High-speed permanent-magnet synchronous machines (HS PMSMs) are a popular topology among modern electrical machines. Suitable applications for such machines are low-power vacuum pumps, compressors, and chillers. This paper describes a systematic design methodology for an HS PMSM using two case studies. The design process for such high-speed (HS) machines is multidisciplinary and highly iterative due to the complex interaction of the many design variables involved. Consequently, no single optimum solution exists, and multiple possible solutions can meet the customer requirements. Practical solutions should be within acceptable thermal limits, should be energy-efficient, and should be rigid enough to withstand the forces exerted during operation. The proposed design flow is divided into steps that are presented in this paper in the form of a flowchart with emphasis on mechanical aspects. Each step represents a task for a thermal, mechanical, or electrical engineer. The features of each step and the prerequisites for moving to the next step are discussed. The described methodology was implemented in the design of two HS PMSMs. The output performance results of the design flow are compared with measured results of the prototypes. The design process described in this paper provides a straightforward procedure for the multidisciplinary design of HS permanent magnet electrical machines.

Multidisciplinary Design Process of a 6-Slot 2-Pole High-Speed Permanent-Magnet Synchronous Machine

High-speed permanent magnet synchronous machines (PMSMs) have attracted much attention due to their high power density, high efficiency, and compact size for direct-drive applications However, the consequent power loss density is high, and hence heat dissipation is a major technical challenge This is particularly the case for high-speed operation In this paper, a MW level high-speed PMSM is designed and its electromagnetic and mechanical power losses comprehensively investigated using finite element analysis The transient machine demagnetization performance is studied, and a composite rotor structure is proposed to improve machine antidemagnetization capability The temperature distribution of the proposed high-speed PMSM is also analyzed using a fluid-thermal coupling method with calculated power loss Experiments conducted on a prototype of the high-speed PMSM demonstrate the effectiveness of the numerical models developed and validate the results obtained

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Power Loss and Thermal Analysis of a MW High-Speed Permanent Magnet Synchronous Machine

Efficient cooling is needed, for example, in traction motors which face regularly high torque peaks and generate high stator Joule losses. This paper studies the feasibility of the direct liquid cooling in the thermal management of a low-power low-voltage permanent-magnet machine. A tooth-coil axial-flux permanent-magnet double-stator-single-rotor test machine was first equipped with indirect liquid cooling using water cooling jackets and then with direct winding cooling. The winding material used is a hybrid conductor comprising a stainless steel coolant conduit tightly wrapped with stranded Litz wire. The performance of the motor is examined at various power levels using oil or water as the cooling fluid. The results confirm that the proposed direct cooling method is practical also in small machines, and furthermore, it offers significant improvements in the machine thermal management, especially, in cases where stator Joule losses dominate.

Direct Liquid Cooling Method Verified With an Axial-Flux Permanent-Magnet Traction Machine Prototype

Permanent-magnet synchronous machines (PMSMs) are considered a very promising machine type for high-speed (HS) applications. As permanent-magnet (PM) materials are generally fragile, a high-strength sleeve is required to protect the PMs from damage due to the extreme centrifugal forces. The rotor sleeve occupies space of the effective airgap of the PMSMs; therefore, it is difficult to perform the electromagnetic (EM) design without an accurate estimation of the sleeve thickness, which is determined by mechanical issues. In this paper, an integrated mechanical- EM design method is proposed for the rotor design of HS PMSMs. A 200-kW 40 000 r/min surface mounted PM machine is taken to illustrate the design procedure of the proposed method. Three commonly used sleeve materials are investigated and their mechanical performances are analyzed. The optimal dimensions for the rotors with different sleeves are obtained by considering the strength and EM limits. The EM, thermal, and rotor dynamic performances of the designed rotors are analyzed and compared. In the end, a new rotor sleeve topology is proposed to reduce the rotor eddy current losses.

Rotor Design for High-Speed High-Power Permanent-Magnet Synchronous Machines

Two-stage oil-free centrifugal air compressors can bring significant advantages and open new market opportunities for compressor manufacturers. One of the core technologies behind this compressor type is the high-speed electrical machine supported by active magnetic bearings. In this paper, the requirements set by the compressor on the electrical machine design are presented. The design solutions aimed to satisfy these requirements are discussed. Two case studies illustrate possible design approaches for the target application with examples of a 120-kW, 60 000-r/min induction machine with a solid rotor and a 225-kW, 50 000-r/min permanent-magnet synchronous machine (PMSM) with a full cylindrical magnet. The system design and simulation results are confirmed by measurements of a PMSM prototype.

Emil Kurvinen

Papers

Multidisciplinary Design Process of a 6-Slot 2-Pole High-Speed Permanent-Magnet Synchronous Machine

Heat-transfer improvements in an axial-flux permanent-magnet synchronous machine

Ball bearing model performance on various sized rotors with and without centrifugal and gyroscopic forces

Development and verification of frequency domain solution methods for rotor-bearing system responses caused by rolling element bearing waviness

Purity and mechanical strength of naturally frozen ice in wastewater basins