This paper presents a division-summation (D-Sigma) digital control based modular multilevel converter. Modular multilevel converters (MMC) have been applied to static synchronous compensators (STATCOM), high-voltage direct-current transmission (HVDCT), back-to-back power transfer systems, wind/solar power generation and battery storage systems. The D-Sigma digital control is adopted to track current reference, balance dc-bus capacitor voltage and regulate cell module capacitor voltage. The adopted D-Sigma digital control can accommodate wide filter inductance variation and take care of source voltage harmonics to achieve fast tracking response and low-distortion output current for the applications of active and reactive power injection and rectification with power factor correction. Based on power-balance principle, the combination of dc offset current and the ac current of each arm can be determined. According to charge-balance principle and with the D-Sigma digital control, dc-bus capacitor voltage balancing and cell voltage regulation can be achieved. To ensure the output current with low harmonics, a limitation factor for cell voltage regulation is discussed. In the paper, the MMC configuration is introduced first, and then the control laws for current tracking and voltage regulation are derived in detail. Simulated and experimental results obtained from a 54 kW MMC have verified the analysis and discussion.