Modeling and Control of Bearingless Linear Motors

Reza Hosseinzadeh

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

This dissertation proposes dynamic modeling and model-based control design for bearingless linear motor systems. A bearingless motor produces both the traction and levitation forces using the same iron core. In bearingless linear systems, the magnetic levitation of the moving part (mover) renders the linear mechanical bearings redundant. However, controlling bearingless systems is more challenging than those with mechanical bearings. Conventional control methods, such as Proportional-Integral-Derivative (PID) controllers, can be employed, but their tuning method is often heuristic. Therefore, this dissertation considers model-based control methods. The prerequisite to this control design methodology is a sufficiently accurate dynamic model of the system. Thus, this dissertation considers two dynamic models for bearingless systems. A dynamic model is presented for a bearingless Linear Flux-Switching Permanent-Magnet (LFSPM) motor. This dynamic model is developed based on magnetic equivalent circuits, including the effects, such as magnetic saturation and airgap variation. For a double-sided bearingless LFSPM motor system, a state-feedback control method is presented. An approximate feedback linearization method is proposed to account for any nonlinear airgap dependency and the cross-coupling between the attraction and thrust forces. For energy efficient control, a resistive-loss minimization method is proposed. The minimization algorithm calculates the minimum reference currents for the given force references and the position of the mover. The results from the optimization method are used in the form of lookup tables and artificial neural networks. A comparison is provided between the two implementation methods. A dynamic model is developed for six-degree-of-freedom bearingless systems. The example system is a quadruple-sided bearingless linear motor system comprising eight three-phase motor units. To model the unbalanced magnetic torque, each motor unit is spatially divided into several submotors. The submotors of a motor unit have the same current, while the flux linkages and forces are different in a tilted position. The developed models can be utilized in time-domain simulations for system analysis and real-time control system development. The methods presented in this dissertation are evaluated using double-sided and quadruple-sided bearingless flux-switching permanent-magnet linear motors.
Translated title of the contributionModeling and Control of Bearingless Linear Motors
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Hinkkanen, Marko, Supervising Professor
  • Martin, Floran, Thesis Advisor
  • Saarakkala, Seppo, Thesis Advisor
Publisher
Print ISBNs978-952-64-2171-1
Electronic ISBNs978-952-64-2172-8
Publication statusPublished - 2024
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • linear motor
  • magnetic levitation
  • magnetic model
  • modeling
  • bearingless
  • flux-switching permanent-magnet machine
  • unbalanced magnetic pull
  • linear actuator
  • lumped element
  • artificial neural networks
  • energy efficiency

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