The influence of peripheral and rotation speed on the design, cooling system, and characteristics of an electric machine in a hybrid system

This article analyzes an electric machine with a 200kW external rotor, providing high specific properties and intended for use in hybrid systems. The design of a high-speed synchronous electric machine excited from permanent magnets and fitted with an external rotor was chosen as the most promising to achieve the required specific properties. The main limitation for obtaining the maximum power density in such designs is the rotor structural performance. In order to determine the achievable level of specific power in electric machines at the existing technology level, the article analyzes the electromagnetic and strength characteristics of the design with different peripheral speeds (u = 200-300 m/s) and rotor speeds (n = 20,000-30,000 rpm). The calculation and analytical research established the following: torque pulsation and cogging torque can be minimized by ensuring a peripheral speed of more than 230 m/s; the optimal ratio of the machine’s active part length to its diameter is 0.24-0.26; it is advisable to use a titanium alloy as a rotor material. The article determined the ranges of peripheral speed and rotation speed that provide maximum specific power (11 kW/kg) and efficiency of a high-speed electric machine given the current level of electrical and structural materials. The design of the cooling system was determined and its power consumption was taken into account to obtain the specified values of specific properties.