Design and Transient Performance Analysis of a Functionally Graded Rotor for High-Speed Synchronous Reluctance Motors in Electric Vehicle

Abstract

This thesis presents the design and performance analysis of a functionally graded (FG) rotor for a high-speed Synchronous Reluctance Motor (SynRM) targeting 150 kW at 18,000 RPM for electric vehicle applications. The core problem addressed is the conflict between mechanical strength and magnetic efficiency in high-speed SynRM rotors, where steel bridges provide structural support but cause q-axis flux leakage that reduces torque production. A functionally graded material system using M-19 silicon steel and phosphor bronze is proposed to replace steel bridges. Three rotor configurations were compared: a solid baseline rotor, a standard bridged rotor, and a bridgeless FGM rotor with phosphor bronze barrier fill. The rotor geometry was designed in Autodesk Inventor Professional as individual lamination profiles. Electromagnetic simulation was performed using FEMM 4.2 in the magnetostatic regime, where a 24-slot 4-pole motor was excited with balanced three-phase peak currents of I_A = 300 A, I_B = I_C = −150 A. Flux linkage, phase inductance, and Maxwell stress tensor torque were extracted from the circuit properties panel for each rotor case. Structural analysis was conducted in ANSYS Static Structural 2026 R1 on individual lamination layers under a rotational body load of 18,000 RPM, with the shaft bore face fixed as the boundary condition. Full rotor stack simulation was not possible due to computational hardware limitations. Electromagnetic results show the FGM rotor reduces q-axis flux leakage by 7.3% and improves the saliency indicator by 58% compared to the standard bridged design. Structural results show the standard steel rotor reaches 289.86 MPa at the barrier ribs with a safety factor of only 1.24, while the FGM rotor reduces peak strain by 58.4% and raises the safety factor to 1.79. Peak copper loss is calculated at 4.08 kW, requiring water jacket cooling. The phosphor bronze fill also improves rotor thermal conductivity from 23 to 50 W/mK. The proposed design uses no rare-earth materials, presenting a sustainable and cost-effective alternative for high-speed EV traction motors and contributing to the development of domestic electric vehicle engineering capability in Mongolia.