Alireza Behbahani

Gain Scheduling Control of Gas Turbine Engines: Stability by Computing a Single Quadratic Lyapunov Function

We develop and describe a stable gain scheduling controller for a gas turbine engine that drives a variable pitch propeller. A stability proof is developed for gain scheduled closed-loop system using global linearization and linear matrix inequality (LMI) techniques. Using convex optimization tools, a single quadratic Lyapunov function is computed for multiple linearizations near equilibrium and non-equilibrium points of the nonlinear closed-loop system. This approach guarantees stability of the closed-loop gas turbine engine system. Simulation results show the developed gain scheduling controller is capable of regulating a turboshaft engine for large thrust commands in a stable fashion with proper tracking performance.Copyright

Gain Scheduled Control of Gas Turbine Engines: Stability and Verification

A stable gain scheduled controller for a gas turbine engine that drives a variable pitch propeller is developed and described. A stability proof is developed for gain scheduled closed-loop system using global linearization and linear matrix inequality (LMI) techniques. Using convex optimization tools, a single quadratic Lyapunov function is computed for multiple linearizations near equilibrium and nonequilibrium points of the nonlinear closed-loop system. This approach guarantees stability of the closed-loop gas turbine engine system. To verify the stability of the closed-loop system on-line, an optimization problem is proposed, which is solvable using convex optimization tools. Simulation results show that the developed gain scheduled controller is capable to regulate a turboshaft engine for large thrust commands in a stable fashion with proper tracking performance.

Distributed Control of Turbofan Engines

Abstract : The purpose of this paper is to develop control theoretic concepts for distributed control of gas turbine engines, and develop a dynamic engine model incorporating distributed components in compressor dynamics, engine cycles, and engine control. The latest results in distributed control combined with adaptive control theory are extended for turbofan engine distributed control. Concepts and architectures for distributed control are developed that create tangible benefits from the distribution of closed-loop feedback around the engine.

Decentralized Adaptive Control of a Turbofan System with Partial Communication

In this paper we develop control theoretic concepts for decentralized adaptive control with partial communication for a twin spool gas turbine engine system. Distributed / decentralized adaptive control architecture creates tangible benets from the distribution of closed-loop feedback around the engine. The idea is to control the two subsystems of the engine without any direct communication between the controllers and also without direct interference of each subsystem dynamics with other subsystem controller. This approach helps to optimize the performance of the engine subsystems separately.

Very High Frequency Monitoring System for Engine Gearbox and Generator Health Management

In cooperation with the major propulsion engine manufacturers, the authors are developing and demonstrating a unique very high frequency (VHF) vibration monitoring system that integrates various vibroacoustic data with intelligent feature extraction and fault isolation algorithms to effectively assess engine gearbox and generator health. The system is capable of reporting on the early detection and progression of faults by utilizing piezoelectric, optical, and acoustic frequency measurements for improved, incipient anomaly detection. These gas turbine engine vibration monitoring technologies will address existing operation and maintenance goals for current military system and prognostics health management algorithms for advanced engines. These system features will be integrated in a state-of-the-art vibration monitoring system that will not only identify faults more confidently and at an earlier stage, but also enable the prediction of the time-to-failure or a degraded condition worthy of maintenance action. The authors have made significant progress toward identifying, computing, and comparing the high frequency feature sets generated with various vibroacoustic measurement techniques. Specifically, the technology has been demonstrated on two subscale test stands. The first is a generator test rig that was equipped with a laser vibrometer and two high-frequency accelerometers. Various mechanical and electrical faults were seeded, with an emphasis on generator bearing faults. Initial results show very good detection capability in frequency bands well above those used in traditional vibration analysis. Another focus, accessory gearbox systems, was addressed for feasibility through a gearbox test rig, which was instrumented with high bandwidth accelerometers and wideband and narrowband acoustic emissions (AE) sensors. Baseline, seeded fault, and fault progression tests were conducted, including tests with various levels of gear tooth corrosion. Successful detection of this fault was then demonstrated using a number of new, innovative approaches. A statistical analysis was also performed to compare the approaches, with narrowband acoustic emission and high frequency vibration features performing the best.

Distributed Architectures Integrated with High-Temperature Electronics for Engine Monitoring and Control

In this paper we give an overview of the distributed engine control system integratedwith high temperature electronics (HTE). The challenges that control designers will en-counter for a distributed engine control design process is threefold. The rst one is themodeling and formulation of uncertainties and de ciencies of electronics systems and equip-ments in high temperature conditions. The second one is a proper communication meansdesigned to handle all or part of these de ciencies. The last one is a proper control structuredesigned to be integrated with the distributed communication system and HTE function-ing as smart nodes (e.g. sensors, actuators and control processors) in this communicationsystem. The tools that are needed to design a distributed engine control system includecontrol theory (feedback systems), information theory (communication bus and networkstructure) and HTE technology. We believe, the algorithm/architecture co-design (AAC)process is a necessary and ex0ecient approach for designing reliable and robust distributedcontrol systems using high temperature electronics. AAC can combine control theory,communication theory and high temperature electronics technology to propose an optimalsolution to the problem.

Distributed Modeling and Control of Turbofan Systems

This paper aims to develop and describe control theoretic concepts for distributed control of gas turbine engines, and also to develop a dynamic engine model incorporating distributed components in compressor dynamics, engine cycles, and engine control. Concepts and architectures for distributed control are developed that create tangible benets from the distribution of closed loop feedback around the engine. Engine dynamics has been divided into two main subsystems including Fan and core subsystems. Separate controllers have been designed for each subsystem. Fuel ow is the control input for the core subsystem, and fan vane angle (or fan exit area) is the control input for the fan subsystem. For each subsystem linear and adaptive controllers are designed. Simulation results indicate that the developed distributed controllers are operating properly.

Physics-Based Dynamic Modeling of a Turboshaft Engine Driving a Variable Pitch Propeller

A physics-based dynamic model of a twin-spool turboshaft engine that drives a variable pitch propeller is developed. The primary purpose for the development of this model is for researchers to use it to develop new engine control algorithms and study/predict off-design transient responses of gas turbine propulsion systems. In this model, the dynamics of the engine are defined to be the two spool speeds, and the control inputs are defined to be the fuel flow rate and the propeller pitch angle. Mockups of the turboshaft engine and the variable pitch propeller are developed using CAD software, and based on the mockups, a test stand for gas turbine engine static tests is developed. Experimental results are used to verify the dynamic model of the JetCat SPT5 turboshaft engine with a variable pitch propeller mounted on it. Based on experimental data, realistic performance maps of the engine components, including the high-pressure compressor, high- and low-pressure turbines, and variable pitch propeller are cons...