Rotor Resonances Analyses of High-Speed High Power Permanent-Magnet Electrical Machines

Abstract

High-speed electric machines (HSEMs) have been widely used in many of today’s applications. The mechanical design of a high-speed electrical machine is a very responsible task because this type of machine is often designed to operate with a speed that is close to the flexural critical speeds. Errors in the prediction of these speeds can lead to unpleasant phenomena such as excessive acoustic noise emissions and catastrophic failures during operation. For high-speed machines, in particular, it is very important to accurately predict natural frequencies of the rotor at the design stage so as to minimize the likelihood of failure. The problem of reliable mechanical design of a high-speed rotor is more serious for a highspeed permanent-magnet (PM) machine because it has a more complex construction than a high-speed induction machine. The high-speed PM machines have some advantages over the high-speed induction machines like better utilization factors, higher power factors and higher efficiencies. The main goal of this project is to contribute to the development of high-speed machines by examining the design issues and performance. For permanent-magnet synchronous motors driven by high-frequency drives, the rotor speed is normally above 30 000 rpm, and it may exceed 100 000 rpm. The choice in this project has been made for a 7-kw permanent magnet synchronous machine at 200,000 rpm. 3D finite element analysis (ANSYS WORKBENCH 15) was used to determine the natural frequencies and rotor patterns of a synchronous high-speed permanent magnetic motor, to assess the impact of leading design parameters, such as length, column diameter, span, bearings, material properties, and to compare the results of the finite element program with the results of analytical methods (i.e. critical speed).