DESIGN OF TRANSIENT AND LIMIT CONTROLLER Chap. 5 AIRCRAFT ENGINE CONTROLS

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1 UNIVERSITY OF SALENTO SCHOOL OF INDUSTRIAL ENGINEERING DEPT. OF ENGINEERING FOR INNOVATION Lecce-Brindisi (Italy) MASTER OF SCIENCE IN AEROSPACE ENGINEERING PROPULSION AND COMBUSTION DESIGN OF TRANSIENT AND LIMIT CONTROLLER Chap. 5 AIRCRAFT ENGINE CONTROLS LECTURE NOTES AVAILABLE ON Prof. Eng. Antonio Ficarella University of Salento - antonio.ficarella@unisalento.it REVIEW R01 DATE 06/12/2013 FILE RESPONSIBLE propaectransientlr01.odp Antonio Ficarella antonio.ficarella@unisalento.it 1/32

2 INTRODUCTION compared to stable cruise conditions, a transient condition experiences much larger performance changes in a relatively short time period transient control to protect the engine to running beyond operating limits shaft speed max temperature burner pressure surge limit 2/32

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4 acceptable transient performance rise time settling time overshoot/undershoot schedule-base control acceleration-based control 4/32

5 SCHEDULED-BASE TRANSIENT CONTROLLER DESIGN the primary control loop is bounded by the acceleration schedule the control variable fuel flow will not be allowed to exceed the scheduled values 5/32

6 CONCEPT OF CONTROL SCHEDULES fuel flow vs. shaft speed (or EPR) control envelope 6/32

7 turbine and compressor temperature limits compressor discharge pressure limit shaft over/under-speed limits 7/32

8 ACCELERATION CONTROL 8/32

9 DECELERATION CONTROL 9/32

10 NON-LINEAR CONSIDERATIONS IN TRANSIENT CONTROL time response of engine near TO is 3-5 times as fast as the response near idle one set of controller gains is only valid for a relatively small neighborhood around the set point for which the control law is designed piecewise linearization (small perturbation) which divides the engine operating lines into multiple nominal points design of set-point controller for each nominal point a methodology is needed to switch between two neighboring set-point controllers switching linear controller non-linear schedule the integral control law will continue to compute integrator wind-up 10/32

11 GAIN SCHEDULING super-controller with parameters that are changed depending on operating conditions scheduling variables one or more state or output variables capable of discerning which of the set-point controllers are most adequate linear model parametrized by these scheduling variables example: 3 linear models (idle, cruise, TO) - k 11/32

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15 INTEGRATOR WIND-UP (IWU) PROTECTION the integral control have to be frozen or trimmed-down when an IWU scenario is active 15/32

16 DECELERATION SURGE when the pumping capacity between the LP compressor and the HP compressor are different spool mismatch 16/32

17 ACCELERATION-BASED TRANSIENT CONTROL DESIGN N-dot control 17/32

18 N-DOT CONTROL CONCEPT speed of the gas generator or the HP shaft 18/32

19 N-dot by differentiating the speed over the time + a digital filter proportional + integral control in N-dot control loop 19/32

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21 OLTF has a guaranteed stability phase-lag at high frequency < 90 deg phase margin of the loop > 90 deg BUT: computational delay, fuel control and actuator dynamics desired rotor acceleration scheduled as function of N transition between set-point and N-dot controller switching cascading (nesting) preferred N-dot control regardless what the state of engine is in 21/32

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25 N-DOT CONTROL FOR A 2-SPOOL ENGINE 25/32

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27 COMPARISON BETWEEN SCHEDULED AND N- DOT advantages of N-dot consistent transient performance for all of the engines regardless of their variations, age, deterioration more responsive engine transient good stability high gain control laws disadvantages of N-dot tendency to drive the engine in stall surge or flame-out scheduled base control minimum time accel or decel high mechanical and thermal stresses emergency power boost (downdraft or wind-shear) during TO or landing 27/32

28 CONTROLLER DESIGN FOR LIMIT PROTECTION potentially damaging conditions exceeding the LP speed N1 can occur when engine is deteriorated or damaged such that the LP- HP speed match has deviate exceeding the HP speed N2 failed speed sensor failed fuel control exceeding the max compressor exit static pressure P3 exceeding the max EGT limit engine over-fueled PID control applied to the feedback error topping governors as a trim or correction to the primary loop avoid when the two controllers fight 28/32

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30 equal-voting or leader-follower 30/32

31 ROTOR-CRAFT ENGINE MANAGEMENT POWER MANAGEMENT multi-engine rotorcraft sharing the load to recover the power promptly when one or more engine fails engine deteriorated or damaged torques measured at the shaft 31/32

32 ADAPTIVE ACCELERATION CONTROL AND SURGE RECOVERY closed-loop control for N-dot/P3 surge detector large negative change of discharge pressure 32/32