Design Process and Verification of SPMSM for a Wearable Robot Considering Thermal Characteristics Through LPTN

Abstract

According to an understanding of wearable robot systems, this article suggests an appropriate design process for surface-mounted permanent magnet synchronous motor (SPMSM) for the joints of wearable robots. The major requirements of SPMSM for the wearable robot are investigated and categorized into the dimensional constraints, electromagnetic performances, and thermal restrictions. Given the defined requirements, the electric motor design process for an actual robot is proposed, considering electromagnetic and thermal characteristics. For thermal analysis, the lumped parameter thermal network (LPTN) is adopted, and the process to compose a precise LPTN for the SPMSM is presented. With given controller and electric motor specifications, the numbers of poles and slots are determined, and fractional-slot concentrated winding is adopted considering the overall behavior of the SPMSM such as torque density and noise and vibration. As a preliminary design, the shape of the rotor including permanent magnets, shape of the stator, and the number of turns are designed via space harmonic analysis which is fast. Subsequently, a detailed design process is performed via finite-element analysis. At this stage, the thermal characteristics considering the driving cycle are analyzed via the LPTN, which is appropriate for parametric design. The final model is determined from electromechanical and thermal viewpoint. Finally, experiments are conducted to validate the proposed design process.