Control for electrically assisted turbines
In accordance with at least one aspect of this disclosure, there is provided a method of accelerating a gas turbine engine. The method includes adding torque to a core of the gas turbine engine to accelerate rotation of the core by controlling fuel flow to a plurality of fuel injectors of the gas turbine engine. The method also includes adding torque to the core by powering an electric machine that is operatively connected to the core. In embodiments, controlling fuel flow to the plurality of fuel injectors is based on feedback from the electric machine.
1 . A method of accelerating a gas turbine engine of an aircraft, the gas turbine engine having a high-pressure spool including a high-pressure turbine drivingly engaging a high-pressure compressor, and low-pressure spool including a low-pressure turbine drivingly engaging a low-pressure compressor, the gas turbine engine having a combustor, the high-pressure spool rotating independently of the low-pressure spool, the method comprising:
accelerating the high-pressure spool by both of causing an electric machine to add torque to the high-pressure spool and injecting a fuel flow into the combustor;
as the high-pressure spool is accelerating:
a) controlling an output torque of the electric machine as a function of a difference between a core rotational speed of the high-pressure spool and a target rotational speed of the high-pressure spool while maintaining a surge margin of the high-pressure compressor below a surge margin threshold;
b) determining the fuel flow to be supplied to the combustor using a feedback from the electric machine indicative of a difference between the output torque of the electric machine and a target output torque of the electric machine, and injecting the fuel flow to the combustor; and
c) repeating steps a) and b) until the difference between the output torque of the electric machine and the target output torque of the electric machine is zero.
2 . The method of claim 1 , wherein the controlling of the output torque while maintaining the surge margin below the surge margin threshold includes:
maintaining a pressure ratio of a pressure at an outlet of the high-pressure compressor to an ambient pressure below a pressure ratio threshold.
3 . The method of claim 2 , includes:
receiving signals from an ambient pressure sensor and a compressor discharge sensor, the signals indicative of the ambient pressure and the pressure at the outlet of the high-pressure compressor.
4 . The method of claim 1 , wherein the repeating of the steps a) and b) includes repeating the steps a) and b) until the output torque of the electric machine is zero.
5 . The method of claim 1 , wherein the electric machine is powered by batteries, the method comprising:
setting the target torque of the electric machine to a negative value such that the high-pressure spool provides torque to the electric machine to recharge the batteries.
6 . The method of claim 1 , comprising:
determining that the core rotational speed reached the target rotational speed; and
increasing the fuel flow to the combustor until the output torque of the electric machine reaches the target torque.
7 . The method of claim 5 , comprising:
once the output torque of the electrical machine reached the target torque, maintaining the fuel flow to a plurality of fuel injectors.