Electro-Mechanical Batteries for low earth orbit satellite with hallow cylinder flywheel machine

Transcription

1 Electro-Mechanical Batteries for low earth orbit satellite with hallow cylinder flywheel achine Ahed M.Atallah, Mahoud M.Kashef, M.A.L.Badr Elec. Dept. Eng, Ain Shas University, Cairo, Egypt Abstract Electroechanical batteries overcoe any probles that ay occur when cheical batteries in low orbit satellites (LEO), In such a configuration of otor generator ode coupling with flywheel is used to store kinetic energy in otor ode through the flywheel during sunlight and supply electrical power fro the stored kinetic energy by generator ode. In this paper design of design of Peranent agnet synchronous achine (PMSM) using hollow cylindrical flywheel for otor generator ode have been done. Fywheel diensions and aterial selection are presented in the paper to achieve optiu weight with the required supplied power. The hollow cylindrical flywheel coposed of two parts shown in fig1 Fig 1 Hallow cylindrical flywheel Peranent Magnet Synchronous Machine Index Ters Electro-Mechanical batteries, Hollow cylindrical flywheel, Surface Peranent agnet synchronous achine, satellite. NOMENCLATURE E kinetic energy stored I oent of inertia ω the angular velocity ρ the density of aterial Z the axial length of the cylinder r2, r1 the outer and inner radius Mn the agnetic vector R6, R4, R5 outer stator, inner and outer PM radius µr, µ air gap flux and Iron pereability p t he nuber of pole pair 1

2 Br, αp agnet renant and PM arc to pole pitch ratio N, Kα coil nuber of turns,first haronic coefficient Nt nuber of tooth R_p,R_t Air gap reluctance front of pole and tooth Wt, Wy thickness of rotor and stator aterial ff, Kcu filling factor and necessary cupper area to flow one apere of current t the tie duration during discharge periodic Ip, Ife, If oent of inertia of peranent agnetic, ferroagnetic and flywheel aterial I. INTRODUCTION LEO satellites usually include nano and icro satellite witch rotate around the earth by period of soe inutes to few hours [2], the ost critical part of these satellites are their batteries which supply power during eclipse period. The advantages of EMB [4], [5], [7], [17] are unliited charge/discharge cycle as well as satellite life tie, ore efficient, ore energy density, ore discharge depths, theral independent, no voltage sag over life, atches well with peak power tracking solar array, uch higher specific energy, easy charge/discharge control as the stored energy depends on the wheel speed alone and hence lower ass and volue. Electro-Mechanical Battery consists of Surface Peranent agnet synchronous achine coupled with flywheel. In this paper we have selected the aterials of rotor, stator and flywheel to iniize the diension while achieving the required agnetic field and stored energy. Selection of aterial for rotor, stator, flywheel is an iportant part to iniize the doination and achieve require agnetic field and stored energy II. PRINCIPLE OF DESIGN The energy storage in a flywheel syste is given by E= Iω (1) So the oent of inertia of hallow cylinder which is ade of a coposite or steel ri attached to a shaft is given by I=.π.Z.ρ.(r r ) (2) Then, substituting equation (2) in equation (1) the energy that can be stored in a flywheel syste as a function of its speed, inner and outer radii is. E=.π.Z.ρ.(r r ).ω (3) 2

