Multi-level inverters - A comparative study

Multi-level Pulse Width Modulated (PWM) inverters are gaining importance due to the fact that the lower order harmonics in the output waveform can be eliminated without any increase in the higher order harmonics, unlike the regular two level PWM inverters. Their unique structure also allows the output to reach a high voltage level from low level of DC voltage without the use of transformers or series connected switching devices. In this paper a comparative study of the multi-level PWM inverters has been taken up. The study has been carried out for three different topologies of the multi-level inverter: diode-clamped type, flying capacitor type and cascaded inverter type. Both the single phase and 3-phase configurations have been considered for 3 as well as 5 levels. Two different modulation techniques namely, DC modulation technique and sinusoidal PWM technique, as applied to multi-level inverters have been analyzed. All these circuit configurations have been modeled in the simulation software PSIM and the results of the analysis have been presented. Ultimately, conclusions have been drawn in terms of the superiority of one configuration over the other and the suitability of each of the configurations for certain applications.