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 position sensing system for generating a rotor position signal that is representative of the angular position of the PM rotor;

a control coil current sensor for generating a control coil current signal that is representative of the level of electrical current in the control coil;

an electrical potential sensor for generating a DC bus potential signal that is representative of the level of DC potential on the DC bus;

an electrical current sensor for generating a DC bus current signal that is representative of the level of DC current that the active rectifier supplies to the electrical load by way of the DC bus;

an output power estimator that compares the DC bus potential signal with the DC bus current signal to generate an output power signal;

a differentiator that receives the output power signal to generate a respective rate of output power signal;

a summer that adds the rate of output power signal with the DC bus potential signal to generate a DC potential feedback signal;

a main active rectifier system for converting multiphase AC power developed by the stator to DC power supplied to the electrical load by way of a DC bus; and

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 the control coil current signal and a DC bus potential feedback loop that comprises the DC potential feedback signal and in a generating mode the main active rectifier and inverter 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 the rotor position feedback loop; and

wherein both the control coil current regulator system and the 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.