Drawbacks of linearization in harmonic analysis and modeling

Power systems invariably have nonlinear loads, which inject harmonics into the system and give rise to nonsinusoidal voltages and currents. Power quality issues are a prime concern of the power industries as well as of customers. Hence under these circumstances, it becomes imperative to study these nonlinear loads, their characteristics and their effects. Qualitative analysis will not help much in the effort to solve this problem and the adverse effect that these nonlinear loads have, needs to be quantified. Harmonic analysis methods can be broadly classified into frequency domain and time domain methods. This paper makes an effort to bring out the differences between these two types of methods by means of results of the simulations carried out. Results are obtained from both types of simulations, which provide an insight into the inaccuracy and inadequacy of the frequency domain method of harmonic analysis. A comparison between linear and nonlinear models for the arc furnace is also presented. Linearized models for nonlinear loads, just as the frequency domain method of analysis give pessimistic results in comparison to more accurate, nonlinear models.