Investigation of modified multilevel inverter topology for PV system

Abstract

Multilevel inverters become an alternative for high power and medium voltage applications in recent years. Multilevel inverters(MLI) are basically classified as Diode Clamped Multilevel inverter, Flying Capacitor Multilevel inverter, Cascaded H Bridge Multilevel Inverter (CHBMLI). The CHBMLI topology which consists of a series of H bridge unit with separate dc sources is mostly prefered to generate higher voltage levels, as it requires fewer components compared to the other topologies. As the level increases, the switching device requirement will be more and the circuit becomes large with this topology. To overcome this and to produce high quality output, reduced switch count topologies are the main focus in recent research.The reduced switch count structures are based on bidirectional switches, modified form of the structures, polarity and level generation based structure, reduced switch structures and hybrid topology structure. This paper proposes a three phase Modified Multilevel Inverter (MMLI) topology with reduced switch count for nine level and the topology is analyzed using different Pulse Width Modulation (PWM) technique. The proposed MLI structure consists of an H bridge unit with voltage conversion cell for each phase. It requires 24 switches for a 3Ф nine level inverter with eight switches per phase compared to 48 switches in CHBMLI. The Total Harmonic Distortion (THD) level of this topology is examined with the PWM techniques for symmetric and asymmetric DC voltage sources. THD results of the proposed MLI are compared with other reduced switch topology structure. The comparison result indicates that the proposed topology shows better harmonic level and reduced switches compared to that structure. A prototype of the proposed topology is built and is tested to validate with the simulation results. Simulation and experimental results show that the proposed topology produces a minimum harmonic level with fewer components.