Modeling and analysis of multilevel inverters using unipolar and bipolar switching schemes

For higher power applications, multilevel inverter structures have the particular advantages of operation at high dc-bus voltages which is achieved using series connection of switching devices. Moreover, a reduction in output voltage harmonics is achieved by switching between multiple voltage levels. The two most common multilevel inverter topologies are the diode clamped inverter and the cascaded inverter. In the paper, we will discuss about the cascaded multilevel inverter. The cascaded multilevel inverter uses series strings of single phase full bridge inverter to construct multilevel phase legs. A particular advantage of this topology is that the modulation, control and protection requirement of each bridge are modular. Moreover, multilevel inverter topologies are able to generate better output quality, while operating at lower switching frequency. This implies lower switching dissipation and higher efficiency. In this paper, the conventional PWM inverter and the cascaded multilevel PWM inverter is modeled in MATLAB Simulink. The analysis of the conventional PWM inverter and the cascaded multilevel PWM inverter using unipolar and bipolar switching schemes is done and finally the results are compared.