In the use of Variable Frequency Drives or Adjustable Speed Drives, several types of emission may be generated on the power line. These might include low-order harmonics, or EMI/RFI noise. To provide a complete power line noise solution, frequencies from the 60Hz power line and above must be considered. This includes EMI/RFI noise in the 150kHz to 30MHz band which may interfere with TV’s, radios, computers, meters and controllers. EMI/RFI Noise ReductionVariable Frequency Drives (VFD’s) produce noise in the 150kHz to 30MHz band, primarily contained in the switching edges of the PWM controller. To reduce noise in that band, a…

Treating harmonics in VFD applications is important in order to ensure that power quality problems are averted but this need not come with a sacrifice in energy efficiency. Find out how. Harmonic currents generated by conventional 6-Pulse Variable Frequency Drives (VFD’s) have been known to cause distortion of the applied voltage leading to power quality issues. To eliminate this concern, low harmonic generating 18-Pulse VFD’s are often specified at a significant premium. Although 18-Pulse VFD’s are very effective in eliminating harmonic problems, they are often at least 2 - 3% points lower in efficiency than conventional 6-Pulse units. This is…

By Steffan Hansen, Ph.D., Danfoss Drives. In variable frequency drive applications, harmonic current distortion and voltage distortion are of interest but have different effects on the power system. It is therefore important to distinguish between them when discussing the effects of ”harmonics.” General information on “harmonics”The term ”harmonics” has often been used in connection with variable frequency drives. But what are harmonics, anyway? Basically, any periodic signal can be represented as a sum of sine-functions with frequencies equal to an integer multiple of the fundamental frequency.