Traditional alternator sets the generation voltage to a fixed setpoint, regardless to vehicle condition. During omologative and real life cycle, vehicle states can be identified according to different energy vehicle request. When vehicle is decelerating or braking with no engine torque demand, alternator generation can be switched on, taking energy from vehicle inertia.

Using combined engine-alternator efficiency map, requested energy is produced just at highest efficiency working point.

Obviously the control system has to manage the battery state of charge. A battery SOC sensor is required. Battery can be managed in a defined range of SOC. Generation towards the battery is avoided if battery is fully charged, avoiding to waste energy.

Alternator generation can be controlled through field excitation current from maximum supplied current to zero current generation. To avoid also mechanical and ventilation losses alternator can be mechanically disengaged from engine (i.e. through an electromagnetic clutch), allowing further fuel saving.