Harmonic mitigation for Variable Frequency Drives (VFDs)

Variable Frequency Drives improve motor control and energy efficiency, but they are also a common source of harmonic distortion. Merus® A2 Active Harmonic Filters provide dynamic VFD harmonic mitigation to improve power quality, protect electrical equipment, and support reliable operation.

Explore Merus® A2 Active Harmonic Filter

Why do Variable Frequency Drives cause harmonics?

Variable Frequency Drives are widely used to control the speed and torque of AC motors in pumps, fans, compressors, conveyors, and other industrial and commercial applications.

While VFDs can significantly improve process control and energy efficiency, they are non-linear loads. Standard six-pulse VFDs draw current in pulses rather than as a smooth sinusoidal waveform, creating harmonic currents that flow through the electrical network.

As the number and capacity of VFDs increase, harmonic distortion can become a significant power quality challenge. Without proper harmonic mitigation, distortion can affect transformers, cables, motors, switchgear, and other equipment connected to the same electrical system.

What is an Active Harmonic Filter?

Did you know? Harmonics are not the only power quality challenge associated with VFDs. Under certain network conditions, VFD-generated harmonics can interact with the electrical system and trigger harmonic resonance, amplifying the distortion.

This means even moderate harmonic currents can lead to unexpectedly high voltage distortion. And because resonance conditions can change as VFDs start, stop, or change load, the problem may only appear under certain operating conditions.

More about harmonic resonance

Common power quality challenges with VFDs

Harmonic distortion from VFDs can affect both electrical performance and the reliability of the processes they control.

Equipment overheating: Harmonic currents increase electrical losses in transformers, cables, motors, and other components.
Reduced system capacity: Additional harmonic current uses electrical capacity that could otherwise support productive loads.
Nuisance tripping: Distortion can contribute to unexpected protection trips and interruptions.
Shorter equipment lifetime: Increased electrical and thermal stress can accelerate component ageing.
Higher electrical losses: Harmonic currents generate additional heat and reduce overall system efficiency.
Power quality compliance: Harmonic levels can make it more difficult to meet applicable standards and grid requirements.
Harmonic resonance: Network conditions can amplify specific harmonic frequencies and lead to excessive voltage distortion.

Quick summary

⚡ Challenge

VFDs generate harmonic currents that can increase losses, reduce system capacity, affect equipment, and create power quality compliance challenges.

🛡️ Solution

Merus^® A2 Active Harmonic Filters dynamically compensate VFD harmonics and can provide centralized harmonic mitigation for multiple drives and other non-linear loads.

📈 Key benefits

Reduce harmonic distortion
Improve system reliability
Support power quality compliance
Reduce electrical losses
Protect electrical equipment
Maintain capacity for productive loads

🏭 Applications

Pumps and fans
Compressors and chillers
Conveyors
Process machinery
HVAC systems
Water treatment

🗣️ Let’s talk!

We identify harmonic distortion and other power quality issues, determine their root causes, and use the measurement data to recommend and dimension the right compensation solution for your system.