This paper presents a study on the Tunisian electrical network with multilateral mixed HVAC and HVDC interconnections. First, a generic average model of the HVDC line is developed. The parameters of the HVDC link power modulation controller are determined and tuned using the Graphical Identification method of "STRECJ". The multilateral ties of the system are studied via different study cases: single, bilateral and trilateral interconnections in DC and AC configurations. In particular, a parallel AC-DC interconnection between Tunisia and Libya is simulated. A special emphasis is given to an HVDC link to the Italian transmission grid. The results confirm the contribution of the HVDC transmission links in improving the Tunisian network stability.