Placement of Hall Effect Sensors in Permanent Magnet Motors Featuring Quasi-Halbach Array Configuration to Detect the Rotor Position Using Orthogonal Flux

Abstract

Knowledge of the rotor position is critical for the control of permanent magnet (PM) motors. Hall effect sensors (HESs) measure magnetic fields and provide a simple, inexpensive solution for determining rotor position. In existing systems, the HESs require the addition of PMs outside the motor, or the HESs are sensitive to the magnetic fields produced by the coil, in addition to the magnetic fields from the rotor PMs. However, quasi-Halbach arrays (QHAs), which are used in high-performance PM machines, produce a magnetic field orthogonal to the plane in which the PMs are magnetized. In this article, we investigate placing HESs to measure this orthogonal magnetic field for a simulated axial flux motor. In addition, we investigate this approach in simulation and experiment for a linear system. Both simulation and experimental results show that placing these HESs to measure the orthogonal magnetic fields generated by QHAs allows for the detection of the rotor position using the existing PMs in the machine and without being significantly affected by the magnetic field produced by the stator. In particular, the HESs should be placed orthogonally beyond the QHA and aligned with a stator slot to achieve the best performance. In both the simulated axial flux machine and the experimental linear system, positioning the HES in this manner yielded very good agreement between the flux density waveforms at no load and full load. In addition, the zero crossings of the flux density waveform, which are important for some control algorithms, were less than 1 electrical degree difference between no load and full load.