###### Abstract  
High-speed interior permanent magnet (IPM) motors require highly reliable rotors. Some measures must be adopted to improve rotor safety, but its electromagnetic performance is seriously affected. It is a challenge to achieve excellent electromagnetic characteristics while satisfying mechanical strength. This paper presents an electromagnetic optimization design of high-speed IPM motors considering rotor stress. Firstly, the permanent magnet (PM) is segmented by adding stiffeners to improve stress distribution. The effects of the bridge and stiffener thickness on the rotor stress and electromagnetic performance are analyzed. Secondly, an electromagnetic optimization model is built based on a three-segment PM rotor structure, aiming for maximum efficiency and minimum rotor core losses. Then, the initial design and optimized scheme are compared, the results show that the efficiency, safety and temperature performance of the motor are improved. Finally, a 140 kW, 18,000 rpm prototype is manufactured and tested. The above analysis provides a valuable reference for the design and widespread application of high-speed IPM motors. high-speed interior permanent magnet motor; electromagnetic optimization; rotor stress +
Footnote †: journal: Applied  
0000-0001-5000-0000-0000-0000-0000-0000-0000-0000-00000-00000-00000-00000-00000-00000-00000-00000-00000-000000-00000-000000-000000-00000-000000-00000-  
distribution in [16]. A design method of a high-speed multilayer IPM motor using ferrite PM is proposed considering mechanical stability and irreversible demagnetization [17]. Efficient design optimization methods are proposed for IPM motors, and computational costs are significantly reduced [18; 19]. A multi-physics design method for V-shape IPM motors based on multi-objective optimization is proposed, an improved multi-objective optimization model considering electro-thermal coupling is studied for an 11 kW, 1500 rpm V-type IPM motor in [20]. A new multi-objective optimization based on the multi-layer optimization strategy is proposed in [21] for a V-type IPM motor rated at 3600 rpm, and the torque and loss characteristics are optimized. Some scholars use artificial intelligence to optimize IPM motors for electric vehicles [22]. From the above literature description, it can be concluded that the influence of rotor design parameters on the electromagnetic performance and rotor stress of the IPM motors is obvious. Especially, for high-speed IPM motors, some measures have to be adopted to ensure rotor mechanical reliability during high-speed rotation, such as large bridge thickness and increasing stiffeners between PMs. Although these special measures increase rotor safety, the electromagnetic performance is seriously affected, resulting in high magnetic flux leakage, a poor power factor. A successful scheme for high-speed IPM motors should meet high rotor reliability and good electromagnetic performance at the same time. Therefore, this paper proposes an electromagnetic optimized design of a high-speed IPM motor considering rotor stress. In response to the above problems and to create a rotor with an excellent electromagnetic performance and high-reliability mechanical strength simultaneously, a multi-objective optimization is proposed to consider the mutual effects of electromagnetic and rotor stress. The key innovations in this paper are as follows:  
On the one hand, rotor stress is considered in the electromagnetic design optimization. To improve the maximum stress distribution of the rotor core, rotor structures with stiffeners are adopted. For the rotor structure, the influence of segment number and stiffener thickness on electromagnetic and mechanical characteristics is analyzed primarily. On the other hand, based on the above analysis, the electromagnetic optimization model considering rotor stress is established, which deals with motor efficiency, rotor core loss, line back- electromotive force (EMF), power factor, and maximum rotor stress.