The Research of External Buoy Wave PermanentMagnet Linear Generator's Design

Baodong Bai , Jin Lu, Bing XuSpecial Motor and High Voltage Apparatus Key Laboratory ofMinistry ofEducation, Shenyang University of

Technology, Shenyang 110870, Chinae-mail:lujin19850428@sina.com

Abstract: The purpose of this design is to make waves canbe converted to electrical energy, and a new wave permanentmagnet linear generator is proposed. The new designedpermanent magnet linear generator moves with the waves upand down, by changing the loop with the reluctance tochange the size of the magnetic flux coupled windings, whichwill have a generator winding EMF. The buoy structure usesthe holistic design that the mover is wrapped by thebuoy.The structural design of the generator is ANSOFT andANSYS finite element analysis which analysis the generatormagnetic field and no-load induced electromotive force.

I. INTRODUCTION

With the increasing exhaustion of fossil energy around theworld and taking into account such issues as environmentalprotection, development and utilization of new energy to solvethe world energy problem has become an inevitable trend. Wavepower, is one of the most clean, inexhaustible renewable energy.Bank ofChina is located in the Pacific Ocean, coastal reserves isextremely rich, as long as the bay where there is an appropriateamount of tidal power stations have established conditions.

This paper presents a wave linear permanent magnetgenerator which can make wave energy converted to electricalenergy.According to the nature of the waves and thecharacteristics of long time work in the sea environment, designa new wave permanent magnet linear generator which can makeocean wave energy directly converted to electrical energy, andimprove the traditional wave generator in the overall structure.Proposed generator structure,using electromagnetic finiteelement analysis of magnetic field analysis the generator anddesigned device buoy structure.

II. GENERATOR STRUCTURE

In this paper, the winding and the permanent magnet are bothplaced on the mover of the generator, and the stator can beslotted silicon steel sheet, or it can inject aluminum orsemiconductor material in order to strengthen and increase thechange in flux during the mechanical movement of the generator.Cut open along the generator axis and Figure. 1shows the finite

element simulation model, in order to reduce magnetic fluxleakage make the mover core be irregular semi-circular, andfurther increase the rate of change of the magnetic flux, theshape of the stator teeth are designed to be Half Dome. The sizeparameters of the wave generator is shown in table (1)

Compared with traditional generators this design has theadvantage of reducing the use of permanent magnet and thewinding number that reduce the cost of the generator.

About sided linear generator, between the primary andsecondary there is large normal component of electromagneticforce.In order to offset the normal component, put the four flatsided linear generators on the side close together to form aunique permanent magnetic linear generator. As shown that infigure (2) shows the overall structure of the wave generator. Inaddition, the permanent magnet pole Nand S pole arrangedalternately ,and we use NdFeB permanent magnet materials.NdFeB permanent magnet materials is the highest performanceand cheap in the current.

Figure .1. Wave generator two-dimensional profile

TABLE ITHE SIZE PARAMETERS OF THE WAVE GENERATOR

Name Value Units

Length of permanent magnetmagnetization direction 8 mm

Width ofpermanent magnet 15 mm

Axial length ofpermanent40 mm

magnet

Permanent magnet type NTP-264HPole pairs 36

Length 0 f stator 3210 mmLength of mover 1452 mmWidth of air gap 0.56 mmWidth of slots 10 mmDepth of slots 7 mm

Number of slots 160

Width oftooth 10 mm

Figure .2. The overall structure of the wave generator

III. EMF SOLUTION

The generator design is the principle ofpower: the differencebetween the teeth and slot reluctance in magnetic circuit causedthe different magnetic flux through the teeth and slots, and thegenerator windings which is coup led to the change magnetic fluxwill produce EMF. Reluctance in locations of each two adjacentalveolar changing make the magnetic flux through the coilschange periodically, so in the coils there is induced potentialwhich changes periodically.According to the structuralcharacteristics of the generator, when induced voltage is in thesolution, we can use two-dimensional electromagnetic fieldanalysis to solve . Analysis with the analysis of electromagneticfield analysis software ANSYS.Figure.3, when the stator and themover teeth are being, the majority of flux at this time through,

and when the stator teeth and mover slots are being, the majorityof flux at this time does not pass.According to Kirchhoff'ssecond law of magnetic circuit (1) magnetic drop is equal to eachmagnetic circuit, and in the process of generator workingreluctance in the circuit of two adjacent locations change, whichwill cause the corresponding magnetic flux change (2).

