Design of High Speed (HS) electric machines is an iterative process that requires a multidisciplinary design team to accomplish the required performance. In this study, a design space method (DSM) is developed to streamline conceptual designing of a high-speed and high-power electric machine. The method uses analytical equations and a rotordynamic model to determine geometrical dimensions based on the application requirements. These dimensions create a feasible baseline design for the particular application. However, considering the dimensions as design variables and using the baseline design as a starting point, a multidimensional combination and interaction of the design variables and the correlated output for the particular topology of motor and performance range can be further studied for design exploration and optimization purposes. The study includes a test case where the baseline dimensions are determined and compared to an existing machine from literature, and then further explored to identify the sensitivity of different outputs with respect to different design variables. The method enables rapid design iterations, rotordynamics and rotor mass optimization. The baseline design can be also used as a starting point for the detailed design.
The optimization of high-speed active magnetic bearing rotor layout concerning the effect of external disturbance is studied. The centrifugal loads and related strain forces in the HS rotors limit the maximum rotational speed and AMB capacity, bandwidth, and location limit control of dynamics. Additionally, external synchronous disturbances, i.e., unbalance forces, rotor runout, application forces from the impeller, and static forces cause adverse effects on active control and pose limitations. Therefore, to achieve a sub-critical rotor, the dimensions of electric machine components, such as bearings, seals, and impellers affect each other and have to be constrained. The proposed method examines the effect of disturbances and locations and resulting dynamic limitations at the conceptual design phase. This enables the design of the AMBs and component layout to the application demands. The method uses maximum singular values to examine the effects of disturbances on bearing forces and rotor displacements at key locations.
The design of high-speed machines requires extensive multidisciplinary approach to achieve a high-performance machine. The design process is highly iterative, and analytical methods can accelerate it with faster design iterations at low computational efficiency to find the optimum parameters at conceptual stage. In this study, an analytical design method for obtaining rotor mechanical limits is developed for squirrelcage slitted high-speed induction machine rotors. In high-speed electric machines, the design is made specifically to meet the application requirements and the objective is to reach a high efficiency. This means that the design needs to be made often from the scratch and existing designs can rarely be used as a starting point. The method developed in this study enables rapid design iterations, especially considering the mechanical limits in the conceptual and layout design phase. The proposed analytical design method is validated with three different case studies.
Solid rotors are preferred choice of topology for high-speed applications due to their robustness against high centrifugal forces at high speeds, ease of manufacturability, and higher temperature range. However, for peripheral speeds lower than 200 m/s, laminated rotor structure is preferred because of lower eddy current losses resulting in higher efficiency. However, laminated rotors are complex to manufacture, sensitive to temperature and have vibration and mechanical integrity related issues. As a compromise between these two designs in terms of mechanical strength and efficiency, this study investigates a radial flux 2 MW, 15 krpm induction motor rotor core made of thick laminations. The baseline dimensions of the thick-lamination rotor design are calculated using analytical equations considering aspects such as mechanical stresses, rotordynamics, and bearing parameters. Lastly, the lamination to lamination contact behavior under unbalance load is analyzed for a simplified model and their effect on natural frequencies is studied.
High-speed machines are used in a growing range of applications, including in compressors and turbines. We spoke to Professor Lassi Aarniovuori, Professor Juha Pyrhönen and M.Sc. Juuso Narsakka about the work of the MUSK 2 project in developing a megawatt class universal high-speed machine, which they ultimately aim to bring to the commercial market.
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