September 2020

IEEE Industry Applications Magazine Sep. 2020

Despite their high costs, active harmonic mitigation solutions such as parallel active power filters (APFs) and active front end (AFE) drives are growing in popu­larity. As the newest technology, they are being touted as a better choice than the various forms of passive harmonic mitigation solutions that are presently avail­able. Is this actually the case? Active solutions incorporate switching strategies using insulated­ gate bipolar tran­sistors (IGBTs) to make the current drawn by the adjustable­ speed drive (ASD), or anoth­er nonlinear load, more sinusoidal. You will rarely hear from manufacturers that this switching introduces higher­ frequency harmonics, normally above the 50th.

When considering a harmonic mitigation solution, the choice between using passive or active harmonic filters is often encountered. While the best choice will depend on the application, this comparison document describes some of the pros and cons to each, and intends to highlight some of the most important considerations.

Topics:

• What are Supraharmonics?
• What Devices Introduce Supraharmonics?
• What can Happen when Supraharmonics are High?
• Power System Resonance and High Frequency Harmonics
• Do Harmonic Standards such as IEEE Std 519-2014 and IEC standards address them?
• Are Supraharmonics a Concern with Passive Rectifiers?
• Summary and Conclusions

Manufacturers of AFE Drives claim benefits such as, reduced line current harmonics, improved power factor and inherent regenerative capabilities when they’re compared with standard 6-Pulse VFDs equipped with diode bridge rectifiers.  But rarely discussed is the overall system efficiency, and the fact that current harmonics are much higher when measured above the 50th and that serious problems can result from the introduction of these higher frequency Supraharmonics.