Research on control law for a sub-idle engine operation

Starting is a process which an gas turbine has to experience before it operating between the idle and maximum power points, and the problem how to ensure an gas turbine succeed to rapidly and safely start is necessary to be taken seriously. Most control laws only address the operating range between the idle and maximum power points because of the lack of models which can simulate a sub-idle engine operation. The paper gives a control law for a sub-idle engine operation based on a existed starting model. A closed loop control law for the total temperature after the primary combustion chamber (TT4) was proposed in order to persistently obtain the maximum surplus power during a whole starting process of an aero-engine. Meanwhile, several limit controllers for surge margin is added to the reference command of the TT4 closed loop, taking into account prevention against surge or stall. Moreover, freezing the integral of the PT controller before the ignition of an engine is introduced to anti-windup. The result of simulation illustrates that an turbofan engine can successfully start from engine off to idle power with a persistent maximum surplus power and the protection of several limit controllers, which can guarantee adequate surge margin of 3 compression components and TT4 to not exceed the maximum value.