A cascaded NPC/H-Bridge inverter with simplified control strategy and minimum component count

Abstract

Multilevel topologies have emerged as a viable technique for medium and high voltage inverters but in the low voltage range they have failed to attract much interest due to their increased cost associated with the additional components and complicated control. This paper proposes a new and simplified control strategy for a nine- cascaded Neutral-Point —Clamped (NPC)/H-Bridge PWM inverter. The new control strategy is achieved by decomposing the nine level output into four separate and independent three- level NPC PWM output. By combining the three- level NPC PWM back to back using DC sources and properly phase shifting the modulating wave and carrier a simplified control strategy is achieved with reduced number of components. The control strategy is applied on cascaded NPC/H-bridge inverter that combines features from NPC inverter and cascaded H-Bridge inverter. A theoretical harmonic analysis of the proposed control is carried out using double Fourier principle. Verification of the analytical results is done using MATLAB simulation.