Problems in the use of Norton equivalent models for single-phase nonlinear loads

This paper illustrates the problems associated with using Norton equivalent models to represent single-phase nonlinear loads. The study is conducted with a specially-developed harmonics testing station that uses feedback to drive the load voltage to a desired target waveform. We apply various voltage waveshapes with 5% THDv to several types of single-phase nonlinear loads which allow us to compute the Norton parameters. The test results show that the Norton equivalent model for a nonlinear load is not unique and varies significantly with applied voltage waveshape.