The diffusion of Plug-in Electric Vehicles (PEVs), is expected to increase considerably over the next few years. Ad-hoc charging systems interacting in real-time with smart grids will be needed increasingly to overcome the severe overload problems in electric distribution grids caused by the huge demand for energy to charge a large number of vehicles. These systems will have to implement the scheduling of the charging process on the basis of negotiation phases between the user and the electric utility in which information about fares, amount of required energy and maximum time available for completing the charging before user drive off are exchanged. Possible smart energy dispatching strategies which take advantage of varying the charging rate during the charging process are analyzed in the paper. As shown, the adoption of a variable charging rate is a very promising solution for developing ad-hoc algorithms to fully exploit the distribution grid capacity, allowing higher customer satisfaction and utility financial profits to be reached with respect to algorithms based on fixed charging rate. The results of the analysis performed give useful guidelines for the development of smart-grid management policies and for the design of next-generation PEVs battery chargers.