Impact of Modern Electronic Equipment on the Assessment of Network Harmonic Impedance

Network harmonic impedance forms the link between harmonic currents emitted by individual devices and the harmonic voltage levels in the grid. It is essential for the definition of current emission limits in order to ensure electromagnetic compatibility between all equipment connected to the grid. Among all electrical equipment in future smart grid electronic devices, like PV inverters, EV chargers or lamps with electronic ballast, will have a dominating share. This is expected to have a considerable impact on the network harmonic impedance characteristic. This paper discusses the frequency-dependent input impedance of different types of modern electronic equipment and its potential impact on the network harmonic impedance. It is shown that the semiconductor switching results in a variation of the impedance within the fundamental cycle. This is not considered by the presently used assessment methods as they assume only passive network elements. Beside a method to measure these variations, several indices are introduced to quantify the level of its impact. This paper aims to provide some impulses for further discussions, particularly about the definition of network harmonic impedance in presence of electronic devices, the necessity to include these variations in realistic harmonic studies and if this has to be considered in the standardization.