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A Magnetic Bearing Suspension System for High Temperature Gas Turbine Applications: Control System Design PUBLIC ACCESS

[+] Author Affiliations
James R. Scholten

The Charles Stark Draper Laboratory, Inc., Cambridge, MA

Paper No. 97-GT-029, pp. V004T15A006; 8 pages
doi:10.1115/97-GT-029
From:
  • ASME 1997 International Gas Turbine and Aeroengine Congress and Exhibition
  • Volume 4: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education; IGTI Scholar Award
  • Orlando, Florida, USA, June 2–5, 1997
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-7871-2
  • Copyright © 1997 by ASME

abstract

A practical magnetic-bearing control system has been designed based upon modeling and simulation of the dynamics of a jet engine turbine shaft and bearing system. Simulations include models for flexible rotor dynamics, magnetic actuators, auxiliary touchdown bearings, ordinary and extraordinary external loads, and disturbances from rotor imbalance, stator vibration, and noise. The shaft model includes a motor-generator which acts as an uncontrolled negative stiffness.

The control system is decentralized, running independently for each of the five physical axes of control (1 axial, 4 radial). The fundamental algorithm is classical PID: proportional for broadband stiffness, integrator (with anti-windup) for high load-carrying capacity, and derivative to dampen disturbances. Additional phase lead is provided via a first-order pole-zero pair. The vibration due to rotor imbalance is eliminated by an autobalancing algorithm. Compensation for magnetic actuator non-linearity and varying rotor-stator gap is provided by feedback of sensed magnetic flux, using sensor coils built into the actuator. The control design can be readily implemented using a commercial Digital Signal Processing system. The magnetic bearing actuators will be driven with commercial power amplifiers via customized front-end electronics.

Based upon simulations, the design goal has been achieved of keeping the shaft within two mils of its desired location at the magnetic bearings, under all normal loads. Under extreme external loads, the capacity of the magnetic bearings will be exceeded and touchdown will occur upon backup mechanical bearings. Simulation shows that the control design handles this critical event, which determines the force slew rate required from the actuators.

Copyright © 1997 by ASME
This article is only available in the PDF format.

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