Systems and methods for power turbine governing

1. A power turbine control system for a gas turbine engine, comprising:

a controller comprising one or more processors in communication with the gas turbine engine, the one or more processors comprising:

an engine control module configured to:

receive a torque request signal,

determine at least one of a fuel flow, a guide vane schedule, or a bleed schedule based on the torque request signal, and

generate a torque achieved signal based, at least in part, on the at least one of the fuel flow, the guide vane schedule, or the bleed schedule;

a rate of change of power turbine speed estimation module configured to receive a power turbine speed signal and the torque achieved signal, wherein the rate of change of power turbine speed estimation module is configured to generate an estimated rate of change of power turbine speed signal based on the power turbine speed signal, the torque achieved signal, and an estimated power turbine torque load signal; and

a dynamic inversion power turbine governor module configured to receive the estimated rate of change of power turbine speed signal and the torque achieved signal, wherein the dynamic inversion power turbine governor module is configured to:

receive a target power turbine speed signal,

determine a desired rate of change of power turbine speed error signal based on a difference between the target power turbine speed signal and the power turbine speed signal,

determine a difference between the desired rate of change of power turbine speed error signal and the estimated rate of change of power turbine speed signal, and

generate the torque request signal using the torque achieved signal and the difference between the desired rate of change of power turbine speed error signal and the estimated rate of change of power turbine speed signal.

2. The power turbine control system of claim 1 , wherein the rate of change of power turbine speed estimation module is configured to:

generate a model-based rate of change of power turbine speed signal; and

generate a sensor-based rate of change of power turbine speed signal.

3. The power turbine control system of claim 2 , wherein the rate of change of power turbine speed estimation module is configured such that the model-based rate of change of power turbine speed signal drives the estimated rate of change of power turbine speed signal during a transient state, and the sensor-based rate of change of power turbine speed signal drives the estimated rate of change of power turbine speed signal in steady state.

4. The power turbine control system of claim 2 , wherein the rate of change of power turbine speed estimation module is configured to generate the model-based rate of change of power turbine speed signal based, at least in part, on the torque achieved signal generated by the engine control module and the estimated power turbine torque load signal.

5. The power turbine control system of claim 4 , wherein the estimated power turbine torque load signal is generated using a pilot input.

6. The power turbine control system of claim 1 , wherein the dynamic inversion power turbine governor module is configured to:

determine a torque request correction signal based on the difference between the desired rate of change of power turbine speed error signal and the estimated rate of change of power turbine speed signal; and

combine the torque request correction signal and the torque achieved signal to generate the torque request signal.

7. The power turbine control system of claim 1 , wherein the controller is configured to control a torque of a power turbine of the gas turbine engine based, at least in part, on the at least one of the fuel flow, the guide vane schedule, or the bleed schedule.

8. The power turbine control system of claim 1 , wherein the rate of change of power turbine speed estimation module generates the estimated rate of change of power turbine speed signal using a complementary filter.

9. A method of controlling a power turbine, comprising:

receiving, by an engine control module of a controller, a torque request signal;

determining, by the engine control module, at least one of a fuel flow, a guide vane schedule, or a bleed schedule based on the torque request signal;

generating, by the engine control module, a torque achieved signal using the at least one of the fuel flow, the guide vane schedule, or the bleed schedule;

receiving, by a rate of change of power turbine speed estimation module of the controller, a power turbine speed signal and the torque achieved signal;

generating, by the rate of change of power turbine speed estimation module, an estimated rate of change of power turbine speed signal based on the power turbine speed signal, the torque achieved signal, and an estimated power turbine torque load signal;

receiving, by a dynamic inversion power turbine governor module of the controller, the estimated rate of change of power turbine speed signal and the torque achieved signal;

receiving, by the dynamic inversion power turbine governor module, a target power turbine speed signal;

determining, by the dynamic inversion power turbine governor module, a desired rate of change of power turbine speed error signal based on a difference between the target power turbine speed signal and the power turbine speed signal;

determining, by the dynamic inversion power turbine governor module, a difference between the desired rate of change of power turbine speed error signal and the estimated rate of change of power turbine speed signal; and

generating, by the dynamic inversion power turbine governor module, the torque request signal using the torque achieved signal and the difference between the desired rate of change of power turbine speed error signal and the estimated rate of change of power turbine speed signal.

10. The method of claim 9 , wherein the engine control module of the controller uses inversion of a dynamic model to generate the torque achieved signal.

11. The method of claim 9 , wherein generating, by the rate of change of power turbine speed estimation module, the estimated rate of change of power turbine speed signal comprises:

generating, by the rate of change of power turbine speed estimation module, a model-based rate of change of power turbine speed signal; and

generating, by the rate of change of power turbine speed estimation module, a sensor-based rate of change of power turbine speed signal using the power turbine speed signal.

12. The method of claim 11 , wherein generating, by the rate of change of power turbine speed estimation module, the model-based rate of change of power turbine speed signal comprises:

determining, by the rate of change of power turbine speed estimation module, the estimated power turbine torque load signal based, at least in part, on pilot input;

determining, by the rate of change of power turbine speed estimation module, a difference between the torque achieved signal and the estimated power turbine torque load signal; and

converting, by the controller, the difference between the torque achieved signal and the estimated power turbine torque load signal to the model-based rate of change of power turbine speed signal.

13. The method of claim 11 , wherein generating, by the rate of change of power turbine speed estimation module, the estimated rate of change of power turbine speed signal further comprises:

inputting, by the rate of change of power turbine speed estimation module, the model-based rate of change of power turbine speed signal into a fusion algorithms module; and

inputting, by the rate of change of power turbine speed estimation module, the sensor-based rate of change of power turbine speed signal into the fusion algorithms module, wherein the fusion algorithms module is configured such that the model-based rate of change of power turbine speed signal drives the estimated rate of change of power turbine speed signal during a transient state, and the sensor-based rate of change of power turbine speed signal drives the estimated rate of change of power turbine speed signal in steady state.

14. The method of claim 9 , wherein generating, by the dynamic inversion power turbine governor module, the torque request signal further comprises:

determining, by the dynamic inversion power turbine governor module, a torque request correction signal based on the difference between the desired rate of change of power turbine speed error signal and the estimated rate of change of power turbine speed signal; and

combining, by the dynamic inversion power turbine governor module, the torque request correction signal and the torque achieved signal.