Modeling and Analysis of Wind Energy Conversion Systems Using Matlab

Size: px

Start display at page:

Download "Modeling and Analysis of Wind Energy Conversion Systems Using Matlab"

Eleanore Singleton
6 years ago
Views:

1 OSR Journal of Electrical and Electronics Engineering (OSR-JEEE) e-ssn: ,-SSN: 0-, Volume 8, ssue (Nov. - Dec. 0), PP Modeling and Analysis of Wind Energy Conversion Systems Using Matlab P.Kumar*, A.Vinoth Kumar Power Systems Division, Assistant Professor DEEE, P.A. College of Engineering and Technology, Pollachi Power Electronics and Drives, Assistant Professor DEEE, P.A. College of Engineering and Technology, Pollachi Abstract: This aer resents modeling and analysis of Wind Energy Conversion Systems (WECS) using MATLAB version R009a. This aer gives the modeling of the various comonents wind turbine, generator, controller system, rectifier-inverter, battery, other load equiments including transformer and grid that together form the Wind Energy Conversion system. A test case for the Wind Energy Conversion System has been formed with the aid of the MATLAB version R009a and also the suggest the ways of imroving the stability of the Wind Energy Conversion System (WECS) on interface with the grid. Keywor: Wind Energy Conversion System (WECS), wind turbine, generator, controller system, rectifierinverter, transformer, grid.. ntroduction The conventional energy sources such as coal, fossil fuels have greater imact on the environment. Futher with the resent day scenario the fossil fuels are getting deleted at a faster rate and the energy reserves may last only for few years. n order to meet the growing energy demand and to rotect the environment, the need of the hour is to look in for the renewable energy sources. Wind is one of the romising energy sources that serve to meet the growing energy demand. The growing concern about the emissions from the fossil fuel generation and increased government suort has heled flourish wind ower installation in ndia and abroad. Provisions of incentives instituted by the Ministry of New & Renewable Energy (MNRE) have made the wind electricity cometitive in ndia.the need of energy generation, the otential and the technological caacity were the reasons to foster the emergence of wind energy. Wind is air in motion and this energy is derived from solar energy. Wind in general is roduced by the uneven solar heating of the earth s atmoshere. The kinetic energy of the wind is used to imart rotational motion to the wind turbine. The shaft of the wind turbine is couled to the shaft of the electric generator. The electric generator can rovide ower over a region acting as standalone or roviding ower to the grid. The Wind Energy Conversion System (WECS) can be used in two ways. The first being isolated standalone system emloyed to cater the nee of small townshis or small scale industries located at far off laces. Usually these systems are set u with the objective to avoid transmission costs over long distances. The second being Grid connected system where emhasis is rovided on integration of renewable energy systems into the grid, which lea to increased energy efficiency, robustness of the system, voltage suort, diversification of energy sources, reduced transmission and distribution losses and reliability of the system.. Variable-Seed And Constant- Seed Wind Turbines A major distinction in the wind turbines includes variable and constant seed wind turbines i.e. the rotor is allowed to run at variable seed or constrained to oerate at constant seed. The constant seed wind turbines allow the use of simle generators whose seed is fixed by the frequency of the electrical system. Although the ower electronics needed for variable seed wind turbines are more exensive, this tye of turbines can send more time oerating at maximum aerodynamic efficiency than constant seed turbines. This can be seen clearly if the erformance coefficient, C of a wind turbine is lotted against the ti seed ratio,. The ti seed ratio,, is defined as the ratio between the seed of the tis of the blades of the wind turbine and the seed of the wind. ti. R () wind where is the blades angular velocity (rad/s), R the rotor radius (m) and the wind seed (m/s). 47 Page

$The coefficient of erformance, C, is defined as the fraction of energy extracted by the wind turbine of the total energy that would have flowed through the area swet by the rotor if the turbine had$

