A software tool for selective harmonic elimination in multilevel inverters using Mathematica and Visual C++

This paper suggests a programming tool to calculate the switching angle required for eliminating the selected harmonics in a multilevel inverter (MLI). A systematic analysis and algorithm based off-line precalculation of switching angle for a range of modulation index using resultant theory is presented. The polynomial reduction is supported by Mathematica 6 and the accurate computation of switching instants is done by developing a tool in Visual C++ with an user friendly interface. The software tool objective is of twofold. The first one is to reduce the lower order dominant harmonics and second one is to minimize the total harmonic distortion (THD). The program developed is first of its kind, and can be successfully applied to n-level MLI. The efficient algorithm calculates all the possible triplent roots in a single step for a given input. Representative discussion and results are presented for a seven level cascaded inverter to eliminate the third, fifth and seventh harmonics. The triumph of the algorithm is validated by using Matlab/Simulink toolbox.