3 The ost efficient way to increase the energy stored in a flywheel is to speed it up and increase its radius as large as possible beside volue and ass optiization. However, the aterials of rotating syste will liit the speed of the flywheel, due to the stress developed, and called tensile strength, σ In this paper, flywheel ass and diensions are iniized using certain of carbon aterial and hollow cylinder flywheel as will be shown. Also, Radial-flux Peranent Magnet (PM) achines are used in the proposed design for efficiency and copact size III. MATERIAL SELECTION The ost iportant part of EMB s is their Electrical achine used for energy conversion and aterial selection. Motor/Generator used in spacecraft EMB is a variable high speed sall achine with soe liitations as theral, heat transfer, volue and ass. Rotor or flywheel is floated by agnetic bearings in EMB s and rotor dissipations excrete by radiation. Therefore the agnets installed on rotor experience high teperature and its variations. The adequate aterial for this part is chosen to be saariu-cobalt (S-Co) [6]. Because of the high electrical frequencies associated with achine operation, a high-frequency ferroagnetic "core" aterial was chosen for the stator. Core losses are particularly iportant in peranent agnet achines, as they represent a constant power loss, relatively independent of the power output of the achine. Many kinds of Ferroagnetic aterials can be used in stator and rotor yokes design such as cobalt-iron alloys, non-oriented nickel-iron alloys, and aorphous etals. Non-oriented nickel-iron alloys have electrical resistivity and saturation flux density approxiately half that of aorphous aterials. So it does not appear to be a viable candidate. Iron-cobalt alloys are often used to achieve high power density because of their high saturation flux density, approxiately 2.2 Tesla [9]. it is also desirable to keep flux densities low in the core aterial at high frequencies to keep core losses reasonable, thus the Benefits of the high saturation flux density of the iron-cobalt aterials is not the ain priorities.the electrical resistivity of aorphous iron aterials are approxiately 5 ties higher than that of the iron-cobalt alloys, and their intrinsic coercively is lower by roughly a factor of 6. Backiron are used for rotor yoke and stator core because of its high resistance (silicon steel) to decrease Eddy currents foration. Frequency properties of the aterial are less iportant, as the flux densities in the rotor are ideally DC, although soe haronics will exist due to the winding structure, current wavefors, and the slotting of the stator iron. However, if a lainated backiron is chosen, losses due to these haronics should be negligible. 3

4 TABLE I REPRESENTATIVE MECHANICAL PROPERTIES OF SOFT FERROMAGNETIC MATERIAL Iron-Cobalt Alloy (annealed) Aorphous Iron Yield strength Modulus of Elasticity 53 Ksi 200 GPa 145 Kpsi 100 GPa A solid backiron (high resistance silicon steel to discourage Eddy current foration) would be preferable to a lainated backiron fro a strictly structural standpoint because of its increased strength. However, the lower odulus of a lainated backiron has the benefit of reducing the axiu principal stresses in the agnets. Representative echanical properties of lainated iron-cobalt and aorphous iron alloys are given in Table [2] where Ksi is thousands of pounds per square inch and GPa is gigapascals. Though their odulus elasticity is about half that of ironcobalt, it was deterined that aorphous aterial is also desirable for the rotor backiron, as their yield strength is about three ties higher when copared to other annealed soft agnetic alloys. In our design an aorphous iron alloy are used for high strength (145Ksi) and suitable saturation flux densities. The aterials that copose flywheel s rotor [3, 9] will liit its rotational speed, due to the tensile strength developed. Lighter aterials develop lower inertial loads at a given speed, therefore coposite aterials, with low density and high tensile strength, are excellent for storing kinetic energy. Table (3) shows characteristics of several aterials used on wheels. The analysis of the table confirs that the carbon coposite aterials will axiize the energy density. Coposite aterials are a new generation of aterials that are lighter and stronger than the conventional ones, such as steel. For the siulations carbon AS4C was chosen because it is the second best on tensile strength and on energy density while the first one (carbon T100) have higher weight (density) which ay be a proble in satellite perforance so carbon AS4C can achieve the required energy stored with optial diension (volue) and optial weight. TABLE II CHARACTERIZES OF COMMON ROTOR MATERIAL Material Monolithic aterial 4340 steel coposites E-glass S-glass Carbon T1000 Carbon AS4C Density(Kg/3) Tensile Strenght (MPa) Max energy density(for 1 kg) 0.19MJ/Kg 0.05MJ/Kg 0.76MJ/Kg 1.28MJ/Kg 1.1MJ/Kg 4