2 The coefficient of erformance, C, is defined as the fraction of energy extracted by the wind turbine of the total energy that would have flowed through the area swet by the rotor if the turbine had not been there. P extracted C () Pwind The coefficient of erformance C has a theoretical otimum of 0.59.Only a ortion of the ower in the wind can be converted to useful energy by wind turbine. The ower available for a wind turbine is equal to the change in kinetic energy of the air as it asses through the rotor. This maximum theoretical C was formulated in 99 by Betz and alies to all tyes of wind turbines. A tyical C vs characteristics is deicted in the figure..the figure. reresents the characteristics of coefficient of erformance, C versus ti seed ratio,.from figure. we infer that maximum value of C i.e. 0.5 is achieved for a ti seed ratio of 0 and itch angle of 0. For a fixed-seed wind turbine, where ω is constant, this correson to a articular wind seed. For all other wind see the efficiency of the turbine is reduced. The aim of variable-seed wind turbines is to always run at otimal efficiency, keeing constant the articular λ that correson to the maximum C, by adating the blades velocity to the wind seed changes. Hence, variable seed wind turbines are designed to oerate at otimum energy efficiency, regardless of the wind seed. On the other hand, due to the fixed-seed oeration for constant seed turbines, all fluctuations in the wind seed are transmitted as fluctuations in the mechanical torque and then as fluctuations in the electrical ower grid. This together with the increased energy cature obtained by using a variable-seed wind turbine rovides enough benefit to make the ower electronics cost effective.therefore, the wind industry trend is to design and construct variable-seed wind turbines. Fig. C vs characteristics The figure. deicts the characteristics of the P,,C versus the wind seed of a tyical wind energy conversion system 48 Page

Fig., P, C vs wind seed characteristics. Modeling Of Wind Energy Conversion System er The kinetic energy in a flow of air through a unit area erendicular to the wind direction is. mass flow rate.

3 Fig., P, C vs wind seed characteristics. Modeling Of Wind Energy Conversion System er The kinetic energy in a flow of air through a unit area erendicular to the wind direction is. mass flow rate. For an air stream flowing through an area A the mass flow rate is.a.,therefore the ower in the wind is given by, where, P (.A. ).. =.. A. () is the air density ( kg / m ) A the area ( m ) the wind seed ( m / s ) P the ower of the wind ( watts or J / s ) A tyical wind energy conversion system is reresented in the figure.. Fig. A tyical wind energy conversion system The wind turbine model, consisting of the rotor aerodynamics, ive train and electrical generator model reresented in the figure.. MODELLNG OF THE BLADES The wind turbine blades extract the kinetic energy in the wind and transform it into mechanical energy. The kinetic energy in air of an object of mass m moving with seed v is given by 49 Page

4 Modeling And Analysis Of Wind Energy Conversion Systems Using Matlab E. m. v (4) The ower in the moving air (assuming constant seed velocity) is equal to de P w.. v dt m (5) where m is the mass flow rate er second. When the air asses across an area A swet by the rotor blades, the ower in the air can be comuted using (). The ower extracted from the wind is given by P BLADE C (, ). Pw C (, )... A. (6) The ower factor has a maximum theoretical value C The rotor ower coefficient is usually given as a function of two arameters: the ti-seed ratio and the blade itch angle (in degrees). The blade itch angle is defined as the angle between the lane of rotation and the blade crosssection chord. The rotor torque Tw can be comuted using the exression (/ ). C (, ).. A. PBLADE Tw (7) m m The area covered by the blades is given by substituting Eq.(8) in Eq.(7) A.R (8) (/ ).. C (, ).. R Tw. (9) m The ower coefficient C can be defined as a function of the ti-seed ratio and the blade itch angle as follows C (, ) with defined as c6. x c.( c. c. c4. c5) e (0) () where the constant values c6 c are given as c.5, c 6, c 0.4, c 0, c 5, c Page

5 . MODELLNG OF THE DRVE TRAN Modeling And Analysis Of Wind Energy Conversion Systems Using Matlab Fig.4 Drive train dynamics The equation of motion of the induction generator is given by H g d g Tm. Te () dt n The mechanical torque T can be modeled with the following equation m T m g m K D. n n. () d dt (4) g m where n is the gear ratio is the angle between the turbine rotor and is the turbine seed m is the generator rotor seed g the generator rotor H H m, g are the inertia constants of turbine and generator resectively K is the ive train stiffness D is the daming constant T is the torque rovided by wind w T is the electromagnetic torque. e. MODELLNG OF THE ASYNCHRONOUS GENERATOR The modelling of the asynchronous generator lays an imortant role in the design of the wind energy conversion system. The asynchronous generator has three hase stator armature winding A, B, C ) and a ( s s s three hase rotor winding ( AR, BR, CR ) as shown in the figure below. The mathematical model of an asynchronous generator for ower system analysis is usually based on the following assumtions. The stator currents are ositive when flowing towar the network. The real and reactive ower are ositive when fed into grid. 5 Page

