Novel analytical approximation method of frequency dependent Thevenin impedance

The Thevenin equivalent representation is widely used in the harmonic distortion studies. For network representation it is necessary to use the driving point impedance in function of the frequency, which can be determined by computer simulation or site measurement. The authors are working on the modeling of penetration and elimination of harmonic disturbance originating from the high power railways. In order to improve the accuracy of calculations the double domain simulation method was introduced, which is a combination of frequency and time dependent modeling. The presented novel approximation of the frequency dependent network impedance results in a further improvement regarding the accuracy of the frequency domain simulation. In this paper the improved accuracy achieved using the proposed analytical approximation method is discussed on the example of a railway substation.