Investeşte în oameni! FONDUL SOCIAL EUROPEAN Programul Operaţional Sectorial Dezvoltarea Resurselor Umane 2007 2013 Axa prioritară: 1 Educaţia şi formarea profesională în sprijinul creşterii economice şi dezvoltării societăţii bazate pe cunoaştere Domeniul major de intervenţie: 1.5 Programe doctorale si postdoctorale în sprijinul cercetării Titlul proiectului: Proiect de dezvoltare a studiilor de doctorat în tehnologii avansate- PRODOC Cod Contract: POSDRU 6/1.5/S/5 Beneficiar: Universitatea Tehnică din Cluj-Napoca FACULTY OF ELECTRICAL ENGINEERING Eng. Dan PĂUNESCU SUMMARY OF PHD THESIS THEORETICAL AND EXPERIMENTAL STUDY OF THE AXIAL FLUX PERMANENT MAGNET SYNCHRONOUS GENERATOR WITH APPLICATION IN MICRO WIND TURBINES PhD Advisor, Prof. dr. ing. Vasile IANCU Evaluation commision of Phd thesis: President: Members: -Prof. Radu CIUPA, PhD.eng - Dean, Faculty of Electrical Engineering, Technical University of Cluj-Napoca; -Prof. Vasile IANCU, PhD.eng. PhD Advisor, Faculty of Electrical Engineering, Technical University of Cluj-Napoca; -Prof.hab. Tudor AMBROS, PhD.Eng - Scientific reviewer, Technical University of Moldavia, Chişinău ; -Cerc.şt.gr.I. Mihail CISTELECAN, PhD.Eng - Scientific reviewer, Research Institute for Electrical Machines, Bucharest; -Prof. Károly BIRÓ, PhD. Eng - Scientific reviewer, Faculty of Electrical Engineering, Technical University of Cluj-Napoca;
INTRODUCTION The lifestyle of the modern society and the comfort which we take for granted depends on the notion of cheap energy, obtained mostly from fossil fuel sources, which are nonrenewable and generate pollution. The depletion or substantial reduction of these fossil fuel energy sources coupled with the greenhouse effect and its implication on the human civilization have put a large pressure on the research and development of unconventional energy sources such as geothermal, wind, photovoltaic, wave energy etc. The conversion of wind energy in electricity benefits at this moment from the most focus regarding research of new generator topologies and investment in new wind farms. This can be explained on the basis of the favorable legislation and funding for the development and use of new forms of wind turbines. The recent development regarding the global installed capacity can be observed in figure 1. Fig.1 Global wind energy development [1] The interest given toward this renewable energy source could not have comed without research, which focused primarily on finding new materials, the development of new topologies for electrical generators and the use of power electronics for obtaining a more efficient wind energy conversion. The development of rare earth permanent magnets has led a boost in the research regarding electrical machines through new topologies to replace the induction, synchronous and doubly-fed induction generators inside medium and high power wind turbines. One of the breakthroughs consisted in the development of the permanent magnet synchronous generators (PMSG) starting from the classical synchronous generator structure for which the electromagnetic excitation has been replaced by permanent magnets, removing thus the need for brushes. The possibility to add a high number of poles and to use the power electronics for the network coupling of these generators, led to the removal of the gear mechanism with positive effects on the energy capture. The necessity to adress the conversion of wind energy in electricity with the help of PMSGs of axial type comes from the study of the state of the art, which revealed the trend to develop alternative topologies or resume older topologies for use in wind turbines. In the former case we can find the axial flux machine for which the contruction difficulties common to the early stages in the development of electrical machines halted its development. The axial flux machine became again the focus of the researchers in the 80s being used primarily 2
in electric cars, ventilation systems, pumps, valve control, industrial equipment and small and medium power generators [2] The oportunity of this PhD thesis is given by the highlighting of certain untreated aspects in the dimensioning and modeling of the axial flux permanent magnet generators of small power destined to be used in micro wind turbines. The general objective of the PhD thesis consists in the study of the double-sided internal rotor axial flux machine with tooth concentrated fractional-slot winding, the physical construction of the rotor, the assembly of the machine and the testing on the test bench. Starting from these considerations the following objectives have been set: - Establishment of a sizing algorithm for the studied axial flux machine - Determination of the harmonic spectrum generated by the winding through analytical and numerical methods and finding methods to reduce it - Validation of the algorithm and performances with the help of Finite Element Analysis (FEA) tools - Establishment of a test bench The thesis consists of five chapters, prefaced by introduction and followed by references and annexes. The introduction presents the actuality and oportunity of the theme. In the following the content of the chapters are presented shortly. Chapter 1,,State of the art regarding the research of the axial flux PMSGs presents a short study regarding the state of the art of axial flux PMSGs in micro wind turbines. The main topologies and aplications using tooth concentrated windings are presented. The end of the chapter highlights some aspects regarding the materials used in these types of generators. Chapter 2,,Analytical calculus of the axial flux PMSGs presents the sizing algorithm of axial flux generators in the following steps: sizing of the geometric dimensions of stator and rotor, volume of the permanent magnet, choosing the type of winding, forming the equivalent magnetic circuit and finding the resulting losses. Fig.2 Main stator dimensions 3
