A Novel Approach to Solving the OHESW Problem for Multilevel Inverters

Abstract

A new method is presented to compute the switching angles in a multilevel inverter using the Optimized Harmonic Elimination Stepped-Waveform (OHESW) technique so as to produce the required fundamental voltage while at the same time not generate higher order harmonics. Previous work has shown that the transcendental equations characterizing the harmonic content of the inverter output can be converted to polynomial equations which are then solved using the method of Resultants from Elimination theory. However, when there are several DC sources, the degree of the polynomials are quite large making the computational burden of their resultant polynomials via elimination theory quite high. The proposed method with fast recursive algorithm is derived that provide the exact on-line solution to the OHESW problem.The proposed algorithm optimization technique is applied to a multilevel inverter to determine optimum switching angles for eliminating low order harmonics while maintaining the required fundamental voltage to drive an induction motor. The proposed method contributes to the existing methods because it not only generates the desired fundamental voltage, but also completely eliminates any number of harmonics. The complete solutions for (5-15) level OHESW switching patterns to eliminate the (3rd-13th) harmonics are given.