Variable Sampling Frequency-Based SM Power Loss Balancing Control for MMCs With Bypassed Faulty SMs

The modular multilevel converter (MMC) is one of the most appropriate topologies for high-power applications due to its high modularity and low harmonic distortion. As faulty submodules (SMs) are bypassed, the capacitor voltage and switching frequency of healthy SMs in the faulty arm will rise, which causes unbalanced power loss distribution among the arms of MMCs and affects the reliability of MMCs. This article proposes a variable sampling frequency-based power loss balancing control (VSF-PLBC), which can balance power loss distribution among the arms of MMCs through adjusting the sampling frequency for an arm inserted SM number to modify switching losses in power devices in the MMC with bypassed SMs. The proposed VSF-PLBC can effectively improve the reliability of the MMC with the balanced power loss distribution among the arms in the MMC with bypassed SMs. The proposed VSF-PLBC is simulated with the professional tool PSCAD/EMTDC and is validated on a down-scale MMC prototype. The simulation and experimental results confirm the effectiveness of the proposed VSF-PLBC.