5 IV. SURFACE PM MACHINE Surface ounted peranent agnet (SMPM) is the ost coon rotor configuration for PM achines. The agnets are placed on the rotor surface. The agnets are glued onto the rotor surface and fixed by a carbon or glass fiber bandage. In relation to other PM concepts, the surface ounted achines are easy to anufacture and consequently the construction cost is low. As the pereability of the agnets is alost the sae as the pereability of air, the d-axis and the q- axis reluctances are equal. Hence, the SMPM achines have no saliency and the torque is only produced by the interaction between the stator currents and the agnets [16]. Fig 2 the proposed surface PM achine A. Machine Design Paraetric design will be done according to Fig (2). Peranent agnet achine design for EMB application consists of the flowing steps [14, 1]: Flax density, coil current and nuber of turns is found according to achine torque and induced voltage [1].Using the equations total nuber of poles = 4, R4=17, R5=18, R6=20. Fro working point below flux density saturation 1.4 T widths of stator and rotor yoke, dent can be calculated as = Φ ( ) (4) W Should be at least equal to so selecting W = Wt α (5) So we will consider the value of Wy = Then the necessary slot space is: A = (6) On the other hand according to Fig.1 available slot space is: 5

6 = ( ) ( ) (7) By equalizing necessary and available space: As = Acu + =0 (8) Solving equation (8) we get R3 = All achine diensions is found except outer radius of flywheel. The kinetic energy stored on a hallow cylinder can be define as: = = ( ) (9) t is equal (30 in). If N1 =20000 rp in speed of flywheel N2=60000 rp ax speed of flywheel Considering a power load of LEO satellite equal to 50 watt So the total energy required fro the flywheel is E= So = g. 2 = + + (10) Now we can apply equation (1) for our design to deterined the diension of flywheel and achieve our target to iniize diension, weight and used aterial. Considering table (3) carbon AS4C will be used as a aterial of the flywheel design. = ( ) (11) = ( ) (12) = ( ) (13) Where = 8400 kg/3 density of peranent agnet aterial = 7400 kg/3 density of ferroagnetic aterial = 1510 kg/3 density of carbon epoxy aterial = - - = g. 2 Now we want to calculate the effect of gap thickness (g) on the outer radius and overall ass of the flywheel. 6

7 TABLE III SELECTION OF OUTER RADIUS OF FLYWHEEL g R8 R9 Mass of achine Fig 2. Effect of gap thickness on the outer radius of the flywheel. Fig 3. Effect of gap thickness on the total ass of flywheel. 7

8 So we can select gap thickness g=.03 to optiize the effect of volue at R8 = 62.4 which given overall ass equal 1.31 kg and R9 =95.6. TABLE VI DESIGN RESULTS FOR THE SURFACE PM MACHINE R1 R2 R3 R4 R R6 R7 R8 R9 Acu TABLE IV USED PARAMETER FOR THE HALLOW CYLINDER MACHINE DESIGN V. CONCLUSION: The Design of an external rotor peranent agnet achine used in spacecraft electro-echanical batteries is presented in this paper. This achine is required to supply a load of 50 watt for 30 inutes, the expected tie of eclipse for LEO Satellite. The used hollow cylindrical flywheel coposed of two parts to iniize its weight rather than only one sold part while storing the sae energy required. The effect of hallow gap thickness on both the overall radius and ass of the proposed hallow cylinder flywheel is depicted Saariu-cobolt is selected in the design of PM aterial for theral and volue decrease, aorphous iron is used as ferroagnetic aterial because of its high strength (145ksi) to withstand high centrifugal force at high speed, Also the use of carbon AS4C as flywheel aterial to decrease the flywheel radius and suitable energy storage capacity. REFERENCES: [1] Ahed M.Atallah, Mahoud M.Kashef, M.A.L.Badr," Designs of Electro-Mechanical Batteries for low Earth Orbit Satellite", presented at IEEE [2] Mukund R. Patel, " spacecraft power syste ",first edition,crc press,

