A Modular Multilevel Converter (MMC) has gained widespread popularity due to its notable advantages, including high efficiency, flexibility, minimal harmonic distortion, lower power device ratings, modularity, and scalability. Despite these benefits, the MMC encounters challenges such as voltage balancing and circulating currents. The primary objective is to balance capacitor voltages in each submodule without excessive power electronic device switching. To address this, a controlled switching frequency technique is employed to reduce the average switching frequency of the devices, mitigating voltage imbalances. However, challenges persist, notably the introduction of even-order harmonics with the second harmonic being particularly prominent in inner current. These even order harmonic components contribute to increased power losses, device stress, and potential system instability. Conventional methods of suppression of circulating currents have limitations in harmonic elimination and complex in implementation. This paper proposes a super twisting sliding mode control (SMC) to concurrently manage balancing of capacitor voltages and control of circulating currents in the MMC. The controller effectively reduces the harmonic components, with a focus on the dominant second harmonic in inner currents. Phase disposition (PD) PWM is utilized for MMC phase control, and the proposed controller, initially implemented for a single-phase MMC, demonstrates potential extension to three-phase systems. Comparative analysis with conventional PI controllers and the presentation of results in the MATLAB/Simulink environment validate the efficacy of the proposed super twsiting SMC controller.