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Nuclear fusion reactors, such as the tokamak in the International Thermonuclear Experimental Reactor (ITER) project, usually involve extremely sophisticated high-voltage power supply systems, which provide exciting research challenges. In the short term, the major challenges in power supplies of the ITER and other fusion reactors include the following: 1) fast current control of vertical stabilization (VS) coils and 2) dynamic compensation of reactive power and harmonics. In the long term, the power supply systems in fusion reactors provide opportunities for optimizations at both component and system levels. In this paper, modular multilevel converters (M2LCs) are adopted to tackle the short-term challenges. Circuit structures, pulsewidth-modulation methods, and fault-tolerant operation strategies are presented. The configuration and control strategies of M2LC in VS coils are fully studied and verified with real-time simulations. Compared with existing circuit solutions in fusion reactors, the M2LC -based circuits will have better dynamic response, higher reliability, smaller footprint, and reduced weight. As an outlook to the long-term developments of the fusion power supplies, comprehensive real-time simulations are also discussed. Furthermore, as the future development direction of power electronic devices, the wide band gap devices are discussed at the end of this paper.