A Simplified Control Set MPC Strategy for Low Switching Frequency in MMC-Based Variable Frequency Drives

In medium and high voltage variable frequency drive systems, Modular Multilevel Converters (MMC) often encounter challenges related to limited switching frequency. Traditional sorting algorithms are highly sensitive to the voltages of submodule capacitors, leading to significant switching state changes even with minor voltage fluctuations. This paper proposes a low switching frequency control strategy for MMCs based on a simplified control set model predictive control (MPC). This strategy simplifies the finite control set, significantly reducing optimization computations without compromising the output performance of the MMC, thereby addressing the excessive computational demands of traditional MPC strategies for three-phase unified modeling optimization. By optimizing the number of priority inputs for submodules and using switching frequency as the priority criterion for submodule activation and deactivation, the proposed method achieves lower switching frequencies and balances the switching frequency among submodules. To verify the feasibility and effectiveness of the proposed control strategy, both simulation and experimental studies were conducted. The results demonstrate that this strategy effectively reduces the switching frequency while maintaining excellent output performance, highlighting its superiority in practical applications.