Methods to quantify and reduce rotor losses in a solid rotor yoke permanent magnet machine

[摘要] ENGLISH ABSTRACT: Certain types of electric machines are particularly susceptible to the proliferation of eddycurrents flowing within the solid conducting regions in the rotor. Single-layer, non-overlappingwindings within uneven open slots are some stator properties that can produce damaging,asynchronous magnetic field harmonics which manifest in the rotor as eddy currents. Theohmic losses caused by these eddy currents are a source of inefficiency and can cause a markedincrease in the temperature of the rotor. This temperature rise can be dangerous for themagnets, which have to be kept within temperature limits to avoid partial or fulldemagnetization.The research work presented here is concerned with reducing the effect of eddy currents in therotor magnets and solid rotor yoke of an electric machine. The work presents analyticalmethods to calculate the magnetic fields, eddy currents and solid loss in an electric machine dueto current in the winding and due to the interaction of the permeance variation in the statorwith the magnets in the rotor. A method is also suggested where the analytical theory can beused with a magnetostatic finite element solution to produce a transient solid loss result. Theresearch work also investigates a method for optimal segmentation in both level andpenetration, and provides some design suggestions.The work presents the method of partial magnet segmentation, which is a technique wherebythin incisions are made into the magnet material from one or both sides. Another method ofpartial rotor segmentation is also presented where the incisions are made into a portion of themagnet-facing solid yoke. These methods attempt to interrupt the flow of eddy currents andincrease the resistance 'seen' by the eddy currents, while also keeping construction difficultyand cost to a minimum. The methods are verified using finite element calculations which arecompared to measured results.The result is that partial magnet segmentation is a very useful, effective and practical method ofsegmenting magnets. The loss reduction profile can be similar to that of traditional fullsegmentation. The method of partial rotor segmentation also shows a large reduction in rotorpower loss. With implementation of these methods on a test machine, one can expect anefficiency increase of more than 4 %

[发布机构] Stellenbosch University