An optimization method for reducing the voltage fluctuation of the floating-capacitor in ANPC five-level inverter

The excessive fluctuation of the floating capacitance's (FCs) voltage affects the output performance and output power of the 3P-5L-ANPC converter. In order to minimize the fluctuation of the FCs voltage, an optimization control method based on zero-sequence voltage (ZSV) injection is proposed. The method takes reducing the maximum amplitude of the voltage fluctuation of the three-phase floating capacitor as the control target. Firstly, the mathematical equation between the modulation voltage and the voltage fluctuation of the FCs are established, and then the maximum fluctuation amplitude of the FCs voltage is obtained by using the established mathematical equations. Secondly, the range of ZSV injection is determined according to the conditions such as the control of neutral point voltage and the limitation of high-phase voltage leaps. Finally, the equations of the maximum amplitude in the voltage fluctuation of the three-phase FCs are established, and the ZSV with the minimum voltage amplitude fluctuation of the FCs is obtained within the effective range of the ZSV injection. Compared with the traditional shifted pulse width modulation (SPWM)/space vector pulse width modulation (SVPWM) method, the proposed method can effectively reduce the fluctuation of the FC voltage by 50%. Simulation and experimental results are presented to verify the effectiveness of the proposed method.