what is the Active Harmonic Filter

An Active Harmonic Filter (AHF) is an advanced power quality device used in electrical systems to eliminate or reduce harmonic distortion caused by non-linear loads, such as variable frequency drives (VFDs), UPS systems, or LED lighting. Unlike passive filters, which use fixed LC components (inductors and capacitors), AHFs are power electronics-based systems that dynamically inject counter-harmonic currents into the power system to cancel out unwanted harmonics.

Key Functions of an Active Harmonic Filter:

Harmonic compensation: Detects harmonic currents and injects equal but opposite harmonic currents to neutralize them.

Power factor correction: Can improve the displacement power factor by compensating for reactive power.

Load balancing: In three-phase systems, it can balance the currents across phases.

Voltage stabilization: Some AHFs also provide support for voltage sags or swells.

How It Works:

A current sensor measures the load current.

A digital controller analyzes the current to determine the harmonic content.

The AHF then generates and injects a compensating current (via power converters) to cancel out the harmonics at the point of connection.

Benefits:

Highly effective across a wide range of harmonic orders.

Adaptive and real-time response to changing load conditions.

Typically smaller and more flexible than passive filters.

Applications:

Industrial plants with heavy use of VFDs and robotics.

Commercial buildings with significant IT or electronic loads.

Renewable energy systems where inverters introduce harmonics.