This thesis addresses the problem of damping power oscillations (inter-area modes) of a meshed transport network - as it is the case of the European network - through a High Voltage Direct Current- (HVDC) link. In this particular context, inter-area modes are at higher frequencies than usual - around 1Hz. This is an important challenge for the control system, as other network dynamics exist in this frequency range. Standard controllers (PSS and POD type IEEE) give un-satisfactory results and other control approaches have been proposed. They take into account more information from the electrical system surrounding the HVDC using a richer control model. Besides, the robustness is improved in order to provide good responses in case of network variations (load evolution, line, and generator trips, ..., etc.) and HVDC line parameters changes. Finally, unstable zeros (non-minimum phase behavior) have been high-lighted and studied in these situations of HVDC inserted in meshed AC networks. The proposed controllers also mitigate the negative effect of these zeros on the performances of the closed-loop. The results are easily implemented in practice because they are feedback controllers. Also, although developed for HVDC, the proposed analysis and control methodologies can be extended to other elements using power electronics such as, for example, renewable energy generators connected to the grid by power converter.