Partitioned Fitting and DC Correction for the Simulation of Electromagnetic Transients in Transmission Lines/Cables

This letter proposes a two-stage fitting procedure for transmission line/cable functions in which low-frequency samples are exclusively considered. At the first stage, fitting is performed for a reduced band by excluding frequencies close to DC. Reducing the fitting range improves the numerical conditioning of the overall system of equations and relieves fitting. The second stage consists of finding a correction term for the out-of-band samples close to DC. The procedure, when used with the recently introduced frequency-dependent cable model approach, allows modeling transmission lines and cables with improved fitting precision at low frequencies. Overall, the new approach is called frequency-dependent model (FDM) with DC correction, i.e., FDM/DC. It can be used to complement the prevailing universal line model in two ways: for reducing the integration errors due to unbalanced fitting and for improving the precision of DC response. Two examples are provided to demonstrate the utility of the new approach.