Design and Application of High-speed Electrically Excited Synchronous Machines

Licentiate thesis, 2026

Electrically excited synchronous machines (EESMs) have emerged as a rare earth free alternative for EV (electric vehicle) traction, offering enhanced sustainability and operational flexibility. Furthermore, high-speed EESMs present a promising solution for achieving compact, efficient, and material-efficient traction systems, and have gained increasing attention in industrial applications.

First, An evaluation of high-speed EESMs based on the WLTC (Worldwide Harmonized Light Vehicles Test Cycle) driving cycle using a light EV model demonstrates that the operating points are distributed over a wide motor speed range. Across representative driving scenarios, including urban, countryside, and highway operation, these operating points are located within high-efficiency regions exceeding 96%, demonstrating that the proposed high-speed EESM consistently operates near its optimal performance. Furthermore, the selected light EV exhibits satisfactory dynamic capability, achieving a 0–100 km/h acceleration time of 8.1 s. This result confirms that the high-speed EESM provides a well-balanced performance, particularly under typical highway driving conditions.


Building upon this, the present study examines AC loss characteristics in a typical EESM equipped with hairpin windings. The results indicate that the solid losses are affected by the stator current angle, reaching a maximum near 45° and a minimum around 180°, with a difference of approximately 17.6% under identical current magnitudes. Furthermore, with a fixed stator current amplitude, increasing the rotor excitation current significantly elevates the AC resistance near 45°, while its effect remains limited near 180°. For the mechanical analysis of high-speed EESMs, both thermal expansion and centrifugal effects are considered. The results show that thermal expansion is the dominant factor influencing rotor stress and deformation, especially at elevated temperatures, while centrifugal force plays a secondary role even under high-speed conditions. Additionally, among the evaluated sleeve materials, carbon fiber provides the most effective structural reinforcement, producing the lowest stress and deformation.

This study presents the analysis of electromagnetic and structural design considerations in high-speed EESMs, providing a useful guidance for achieving improved performance, durability, and robustness in industrial applications.