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TECHNICAL PAPERS: Gas Turbines: Structures and Dynamics

Transient Rotor/Active Magnetic Bearing Control Using Sampled Wavelet Coefficients

[+] Author and Article Information
Iain S. Cade

Department of Mechanical Engineering, University of Bath, Bath BA2 7AY, UKi.s.cade@bath.ac.uk

Patrick S. Keogh, M. Necip Sahinkaya

Department of Mechanical Engineering, University of Bath, Bath BA2 7AY, UK

J. Eng. Gas Turbines Power 129(2), 549-555 (Jul 14, 2006) (7 pages) doi:10.1115/1.2436570 History: Received July 05, 2006; Revised July 14, 2006

A novel method for transient rotor/active magnetic bearing control using sampled wavelet coefficients is proposed. Control currents are formulated in the wavelet transform domain, prior to signal reconstruction. The wavelet based controller is designed from target transient responses due to step changes in wavelet coefficients of applied forces. Transient system dynamics are embedded in the controller and evaluated from on-line system identification. Experimental validation is undertaken using a flexible rotor/active magnetic bearing system. Mass loss tests were performed at two critical speeds corresponding to near sudden changes in unbalance that are capable of exciting rotor dynamic modes in a transient manner. The controller is shown to suppress the transient responses within a finite settling time.

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Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Block diagram showing feedback control structure in the wavelet coefficient domain

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Figure 2

Experimental flexible rotor/ active magnetic bearing facility. Sensors measuring displacement relative to base motion are shown as 1-8. Experimental mass loss plane is also shown.

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Figure 3

System identification at sensor 1 due to wavelet harmonic forcing in control axis 1 at rotational speed of 11Hz: (a) measured synchronous harmonic wavelet coefficients; (b) tenth-order inverse transfer function; and (c) fifth-order inverse transfer function.

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Figure 4

Acceptable performance diagram for a prescribed transient exponential decay at a rotational speed of 11Hz

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Figure 5

Measured mass loss response at the nondriven end and driven end AMB at a rotational speed of 11Hz: (a),(b) show uncontrolled response and (c),(d) show controlled response. Wavelet coefficients are shown in (e),(f).

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Figure 6

(a) and (b) show the wavelet control forces at nondriven end and driven end active magnetic bearing at a rotational speed of 11Hz; and (c) and (d) show the total control force

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Figure 7

Measured mass loss response at the nondriven end and driven end AMB at a rotational speed of 18Hz: (a),(b) show uncontrolled response and (c),(d) show controlled response. Wavelet coefficients are shown in (e),(f).

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Figure 8

Measured mass loss response and wavelet coefficients at the nondriven end at a rotational speed of 11Hz: (a) and (b) correspond to a fast exponential decay rate; (c) and (d) correspond to a slow exponential decay rate; and (e) and (f) show a prescribed linear decay.

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