Engine and secondary power unit integrated operation

1. An engine system comprising:

a gas turbine engine comprising a first compressor, a first combustor, and a first turbine;

a secondary power unit comprising a second compressor, a second combustor, a second turbine, a third compressor coupled to the second compressor, and an electric motor-generator, wherein the secondary power unit is coupled to the gas turbine engine, and wherein the secondary power unit further comprises a heat exchanger configured to receive pressurized air from the first compressor; and

a controller operable to:

determine an operating mode of the engine system;

select an input energy source and an output type of the secondary power unit based on the operating mode, control the secondary power unit based on the input energy source and the output type as selected;

detect a change in the operating mode of the engine system; and

modify the input energy source and/or the output type of the secondary power unit based on the change in the operating mode.

2. The engine system of claim 1 , wherein the operating mode comprises a source electric power mode with the electric motor-generator in a generator mode to provide electric power as the output type.

3. The engine system of claim 1 , wherein the input energy source of the secondary power unit comprises fuel to the second combustor, and wherein the controller is configured to switch the input energy source from the pressurized air to fuel based on the operating margin of the gas turbine engine being within a predetermined threshold.

4. The engine system of claim 1 , wherein the operating mode is selectable between a ground start operating mode, an engine-assisted start operating mode, a source electric power mode, and a compressed air output mode.

5. The engine system of claim 4 , wherein the operating mode is established based on one or more events comprising: an engine start request, a restart request, an electric power demand, a compressed air demand, and a conditioned air demand.

6. The engine system of claim 5 , wherein the input energy source of the secondary power unit comprises fuel to the second combustor and/or electric power at the electric motor-generator in a motor mode.

7. The engine system of claim 1 , wherein the controller is operable to select the input energy source and the output type of the secondary power unit based on a current condition of the engine system.

8. The engine system of claim 1 , wherein the second turbine is configured to output conditioned air as a cooling source.

9. The engine system of claim 8 , wherein the electric motor-generator is configured in a generator mode to provide electric power as the output type.

10. The engine system of claim 8 , wherein the third compressor is configured to provide compressed air as the output type.

11. A method comprising:

determining an operating mode of an engine system comprising a gas turbine engine and a secondary power unit, wherein the gas turbine engine comprises a first compressor, a first combustor, and a first turbine, and the secondary power unit comprises a second compressor, a second combustor, a second turbine, a third compressor coupled to the second compressor, and an electric motor-generator, wherein the secondary power unit is coupled to the gas turbine engine, and wherein the secondary power unit further comprises a heat exchanger configured to receive pressurized air from the first compressor;

selecting an input energy source and an output type of the secondary power unit based on the operating mode;

controlling the secondary power unit based on the input energy source and the output type as selected;

detecting a change in the operating mode of the engine system; and

modifying the input energy source and/or the output type of the secondary power unit based on the change in the operating mode.

12. The method of claim 11 , wherein the operating mode comprises a source electric power mode with the electric motor-generator in a generator mode to provide electric power as the output type.

13. The method of claim 11 , wherein the input energy source of the secondary power unit comprises fuel to the second combustor, and further comprising switching the input energy source from the pressurized air to fuel based on an operating margin of the gas turbine engine being within a predetermined threshold.

14. The method of claim 11 , wherein the operating mode is selectable between a ground start operating mode, an engine-assisted start operating mode, a source electric power mode, and a compressed air output mode.

15. The method of claim 14 , wherein the operating mode is established based on one or more events comprising: an engine start request, a restart request, an electric power demand, a compressed air demand, and a conditioned air demand.

16. The method of claim 15 , wherein the input energy source of the secondary power unit comprises fuel to the second combustor and/or electric power at the electric motor-generator in a motor mode.

17. The method of claim 11 , further comprising selecting the input energy source and the output type of the secondary power unit based on a current condition of the engine system.

18. The method of claim 11 , wherein the second turbine is configured to output conditioned air as a cooling source.

19. The method of claim 18 , wherein the electric motor-generator is configured in a generator mode to provide electric power as the output type.

20. The method of claim 18 , wherein the third compressor is configured to provide compressed air as the output type.