Electrical starter generator system for a gas turbine engine
A starting system and method for a gas turbine engine applies a change in conventional starter generator torque profiles near the conclusion of the start cycle after the engine self sustaining speed and just prior to starter generator cut-out. By decreasing the applied torque to zero prior to transition from a start mode to a generator mode, both the mechanical and electrical transients are greatly decreased.
1. A method of operating a starter generator system comprising the steps of:
(1) operating a starter motor to generate an output torque;
(2) spooling up an engine with the output torque from the starter motor;
(3) reducing the output torque from a constant power region in which the output torque is decreased in response to an increase in engine speed so as to maintain a generally constant power output, then reducing the output torque according to a ramp function having a slope steeper than that within the constant power region to approximately zero in response to transitioning the starter motor from a start mode in which the starter motor drives the engine to a generator mode in which the starter motor is driven by the engine.
2. A method as recited in claim 1 , wherein the engine achieves a self-sustaining speed during said step (3).
3. A method as recited in claim 2 , wherein the self-sustaining speed is an engine speed in which the engine achieves an approximately zero drag torque.
4. A method as recited in claim 1 , further comprising the step of:
(4) operating the starter motor as a generator after the engine lights off.
5. A method as recited in claim 1 , wherein said step (3) includes:
(a) reducing the output torque from a speed which relates to a predetermined engine operating speed to zero commensurate with transition from the start mode to the generator mode, the reduction represented as a ramp function in a starter generator torque profile curve.
6. A method of starting a gas turbine engine comprising the steps of:
(1) operating a starter motor within a constant torque region to generate an output torque;
(2) spooling up an engine with the output torque from the starter motor in response to said step (1);
(3) operating the starter motor within a constant power region in which the output torque is decreased in response to an increase in engine speed so as to maintain a generally constant power output;
(4) lighting off the gas turbine engine during said step (3);
(5) reducing the output torque after said step (4) according to a ramp function having a slope steeper than that during said step (3) to approximately zero in response to transitioning the starter motor from a start mode in which the starter motor drives the engine to a generator mode in which the starter motor is driven by the engine.
7. A method as recited in claim 6 , wherein said step (5) includes:
(a) reducing the output torque from a speed which relates to a predetermined engine operating speed to zero commensurate with transition from the start mode to the generator mode, the reduction represented as a ramp function in a starter generator torque profile curve.
8. A method as recited in claim 6 , wherein said step (5) includes:
(a) reducing the output torque according to the algorithm
T
=
K
n
[
n
2
-
n
n
2
-
n
1
]
until a speed n 2 where T=Torque; K=Constant; n=speed; n 1 =speed at which the linear ramp function begins at the transition between the start mode and the generator mode; n 2 =speed at which the linear ramp function reaches zero torque.
9. A method of starting a gas turbine engine comprising the steps of:
(1) operating a starter motor within a constant torque region to generate an output torque;
(2) spooling up an engine with the output torque from the starter motor in response to said step (1);
(3) operating the starter motor within a constant power region in which the output torque is decreased in response to an increase in engine speed so as to maintain a generally constant power output;
(4) lighting off the gas turbine engine;
(5) reducing the output torque to approximately zero in response to the gas turbine engine reaching a self-sustaining speed in which the engine achieves an approximately zero drag torque including reducing the output torque according to the algorithm
T
=
K
n
[
n
2
-
n
n
2
-
n
1
]
until a speed n 2 where T=Torque; K=Constant; n=speed; n 1 =speed at which the linear ramp function begins at the transition between the start mode and the generator mode; n 2 =speed at which the linear ramp function reaches zero torque.
10. A method as recited in claim 9 , further comprising the step of:
(6) operating the starter motor as a generator after the engine achieves the predetermined speed.
11. A method as recited in claim 9 , wherein said step (5) includes:
(a) reducing the output torque from a speed which relates to a predetermined engine operating speed to zero in response to transitioning the starter motor from a start mode in which the starter motor drives the engine to a generator mode in which the starter motor is driven by the engine.
12. A method of operating a starter generator system comprising the steps of:
(1) operating a starter motor to generate an output torque;
(2) spooling up an engine with the output torque from the starter motor;
(3) reducing the output torque to approximately zero in response to transitioning the starter motor from a start mode in which the starter motor drives the engine to a generator mode in which the starter motor is driven by the engine including reducing the output torque according to a linear ramp function algorithm
T
=
K
n
until a speed n1 where T=Torque; K=Constant; and n=speed, where n 1 =speed at which the linear ramp function begins at the transition between the start mode and the generator mode; and reducing the output torque according to the algorithm
T
=
K
n
[
n
2
-
n
n
2
-
n
1
]
until a speed n 2 where n 2 =speed at which the linear ramp function reaches zero torque.
13. A method of starting a gas turbine engine comprising the steps of:
(1) operating a starter motor within a constant torque region to generate an output torque;
(2) spooling up an engine with the output torque from the starter motor in response to said step (1);
(3) operating the starter motor within a constant power region in which the output torque is decreased in response to an increase in engine speed so as to maintain a generally constant power output;
(4) lighting off the gas turbine engine;
(5) reducing the output torque to approximately zero in response to transitioning the starter motor from a start mode in which the starter motor drives the engine to a generator mode in which the starter motor is driven by the engine including reducing the output torque according to a linear ramp function algorithm
T
=
K
n
until a speed n1 where T=Torque; K=Constant; and n=speed, where n 1 =speed at which the linear ramp function begins at the transition between the start mode and the generator mode.
14. A method of starting a gas turbine engine comprising the steps of:
(1) operating a starter motor within a constant torque region to generate an output torque;
(2) spooling up an engine with the output torque from the starter motor in response to said step (1);
(3) operating the starter motor within a constant power region in which the output torque is decreased in response to an increase in engine speed so as to maintain a generally constant power output;
(4) lighting off the gas turbine engine;
(5) reducing the output torque to approximately zero in response to transitioning the starter motor from a start mode in which the starter motor drives the engine to a generator mode in which the starter motor is driven by the engine including reducing the output torque according to the algorithm
T
=
K
n
[
n
2
-
n
n
2
-
n
1
]
until a speed n 2 where T=Torque; K=Constant; n=speed; n 1 =speed at which the linear ramp function begins at the transition between the start mode and the generator mode; n 2 =speed at which the linear ramp function reaches zero torque.