The three-phase MISN-PFC multilevel converter has the potential to deliver enhanced efficiency and a higher power density. In contrast to other multilevel converters, the MISN converter uniquely integrates the benefits of a single output bus with modular design, which is conducive to the implementation of redundancy protection or hot standby in multilevel networks, thereby enhancing the overall reliability of the converter. Despite these advantages, the MISN converter presents a significant challenge in maintaining voltage balance across its multiple cells. This research conducts a thorough modal analysis to construct a mathematical model that delineates the influence of duty cycle deviation on the voltage imbalance within the MISN converter. The analysis reveals a direct correlation between the magnitude of duty cycle deviation and the severity of voltage imbalance. To address this issue and ensure voltage equalization even in the presence of considerable duty cycle deviation, a novel voltage balancing control strategy is introduced based on ripple current detection. This approach effectively streamlines the complexity of the voltage detection circuit in multi-cell MISN converters. Experimental results corroborate the effectiveness of our proposed voltage balancing control strategy, demonstrating that it achieves performance comparable to traditional voltage detection methods.

Fig. 1 The diagram of the proposed voltage balancing control strategy.

Fig. 2 The performance comparison of different voltage balancing controls. (blue: no voltage balancing control; red: balancing control based on current ripple detection; yellow: balancing control based on voltage detection)