Design and Hardware Implementation of the Peak Current Mode Switching Cycle Control for Voltage Balancing of Modular Multilevel Converters

The voltage balancing control of cell capacitors and energy storage reduction is one of the key issue in the development of the modular multilevel converters (MMCs). This paper proposes a peak current mode switching cycle control (PCM-SCC) for the capacitor voltage balancing control of MMCs. The proposed method utilizes the shoot-through states of one phase leg that are seldomly used in conventional control methods to charge and discharge the cell capacitors once per switching cycle. The duration of the shoot-through states within each switching cycle is indirectly determined by controlling the peak value of the arm inductor current. The average value of each cell capacitor voltage is regulated at a given voltage reference level in a closed-loop form. With the proposed control method, the line frequency voltage ripples on cell capacitors are significantly reduced. Therefore, the requirement on the cell capacitance is remarkably released to achieve high power density and lower cost. Simulation and experimental results are provided to validate the effectiveness and performance of the proposed capacitor voltage balancing control method.