的电流转移型混合式限流技术是当前限流技术的研究热点。. 混合式限流中电流转移过程机械开关触头间隙介质恢复特性及机械开关和电力电子器件的合理匹配是决定电流快速可靠转移的关键。项目首先基于化学反应动力学与磁流体动力学理论，建立了空气电弧过零期间的化学非平衡模型，分析了电弧电流过零阶段的宏观特性和微观粒子分布规律，并通过汤逊散射方法测量弧后阶段的电子数密度验证了化学非平衡模型对于电弧电流过零期间动态行为预测的有效性；通过将化学非平衡的计算结果与高温气体临界击穿特性的分析方法相结合，获得了电弧电流过零后的临界击穿场强分布和不同时刻电弧区域的耐压情况。随后，通过仿真建模研究了真空触头间隙电弧过零后的鞘层发展阶段和金属蒸气击穿阶段的内在机理。之后，基于混合式限流原理，提出了三种限流拓扑结构，并通过非线性电路模型分析了不同拓扑结构的特点和电流转移过程与限流特性的影响因素；最后基于负压式转移的混合限流拓扑结构研制了10kV限流器样机，通过实验测试验证了限流器的限流特性，并以10kV直流微网系统为例，分析了限流器在直流系统不同短路故障下的限流特性及影响因素，为限流器在系统的应用提供了依据。. 本项目对混合式限流中大电流转移及开关介质恢复机理开展了理论和实验研究，研究成果可为混合式限流技术在中压直流系统的应用提供理论依据和指导。