Effect of minor harmonics on the performance of resonant harmonic filters in distribution systems

In spite of developing new methods for reducing waveform distortion in distribution systems, resonant harmonic filters (RHFs) remain the main devices for harmonic suppression. With an increase in the number of harmonic generating loads, RHFs often work at the voltage distorted by distant loads inside the supply system. Such filters are used, moreover, for harmonic suppression of not only single loads but also distributed nonlinear loads with a dense harmonic spectrum. Because of this, the load current may contain harmonics other than only those to which the filter is tuned. The voltage harmonics, as well as the current harmonics other than those to which the filter is tuned, are referred to as ‘minor harmonics’ in the paper. These harmonics are often magnified by RHFs. It causes a reduction of the filter effectiveness or even an increase in the waveform distortion. Factors that shape properties and performance of RHFs in distribution systems with minor harmonics are discussed.