Ultracap-based solutions for ride-through of synchronous machine drives

A DC excitation circuit for a synchronous machine, the circuit comprising:

• a converter structured to receive power from a power source and output DC power;
• a DC bus including a positive rail and a negative rail, the DC bus structured to receive power from the converter and provide power to a field winding of a synchronous motor;
• and
• a varistor coupled across the DC bus;
• an energy storage circuit including at least one ultracapacitor structured to receive power from the power source, store the power, and passively provide power to the field winding when the voltage of the DC bus falls below a predetermined level,
• wherein the power flowing from the ultracapacitor to the field winding flows through only uncontrolled passive devices and wherein the ultracapacitor is coupled to the DC bus to discharge current to a first node downstream from the varistor and upstream from the field winding.

A method for operating a synchronous machine comprising:

• providing power from a power supply to an exciter circuit comprising a power converter and DC bus including a varistor coupled across the DC bus;
• providing power from the exciter circuit to power a field winding of a synchronous machine;
• charging an ultracapacitor using power from the power supply;
• and
• in the event of a low power condition of the power supply, discharging the ultracapacitor to power the field winding without controlling a switching device to operatively connect the ultracapacitor to the field winding;
• wherein discharging the ultracapacitor provides current to the DC bus at a first node downstream from the varistor and upstream from the field winding.