9 [3] Bolund, Bjorn; Bernhoff, Hans; Leijon, Mats; Flywheel Energy and Power Storage Systes, Renewable and Sustainable Energy Reviews 11, pp , [4] J.A. Kirk, P.A. Studer, Flywheel Energy Storage Int. J. ech. Sci., VoL 19, pp Pergaon Press [5] G.E. Rodriguez, P.A. Studer, D.A. Baer, Assessent of Flywheel Energy Storage for Spacecraft Power Systes, NASA Technical Meorandu, May 1983 [6] M. A. Arslan, Flywheel geoetry design for iproved energy storage using finite eleent analysis, ELSEVIER Transaction on aterial and design, [7] Abdi, J. Milionfared, J. S. Moghani "Siplified design of PM Machine for spacecraft Elect Electro Mechanical Batteries ".S. Moghani,5th IET International Conference on Power Electronics, Machines and Drives 2010 [8] B. Abdi, J. Milionfared, J. S. Moghani, A. K. KAVIANI, "Siplified Design and Optiization of Slotless Synchronous PM Machine for Micro-Satellite Electro-Mechanical Batteries",5th IET International Conference on Power Electronics, Machines and Drives [9] António José Rodrigues," Design and Control of an Electrical Machine for Flywheel Energy- Storage Syste" Master in Electrical and Coputer Engineering,Maria Inês Lopes Marques. [10] W. Wang, D. Zhong, H. Hofann, J. Noland, C. E. Bakis, "Design of High-Speed Peranent Magnet Machine for Sall Flywheels", 1st International Energy Conversion Engineering Conference, August [11] A.S. Nagorny, N.V. Dravid, R.H Jansen, B.H. Kenny, Design Aspect of a High Speed Peranent Magnet Synchronous Motor/Generator for Flywheel Applications, IEEE Conference, [12] S. M. Jang, S. S. Jeong, D.W. Ryu, S.K. Choi, Design and Analysis of High Speed Slotless PM Machine with Halbach Array, IEEE Transaction on Magnetics, VOL. 37, NO. 4, JULY 2001 [13] Stephan Meier 'Theoretical design of surface-ounted peranent agnet otors with field weakening capability " Master in Electrical and Coputer Engineering, Royal Institute of Technology, Stockhol,2002 [14] J. F. Gieras, M. Wing, Peranent Magnet Motor Technology, Design and Applications, Second edition, Marcel Dekker, [15] T. Finken, M. Hobitzer, K. Haeyer " Study and coparison of several peranent-agnet excited rotor types regarding their applicability in electric vehicles ", Eobility - Electrical Power Train Conference, 2010 [16] Alexander Stening," Design and optiization of a surface-ounted peranent agnet synchronous otor for a high cycle industrial cutter ", Master in Electrical and Coputer Engineering, Royal Institute of Technology, Stockhol,2006 [17] W. Wang, Design of High Speed Flywheel Motor/Generator for Aerospace Applications, PhD Thesis, The Pennsylvania State University, [18] D. M. Ionel, M. Popescu, M. I. McGilp, T. J. E. Miller, S. J. Dellinger, Assessent of Torque Coponents in Brushless Peranent-Magnet Machines Through Nuerical Analysis of the Electroagnetic Field, IEEE Transaction on Industry Applications, VOL. 41, NO. 5, SEPTEMBER/OCTOBER [19] S. R. Hol, H. Polinder, J. A. Ferreira, Analytical Modeling of a Peranent-Magnet Synchronous Machine in a Flywheel, IEEE Transaction on Magnetics, VOL. 43, NO. 5, MAY [20] Z. Q. Zhu, D. Howe, Instantaneous agnetic field distribution in peranent agnet brushless DC otors, IEEE Transactions on Magnetics Volue 29, Issue 1, Jan