Voltage Balancing Analysis of DC-Link Capacitors in Six-phase Three-Level T-Type Inverters.

The request for converters with high power density, efficiency, and reliability poses increasing design challenges. To meet this request, two technologies have established themselves in recent years: multi-phase and multilevel converters. Each of them allows the power level and reliability of the system to increase. One of the most traditional issues of multilevel converters is the voltage unbalance of the dc-link capacitors. This problem can be solved in a multi-phase multilevel converter through the numerous degrees of freedom typical of this technology. A technique capable of nullifying the voltage oscillations for six-phase three-level inverters is presented in this paper. The proposed solution can also reduce the number of commutations in the switching period while the voltage oscillations are suppressed. Finally, the developed solution is compared with the double three-phase counterpart with two isolated dc-bus neutral points to underline the advantages. Experimental tests have been carried out on a six-phase induction motor with two isolated three-phase star-connected stator windings to validate the proposed solution.