Basics of Active Harmonic Filter:
Modern industries are defined by widespread use of non-linear loads such as DC drives, VFDs etc. which introduce large content of harmonics into the system and its subsequent effects. There arises the need for intelligent solutions for harmonic mitigation. Active harmonic filters have developed as the most ideal solution for harmonic filtering in both industrial and commercial facilities. Added advantage is that they also offer solutions for phase balancing and power factor improvement. This article briefs about its basic principle of operation, need for active compensation and sizing.
Principle of Operation
An active harmonic filter is based on the following principle:
I filter = I main - I load
It detects the difference between the ideal current sine wave (I main) and the actual current which has been deformed by harmonics (I filter). It, then, injects this difference (I load), which is the negative of the harmonic currents present in the load current, into the system on a real-time basis. This cancels out the high frequency harmonics and results in almost pure sine wave.