Multi-objective Circulating Current Control with Optimal Energy Ripple Minimization for MMC: In MMC, the submodule capacitor occupies nearly 50% of the volume and 80% of the weight. The second harmonic circulating current (CC) is properly controlled with a predefined phase and amplitude to minimize the energy storage requirement and reduce the submodule capacitance. This multi-objective control method does not compromise the semiconductor device's rating and efficiency.

Arm Energy Estimation based Improved Arm Current Sensor-less Circulating Current Control in MMC: Conventional circulating current control utilizes six arm current sensors and one PI or PR controller per phase. To avoid the arm current sensors and feedback-based closed-loop controller, an arm energy estimation-based CC control is proposed utilizing estimated instantaneous capacitor voltages.

Circulating current suppression control (CCSC) using negative insertion in MMC: The maximum value of modulation index is limited to less than 1 to implement the CCSC. The proposed method suppresses the circulating current without limiting the modulation index which allows the MMC to operate at its full power capacity.