模块化多电平换流器子模块IGBT损耗优化控制策略

模块化多电平换流器(MMC)因具备模块化、调度灵活等优势得到广泛应用.然而,逆变工况下,MMC子模块上下管绝缘栅双极型晶体管(IGBT)的损耗分布不一致,导致子模块内各器件的寿命差异大,而系统可靠性取决于寿命最低的器件,因此,子模块器件的可靠性将严重威胁到换流器的安全可靠运行.为此,文中提出了一种MMC子模块IGBT损耗优化控制策略.所提策略可以在不影响输出外特性的同时,改善子模块内部器件的损耗分布,提高系统的可靠性.具体而言,分析了模块内部损耗不平衡产生的机理,并通过在调制信号中叠加修正量的方式,减小子模块上下管IGBT的损耗偏差,实现了结温均衡.最后,通过损耗优化的数学证明及热-电联合仿真和器件寿命计算,验证了损耗分析的正确性及所提损耗优化控制策略的可行性.

Loss Optimization Control Strategy for IGBT in Sub-module of Modular Multilevel Converter

Modular multilevel converters (MMCs) are widely used because of their modularity and flexible management. However, there is inconsistency in the loss distribution of the upper and lower insulate-gate bipolar transistors (IGBTs) in the sub-module (SM) of MMC during the inverter operation condition, which results in a large difference in the lifetime of each device in the SM. Since the system reliability depends on the device with the lowest lifetime, the safe and reliable operation of the converter will be seriously threatened by the reliability of the device in the SM. Therefore, this paper proposes a loss optimization control strategy for IGBT in the SM of MMC. Moreover, the proposed strategy can improve the loss distribution of devices in the SM without affecting the external characteristics of the output, and enhance the reliability of the system. Specifically, the mechanism of the internal loss imbalance of the SM is analyzed. The loss deviation between the upper and lower IGBTs in the SM is reduced by superimposing the correction quantity in the modulation signal. Thus, the junction temperature equilibrium is realized. Finally, through the mathematical proof of loss optimization, the thermo-electric co-simulation and the device lifetime calculation, the correctness of the loss analysis and the feasibility of the proposed loss optimization control strategy are verified.