On eddy-currents losses determination in permanent magnets of high-speed electromechanical energy converters

Аuthors

Ismagilov F. R., Vavilov V. E.^*

Ufa State Aviation Technical University, USATU, 12, K. Marx str., Ufa, 450008, Republic of Bashkortostan, Russia

*e-mail: s2_88@mail.ru

Abstract

The industry demand for high-speed electric motors with rotation frequency of 48,000 rpm to 120,000 rpm and power of 5 to 250 kW increases from year to year. A number of technological problems exists herewith, which retards the high-speed electric motors market growth. These problems relate to the issues of their output voltage stabilization, which are solved by employing static converter, stator back magnetizing, or rectifier; ensuring bearing assembly reliability, which are solved by employing non-contact bearing assembly, as well as the problems of rotor heat evolution reduction. The latter are stipulated by the complexity of fast-rotating rotor's cooling.

To solve this problem, the article studies losses caused by eddy currents in permanent magnets of high-speed electromechanical energy converters.

The eddy currents losses in permanent magnets and rotor retaining shell are generated by spatial harmonics caused by electric motor structural specifics, stator serration, windings diagram and distribution ratio, as well as temporal harmonics, stipulated by the external circuit, such as inverter. Moreover,with the improper selection of the electric motor parameters eddy current losses may lead to the permanent magnets overheating and their demagnetizing under the effect of this overheating.

It is generally assumed, that the losses stipulated by temporal harmonics are higher than the losses caused by the spatial harmonics. This statement is valid only for a number of structural schemes of high-speed electric motors. For example, the electric motors with toothed windings feature significant spatial harmonics. And losses caused by these harmonics are higher than the losses caused by temporal harmonics.

It is found that with rotation speed increasing the losses in permanent magnets have maximum point, after which they start decreasing. This is explained by the fact that with rotor rotational speed increase, the magnetic field penetration depth into the permanent magnet body and bandage reduces. Thus, the losses reduce either.

The article shows also that the magnetic system does not exert a significant effect on the eddy current losses, created by spatial harmonics, in permanent magnets. The eddy currents losses in permanent magnets herewith may alter significantly due to load angle variation.

The article individually considers the losses caused by temporal and space harmonics. It also presents their numerical evaluation and describes of their minimization techniques.

Keywords:

high-speed electric motors, spatial and temporal harmonics, eddy current losses

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