Research On Measurement Model And Error Correction Of Redundant Displacement Sensors In Magnetic Bearings

Magnetic bearings depend on the controllable electromagnetic force to suspend the rotor in the set position, which have the advantages of no mechanical contact, no friction and on wear. Therefore, magnetic bearing has become the ideal supporting pattern of high-performance rotor system in key equipments such as machine tool spindles, maglev electric engines and so on. With the reliability demands of equipments becoming higher and higher, the reliability problem has become the research emphasis of magnetic bearing technology at present.The magnetic bearing relies on the control loop to realize its performances, so the displacement sensors are the key components. If the displacement sensor fault occurs, the bearing system will lose the stability conditions of corresponding degree of freedom, which causing the rotor's instability. The redundant sensor technology can improve the reliability of magnetic bearing system significantly. However, during the use of redundancy displacement sensors, as the layout and assembly of the sensors are often not ideal, measurement errors are introduced to control system, which directly affect the system's control accuracy and reliability.In this paper, the redundant sensor technology of magnetic bearing is researched. Firstly, the mechanical and control structure of magnetic bearing system were analyzed, and the measurement model of the displacement sensor under different installation angles was established. Secondly, the different error factors were analyzed, such as the non-parallel of the stent, installation inclination of the sensors, the misalignment between detection center and mechanical center. The influence mechanism of the above factors on the magnetic rotor displacement detection precision was analyzed as well. Thirdly, the magnetic bearing control system containing redundant sensors was built and the models of each component in the control system were established. The error correction was simulated based on the Matlab- simulink platform. Finally, the off-line iteration algorithm was proposed and experimental verification of the redundant displacement sensor based on coordinate transformation was carried out. The experimental results show that the measuring error generated by redundant displacement sensor may cause the precision of magnetic bearing control system decrease, even out of control. The method discussed in the paper can effectively reduce the effects of the sensors' non-ideal layout and assembly on the rotor's control precision and reliability.The innovation points of the paper lie in:(1) the strategy model of magnetic bearing system under redundant sensor structure was built. The formation mechanism and correction strategy of measuring errors under different error factors were analyzed and verified by simulation.(2) The off-line iteration algorithm was proposed to correct the measuring errors caused by the sensors' non-ideal layout and assembly.The researches in the paper not only improve the displacement measuring precision under the installation of redundant sensors, but also provide some supporting for the application of the redundant sensor technology in the magnetic bearings, which has important significance to improve the reliability of magnetic bearing in high-performance equipments.