Real-Time Lagrange-Polynomials Selective Harmonic Elimination for Unbalanced Five-Level Inverters

The effects of DC source voltage unbalance on the CHB inverter, if not properly managed, reduce the efficiency of the whole power system and generate unwanted harmonics in the output voltage with increased THD. In this paper, an SHE technique operating at the fundamental frequency has been proposed for unbalanced five-level CHB inverters to fix the amplitude of the fundamental harmonic, set the amplitude of the lower order harmonics to zero and achieve high efficiency performance. A preliminary off-line graphical approach was used to determine the switching angles at some modulation index values. Subsequently, a real-time interpolating Lagrange polynomial-based approach is proposed to obtain a continuous modulation index range. The study has been preliminarily analyzed in a simulation environment and subsequently validated experimentally.