Fitting Functions for Low Frequency Transformer Admittance Curves

RL networks are described that can accurately represent the low frequency part (up to 10 kHz) of measured admittance curves. Existing methods use only one circuit configuration and try to fit all admittance curves according to this circuit [1], [2]. Such methods may produce some negative RL parameters that can cause instability during time domain simulations. The approach described below uses different circuit configurations for different cases and makes it possible for all measured admittance curves to be fitted with positive circuit parameters, which guarantees the passivity of the RL networks.