Active Harmonic Filter (AHF)

Active Harmonic Filter (AHF)

Active harmonic filters (AHF) are the ultimate answer to power quality problems caused by waveform distortions, low power factor, voltage variations, voltage fluctuations and load unbalance for a wide range of segments and applications. They are a high performance, compact, flexible, modular and cost-effective type of active power filters (APF) that provide an instantaneous and effective response to power quality problems in low or high voltage electric power systems. They enable longer equipment lifetime, higher process reliability, improved power system capacity and stability, and reduced energy losses, complying with most demanding power quality standards and grid codes.

A2 Series

AHF Module Rate 400 V 50/60 Hz 100A

AHFs eliminate waveform distortions from the loads like harmonics, interharmonics and notching, and harmonic voltages caused by harmonic currents, by injecting in real-time the distorted current of same magnitude but opposite in phase in the electric power system. In addition, AHFs can take care of several other power quality problems by combining different functions in a single device:

• Elimination of harmonics and interharmonics.
• Power factor correction (lagging and leading).
• Reduction of voltage variations (sags & swells).
• Mitigation of voltage fluctuations (flicker).
• Load balancing in three-phase systems.
• Controlled and selectable harmonic generation.

Operating principle

An AHF is a power electronics-based device connected in parallel with the load that requires harmonics and interharmonics mitigation. The AHF works as a controlled current source providing any kind of current waveform in real time. AHFs monitor the currents of the load and compensate produced harmonic and interharmonic currents by generating a compensation current for each selected order in phase opposition. The result is a reduction on the levels of harmonics and interharmonics of the installation to the limit requested by the customer ensuring compliance with power quality standards & recommendations.


The main benefits of AHFs are:
• Protection of loads and equipment from waveform distortions, voltage variations and fluctuations, low power factor and unbalance.
• Optimized design for system integrators and OEMs for building together with VSDs low-cost ultra-low harmonic drives with low losses.
• Simple dimensioning and installation.


• Specifications from 50 A to 200 A (200-690 V) in 3- and 4-wire systems can be covered by a single module. Unlimited amount of AHF modules can be connected in parallel.
• Simple connection to high voltage systems.
• 3-level NPC inverter topology reduces losses, noise, size and extends module's lifetime.
• Overall response time <100 microseconds.
• Elimination of harmonic and interharmonic currents up to the 50th order (odd and even). <
• Instantaneous, precise & stepless power factor correction of inductive and capacitive loads. Capability of switching contactors or thyristor switches of detuned filter capacitor bank steps.
• Load balancing and unloading of neutral wires.
• Capability of switching contactors or thyristor switches of detuned filter capacitor bank steps.
• Compact and modular design optimized for installation, commissioning and maintenance.
• Remote monitoring & analysis capability ? lloT.

Typical segments

AHFs can be applied to small, medium or large appication in a wide range of segments.

Typical applications

AHFs have many low and high voltage potential applications where their use offers many benefits.
• Equipment using variable speed drives (VSD).
• Arcing devices: Electric arc furnaces (EAF), ladle furnaces (LF) and arc welders.
• Switch mode power supplies: Computers, TVs, photocopiers, printers, air cons, PLCs, etc.
• Battery chargers (incl. EV charging stations).
• Off-line, on-line & line-interactive UPS systems.
• Medical devices: MRI scanners, CT scanners, X-rays machines and linear accelerators.
• Lighting devices: LED, fluorescent, mercury vapor, sodium vapor & ultraviolet (UV) lamps.
• Solar inverters and wind turbine generators.
• Modulated phase controllers, cycloconverters and thyristor-controlled AC voltage regulators.
• Saturable/rotating devices: Induction heaters, transformers, generators, reactors and motors.
• Energy efficiency and savings: Lower energy losses and a higher efficiency of the system.
• Reduced production or installation downtime.
• Increased lifetime of electrical equipment.
• Better use of transformers and generators.
• Can take care of individual disturbance patterns and automatically adapt to changing load conditions and network topologies.
• Compliance with the strictest power quality standards and grid codes including G5/4, IEEE 519, IEC 61000 3-2/3-4 and EN 50160.

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