An electromechanical power transfer system that transfers power between a prime mover and a direct current (DC) electrical power system, comprises: a permanent magnet machine (PMM) that has a permanent magnet (PM) rotor coupled to the prime mover, a stator with a multiphase alternating current (AC) winding coupled to an AC bus and a control coil with a winding that has a configuration to generate a magnetic field with flux that varies the reactance of the stator winding with the application of control coil current; a control coil current regulator system to regulate the control coil current; wherein the control coil current regulator system generates a level of the control coil current that regulates current in the stator to a desired level in response to a control coil current feedback loop that comprises a control coil current signal and a DC bus potential feedback loop that comprises a DC potential feedback signal and in a generating mode the main active rectifier system maintains a constant potential on the DC bus regardless of sudden changes in electrical load on the DC bus in response to the DC bus potential feedback loop and a rotor position feedback loop; and wherein both the control coil current regulator system and a main active rectifier system switch from an active regulating mode to a protection non-regulating mode upon detection of a fault in the DC bus.