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. © 2021 Automation of Electric Power Systems Press.