Modelling approach for multi-carrier-based pulse-width modulation techniques utilised in asymmetrical cascaded H-bridge inverters

The increasing use of medium-voltage drives and high-power equipment requires a detailed study on the switching method and topology of multi-level inverters. Asymmetric cascaded H-bridge topologies that have unequal input dc voltages with different devices in various parts of the cascaded H-bridge inverter (CHB) are representative of significant improvements in medium-voltage industrial drives. Various modulation strategies are used in multi-level power conversion applications. In the multi-carrier switching method for asymmetric CHB, the number of switches is less than carriers and is usually used in the off-line switching method. These methods of switching are not applicable to online systems. In this study, equations for combining different pulse-width modulation (PWM) to use the controllability advantage of the multi-carrier method are introduced in asymmetric topologies. Then, the dual Fourier series equations are applied to model each inverter switching relation of the asymmetric cascaded blocks. To model each inverter switching relation of the asymmetric blocks using sinusoidal PWM, the dual Fourier series equations were applied. The presented analytical modelling switching method was validated using simulation and experimental case studies.