Mine hoist is key vertical transportation equipment within the mine. Its drive system adopts modular multilevel converter (MMC)

which can meet the hoisting requirements of high shaft depth and heavy load in deep mines. However

extremely low-frequency operation condition causes significant capacitor voltage fluctuation and affects output waveform quality in the MMC

thereby reducing converter drive capability and limiting MMC application in deep mine hoisting variable-frequency drive system. This paper proposes an extremely low-frequency MMC topology that significantly increases arm voltage level number without increasing the number of submodules

while introducing the dual L-C filter circuit to suppress the second harmonic circulating current in the arm current at the rated output frequency. Based on the mathematical model of extremely low-frequency MMC

the suppression method for extremely low-frequency capacitor voltage fluctuation is proposed

ensuring the improvement in the output waveform. A performance analysis of this control method is conducted on capacitor voltage fluctuation and switching device power loss. Finally

simulation model and experimental prototype of extremely low-frequency MMC are established. Both simulation and experiment results demonstrate the feasibility and effectiveness of the extremely low-frequency MMC topology and its control method.