y F == ~ <I>Rm (1)

~<D == F Am (2)

According to the changes in magnetic flux flux linkage If/i

through a coil in this position can be calculated, then this

position a stator tooth flux is as N If/i where N is winding turns.

Change the position of mover to make displacement ~s fluxchanges condition through a mover pole in different stator

positions can be calculated.When ~s is small enough we canregard that:

e(i) == -(~lf/i / ~s)[(~s / ~t) == -(~lf/i / ~t)[V (3)

Where the ~ If/i == If/i+l -If/i is that the total flux difference

of stator teeth when the mover in the two adjacent position arethe total flux of the poor.

Figure .3. Generator magnetic circuit

IV. ELECTROMAGNETIC FIELD FINITE ELEMENT ANALYSIS OFWAVE GENERATORS

A. Establish the motion model

Wave movement is affected by climate, topography and otherfactors, that it is irregular movement.Based on our coastal areaswave characteristics, in order to facilitate research, make theideal wave be simulated as vertical reciprocating motion, and thekinetic energy spread in the form of sine wave. The generator isfor the wave height 1m, angular velocity 2.8rad / s waves in the

design, and make the wave displacemen S == 0.5*sin(2.8t) ,speed

V == 1.4 *cos(2.8t) as the movement model of the fmite element

analysis.According to the characteristics that the new permanent

magnet linear generator is a four-sided type and the need forpractical calculation, it needs to make certain premises: 1) ignorethe linear generator's edges at effect; 2) along the direction of thelaminated core the magnetic field is same; 3) ignore theinfluence which electrical resistance in the mover windingmagnetic fields produce; 4) mover core has smooth surface

B. Results Analysis

Through the above description of the permanent magnetlinear generator with ANSOFT we make a simulation operation,and calculate that the parameters of the electromagneticgenerator have reached the requirements.As shown in Figure .4that the generator magnetic field distribution, when the mover isin reciprocating movement,the magnetic flux in the stator ofcross-linking will change with the mover position,.The motion ofthe mover can be seen as cosine, so the induced EMF is alsosimilar to the cosine wave, as shown in Figure .5 that thereaction force. It is the most basic and most important electricalparameters and it has a direct impact on the magnetic pull of thegenerator,rated current and other performance indicators, soaccurately calculating EMF waveform of the generator is thebasic ofgenerator design and performance analysis.

Figure .4. Magnetic flux density distribution

Figure .5. EMF waveform response

The amplitude can be obtained for 1160V.

V. ELECTROMAGNETIC FIELD FINITE ELEMENT ANALYSIS OF

WAVE GENERATORS

A. Integral structure

Structure designed to buoy in this paper set in space with theprevious wave permanent magnet generator buoy set differ. Thetraditional wave buoy and the generator is a separate structure,that the buoy float in the sea and the the generator is in the airabove sea level. The overall structure of this linear generator isthat the mover is wrapped in a buoy and the mover moves withthe buoys up and down. Because the design of generator is thatpermanent magnet and coils are both placed on the mover, thisdesign has the advantage of reducing the corrosion of seawaterand extending the useful life of the generator. This paper shapesthe buoy design for the ball that can make buoy's volume andquality calculated easily,and the bottom of the buoy can have alarge buoyancy.

The overall structure of the generator and buoy as shown inFigure.6

Figure .7. Tangential component of the electromagnetic force

B. Buoy force analysis

When the wave generator is running, the buoy moves withthe waves as longitudinal reciprocating motion.And it mainlyaffected by the three power: the buoyancy in seawater in, buoys'own gravity, and the generator's electromagnetic force. Andbuoys' own gravity includes generator's gravity and outer buoy's

gravity. So the buoy's resultant force is "LF as:

"LF == Fbuoyancy - G - F:lectromagnetic force (4)

Requirements is that when "LF ~ o,the buoy can move withthe waves as longitudinal reciprocating motion.

