Design of an Ultra-High-Speed Permanent-Magnet Motor for an Electric Turbocharger Considering Speed Response Characteristics

This paper presents a design methodology and analysis for a 4-kW 150-krpm ultra-high-speed surface-mounted permanent-magnet synchronous motor (SPMSM) to electrically assist a turbocharger. The proposed design methodology is aimed at achieving a required torque and speed. In addition, this study seeks a fast-speed response as a design objective to eliminate turbo lag more effectively. First, an existing prototype that does not meet the target performance is presented. The loss for the prototype, which is difficult to obtain theoretically, is obtained experimentally and reflected in the design. The speed response characteristic of the machine is analyzed through the electromechanical undamped natural frequency and damping ratio. Design parameters such as the permanent-magnet (PM) grade, the turn number of coils, and the axial length of the motor are designed. The resulting improved motor achieves higher power density as well as faster speed response than the prototype. Experiments verified the effectiveness of the motor in the electrically assisted turbocharger. In system experiments with the turbocharger, the rising speed of the boost pressure is improved by 44.9% due to the designed motor.