Optimized rotor structural design methodology for high-speed electrical machines based on mechanical characteristics

In high-speed electrical machines (HSEM), mechanical vibration associated with critical speeds of rotor systems can be detrimental to the machine operational stability, especially for vibration near resonances. The structural sizing of a rotor system is often constrained to its mechanical parameters, such as its overall weight, maximum torque, and rated power, which complicate the design, necessitating an iterative design optimization process. This work presents a systematic and iterative rotor structural sizing optimization methodology that incorporates semi-analytical and numerical modeling, specifically taking into account multiple mechanical design parameters from the static, rotordynamic, and electromagnetic-thermal evaluation. The proposed methodology provides an effective design optimization procedure for a general application of HSEM to accelerate its design process, by which the power density and the dynamics stability during high-speed operation are optimized simultaneously. A parametric analysis was carried out where a 24-kW, 12,000-rpm aviation starter-generator was optimized. It was demonstrated that the power density of the machine could be increased by 14.7% from 2.3 to 2.6 kW/kg, while the critical speed was increased by 128.6% from 1,400 to 3,200 Hz.