Fig.3 Main rotor dimensions The positions of the coils for single and double layer tooth concentrated winding with fractional number of slots per pole and phase (q=0.4) are presented in the following figures Fig.4 Coil positions for single layer tooth concentrated winding Fig.5Coil positions for double layer tooth concentrated winding Fig.2.7 Threephase current linkage waveform and harmonic content 4
Chapter 3,,Numerical modelling of the axial flux PMSGs represents a summary of the main modelling methods used for the axial flux permanent magnet machines. 2D modelling methods at the arithmetical and geometrical mean radius are presented along the 3D modelling of the axial flux machine. Both modelling methods are compared to each other and are found to be in good agreement. Simulations for no load and load are carried out which confirm the results obtained by analytical methods. a) b) Fig. 3.6 a) Airgap flux density distribution for a pole pair (with slots) a) Harmonic content of airgap flux density (with slots) Table 1 Comparison of flux densities in tooths and joke Parameter Analytical Magnetic 2D model 3D model sizing eq.circuit Flux density in the tooths for the 1.117 1.3 1.269 1.258 mean radius [T] Flux density in the tooths for the 1.159-1.279 1.252 geometric radius [T] Flux density in the tooths for the 1.421-1.355 1.312 minimum radius [T] Flux density in the tooths for the 0.982-1.104 1.184 maximum radius [T] Flux density in the joke [T] 0.801 0.735 0.723 0.756 Flux density in the rotor [T] - 0.022 0.025 0.024 Fig.3.11 a) Induced phase voltage for no load b) Harmonic content of the induced voltage 5
Table. 3.5 Comparison of induced voltage between modeling and analytical results Parametru Analytical sizing 3D modeling 2D modeling mean radius 2D modeling geom. radius RMS value of induced phase 56.53 56.11 54.73 54.66 voltage [V] Peak value of induced phase 79.94 79.36 77.4 77.31 voltage [V] Value of line voltage [V] 97.91 97.18 94.79 94.67 Chapter 4,,Construction and testing of the generator presents the practical construction of the axial flux permanent magnet generator, the fixing of the generator on the test bench and its testing. The main components are presented and the way in which it was built and assembled. The final generator was run firstly at the no load situation to determine the induced voltage and its variation with the speed. For the load situation the generator was run at diffent speeds with resistive, inductive and capacitive loads for different values of the load current. An induction machine fed by a frequency converter acted as the prime mover for the electrical generator. a) b) Fig.4.9 a) Test bench b) Layout of the test bench Chapter 5,,Final conclusions sets the final conclusions regarding the obtained results, the personal contributions, use of the results and proposes new research directions. Perspectives to continue the reseach and to improve the obtained results are presented. Compared to the proposed objectives: - Analytical design of the axial flux PMSG - Numerical field modelling to confirm the analytical results - Electro-mechanical design of the generator - Construction of the generator to analyse its performance in micro wind turbines - Building of a test bench 6
The main contributions of this thesis are: State of the art study, regarding the manufacturing of different types of axial flux machines and appearance of axial forces which are exercited between the two stators has led to the solution adopted in the thesis of a double sided internal rotor axial flux permanent magnet synchronous generator Development of Matlab programs for the study of the current linkage in single and double layer tooth concentrated windings which led to the choice of double layer winding Construction of a prototype using existing feromagnetic iron from steel sheets (2 stators), construction of an stainless steel rotor with NdFeB permanent magnets embedded in the rotor in 2 variants: aligned on the radius and skewed Determining of an analytical calculation method for the resulted prototype Numerical modelling with the aid of Finite Element Method in 2D and 3D and comparison of the obtained results with those of the analytical calculation Test bench and the obtained results which confirm the hypothesis taken into consideration when choosing the solutions regarding the prototype The perspectives to continue the research are numerous. The most obvious of these is related to the change of the present rotor with the second one containing skewed magnets and evaluation of the performance of the generator in this configuration. The research of other forms of permanent magnets placed on the surface of the rotor disc or inside the disc and consideration of other skewing angles can be considered another direction of research. The analytical solution to reduce the harmonics generated by the tooth concentrated winding can be turned into practice and validated through experimental testing. Another research direction consists in studying the oportunity to construct a modular structure consisting of many more stators and rotors to increase the power of the generator. The study of the contructed generator can be completed with a thermic study to confirm the increased cooling capacityot the axial flux permanent magnet synchronous machines in comparison to the radial flux ones. 7
REFERENCES [1] World Wind Energy Association (WWEA):,,World Wind Energy Report 2010, 2011 http://www.wwindea.org/home/index.php [2] Gieras, J.F., Wang, R-J, Kamper, M.J.:,,Axial Flux Permanent Magnet Brushless Machines, Kluwer Academic Publishers, 2008, ISBN 978-1-4020-6993-2 8