Iron Saturation Impact on High-Frequency Sensorless Control of Synchronous Permanent-Magnet Motor

An increasing interest for permanent-magnet (PM) synchronous machines equipped with fractional-slot concentrated winding is observed. Among others, the surface-mounted PM (SPM) machines are widely used by motor manufacturers. The spoke-type interior PM (IPM) machines are also particularly attractive. Nowadays, PM machines are often selected for variable-speed applications without precise positioning requirements, taking the advantage of sensorless control algorithms. However, the capability to detect the electrical rotor position without sensor also at zero speed (by means of techniques based on high-frequency signal injection) is an enhancing feature that requires a proper machine design. The aim of this paper is to evaluate the impact of both rotor and stator modifications, taking a commercial motor as a reference geometry. The analysis of both SPM and IPM rotor structures, as well as stator tooth geometry variations, pointed out how the machine geometry greatly affects the sensorless capability due the injection of a high-frequency voltage. Finite-elements simulations have been validated by experimental tests on two IPM motors manufactured with a different stator design.