English

Harmonic Solution for VFD system

Harmonic pollution in variable frequency drive (VFD) systems causes severe hazards to equipment, grids, and production safety. Optimizing power quality and lowering comprehensive costs requires implementing three mainstream mitigation solutions: line reactors, passive filters, and active power filters
Solution Overview Harmonic Hazards Real-World Pain Points Solutions Solution Comparison Suggestions

An Executive Guide to Power System Harmonic Mitigation

With the widespread application of power electronics technology, the proportion of non-linear loads in the power grid is increasing day by day. This has led to harmonic pollution becoming a key issue affecting power quality, equipment safety, and stable system operation.

The purpose of harmonic mitigation is to eliminate or suppress harmonic currents and voltages generated by non-linear loads in the power system, ensuring that the power supply complies with national standards and extends equipment lifespan. The following provides a detailed explanation from four aspects: harmonic hazards, mainstream harmonic mitigation solutions, a comparison of different solutions, and implementation recommendations.

Product or Solution Inquiry
The Multiple Aspects of Harmonic Hazards
The core of a variable frequency drive (VFD) system is AC-DC-AC power conversion. The non-linear characteristics of the rectification and inversion stages generate characteristic harmonics, primarily the 5th, 7th, 11th, and 13th orders. These harmonics act like 'invisible viruses' in the power system, causing damage on three levels: equipment, power grid, and safety.
  • Sharp reduction in equipment lifespan
    Harmonic currents can increase copper and iron losses in transformers by 30%–50%, leading to localized overheating of the core, accelerated insulation aging, and a 20%–30% reduction in service life. Motors affected by harmonics experience additional vibration and audible noise, and the stator insulation is more prone to breakdown from high-frequency currents. In one factory, harmonics caused three motors to fail one after another within just six months, resulting in repair costs exceeding ten thousands of usd.
  • Sharp increase in grid losses
    The "skin effect" caused by harmonics can increase the equivalent resistance of lines by up to 40%, and in areas with severe harmonic pollution, grid losses can be 15%–20% higher than normal levels. At the same time, harmonics can lead to a reduced power factor. When the power factor falls below 0.85, a company's monthly electricity bill will increase by 6.5%; if the power factor drops below 0.65, an additional 2% surcharge will be applied for every 0.01 decrease below that threshold.
  • Safety and production risks
    Third-order harmonics can cause the neutral line current to exceed the phase line current by up to three times. In one office building, harmonics from fluorescent lights caused the neutral line temperature to rise to 120°C, leading to a fire. Harmonics can also interfere with control systems such as PLCs and sensors. On an automotive production line, harmonics caused a robot positioning deviation of up to 2 mm, resulting in an emergency shutdown of the production line and losses around two hundred thousand usd.
Real-World Pain Points
Feedback from industrial sites reveals that harmonic issues faced by users exhibit three major characteristics: concealment, suddenness, and conductivity.
  • 1

    Difficulty in fault tracing

    Harmonic interference often manifests as non-obvious faults such as random equipment shutdowns and distorted instrument readings, which are easily misdiagnosed as equipment quality issues in the early stages. In one chemical plant, abnormal readings from a level gauge caused by harmonic interference led to repeated instrument replacements before the root cause was finally identified.
  • 2

    High mitigation costs

    Blindly adding filtering equipment may result in insufficient mitigation effectiveness due to improper selection. One chemical enterprise initially selected a general-purpose active harmonic filter, achieving a mitigation rate of only 68%; only after re-selection did the rate improve to 95%.
  • 3

    Poor system compatibility

    Some mitigation solutions may resonate with existing reactive power compensation devices, in turn amplifying harmonic hazards. In one logistics center, resonance caused by mixed loads sharing a transformer led to the burnout of capacitor banks.
Active Power Filter (APF) Line reactor Passive Harmonic Filter (LC Filter)

Active Power Filter (APF)

Working Principle

The harmonic current on the load side is collected in real time via a current transformer (CT). The controller then calculates and generates a compensation current that is opposite in phase and equal in amplitude to the harmonics, injecting it into the power grid to cancel out the harmonics. It enables dynamic compensation for harmonics of any order within the 0–2 kHz range, reducing THDi to below 5%.

Comparison of Pros and Cons

Pros Cons
full harmonic mitigation, capable of filtering out harmonics of various orders simultaneously, adapting to complex and variable load scenarios higher cost
fast response time, with compensation completed in less than 100 μs, enabling tracking of dynamically changing harmonics relies on power electronic components, resulting in a higher failure rate compared to passive filters
with reactive power compensation function and three-phase balancing functions, improving overall power quality Installation and commissioning are complex, requiring professionals to set parameters based on on-site harmonic data

Applications

Suitable for high-precision, high-reliability applications such as hospital MRI equipment, single-crystal furnaces in electronics manufacturing plants, data centers, or automated production lines with dense VFD installations.

