TY - JOUR

T1 - Methodology to Evaluate the Mechanical Stress in High-Speed Electric Machines With Buried Magnets

AU - Gerlach, Martin Enno

AU - Zajonc, Maximilian

AU - Ponick, Bernd

N1 - Funding Information: Paper 2020-EMC-1314.R2, presented at the International Symposium on Power Electronics, Electrical Drives, Automation and Motion, Sorrento, Italy, Jun. 24–26, and approved for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Electric Machines Committee of the IEEE Industry Applications Society. This work was supported by the Federal Ministry of Economic Affairs and Energy on the basis of a decision by the German Bundestag. (Corresponding author: Martin Enno Gerlach.) Martin Enno Gerlach and Bernd Ponick are with the Institute for Drive System and Power Electronics, Leibniz University Hannover, 30167 Hannover, Germany (e-mail: martin.gerlach@ial.uni-hannover.de; ponick@ial.uni-hannover.de).

PY - 2021/5/4

Y1 - 2021/5/4

N2 - High-speed electric machines are gaining importance due to their high power density. The evaluation of the mechanical stress in the rotor is a crucial part of the design process for this type of machines. It is insufficient to evaluate just the static mechanical stress at maximum speed. The dynamic mechanical stress between the state of standstill and maximum speed needs to be considered as well to ensure the high fatigue strength of the rotor. One criterion that is commonly used to analyze the dynamic load in a material is the Smith diagram. In this work, a new methodology is introduced to consider both, the dynamic and the static mechanical stress, in the rotor of a high-speed electric machine. First, the von Mises stress criterion is used to examine the static mechanical stress in the rotor core. Second, the Smith diagram is used to evaluate the dynamic mechanical stress and the high fatigue resistant of the rotor. The methodology is, then, applied to a high-speed electric machine with two different types of buried magnets: 1) a rotor with buried magnets in v-shape and 2) a rotor with a buried bar magnet. Both rotors are analyzed concerning their state of stress. It can be seen that high dynamic stress occurs at the bridges in the rotor. The stress alternates with an amplitude up to $\sigma _\text{alt}=290\,\text{MPa}$. The designs are though limited due to the high static stress at the bridges of the magnet slot.

AB - High-speed electric machines are gaining importance due to their high power density. The evaluation of the mechanical stress in the rotor is a crucial part of the design process for this type of machines. It is insufficient to evaluate just the static mechanical stress at maximum speed. The dynamic mechanical stress between the state of standstill and maximum speed needs to be considered as well to ensure the high fatigue strength of the rotor. One criterion that is commonly used to analyze the dynamic load in a material is the Smith diagram. In this work, a new methodology is introduced to consider both, the dynamic and the static mechanical stress, in the rotor of a high-speed electric machine. First, the von Mises stress criterion is used to examine the static mechanical stress in the rotor core. Second, the Smith diagram is used to evaluate the dynamic mechanical stress and the high fatigue resistant of the rotor. The methodology is, then, applied to a high-speed electric machine with two different types of buried magnets: 1) a rotor with buried magnets in v-shape and 2) a rotor with a buried bar magnet. Both rotors are analyzed concerning their state of stress. It can be seen that high dynamic stress occurs at the bridges in the rotor. The stress alternates with an amplitude up to $\sigma _\text{alt}=290\,\text{MPa}$. The designs are though limited due to the high static stress at the bridges of the magnet slot.

KW - High fatigue strength

KW - high-speed electric machines

KW - Hooke's law

KW - mechanical stress

KW - Smith diagram

KW - static strength

KW - von Mises stress

KW - von Mises stress.

KW - Hooke’s law

UR - http://www.scopus.com/inward/record.url?scp=85105889323&partnerID=8YFLogxK

U2 - 10.1109/TIA.2021.3077527

DO - 10.1109/TIA.2021.3077527

M3 - Article

VL - 57

SP - 3643

EP - 3653

JO - IEEE Transactions on Industry Applications

JF - IEEE Transactions on Industry Applications

SN - 0093-9994

IS - 4

M1 - 9423535

ER -