Modular Multilevel Converter Topology Based on Half-Bridge Submodules Using a Si/SiC Hybrid Approach for Integration of Wind Energy Systems

Athwer, A. and Badawy, Ahmed and Ma, Xiandong (2026) Modular Multilevel Converter Topology Based on Half-Bridge Submodules Using a Si/SiC Hybrid Approach for Integration of Wind Energy Systems. PhD thesis, Lancaster University.

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Abstract

This research project proposes a configuration of the MMC topology based on a conventional half-bridge submodule (HBSM), utilizing a SiC MOSFET and Si IGBT hybrid approach to improve the performance of the MMC topology based on conventional Si devices. The combination of SiC and Si-based devices offers massive advantages by utilizing the high performance and high switching frequency capabilities of SiC MOSFETs, including low switching and conduction power losses along with the cost-effectiveness and high voltage capability of Si IGBTs. A SiC MOSFET and Si IGBT hybrid HBSM structure-based MMC model simplifies the converter model by reducing the required number of switching devices, withstanding high switching frequencies and temperatures, lowering the complexity of the MMC voltage balancing control, and minimizing the total power losses in each SM cell. A single-phase MMC model based on the proposed hybrid configuration was simulated using both MATLAB and PLECS® Standalone tools to verify the effectiveness of the converter operation using hybrid system, resulting in normal voltage and current waveforms. A small prototype with a low voltage level was developed in laboratory to validate the performance of the proposed MMC model in comparison with the simulation results, which demonstrated normal voltage and current behaviour across the submodules and both converter arms. A switching power loss test was performed on the selected power switches based on different semiconductor technologies to investigate their power losses and operational behaviour. The obtained results were subsequently used in the analysis of the power loss at both the submodule level and the overall converter model. The results indicate that the SiC MOSFET exhibits faster switching speeds and lower switching and conduction losses compared with the Si IGBT device. Furthermore, the submodule employing a hybrid SiC MOSFET–Si IGBT configuration demonstrated an approximate 43.5% reduction in power consumption compared with a cell utilizing only IGBT switches, achieving an improved submodule efficiency of about 96%. In addition, the total power loss of a single-phase MMC model comprising eight submodules based on the MOSFET/IGBT hybrid configuration was evaluated, showing nearly half reduction in power loss compared with conventional configurations, and resulting in an overall efficiency improvement of approximately 17%. Finally, a three-phase MMC model connected to the grid was simulated in PLECS using SiC MOSFET and Si IGBT devices. The simulation results demonstrated stable and normal operation under grid-connected conditions. The power losses were evaluated, showing an approximate 43% reduction compared with the conventional model, along with an overall efficiency improvement to about 97%, achieved at a reasonable cost.