A circuit for boosting the voltage output of an alternator utilizes the armature coils of the alternator as part of the boost circuit. The circuit and methods utilizing this circuit can enable refined control strategies for operating a plurality of engine systems during propulsion, idling and braking and is applicable to large systems such as trucks, ships, cranes and locomotives utilizing diesel engines, gas turbine engines, other types of internal combustion engines, fuel cells or combinations of these that require substantial power and low emissions utilizing multiple power plant combinations.