A thermal balancing method for MMCs under capacitor deterioration.

• In this paper, the loss and thermal stress distribution among SMs of MMC have been investigated which under different capacitance. The relationship between the degree of capacitance degradation and the junction temperature difference among SMs is revealed. • The switching principle of thermal balancing control is studied by analyzing the trend of junction temperature changes in power semiconductor devices. • A thermal balancing method is proposed, offering advantages such as reducing the demand for temperature sensors and eliminating the reliance on high-precision capacitance monitoring technology. The proposed method can effectively achieve balanced junction temperatures of power semiconductor devices among different SMs under capacitor deterioration. Thermal control of semiconductor devices in the submodules (SMs) is a key factor for the safe and reliable operation of modular multilevel converters (MMCs). During normal operation, significant thermal differences can arise among SMs due to the manufacturing tolerance and aging effect of capacitors, which can affect the lifespan of semiconductor devices and even lead to equipment failure. To address the problem, this paper presents a method for achieving thermal balancing among SMs with different capacitances by adjusting their switching principle. Firstly, the relationship between the degree of capacitance degradation and the junction temperature difference among SMs is revealed. Then, by setting data windows to capture the dynamic losses of power devices, which can reflect the trend of junction temperature. The switching principle of thermal balance among SMs is studied based on the trend of junction temperature in power devices. The thermal balancing method has advantages including not requiring high-precision temperature sensors and eliminating the reliance on capacitance monitoring technology. Finally, the simulation and experimentation results demonstrate that the proposed method can effectively achieve balanced junction temperatures of power devices among different SMs. [ABSTRACT FROM AUTHOR]