Power systems and methods using an induction generator in cooperation with an uninterruptible power supply
A power system includes a load bus configured to be connected to a power source, a generator and an uninterruptible power supply (UPS). The generator is operated as an induction generator to provide power to the load bus while providing reactive power to the load bus from the UPS. In some embodiments, prior to operating the generator as an induction generator, the generator is operated as an induction motor while the load bus is receiving power from the power source. Responsive to loss of the power source, the UPS may be used to maintain operation of the generator as an induction motor while the prime mover accelerates up to a speed sufficient to drive the generator as an induction generator.
1. A method of operating a power system comprising a load bus configured to be connected to a power source, a generator and an uninterruptible power supply (UPS), the method comprising:
operating the generator as an induction generator to provide power to the load bus while providing reactive power to the load bus from the and then
transitioning to operating the generator as a synchronous generator to provide power to the load bus.
2. The method of claim 1 :
wherein operating the generator as an induction generator to provide power to the load bus while providing reactive power to the load bus from the UPS is preceded by operating the generator as an induction motor while the load bus is receiving power from the power source; and
wherein operating the generator as an induction generator to provide power to the load bus while providing reactive power to the load bus from the UPS comprises driving the generator with a prime mover responsive to a loss of the power source.
3. The method of claim 2 , wherein driving the generator with a prime mover responsive to a loss of the power source is preceded by driving the generator with the UPS responsive to the loss of the power source to maintain operation of the generator as an induction motor.
4. The method of claim 3 , further comprising powering a load from the UPS via the load bus while the UPS drives the generator.
5. The method of claim 3 , wherein driving the generator with a prime mover responsive to a loss of the power source comprises:
accelerating the prime mover while driving the generator with the UPS; and
engaging the generator with the prime mover responsive to a status of the prime mover meeting a predetermined criterion.
6. The method of claim 1 , wherein the UPS comprises a converter having a first port configured to be coupled to the load bus and a second port configured to be coupled to a UPS auxiliary power source, and further comprising providing power to the UPS auxiliary power source from the load bus via the converter while operating the generator as an induction generator.
7. The method of claim 1 :
wherein operating the generator as an induction generator to provide power to the load bus while providing reactive power to the load bus from the UPS comprises shorting a rotor field winding of the generator; and
wherein operating the generator as a synchronous generator to provide power to the load bus comprises applying an excitation current to the rotor field winding.
8. A power system comprising;
a generator configured to be coupled to a load bus;
a UPS configured to be coupled to the load bus; and
a control circuit operatively associated with the generator and the UPS and configured to detect a loss of a power source coupled to the load bus and to responsively operate the generator as an induction generator to provide power to the load bus while providing reactive power to the load bus from the UPS and to then transition the generator from operation as an induction generator to operation as a synchronous generator.
9. The system of claim 8 , further comprising a prime mover operatively associated with the control circuit and wherein the control circuit is further configured to operate the generator as an induction motor while the load bus is receiving power from the power source and to cause the prime mover to drive the generator as an induction generator responsive to a loss of the power source.
10. The system of claim 9 , wherein the control circuit is configured to cause the UPS to drive the generator responsive to the loss of the power source to maintain operation of the generator as an induction motor.
11. The system of claim 10 , wherein the control circuit is further configured to cause the UPS to serve a load via the load bus while the UPS drives the generator.
12. The system of claim 11 , wherein the control circuit comprises at least one circuit interruption device configured to selectively connect the load.
13. The system of claim 8 , wherein the control circuit is configured to short a rotor field winding of the generator when operating the generator as an induction generator and to apply an excitation current to the rotor field winding when operating the generator as a synchronous generator.
14. The system of claim 8 , wherein the UPS comprises a converter configured to support concurrent power flows to and from the load bus.
15. An apparatus for controlling a power system comprising a load bus configured to receive power from a power source, a generator configured to be coupled to the load bus and a UPS configured to be coupled to the load bus, the apparatus comprising:
a generator control circuit configured to selectively operate the generator as an induction motor and an induction generator responsive to a status of the power source; and
a UPS control circuit configured to selectively provide real and reactive power to the load bus from the UPS in cooperation with the generator control circuit, wherein the generator control circuit is configured to operate the generator as an induction motor while the load bus is receiving power from the power source, to cause a prime mover to drive the generator as an induction generator responsive to a loss of the power source and to transition the generator from operation as an induction generator to operation as a synchronous generator.
16. The apparatus of claim 15 , wherein the UPS control circuit is configured to cause the UPS to deliver reactive power to the load bus when the generator is operating as an induction motor.
17. The apparatus of claim 15 , wherein the UPS control circuit is configured to cause the UPS to provide power to the generator responsive to the loss of the power source to maintain operation of the generator as an induction motor.
18. The apparatus of claim 15 , wherein the UPS comprises a bidirectional power converter circuit, and wherein the UPS control circuit is configured to cause the bidirectional power converter circuit to support concurrent power flows to and from the load bus.