电磁场计算

The Dynamic Analysis of a Spoke-Type Permanent Magnet Generator With Large Overhang

Ki-Chan Kim and Ju Lee,Senior Member,IEEE

Energy Conversion Laboratory,Department of Electrical Engineering,Hanyang University,Seoul,133-791,Korea

The purpose of this paper is characteristic analysis of a permanent magnet generator(PMG)for automatic voltage regulator(A VR) power of a brushless synchronous generator.However,this PMG has a spoke-type permanent magnet rotor with a large overhang for high power density;characteristic analysis considering the concentration effect of the air-gapflux density due to the overhang should be performed.Three-dimensional(3-D)transientfinite element method(FEM)analysis is a good solution for the overhang parameter,but this method needs too much calculation time.In this paper,we examined the overhang effects based on overhang length and material of rotor core by using two-dimensional(2-D)and3-D static FEM analysis,and proposed a2-D dynamic FEM model considering the overhang parameter,which gives good and rapid results.The proposed method is verified by the test results of no-load,load,and short-circuit test.

Index Terms—Finite element method(FEM),overhang,permanent magnet generator(PMG),spoke-type rotor.

I.I NTRODUCTION

A UTOMATIC voltage regulator(A VR)in a brushless-type

three-phase synchronous generator is an essential part to control and regulate the output voltage of a generator.The power-supplying methods to this A VR are classified into shunt, auxiliary winding,and permanent magnet generator(PMG) type.PMG type has the lowest influence on harmonics and the highest durability among these,so it is used for the purpose which requires reliance.The PMG model in this paper has a spoke-type permanent magnet rotor and rotor overhang,which makes the linkageflux to a stator winding maximize[1],[2]. Air-gapflux density is changed according to the overhang length.Therefore,a winding design of PMG related to output voltage level is difficult in PMG model with overhang.Even if it is possible to design an overhang parameter with equiva-lent magnetic circuit approximately by using an overhang coef-ficient,this method is not a good solution for a large overhang model,because nonlinearity in an overhang coefficient occurs irregularly at a large overhang due to excessive concentration of air-gapflux density.The causes of this phenomenon are not only the leakageflux which cannot be added up to air-gapflux density over some extent of overhang but also saturation in a stator core.Therefore,we should analyze the overhang param-eter by thefinite element method(FEM).However,the over-hang problem cannot be analyzed by two-dimensioanal(2-D) FEM.Three-dimensional(3-D)FEM should be used to analyze the concentration of air-gapflux density due to overhang.How-ever,a3-D FEM of a transient problem such as no-load,load, and short-circuit characteristics needs too much calculation time and memory.

In this paper,we examined overhang effects based on over-hang length and material of core by using2-D and3-D static FEM analysis,and we proposed the dynamic analysis solution by only2-D FEM considering the overhang parameter,which gives good and rapid results.The proposed method is verified by the test results of a no-load,load,and short-circuit test.

Digital Object Identifier10.1109/TMAG.2005.854934

TABLE I

S PECIFICATIONS OF THE A NALYSIS M

ODEL

Fig.1.Permanent magnet generator.

II.A NALYSIS M ODEL

Specifications of the PMG are shown as Table I.The length of overhang is13mm,and the material of the permanent magnet is a ferrite type,which is adequate to a spoke-type rotor.Fig.1 shows the PMG model.

III.A NALYSIS M ETHOD OF PMG C ONSIDERING O VERHANG First of all we should analyze the variation of the air-gapflux density level due to overhang.So we perform static analysis by using a2-D FEM for PMG with0-mm overhang,which cor-responds to a generator with34-mm axial length in stator and rotor.And we calculat the e distribution of the air-gapflux den-sity.Next,we perform static analysis with a real model whose overhang is13mm by3-D FEM and also calculate the air-gap flux density distribution over the arc line in the axially center po-sition of the air-gap.Finally,in order to correct the air-gapflux

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