I. Introduction
On board sensors used for continuous monitoring or tracking of freight railcars need energy supply for measuring and for transmitting information. The lack of electricity in freight cars can be overcome by resorting to the harvesting of wasted energy [1]–[3]. In particular, regenerative suspensions are aimed at the harvesting of the vibrations’ mechanical energy otherwise dissipated in traditional railcar suspensions. Different regenerative suspensions have been proposed in literature and the great majority of them exploit an electromagnetic generator to convert the mechanical energy into electrical energy [4].