Guide to Harmonics 
with AC Variable Frequency Drives

Contents

• Introduction
• Basics of the harmonics phenomena
• Harmonic distortion sources and effects
• Harmonic distortion calculation by using DriveSize software
  • Circuit diagram for the calculation example
  • Input data for motor load
  • Motor selection
  • Inverter selection
  • Inverter supply unit data
  • Network and Transformer data input
  • Calculated harmonic current and voltage
  • Calculated harmonic currents in graphical form
  • Part of the printed report
• Standards for harmonic limits
  • EN61800-3 (IEC1800-3) Adjustable speed electrical power drive systems
  • IEC1000-2-2, Electromagnetic compatibility (EMC)
  • IEC1000-2-4, Electromagnetic compatibility (EMC)
  • IEC1000-3-2, Electromagnetic compatibility (EMC)
  • IEC1000-3-4, Electromagnetic compatibility (EMC)
  • IEEE519, IEEE Recommended practices and requirements for harmonic control in electrical power systems
• Evaluating harmonics 
• How to reduce harmonics by structural modifications in the AC drive system
  • Factors in the AC drive having an effect on harmonics
  • Table: List of the different factors and their effects
  • Using 6-pulse diode rectifier
  • Using 12-pulse or 24-pulse diode rectifier
  • Using phase controlled thyristor rectifier
  • Using IGBT bridge
  • Using larger DC or AC inductor
• Other methods for harmonics reduction
  • Tuned single arm passive filter
  • Tuned multiple arm passive filter
  • External active filter
• Summary of harmonics attenuation
  • 6-pulse rectifier without inductor
  • 6-pulse rectifier with inductor
  • 12-pulse rectifier with polycon transformer
  • 12-pulse with double wound transformer
  • 24-pulse rectifier
  • Active IGBT rectifier
• Definitions

Summary of harmonics attenuation

There are many options to attenuate harmonics either inside the drive system or externally. They all have advantages and disadvantages and all of them show cost implications. The best solution will depend on the total loading, the supply to the site and the standing distortion. In the following tables different internal actions are compared to the basic system without inductor. The harmonic content is given with 100% load. The costs are valid for small drives. For multidrive the 12-pulse solution is quite a lot cheaper. 

6-pulse rectifier without inductor 

Manufacturing cost 100% Typical harmonic current components. 

Fundamental 5th 7th 11th 13th 17th 19th 100% 63% 54% 10% 6,1% 6,7% 4,8%

6-pulse rectifier with inductor 

Manufacturing cost 120%. AC or DC choke added Typical harmonic current components. 

Fundamental 5th 7th 11th 13th 17th 19th 100% 30% 12% 8,9% 5,6% 4,4% 4,1%

12-pulse rectifier with polycon transformer 

Manufacturing cost 200% Typical harmonic current components. 

Fundamental 5th 7th 11th 13th 17th 19th 100% 11% 5,8% 6,2% 4,7% 1,7% 1,4%

12-pulse with double wound transformer 

Manufacturing cost 210% Typical harmonic current components. 

Fundamental 5th 7th 11th 13th 17th 19th 100% 3,6% 2,6% 7,5% 5,2% 1,2% 1,3%

24-pulse rectifier with 2 3-winding transformers 

Manufacturing cost 250% Typical harmonic current components. 

Fundamental 5th 7th 11th 13th 17th 19th 100% 4,0% 2,7% 1,0% 0,7% 1,4% 1,4%

Active IGBT rectifier

Manufacturing cost 250%. Not significant if electrical braking is anyway needed. 
Typical harmonic current components.

Fundamental 5th 7th 11th 13th 17th 19th 100% 2,6% 3,4% 3,0% 0,1% 2,1% 2,2%