A Medium-Voltage Motor Drive with Modular Multilevel Converter Based on Nearest Level Modulation

Nearest level modulation (NLM) is the most commonly used modulation method for modular multilevel converter (MMC). When the number of levels is small, the output voltage and current harmonics of the NLM are severely distorted, and it cannot be used in MMC based medium-voltage motor drive system. In this paper, the switching process of the deadbeat current control under NLM is analyzed in detail, and it is pointed out that the MMC deadbeat current control under NLM modulation has hysteresis characteristics. The hysteresis loop width of MMC deadbeat current control under NLM is quantitatively analyzed, and the expression of hysteresis loop width and output current fluctuation range is obtained. At the same time, the integrated control scheme of MMC based motor drive system is designed. Compared with the traditional scheme, the proposed scheme has the advantages of simple control structure, low switching frequency, easy realization of circulating current suppression and good dynamic characteristics. The 11-level back-to-back MMC motor drive model was built in Matlab/Simulink to verify the correctness and effectiveness of the proposed control scheme. © 2020, Electrical Technology Press Co. Ltd. All right reserved.