A new three-phase AC-DC-AC multilevel onverter based on cascaded three-leg converters

Static power converters are used for many applications, such as either uninterrupted power supply (UPS) or unified power quality conditioner (UPQC) without isolation transformer. Multilevel converter technologies have been widely recognized as a viable solution to overcome current and voltage limits of low power switching converters in high-power medium-voltage applications. This paper proposes and investigates a new three-phase AC-DC-AC multilevel converter obtained from cascaded three-leg converters. The operating principles, the pulse-width modulation (PWM) techniques and the overall control strategy are presented. The operation with different DC-link voltage values and balancing method are discussed and supported by simulation and experimental results. Simulation results are used to compare the proposed configuration with the conventional solution in terms of harmonic distortion and semiconductor losses. Experimental results demonstrate the feasibility of the studied converter and were obtained by using insulated gate bipolar transistors (IGBTs) with dedicated drives and a digital signal processor (DSP) with appropriated plug-in boards and sensors.