Novel discontinuous PWM for dc-link voltage balancing of multilevel quasi-nested topologies

The use of multilevel power converters for its application in high demanding industrial processes and grid connected renewable energy conversion systems has nowadays become the most suitable solution. The main advantages of these converter configurations are: reduction in the blocking voltage stress, lower harmonic ratings, smaller filters for output and input stages. The proposed quasi-nested topology merges the advantages of the classical multilevel topologies, such as the NPC and ANPC configurations, addressing less active switching devices, lower blocking voltage stress. A novel discontinuous modulation technique, with controlled discontinuous gain, is implemented in order to deal with the dc-link voltage unbalance. Simulation and experimental validation results in a scaled-down power 1,5 kW three-phase converter prototype under different operational conditions using different modulation index are presented. The proposed four-level converter topology allows generating an additional output voltage level with the same semiconductor count as conventional three-level inverters such as NPC and ANPC with superior waveform quality, with a THDv reduction of 34.54% in comparison to the clamped inverters. Experimental tests carried out in a 1.5 kW setup verify the feasibility of the proposed topology and the developed discontinuous modulation scheme, to achieve dc-link voltage compensation.