Partitioned fitting and DC correction in transmission line/cable models for wideband EMT studies

• Published in: Electric power systems research 2020-12, Vol.189, p.106809, Article 106809
• Main Authors: Cervantes, Miguel, Kocar, Ilhan, Mahseredjian, Jean, Ramirez, Abner
• Format: Article
• Language: English
• Subjects: Cables; Electric currents; Electric power lines; Frequencies; Interpolation; Mathematical models; Numerical analysis; Numerical stability; Studies; Transmission lines
• ISSN: 0378-7796; 1873-2046
• DOI: 10.1016/j.epsr.2020.106809

•The transient analysis of DC transmission lines has become of special interest in HVDC systems.•The DC response in the ULM can be captured by specifying a very low frequency for fitting line functions.•Partitioning the frequency band improves fitting precision in transmission line modeling.•Adapting more accurate integration/interpolation techniques helps maintaining numerical stability.•FDM/DC approach complements the prevailing ULM by reducing numerical instabilities due to large residue/pole ratios while delivering accurate DC response. This paper extends the applications of and provides further insights about partitioned fitting procedure. At the first stage of this procedure, the fitting is performed at a high frequency band by excluding frequency samples close to DC. The second stage finds a correction term for those excluded samples. This procedure achieves improved accuracy for the demonstrated case of transmission lines and cables used for HVDC transmission. The new approach complements the prevailing Universal Line Model (ULM) by reducing numerical instabilities due to large residue/pole ratios while delivering accurate DC response. This paper provides also time-domain implementation details of the state space realization obtained with partitioned fitting. The numerical stability performance of the improved fitting approach is demonstrated, through a set of test cases by applying different integration and interpolation schemes.