FDTD法に基づく瞬時値解析用周波数依存線路モデルの検討

Abstract

Electromagnetic transient (EMT) simulations of power systems require accurate representation of models in a wide range of frequencies. This of course applies to the representation of transmission lines, and the phase-domain frequency-dependent line model is often used to this end. The phase-domain line model does not require modal transformation in EMT simulations but requires modal decomposition at its model identification stage, and there are cases where it fails to fix switchovers of propagation modes with respect to frequency. Thus, a frequency-dependent line model which essentially avoids modal decomposition is desired. This paper studies the possibility of a frequency-dependent line model based on the FDTD (Finite Difference Time Domain) method as a candidate which satisfies the above-mentioned requirements. First, improvements regarding computational efficiency and numerical stability are made to Kordi's FDTD-based frequency-dependent line model. Then, the following points are clarified using the developed model: (i) Waveform deformations due to propagation modes with different velocities can be reproduced completely without modal decomposition; (ii) As the time step size becomes larger, waveforms obtained by the developed model become less accurate due to the embedded filter for numerical stability. These points assure, if the error due to the embedded filter is reduced, that the developed model can become a useful frequency-dependent line model without model identification problems.