A New SPWM Strategy for Five-Level ANPC Converters

The five-level active neutral-point clamped (5L- ANPC) converter has the advantages of large output power, small number of floating capacitors, and only one midpoint of the bus. In recent years, it has received extensive attention from scholars. However, the existing modulation strategies still have some drawbacks. For sinusoidal pulse width modulation (SPWM), the DC side voltage utilization is low and the calculation of the NP potential balance control is complicated. For space vector pulse width modulation (SVPWM), the digital implementation is difficult. This paper proposes a new SPWM strategy for 5L-ANPC converters based on the essential connection between SVPWM and SPWM. This strategy first equates SVPWM to SPWM, and then achieves free selection of switching sequence by injecting zero-sequence voltage. It can effectively suppress NP potential fluctuations, and achieve NP potential balance. According to the voltage offset of the floating capacitor, the equivalent PD-SPWM type is adjusted in real time to realize the control and balance of the voltage of the floating capacitor. This strategy is an optimized modulation algorithm with high degrees of freedom, high DC voltage utilization, and it is very easy to implement digitally.