Practical implementation of the coupled norton approach for nonlinear harmonic models

Because of an expected increasing use of harmonic producing devices, the harmonic content in electrical distribution networks attracts more and more attention. Primarily, harmonics are caused by modern loads, which are connected to the electrical grid by power electronic interfaces. In order to analyze the effects of a widespread use of such nonlinear appliances, suitable nonlinear models have to be developed. This paper focusses on the practical implementation of an advanced mathematical approach, which is described theoretically in literature as the coupled Norton model. In order to consider the voltage dependency of current distortions, this approach describes the nonlinearity in time domain as a linear set of equations in frequency domain. This theoretical idea is analyzed and verified by suitable measurements. The model parameters are evaluated and validated for different groups of nonlinear devices. Because of a significant dependency of the model parameters on the underlying measurement set, special requirements are outlined. Furthermore, in order to apply the resulting nonlinear models in harmonic studies, an iterative harmonic load flow is proposed.