This paper presents and analyses a represented ac system with an overlay HVDC network based on multi-terminal VSC. A state space representation and a method of the automatic development of the small signal model of the hybrid ac/dc system is achieved. The methodology to develop the small signal model is composed of four steps being construction of sub system units; development of state space models for each unit; linearization of nonlinear models and integration of all linearized models. The control architecture schemes for VSC systems are also presented in order to obtain control objectives such as control active and reactive power, and dc voltages. Based on the developed platform, the small signal stability is analyzed to investigate the effect of different control strategies as well as controller parameters on the system performance.