Speed Permanent Magnet Machines Research Articles

Rotor Stress Analysis of High-Speed Permanent Magnet Machines With Segmented Magnets Retained by Carbon-Fibre Sleeve

In this article, the rotor stress is analysed for a high-speed permanent magnet (PM) machine (HSPMM) with segmented magnets retained by a carbon-fibre sleeve. The influence of rotor PM segmentation is firstly considered in the stress analysis. It is found that when the segmented magnets are under tensile stress, significant sleeve stress concentration will occur due to magnet edging effect. By contrast, the PMs will benefit from the segmentation with reduced tangential stress. This stress reduction effect is enhanced when the number of PM segments is larger. Furthermore, the influence of PM segmentation on the worst operating scenario is determined. In order to avoid stress concentration due to PM segmentation, the design guidelines are then given by investigating the influence of sleeve thickness and interference fit. A new design scheme of sleeve thickness is proposed based on the identified worst case scenarios. Finally, a 6-slot 4-pole high speed PM machine with segmented magnets retained by carbon-fibre sleeve is prototyped and tested at the speed of 90 krpm. The rotor stability indirectly indicts the validity of the theoretical analysis and design scheme.

Optimal split ratio in small high speed PM machines considering both stator and rotor loss limitations

The split ratio which is defined as the ratio between rotor and stator outer diameters is critical for permanent magnet (PM) machines. In this paper, the split ratio in small high speed PM machines is optimized analytically by considering both stator and rotor loss limitations. By this way, the thermal constrains in both stator and rotor parts can be taken into account. It shows that both losses can significantly affect the optimal split ratio and the machine performance. By considering the influence of rotor losses, especially the rotor eddy current loss, the optimal split ratio is increased significantly in certain scenarios. The output torque is calculated analytically and the influences of several key design parameters on the optimal split ratio, i.e. slot/pole combinations and magnet materials, are also investigated in details. Finally, finite element (FE) analyses are carried out for validating of the analytical model.

Investigation of Optimal Split Ratio for High-Speed Permanent-Magnet Brushless Machines

The split ratio, i.e., the ratio of rotor outer diameter to stator outer diameter, is one of the most vital design parameters for permanent-magnet (PM) machines due to its significant impact on the machine torque or power density. However, it has been optimized analytically in the existing papers with due account only for the stator copper loss, which is reasonable for low-to-medium speed PM machines. For high-speed PM machines (HSPMMs), the negligence of stator iron loss and the mechanical stress on the rotor will lead to a deviation of optimal split ratio and actual torque capability. In this paper, the optimal split ratio of HSPMM is investigated analytically with the consideration of stator iron loss as well as the mechanical stress on the rotor. The influence of air-gap length and rotor pole pairs on the optimal split ratio is elaborated. Both the analytical and finite-element analysis reveal that the optimal split ratio for HSPMM will be significantly reduced, when stator iron loss and mechanical constraints are taken into account.

Experimental verification of winding switching technique to enhance maximum speed operation of surface mounted permanent magnet machines

Flux weakening is an inevitable requirement in the operation of variable speed permanent magnet (PM) machines for high-speed applications due to inverter voltage limits. A new winding switching technique is experimentally validated in this study that can extend the speed range of such PM machines. A drive topology is proposed that utilises two current regulated voltage source inverters to control the machine in a dual inverter fed configuration before transitioning into an open winding configuration after winding switching. The proposed drive topology extends the constant torque region of the machine and boosts its maximum output power capability. Complete experimental results are provided to demonstrate the effectiveness of the proposed machine drive system for continuous operation over the entire speed range.

Design and Analysis of Fan-Cooling for High Speed Permanent Magnet Machine Rotor

Compared with common permanent magnet (PM) machine, the high speed PM machine has smaller size and larger power density. However, owing to high-speed high frequency and small volume, the PM rotor is more easily to become overheated so that irreversible demagnetization of the PM is induced. Traditional cooling methods of machine directly cool the machine stator, the temperature rise of rotor is reduced through heat exchange among stator, air gap and rotor. Owing to rapid temperature rise of high speed PM machine rotor, the method of indirect cooling rotor does not effectively protect PM rotor from overheating. To directly reduce the temperature rise of PM rotor and the volume of machine, design method of fan-cooling for high speed PM machine rotor is proposed in this paper, that is, high speed axial fan rotating synchronously with the high speed PM machine rotor is designed. Finally, the temperature rise of high speed PM machine rotor with the structure of high speed axial fan is analyzed based on the coupling method of fluid-solid, the validity is verified.

Study on Anti-Demagnetization of Magnet for High Speed Permanent Magnet Machine

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Compared with common permanent magnet (PM) machine, the high speed PM machine has smaller size and larger power density. However, the heat dissipation of the high speed machine becomes a serious problem due to the small size and high power loss density. More attention should be paid to the protection of the PM rotor from overheating demagnetization. In this paper, the magnetic properties of high speed PM rotor for different machine structure and speed are studied based on the combined analysis of magnetic, temperature and fluid fields. In order to protect the PM rotor from overheating demagnetization, a new structure of high speed machine having PM rotor with nonmagnetic enclosure and stator with inner and outer cooling vents is proposed. The theoretical analysis and experiment result of high speed PM machine show the validity of the proposed anti-demagnetization approach. </para>

Losses in High Speed Permanent Magnet Machines Used in Microturbine Applications

High speed permanent magnet (PM) machines are used in microturbine applications due to their compactness, robust construction, and high efficiency characteristics. These machines are integrated with the turbines and rotate at the same speeds. This paper discusses in detail the losses in high speed PM machines. A typical PM machine designed for microturbine application is presented with its detailed loss calculations. Various loss verification methods are also discussed.