高压大容量混合型MMC半桥子模块下部IGBT损耗优化控制策略

混合型MMC存在器件损耗分布不均的问题，尤其是在逆变工况下，半桥子模块下部IGBT损耗远高于其他器件，导致其热应力与故障率均较高，是换流器可靠性的薄弱环节。为此，本文提出一种器件损耗分布优化控制策略。首先，计算混合型MMC中各器件的损耗，分析器件损耗的分布特性，确定损耗优化的主要目标。其次，根据损耗计算公式，明确降低半桥子模块电容电压方法可用于降低其下部IGBT的损耗。然后，通过三次谐波电压注入，初步降低半桥子模块的电容电压，再通过桥臂输出电压指令值差异化分配，进一步降低半桥子模块的电容电压，进而最大程度减小其下部IGBT损耗，实现器件损耗分布优化。最后，通过MATLAB/Simulink和PLECS的联合仿真以及MMC样机实验验证，证明了所提控制策略可以改善混合型MMC损耗分布不均的问题，能够提高换流器的整体可靠性。

Loss optimization control strategy for IGBT in half bridge sub-module bottom of high voltage and large capacity hybrid MMC

Hybrid MMC has the problem of uneven distribution of device losses, especially under the inverter condition, the IGBT loss of the lower part of the half-bridge sub-module is much higher than that of other devices, resulting in high thermal stress and failure rate, which is the weak link of the converter reliability. Therefore, this paper proposes a device loss distribution optimization control strategy. Firstly, the loss of each device in the hybrid MMC was calculated, the distribution characteristics of the device loss are analyzed, and the main goal of loss optimization is determined. Secondly, according to the loss calculation formula, it is clear that the method of reducing the capacitor voltage of the half-bridge sub-module can be used to reduce the loss of its lower IGBT. Then, the capacitor voltage of the half-bridge sub-module is initially reduced by the third harmonic voltage injection, and the capacitor voltage of the half-bridge sub-module is further reduced by the differential distribution of the output voltage command value of the bridge arm, so as to minimize the IGBT loss of the lower part to realize the optimization of device loss distribution. Finally, through the co-simulation of MATLAB/Simulink and PLECS and the experimental verification of MMC prototype, it is proved that the proposed control strategy can improve the uneven loss distribution of hybrid MMC and improve the overall reliability of the converter.