Magnetic field model for direct field-feedback control of a permanent magnet spherical motor

This paper presents a forward magnetic-field model for real-time control of a permanent magnet spherical motor (PMSM). Utilizing the rotor magnetic field on a 2-dimensional (2D) domain, this model can precisely compute the magnetic fields at embedded sensors for any 3-DOF rotor orientation, providing magnetic-field references which allows for feedback with magnetic field measurements (instead of explicit orientation) in a PMSM control system. The 2D magnetic field data can be acquired from either theoretical computations or experimental calibrations, hence capable of taking into accounts the inaccuracies in a real system. Meanwhile, the algorithms involved in this model only require vector computations and are applicable for real-time implementations. This forward model is numerically validated on a 3-DOF PMSM with an existing magnetic field model and an orientation control simulation is performed incorporating the forward magnetic-field model.