Linear Hall sensors for rotor position detection in external rotor permanent magnet synchronous motors

Traditional rotor position detection schemes typically mount Hall sensors on the stator or motor base to measure the air-gap magnetic field or permanent magnet leakage. However, armature reaction significantly influences detection accuracy. This study proposes mounting Hall sensors on printed circuit boards (PCBs) external to the rotor of an external rotor permanent magnet synchronous motor (PMSM). With the permanent magnet slightly extending beyond the rotor yoke, rotor position is determined by detecting the magnet's field, which is minimally influenced by armature reaction. Theoretical and experimental analyses reveal that when two Hall sensors are placed at a 90° interval on the PCB, the fundamental phases of their signals are not orthogonal, resulting in position errors. To resolve this, it is shown that orthogonal fundamental phases are achieved when the sensors are spaced at an interval of 90° · P_r/(P_r+1). The theoretical predictions are validated through ANSYS Maxwell finite element simulations and physical motor experiments, confirming the feasibility of the proposed position detection scheme.