Analytical model of radial forces considering mutual effects between torque and levitation current space vectors in 5-phase PM bearingless motors

The interaction between the current space vector producing torque and the one producing radial forces in a multiphase bearingless Surface-Mounted Permanent Magnet Synchronous Motors (SPMSM) is investigate. In fact, due to the spatial harmonic content of the stator mmf and the rotor magnets, it is necessary to consider not only the mutual effect between the magnetic field related to a single stator current space vector and the rotor magnetic field produced by the magnets, but also to take into account the coupling between the different stator current space vectors, that give non predictable effects on the radial forces distribution. The purpose of this work is to create a model allowing to predict amplitude and direction of the force produced in "bearingless" motors. This will give a powerful tool for the design of the levitation control system. An analytical model to calculate the radial forces is presented, based on the Fourier series harmonic distribution, considering all the interactions between the magnetic fields given by every stator current space vector and by rotor magnets. The accuracy of calculations is then verified by comparing the obtained results with FE analysis.