Active Harmonic Filter (AHF)

  • An AHF is connected in parallel (shunt) to the electrical system — typically at the point of common coupling (PCC).
  • It continuously monitors the load current waveform, detects harmonic components (i.e. frequencies that are integer multiples of the fundamental), and injects compensating currents that are equal in magnitude but 180° out of phase with the harmonic currents — effectively canceling the harmonics and restoring near-sinusoidal currents.
  • As a result: harmonic distortion (THDi) is reduced, power factor can improve (since distortion PF is corrected in addition to displacement PF), and three-phase current balance / neutral current compensation is often possible (especially in 4-wire systems). 
  • AHF are dynamic, fast-responding, and more flexible than traditional passive filters — making them particularly suitable for modern industrial/commercial facilities with varying loads.

Key benefits of AHF

  • Significant reduction of harmonics: mitigates a wide range of harmonic orders (often up to 50th) depending on design.
  • Improved power quality: cleaner current waveform → less overheating, less stress on transformers/cables, lower losses, fewer nuisance trips, improved reliability/lifespan for equipment.
  • Power factor correction and load balancing (in addition to harmonic mitigation) in many AHF designs.
  • Flexible and adaptive: suitable for dynamic, non-linear, and varying load conditions common in industrial/commercial plants — unlike passive filters which are fixed-frequency tuned and may cause resonance or over-compensation.