Low-Capacitance Modular Multilevel Converter Operating With High Capacitor Voltage Ripples

To provide a reliable approach that can significantly decrease energy storage requirements, this paper proposes a low-capacitance modular multilevel converter (MMC) operating with high capacitor voltage ripples. In the proposed MMC with high ripples (HR-MMC), the dc value of the capacitor voltage is slightly decreased by slightly increasing the number of series-connected submodules in each arm. Therefore, the MMC can operate under a higher capacitor voltage ripple without changing the peak capacitor voltage. Evaluation shows that the cost and volume of the HR-MMC can be reduced due to the reduction of energy storage requirements. The volume reduction effect is particularly obvious. The impacts of the capacitor voltage ripple on the linear modulation region are also analyzed. The obtained active and reactive power diagram shows that the active power and capacitive reactive power ratings are not affected by the high capacitor voltage ripple. The high capacitor voltage ripple only results in a reduction of inductive reactive power rating. The correctness of the theoretical analysis and the feasibility of the HR-MMC were verified through simulations and experiments.