Device Loading and Reliability Analysis of Modular Multilevel Converters With Circulating Current Control and Common-Mode Voltage Injection

The submodule (SM) capacitor voltage ripple and circulating current (CC) are major technical challenges in modular multilevel converters (MMCs). The generation of CC in the MMC results in an increase of SM capacitor voltage ripple, voltage/current stress on power switching devices, and power losses. Therefore, minimizing the CC and SM capacitor voltage ripple is essential for the smooth operation of an MMC. Prior studies and research have focused on different control strategies and modulation schemes to minimize the CC and SM capacitor voltage ripple. This paper presents an impact of active CC control and common-mode voltage (CMV) injection on thermal loading of power switching devices. To evaluate the performance comparison between different control approaches, a generalized control framework for MMC is established. An electrothermal simulation is performed to study the thermal loading on power switching devices. The efficacy of the generalized control scheme is evaluated through PLECS simulations and hardware-in-the-loop experiments. Finally, the thermal loading and reliability of MMCs are evaluated for different modulation schemes with the active CC control and CMV injection.