A new approach to enhance the accuracy of selective
harmonics-elimination technique for digital controllers

Hany A. Hamed – Fatima N. Al Mansoori – Ehab Bayoumi

   The selective harmonic elimination (SHE) is a preferable modulation technique in medium and high power converters applications as it enables for using low switching frequency with high flexibility to eliminate specific harmonics. The digital implementation of the SHE is a challenging issue as it requires a very accurate generation of the switching pulses. The theoretical calculation of the switching angles cannot guarantee the same results when digitally implemented by digital controllers. The digitizing process with a relatively low sampling frequency due to the digital implementation introduces error for each applied switching angle. Consequently, the applied switching angles will not match the theoretical ones resulted in residual errors for the selected harmonics that should be eliminated. This paper presents a new approach to improve SHE accuracy by online prediction and implementing of the closest true angles to minimize the residual harmonics. As a result, the accuracy of the digitized switching angles is improved while keeping the same digital controller sampling frequency. The proposed technique is validated through simulation and experimentally using a single-phase three level neutral point clamped inverter (3L-NPC).

Keywords: selective harmonic elimination, digital controllers, three-level neutral-point clamped converters

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