Sensitivity of parallel harmonic filters to parameters variations

• The resonance frequency of harmonic filters changes with age and temperature.
• The typical 95% expanded uncertainty of a resonant filter ranges from 1.5% to 3%.
• The anti-resonance frequency is affected by the short circuit current of the system.

Parallel filters for industrial and large commercial plants are often not as effective as expected. Several factors contribute in modifying their filtering characteristics, so reducing the filter effectiveness. The paper defines these factors, indicates their expected range of variation, and shows how to calculate their effects on the impedance profile of a filter. The maximum range of variation of resonance and anti-resonance frequencies is calculated and their loci are sketched. The sensitivity of the filter characteristic to each parameter is calculated and discussed.