Selective Harmonic Controlling for Three-Level High Power Active Front End Converter with Low Switching Frequency

Controlling of a specific harmonic by a switching converter with switching frequency lower than 1 kHz was originally implemented by two-level optimal pulse pattern with unsymmetrical switching angles, namely by OPUS-technique. That means, given a desired fundamental and one or more specific harmonics, the problem is to find the switching times (angles) that produce the fundamental while generating specifically all chosen harmonics. Based on the OPUS-technique a three-level optimal pulse pattern is proposed for high power level applications with low switching frequency. The transcendental mathematical equations are developed. Using the prior results of all complete solutions of selective harmonic elimination (SHE) the solutions of the new equations can be found by Newton iteration method. In particularly, the modulation performance of OPUS-technique for three-level optimal pulse pattern with unsymmetrical switching angles is demonstrated by the trajectory of the converter voltage space vector integral. Finally, the control range of a specific harmonic is given by OPUS-technique