A new modulation technique for 15-level asymmetric inverter operating with minimum THD

Multilevel inverters are the alternative for medium voltage applications. Within the inverters types there are symmetric and asymmetric topologies. The asymmetric inverters have different DC voltage values. The most common topology is when the different cells are implemented in cascade arrangement, where the DC voltage are in multiples of 3, obtaining an AC voltage with 3ⁿ = 27 levels (n = 3 cascaded inverters). This topology provides a load voltage with low harmonic content, THD <; 3%. However, this high quality voltage has a non-negligible drawback, which is the presence of regeneration in some of the inverters, independent of load type. This phenomenon is due to the modulation technique (Nearest Level Modulation) used by this inverter. In this work, the asymmetric 15 level inverter is presented. This inverter is designed to avoid the regeneration problem - power flow from the load to the inverter - in some of the power cells. This is achieved by obtaining the firing angles associated with the power cells considering a minimum load voltage THD. Finally, a power flow analysis is accomplished and simulated results show the feasibility of this approach.