2004 an modular-type axial-flux permanent magnet synchronous generator for gearless wind power...

8/14/2019 2004 an Modular-Type Axial-Flux Permanent Magnet Synchronous Generator for Gearless Wind Power Systems

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The 3Mh Annual Conferenceof the IEEE Industrial Eleclronics Society, Novemb er 2 6 2004 Busan, Korea

An Modular-type Axial-flux Permanent Magnet Synchronous Generatorfor Gearless Wind Power Systems

4Don-Ha HWangf, Member, IEEE, Ki-Chmg Lee2,DO-Hyul Kang3, Member, IEEE, Yong-Joo b m Member, IEEE,Kyeong-Ho Choi , andDoh-Young Park6,Member, iEEE

123,4 Industry Applications Research Laboratory, Korea Electrotechnology Research Institute KEN),P.O. Box 20, Changwon, Gyeongnam, 641-600, KOREA, e-mail : [email protected]

Dept. of Digital Electric Design, Kyungbuk College, Youngju, Kyungbuk, KORE A, e-mail : [email protected] and Associates, Inc. PAl), Kingston, Ontario, K7L2Y8, CANADA, e-mail :yparkaparker-inc.com

Abst rac t - In this paper, the design and characteristics analysisof dual axial-flux permanent magnet synchronous generator, 60[Hzl, 10 IkVAJ,300 [rpml for wind energy system application arepresented. The dual axial-flux generator bas inherently desirablefeatures such as; I) by employing two air gapa, the rotor-statorattractive forces are balanced and no net axial o r thrust load isapplied on the generator bearings; 2) heat produced by the sta torwindings appears on the outside of t h e generator, and it i s easy toremove t he heat.

This paper describes characteristics of a dual axial-flux typ epermanent-magnet generator for a geariess wind energy system,which aims to satisfy the variable operating conditions. Finite-element method FEW is applied to analyze generatorperformance at variable loads. The results of FE analysis showthis generator has a promising future for wind turbineapplications.Index Terms-Axial-flux machines, finite-element analysis,permanent magnet synchronous generator, wiud power system

I. INTRODUCTIONRecently, permanent-magnet (PM) generators have becomeattractive because o f the significant improvements inpermanent magnets o ver the past decade, similar improvementsin power electronic devices, and the ever increasing need to

develop smaller, cheaper, and more energy-efficient generators.Especially, PM axial-flux generators are attractive candidatefor wind power generation because they have higher efficiency,power factor, output power per mass and better dynamicperformance than other electrical machin es [ I]-[5].

Conventional generators are installed at the top of the towersand require step-up gearbox so that the type of generator forthis application is required to be compact and light. Thegearbox of a wind generator is expensive , subject to vibration,noise and fatigue, and needs lubrication as well a s maintenanceat appreciable cost [2]-18].

In this paper, a gearlesswind energ y system co upled directlyto a PM synchronous generator, 10 [LVA], 300 [rpm], isintroduced. A modular concept is proposed to reducemanufacturing costs as well.

In order to analyze the characteristics of proposed generator,an equivalent model of two-dimension (2-D) i s developed andfinite-element (FE) analysis is applied. Three-dimensional(3-D) FE analysis takes long time to calculate transient state.Both steady state and transient analysis is performed. Resistiveand inductive loads as variable load are applied in order toanalyze driving characteristics.Experimental tests are conducted to verify the drivingcharacteristics of the generator. A comparison between FEanalysis and testing results is presented. The results are verysimilar to predicted performance of design.

11. DESIGN N D CONSTRUCTIONThe basic specification of the PM generator is shown inTable 1 . One unit module of this generator with axial-flux,double-side and disc-type, shown in Fig. 1, has rating of 10

[kVA]. Unit modules can be combined into multi unitgenerators to increase power rating. The 10 EVA] generatorconsists of a rotor between tw o stators. The stator windings areconnected in series so that induced voltag es from the stators areunited together.The disc type rotor consists of 24-pole and one permanentmagnet per a pole, is shown Fig. 2 (a). The rotor is made ofstainless steel an d it is designed to reduce the leakage flux.Single-layer lap winding is used in two stators foreconomical construction and reduced volume as shown in Fig.The material of core is S-18, and silicon iron whose

thickness is 0.5 [mm] is used. In order to reduce eddy current,the core is laminated in the radial direction. T he number of slotis 72 and he number of conducto r is one per phase per pole.

