Important modifications of the electricity generation landscape are expected in the next decades. This is mainly due to the increase of the demand, the limitation of traditional resources as fossil fuel energy resources and the development of renewable energy resources, especially the wind power. Consequently, hydraulic pumped storage power plants, whose main advantage is the ability to store big amounts of energy and to compensate very fast power fluctuations in the grid, will play a very important role. So it is essential to find and develop solutions to optimize the performances of this type of power plant. Nearly all the pumped storage power plants in operation today are equipped with groups working at constant speed consisting of synchronous motor-generators. Nevertheless, efficiency and dynamic performances of such power plants can be significantly improved by using variable speed motor-generators. The main objective of this work is to propose and develop control strategies and operation procedures for a variable speed pumped storage power plant in order to optimize its efficiency and to guarantee the stability of the grid. Such a study requires three main steps, which are theoretical development, modelling and validation through simulation results. The power plant considered in this study is fully and in detail modelled, the model including the electrical system and the converters, the hydraulic part and the control equipments. The simplification of the electrical part, and more particularly the replacement of the converters by controlled voltage sources, pseudo-continuous model, leads to a drastic simulation time reduction. Proposed control strategies enable the optimal operation of the variable speed group in the case of interconnected and isolated grid topologies and for both generating and pumping modes. The dynamic performances achieved are better than those obtained when considering an equivalent group working at constant speed, even if important electrical faults occur in the grid. Moreover the proposed procedures of start-up and synchronization related to the commissioning of the group operating in pumping mode do not require any supplementary equipment and enable to start the group in a short time. These different control strategies and procedures have been validated by simulations realized with the program SIMSEN.