PhD Amjad MOUHAIDALI

“Contribution to the modelling of HVDC cables for electromagnetic transient simulations”

The integration of new technologies in the electric grids made them more and more complex, and most likely future growth of power grids will be based more on underground cables than overhead lines. One problem here, is that the mathematical model for electromagnetic simulation of power cables still has some shortcomings regarding stability, accuracy and passivity. In this thesis, we evaluate the cable parameters using analytical and numerical methods. The cable physical parameter dependency on frequency and temperature is investigated and a parametric study is done. The resulting frequency dependent admittance and propagation matrices describes accurately the cable behavior over a wide frequency range. The Wide Band model is reformulated using an original and robust fitting method. This method is based on the rational Krylov approximation algorithm. The admittance and propagation matrices are fitted in the frequency domain using the Krylov based method. We found that this approximation method is more accurate than that used in the original implementation of the wide band model known as Vector Fitting. Krylov based approximation showed an enhancement in the fitting and especially at low frequency for HVDC transmission. Time domain simulation based on the Numerical Laplace Transform are used to assess the accuracy of the aforementioned model. An original and robust passivity enforcement algorithm is proposed to fulfill the passivity criteria on a passivity violated model. This algorithm tries to iteratively improve the accuracy of the rational approximation that relates to the passivity violation. It was shown that after few iterations the algorithm renders a passive and a stable cable model. Finally, based on these developments, further research themes are proposed.