Compensator device, for the stabilisation of electromechanical oscillations destined to provide a reference signal to a voltage regulator device of a synchronous alternator for the delivery of electrical power to a distribution network, said device including: first processing means to receive electrical measurement signals representing operative parameters characteristics of said synchronous alternator and/or to generate an electrical signal to be controlled; and a first electrical signal corresponding to a sliding surface of a control of the "sliding modes" type, second processing means of the first signal to generate the reference signal so that it has a first order "sliding modes" profile.