Abstract：The 7-level active neutral point clamped (ANPC) topology effectively reduces the need for filter inductance, offering the potential for higher power density and efficiency. However, under phase-shifted pulse width modulation (PS-PWM), the voltage regulation capability of the flying capacitors is limited, and imbalances in flying capacitor voltage can degrade converter reliability and output power quality. This paper proposes a flying capacitor voltage regulation method based on PS-PWM. This method adjusts the PWM phase of the flying capacitor unit to modulate the ripple shape of the inductor current, thereby modifying the charging/discharging current of the flying capacitor. The method is fundamentally unaffected by load current polarity and does not alter the effective duty cycle of the converter output. In the 0~1/3 modulation range, the charging current of the source-side flying capacitor is primarily related to the inductor current during the high-level period of the PWM-A signal near the source side. It is independent of the high-level periods of PWM-B and PWM-C signals. Moreover, the high-level period of the PWM-A signal does not affect the charging and discharging process of the load-side flying capacitor. Given a duty ratio D, adjusting the phase φA of the PWM-A signal can linearly modulate the average amplitude of the corresponding inductor current ripple without changing its ripple duration. This adjustment allows precise control of the source-side flying capacitor’s charge over the switching period, thereby regulating its voltage. During this process, the charging/discharging state of the flying capacitor only occurs during the high-level periods of the PWM-A, PWM-B, and PWM-C signals. By ensuring that the high-level periods of the PWM signals do not overlap, the source-side flying capacitor voltage can be independently controlled without affecting the load-side flying capacitor. Similarly, adjusting the phase φC of the PWM-C signal can linearly modulate the discharge current amplitude of the load-side flying capacitor. As long as the high-level periods of the PWM signals do not overlap, the load-side flying capacitor voltage can be independently controlled. In the 1/3~2/3 modulation range, changes in the PWM signal phases affect the flying capacitor’s charging and discharging current amplitude and duration. By deriving the phase-shift modulation model of the average charging current of the source-side and load-side flying capacitors over the switching period concerning the PWM-A and PWM-C signal phases φA and φC, the charging/discharging states of the two-stage flying capacitors can be determined under the single PWM phase degree of freedom. An appropriate voltage modulation strategy can be selected depending on the degree of flying capacitor voltage offset. Subsequently, adjusting the phases of PWM-A or PWM-C can improve the voltage offset of the flying capacitors and optimize the voltage balance between the source and load-side flying capacitors. In the 2/3~1 modulation range, the charging and discharging states of the flying capacitors occur during the low-level periods of the PWM-A, PWM-B, and PWM-C signals. The regulation principle in this range is similar to that in the 0~1/3 modulation range. In this case, adjusting the phases φA and φC of the low-level periods of PWM-A and PWM-C signals can achieve independent and linear voltage regulation for the source-side and load-side flying capacitors. Thus, the proposed improved PS-PWM phase modulation method can effectively address the voltage imbalance in the flying capacitors over the entire 0~1 modulation range.
李祥, 丰昊, 冉立. 七电平有源中点钳位式逆变器中飞跨电容电压平衡的移相调控方法[J]. 电工技术学报, 2025, 40(24): 8066-8079.
Li Xiang, Feng Hao, Ran Li. Phase-Shift Method for Seven-Level Active Neutral Point Clamped Inverter Flying Capacitor Voltage Control. Transactions of China Electrotechnical Society, 2025, 40(24): 8066-8079.
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