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Technical Briefs

Quantitative Fault Tolerant Control Design for a Leaking Hydraulic Actuator

[+] Author and Article Information
Mark Karpenko

Department of Mechanical and Aerospace Engineering, Naval Postgraduate School, Monterey, CA 93943

Nariman Sepehri1

Department of Mechanical and Manufacturing Engineering, Fluid Power Research Laboratory, University of Manitoba, Winnipeg, MB, R3T 5V6, Canadanariman@cc.umanitoba.ca

1

Corresponding author.

J. Dyn. Sys., Meas., Control 132(5), 054505 (Aug 19, 2010) (7 pages) doi:10.1115/1.4001707 History: Received June 13, 2008; Revised February 23, 2010; Published August 19, 2010; Online August 19, 2010

This paper documents the design of a low-order, fixed-gain, controller that can maintain the positioning performance of an electrohydraulic actuator operating under variable load with a leaking piston seal. A set of linear time-invariant equivalent models of the faulty hydraulic actuator is first established, in the frequency domain, by Fourier transformation of acceptable actuator input-output responses. Then, a robust position control law is synthesized by quantitative feedback theory to meet the prescribed design tolerances on closed-loop stability and reference tracking. The designed fault tolerant controller uses only actuator position as feedback, yet it can accommodate nonlinearities in the hydraulic functions, maintain robustness against typical parametric uncertainties, and maintain the closed-loop performance despite a leakage fault that can bypass up to 40% of the rated servovalve flow across the actuator piston. To demonstrate the utility of the fault tolerant control approach in a realistic application, the experimental fault tolerant hydraulic system is operated as a flight surface actuator in the hardware-in-the-loop simulation of a high-performance jet aircraft.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the hydraulic actuator for mathematical modeling

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Figure 2

Two degree of freedom QFT control system with nonlinear hydraulic actuator modeled by LTIE plant set Pe

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Figure 3

Time histories of acceptable plant responses using Eq. 6 with p1=15, p2=20, ωp=85, ζp=1.0, and λ∊[14,33]: (a) acceptable position responses (output); (b) typical valve spool displacements (input)

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Figure 4

Templates of the LTIE plant set Pe(ω) at selected frequencies ω (rad/s), with several LTIE frequency response curves included for reference

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Figure 5

QFT bounds B(ω) and designed nominal fault tolerant loop transmission L(jω)

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Figure 6

Reference tracking envelope formed by TL and TU with typical closed-loop frequency responses F(GPe/1+GPe) over the range of internal leakage magnitudes and parameter uncertainties

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Figure 7

Experimental setup: (a) photograph of hardware-in-the-loop test rig; (b) schematic of the test rig architecture

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Figure 8

Typical experimental step responses for different loading rates (0–80 kN/m) under normal and faulty operations: (a) actuator position; (b) internal leakage magnitude; (c) tracking error; and (d) control signal

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Figure 9

Roll attempt in the presence of internal leakage fault using fault tolerant controller: (a) left tail deflection; (b) internal leakage magnitude; (c) actuator control signal; (d) applied aerodynamic force; (e) bank angle; and (f) attack and sideslip angles

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Figure 10

Roll attempt in the presence of internal leakage fault using conventional controller: (a) left tail deflection; (b) internal leakage magnitude; (c) actuator control signal; (d) applied aerodynamic force; (e) bank angle; and (f) attack and sideslip angles

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