In this work, an improved Particle Swarm Optimization (PSO) algorithm is employed to perform the Maximum Power Point Tracking (MPPT) of a 1.2 MW Photovoltaic farm under Partial Shading Conditions (PSC). High efficiency, low complexity and reduced tracking time are the main features achieved by integrating the ability to ensure a Global Maximum Power Point (GMPP) operation provided by PSO and the fast convergence of Perturb and Observe (P&O) algorithm. In addition, Sliding-Mode Control (SMC) is used on a cascade scheme on the DC-DC power converters in order to achieve a suitable energy conversion. Thus, the design of the SMC is achieved by using the space state representation of the power converters. Finally, photovoltaic system performance is analyzed for different solar radiation profiles. The obtained results show the proper dynamic and steady-state responses.