2 @I

TABLE I. BASIC SPECIFICATlON OF THE GENERATORRated power 10000 [VA]Rated speed 300 [rpm3Rated voltage 380 [VINumber of poles 24Number of phase 3Type Axial-fluxPhase connection Y

0-7803-8730-9/04/ 20.002004 IEEE1396
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a) the sbucture @) uoss sectionFig. 1. Axial-fluxtype pennanenl-magnet generator.

a) rotor @)statorFig. 2. Rotor and stator of10 [ W A ] unit module.

The configuration of permanent magnet is similar to a fanshape. By using NdFeB magnets, volume and weight can bereduced.111. FINITEELEMENTNALYSIS

A. Equivalent 2-D ModelThe wind-power generator consists o f one rotor -which has

24 numbers of permanent magnet poles nd two stators. Forthe modeling purpose, the equivalent 2-dimensional model forFEM analysis, shown in Fig. 3, is used. In this model, only 2poles among 24 poles o f rotor are modeled using the averagevalue of circumferential length of the permanent. In order tocalculate induced EMF, extemal circuit is connected so thatdriving characteristics at no-load, resistive load, and resistive-inductive load are analyzed.

The basic equations of motion are mechanical acceleration asshown in 1).

dxV = -t

where m is the mass, F is the velocity, x i s position, /z isthe damping coefficient, F is the electromagnetic force, andF, is the extemalfy-applied mechanical force load).

The electromagnetic force, F may be written in terms ofmagnetic field equations for the magnetic vector potential (A).The magnetic force is proportional to square of flux density asshown in (2).

The transient equations coupled by magnetic field, circuit,and motion are summarized as follows;Y dAV X V V X A = O - - G - + X V X A 3)

t

where L is the electrical conductivity, 1 is the iron length,is the applied voltage, v is the reluctivity, V is the velocity ofthe conductor with respect to flux.

E . FEAnalysisThe magnetic flux density waveform in air gap is shown in

Fig. 4.The calculated RMS value was 0.446 [TI, whereas theFE analysis result was 0.51 (TI.

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Fig. 9. The PM enerator (axial-fluxw ,7

sP=f [CSmFig. 10. Output voltagesat no load for different speeds

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Fig. 1 I Line-line rms voltages VS. urrent

Fig. 12. Induced EMF w aveform with no load.

V. CONCLUSIONIn this paper, the design, analysis and test results of anaxial-flux type PM synchronous generator, 10 [kVA], 300[rpm],or direct-driven wind turbine applicationsare presented.In order to analyze the performance of the axial-flux PMgenerator, FE analysis is used with 2-D equivalent model. T hesteady state and transient characteristics are respectivelyanalyzed at no-load and RL-load. The results of FE anafysisand test are very similar under both R-load and RL-load. It canbe concluded that the proposed generator is very promising touse for a wind turbine.

REFERENCESW S . Leung and J.C.C. Chan, A new design approach for axial-fieldelectrical machines,IEEE Transactionson Power Apparutus System,vol.PAS-99, pp. 1679-1685, July/Aug. 1980.D.H. Kang P. Curiac, and J. Lee An axial flux interior PM synchronousmachine, in Pvaceedinzs of the ICEM ZOOO, Finland vol. 3, pp. 1475-1479, Aug. 28-30,2000.V. Cingoski, M. Mikami, and H. Yamashita, Computer simulation of athree-phase brushless self-excited synchronous generator, IEEETransactionson Magnetics,vol. 35, no. ,pp. 1251- 1254, May 1999.G sekouras, S. Kiartzis, A.G. Kladas, and J.A. Tegopoulos, Neuralnetwork approach compared to sensitivity analysis based on finiteelement technique for optimization of permanent magnet generators,IEEE mnsacfiuns n Magnetics, vol. 37, No. 5 pp. 3618-3621, Sep.2001.J . Ched, C.V. Nayar, and L. Xu, Design a ndfinite

2004 an modular-type axial-flux permanent magnet synchronous generator for gearless wind power...

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