Dual modulation strategy for capacitor size reduction and voltage balancing in five-level inverter

Switched-capacitor-based level-doubling networks are widely employed in cascaded multilevel inverters to increase the number of output voltage levels using only two additional switches. However, the switched capacitors undergo charging and discharging during every half cycle of the fundamental output voltage, resulting in large capacitance requirements and increased capacitor voltage ripple. This work aims to reduce the capacitance requirement while preserving the level-doubling capability and output voltage quality. To achieve this, a full-bridge-based level-doubling network is employed instead of the conventional half-bridge configuration, enabling additional switching states for flexible capacitor control. A dual modulation strategy is further proposed to regulate the capacitor charging and discharging actions within every carrier cycle, thereby reducing the charge associated during the discharge interval. The proposed approach is validated through detailed simulation and experimental studies under varying modulation indices and load conditions. The results demonstrate that the proposed technique achieves a capacitance reduction by a factor of fcarrierfoutput, while maintaining capacitor voltage ripple and output voltage THD comparable to the conventional level-doubling network.