Through the analysis of the electromagnetic field analysissoftware ansoft which calculated out electromagnetic force'stangential component electromagnetic force of the wavegenerator as shown in figure.7 .

VI. THE WAVE GENERATOR'S POWER POS T-PROCESSING

Because the EMF generated by the generator is irregularcosine wave, and wave speed and frequency are constantlychanging, the Induction voltage of the linear wave powergenerator can not be directly used for practical applications, so itneeds to design a external circuit to make postprocessing torectify , filter and make it contravariant that the generator'soutput power can be put into use.

The wave generator designed in this paper is be composed ofeach unit of four unilateral flat linear generators which are byplace of face to face, so it is preliminary designed that rectify andfilter each generator's EMF , then add them, and finally make itcontravariant.The whole post-processing circuit is shown infigure .8.

In

Figure .8. The wave generator's electric power post-processing circuit

-w,- Li::b----~-S-";"-RLC-----.JT ~ Diede

I 1 1

Figure .9 shows the rectifier filter circuit of each subsystem.

We can see the peak of the downward electromagnetic forceis 44 kN

In this paper the materials of the wave permanent magnetlinear generator are that: permanent magnet's model number isNTP-264 H, siliconized plate' model number is DW360-50, thecopper wire line diameter is 1.06 mm and insulation paint filmthickness is 0.08 mm Through calculating all parts of the bodyquality of the wave generator that the overall quality of the wavegenerator is 74396.225592 kg, so gravity is 729083.0108016 N.

In this paper the design of the buoy is a 0.2 m wall thicknesssphere.The material of the buoy is high molecular weight highdensity polyethylene (HMWHDPE),and its characteristic whichis resistant to stress cracking, the impact strength , the tensilestrength ,rigidness, abrasion resistance and chemical stability areall very good,so it can be used for a long time in bad

environment Its material density is 9 5 0 kg / m 3 • Consider

. p ==1030kg/m3

the density of seawater seawater .When the wholebuoy dip into the sea that the buoyancy is biggest, so there is thefollowing equations:

R >G +F +Gbuoyancy generator electromagnetic force buoy

(5)

Figure .7. Tangential component of the electromagnetic force

Calculation process as follows :

4Pseawatorgnr~ /3 Z 905083.0108016N-+4PbuoygJr(r~-lj) /3

~ut -lin==0.2m

103Or;ut +48li~ +9.6lin 2::22058.773

The buoy's inner radius can calculate between 2.76 m and2.77. In this paper, consider the inner radius of2.8 m, the outerradius of 3m.

Figure .9. Single wave generator's rectification filter circuit

VII. CONCLUSION

This paper introduces the design of permanent magnet lineargenerator which can directly convert wave energy into electricalenergy, that reduce the energy transfer link and improve thewave power efficiency.In this paper, analysis the lineargenerator's electromagnetic fields and linear generator's internalfield by fmite element analysis,and draw the magnetic line offorce of linear generator with ansys software. Use softwareansoft to calculate the reaction EMF oscillogram and

electromagnetic force oscillogram. Design of the structure andsize of generator's buoy, and preliminary design power the post-processing circuit of the linear generator. The whole work is inorder to the combined to the grid of the wave generator.

VIII. REFERENCES

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[2] K. Rhinefrank, E. B. Agamloh, and A.Von Jouanne et al., "Novel oceanenergy permanent magnet linear generator buoy," Renewable Energy, vol.31, pp. 1279-1298,2006.

[3] Nikolaos M. Kimoulakis, Antonios G. Kladas, "Cogging ForceMinimiaztion in a Coupled Permanent Magnet Linear Generator for SeaWave Energy Extraction Applications" CEFC2008 Session PA2-4

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