The ITER large power supplies of the superconducting magnets and heating and current drive systems, fed by the Pulsed Power Electrical Network, can absorb from the grid active and reactive power up to 500 MW and 950 Mvar respectively. In this paper, a new analytical approach based on the state space formulation is proposed to investigate the dynamic stability of such complex system, including the main power components and their control, with the aim of identifying possible instability phenomena due to interactions among the ac/dc converters, reactive power compensation systems and related controllers. This model describes the dynamics of the main components of the ITER pulsed power supply systems and it is based on small signal approach to tackle the non linearity of the ac/dc conversion and reactive power compensation systems; the discrete phenomena have been approximated by continuous transfer functions, so the linear control theory can be applied for the stability analysis, making this method very effective and fast. Moreover a modular approach is adopted; thus this analytical model can be also easily adapted to other similar electrical power systems.