Modelling and identification for control of gas bearings

Abstract

Gas bearings are popular for their high speed capabilities, low friction and clean operation, but suffer from poor damping, which poses challenges for safe operation in presence of disturbances. Enhanced damping can be achieved through active lubrication techniques using feedback control laws. Such control design requires models with low complexity, able to describe the dominant dynamics from actuator input to sensor output over the relevant range of operation. The mathematical models based on first principles are not easy to obtain, and in many cases, they cannot be directly used for control design due to their complexity and parameter uncertainties. As an alternative, this paper presents an experimental technique for "in situ" identification of low complexity models of the entire rotor-bearingactuator system. Using grey-box identification techniques, the approach is shown to be easily applied to industrial rotating machinery with gas bearings and to allow for subsequent control design. The paper shows how piezoelectric actuators in a gas bearing are efficiently used to perturb the gas film for identification over relevant ranges of rotational speed and gas injection pressure. Parameter-varying linear models are found to capture the dominant dynamics of the system over the range of operation. Based on the identified models, decentralised proportional control is designed and is shown to obtain the required damping in theory as well as in a laboratory test rig.

Controllable Sliding Bearings and Controllable Lubrication Principles—An Overview

“…Theoretical and experimental results show a significant increase in the damping ratio, enabling the flexible (and relatively heavy) rotor to run safely across the critical speeds (without significant vibration amplifications) and extending its operational range 50% over the first critical speed without any instability problems. The damping ratio associated to the first flexural bending mode is increased by a factor of nine in comparison to the hybrid lubrication (without feedback control) as documented in [40][41][42]. It is important to highlight that a further increase of rotor angular velocity is not limited by new instability problems caused by fluid film forces but by large lateral vibrations associated with a second resonance in which the flexible rotor and turbine connected by the flexible coupling vibrate out-of-phase.…”

Enhancing damping of gas bearings using linear parameter-varying control

“…Mechatronic systems are an attractive active solution where electromechanical actuators are embedded into the bearings with advanced control systems. A promising design solution is the controllable gas bearing where pressurised air is injected through piezo-actuators [4,6,7]. Active gas bearings are attractive for a number of applications including compressors, atomisers and turbochargers, but the bearing development is still in its early stage.…”

“…Due to the multi-physics nature of the system high-fidelity models as those presented in [4,9] result in large dimensionality (model order higher than hundred), which is generally unsuitable for control system design. Therefore an alternative approach has been explored in [7], where a linear parameter-varying (LPV) identification method was applied to identify low-complexity models of the entire rotor-bearing actuator-sensor system. The obtained model captured the dynamics of the machine and its parameters are scheduled with the shaft angular velocity and air injection pressure.…”

Modeling of Flexible Beam Using System Identification Approach

“…Noor Fadhilah Mat Ros, Mohd Sazli Saad, Mohd Zakimi Zakaria, Intan Zaurah Mat Darus as flexible single link system [11], automotive engine fuelled [12], internal combustion engine [13], rotor bearing foundation system [14], control of gas bearings [15] and turbojet engine [16]. From the review, system identification is obviously seen to be used successfully in modeling of any system and becomes one of the preferred methods.…”