Harmonic modelling of non-linear devices in electrical networks

by Lance P. Frater, Neville R. Watson and Alan R. Wood.

Harmonic distortion in electrical networks continues to rise due to the wide scale adoption of power electronic based non-linear loads. The modelling of harmonic producing loads is a difficult task with large, interconnected systems, containing thousands of distributed loads. This paper presents a comparison of three harmonic load models; a Harmonic Current Source, a Norton Equivalent and a Harmonic Cross Coupled Norton Equivalent. These models are derived experimentally by a sequential harmonic voltage injection technique. This results in a linear and computationally efficient model for simulation of large systems with dispersed harmonic sources.

The use of energy efficient Compact Fluorescent Lamps (CFLs) has increased in the last few years raising concern over their harmonic impact. As an example case, the models of five lamps, representing a range of typical CFLs available in New Zealand, are given. The models are validated in small system against experimental measurements. More importantly this shows the importance of the selection of an appropriate load model to achieve the desired accuracy.