Optional Product Series

The corresponding product series from Sikes: APF Active Power Filter

.subsolution-0 h4

Line reactor

Working Principle

The line reactor is connected in series on the input side of the variable frequency drive (VFD). By increasing the impedance on the power supply side, it suppresses the harmonic current generated by the rectifier circuit and also mitigates the impact of sudden grid voltage changes on the VFD. Typically, a reactor with an impedance factor of 3%–5% , which can reduce the Total Harmonic Distortion of the input current (THDi) from approximately 35% to around 20%.

Comparison of Pros and Cons

Pros Cons
simple structure, cost efficient only suppresses low-order harmonics such as the 5th and 7th; limited effectiveness in mitigating high-frequency harmonics
easy installation, no additional commissioning required, can be directly connected in series with the input circuit unable completely eliminate harmonics, only reducing THDi to 10%–20%, making it difficult to meet the requirements of high-precision applications
providing reactive power compensation, improving the input-side power factor to above 0.9 Introduces a certain voltage drop, with voltage loss of approximately 3%–5% at full load—grid margin must be taken into account.

Applications

Suitable for small or middle load scenarios with light harmonic pollution, such as general-purpose VFD systems for fans, pumps, etc., or as a pre-treatment stage in complex scenarios.

Optional Product Series

The corresponding product series from Sikes: ACL Input Filter

.subsolution-1 h4

Passive Harmonic Filter (LC Filter)

Working Principle

A tuning circuit composed of reactors and capacitors provides a low-impedance path for specific harmonic orders, directing harmonic currents into the filter branch A tuning circuit composed of reactors and capacitors provides a low-impedance path for specific harmonic orders, directing harmonic currents into the filter branch rather than into the power grid. A common configuration is the 5th and 7th double-tuned filter, which can filter out the corresponding harmonic orders respectively.rather than into the power grid. A common configuration is the 5th and 7th double-tuned filter, which can filter out the corresponding harmonic orders respectively.

Comparison of Pros and Cons

Pros Cons
highly targeted, with mitigation efficiency exceeding 90% for specific harmonic orders only filters out preset harmonic orders, with poor mitigation performance for non-characteristic harmonics
stable operation, no active components, low failure rate, service life of over 10 years prone to resonance with the power grid, requiring precise calculation of grid impedance and filter parameters
moderate cost, low maintenance requirements—only regular dust removal and capacitance value testing are needed relatively large in size, occupying a certain amount of distribution space.

Applications

Suitable for industrial scenarios with stable harmonic characteristics, such as high-power VFD systems in metallurgy, cement, and other industries. Can be used in combination with input reactors to further improve mitigation performance.

Optional Product Series

The corresponding product series from Sikes: OSK 5% Harmonic Filter, OSK 10% Harmonic Filter, PHF 5% Harmonic Filter, PHF 10% Harmonic Filter, PIHF Harmonic Filter, HFI Harmonic Filter

.subsolution-2 h4
Solution Selection Comparison
Compare the differences between each solution in a table
Solution Line Reactor Passive Harmonic Filter Active Harmonic Filter
Mitigation efficiency ★★☆☆☆ ★★★★☆ ★★★★★
Cost effectiveness ★★★★★ ★★★☆☆ ★☆☆☆☆
Application scenarios small or middle general load high-power fixed harmonic load high-precision dynamic load
Installation ★★★★★ ★★★☆☆ ★★☆☆☆
Maintenance ★★★★★ ★★★☆☆ ★★☆☆☆
SIKES Series ACL OSK, PIHF, PHF, HFI APF
Suggestions
Monitor first, adopt cost-effective hybrid filters with Sikes Electric, and maintain systems for long-term power stability.
  • Monitor before mitigating
    Use a power quality analyzer to conduct continuous monitoring for at least 7 days, focusing on the 95% probability value. Identify harmonic orders, content, and variation patterns to avoid wrong selection.
  • Hybrid solution optimization
    For centralized VFD cluster scenarios, a hybrid solution combining "active filters + passive filters" can be adopted. Use active filters in centralized areas to handle dynamic harmonics and passive filters at distributed endpoints to filter out fixed harmonics. This approach can reduce comprehensive mitigation costs by 22%.
  • Contact Sikes Electric
    Our engineers will provide you with professional and reasonable solutions tailored to your operating conditions and requirements.
  • Long-term monitoring and maintenance
    Establish a power quality monitoring system. Regularly inspect the status of filtering equipment—such as the capacitance of passive filters and the IGBT module temperature of active filters—to ensure long-term stability of the mitigation performance.
Harmonic Filters for VFDSine Wave Filters for VFDAC Line ReactorHarmonic Filters matched with ABB Low Voltage DriveDC Resistive load bank
English
Copyright © 2026, Shenzhen Sikes Electric Co., Ltd, All Rights Reserved. All Tags Cookie Notice Privacy Policy Terms of Use