三相MISN-PFC多电平变换器可以实现更高的效率以及功率密度，而且与同类多电平变换器相比，MISN变换器同时兼顾单输出母线和模块化的优点，有利于实现多电平网络的冗余保护或者热备用，提高变换器的可靠性。但同时MISN变换器也带来了多电平单元均压的挑战。本工作通过模态分析，建立了描述占空比偏差影响MISN变换器均压的数学模型，揭示了单元不均压度会随着占空比偏差的增加而增加。为保证在大占空比偏差时MISN变换器良好均压，提出了基于纹波电流检测的均压控制策略，有效简化了多单元MISN变换器电压检测电路。最后，通过实验验证，该均压控制策略能够达到传统直接电压检测均压控制策略的均压效果。

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)