6 Fig.5 windings in the asynchronous generator. The stator and rotor windings are laced sinusoidally along the air-ga as far as the mutual effect with the rotor is concerned. 4. The stator slots cause no areciable variations of the stator inductances with rotor osition. 5. The rotor slots cause no areciable variations of the stator inductances with rotor osition. 6. Magnetic hysteresis and saturation effects are negligible. 7. The stator and rotor windings are symmetrical. 8. The caacitance of all the windings are neglected. The set of equations of the asynchronous generator model is usually converted into a model related to an arbitrarily set reference frame called odq reference frame model. The dq axis reresentation of induction generator is used for simulation, taking flux linkage as basic variable. t is based on fifth-order two axis reresentations. Mathematical transformations are used in the analysis and simulation of three-hase systems, mostly to decoule variables, to facilitate the solution of difficult equations with time-varying coefficients. Park s transformation decoules and rotates the stator variables into a dq reference frame. The ositive d-axis of the dq frame is aligned with the magnetic axis of the field winding, that of the ositive q-axis is ahead in the direction of rotation or lead the ositive d-axis by. and qs corresond to stator direct and quaature axes. and qr corresond to rotor direct and quaature axes. For ower system transient studies, the inclusion of the network transients and generator stator transients increases the overall system model, thus limiting the size of the system that can be simulated. Furthermore, a small time ste is required for numerical integration resulting in an increased comutational time. For these reasons, it has become conventional to reduce the order of the generator and neglect the network transients for stability analysis. A standard method of reducing the order of the induction generator model was considered where the rate of change of stator flux linkage is neglected. To be able to simulate the induction generator and wind generation system, an equation relating V, V qs, the stator direct and quaature axis voltages and, qs,the stator direct and quaature axis currents is required. The comlete model of an asynchronous generator, exressed in a odq reference frame rotating at synchronous seed and taking ositive currents going out from the machine consists of the following equations. X s. X m. (5) qs X s. qs X m. qr (6) X r. X m. (7) qr X r. qr X m. qs (8) Equations (5),(6),(7),(8) reresent the flux linkage equations on direct axis and quaature axis resectively. 5 Page

7 V V Modeling And Analysis Of Wind Energy Conversion Systems Using Matlab Rs. s. qs (9) qs Rs. qs s. (0) d Rr. s. s. qr dt dqr Rr. qr s. s. dt 0 () 0 () Equations (9),(0),(),() reresent the voltage equations on direct axis and quaature axis resectively. The electrical arameters of the machine R X, X, R, X reactance, mutual reactance and rotor resistance and reactance resectively. The sli of the rotor is defined as follows, s The electrical torque is given by s s g () T. e qr. qr (4) s, stand for the stator resistance and The develoed torque is ositive for motoring oeration and negative for generation oeration. The wind turbine active, reactive and aarent ower outut are given by the following equations P. active V. Vqs qs (5) reactive Vqs. V qs (6) Q. S P active Q reactive V. Vqs. + V qs. V. qs (7) S qs n order to reduce the overall system model and to reduce the comutational time involved, the system is modelled with the order of the generator is reduced and the network transients are neglected for stability studies. s m r r V. Simulation And Results Fig.6 Wind Energy Conversion System Model 5 Page

7 WECS simulation before grid interfacing Fig.

8 The figure 6 gives the comlete model of the wind energy conversion system model formulated in MATLAB version R009a.The simulation of the wind energy conversion system before and after interfacing with the utility grid is reresented in the figures 7 and 8 resectively. Fig.7 WECS simulation before grid interfacing Fig.8 WECS simulation after grid interfacing From figure 7 we observe before the interface of the wind energy conversion system with grid, the utility grid voltage Vabc and current abc remains sinusoidal without any disturbances in Vabc and abcresectively. From figure 8 we observe after the interface of wind energy conversion system with the grid, the utility grid voltage V abc remains unaffected but considerable disturbances are observed in the grid current abc.these disturbances generally arises due to variable nature of the wind.norder to imrove the stability of 54 Page

9 wind energy conversion system on interface with the grid the stability of the wind energy conversion system has to be imroved. For the analysis of the stability and the dynamic erformance of the wind energy conversion system a detailed model of the wind energy conversion system has been formed in MATLAB R009a.The model is deicted in the figure 9 Fig.9 Detailed model of Wind Energy Conversion System The detailed model includes the detailed reresentation of ower electronic GBT converters.norder to achieve an accetable accuracy with 60 Hz and 700 Hz switching frequencies the model must be discretized at a relatively small time ste(5 micro secon).this model is well suited for observing harmonics and control system dynamic erformance over relatively short erio of time. A 9 MW wind farm consisting of six.5 MW wind turbines connected to a 5 kv distribution system exorts ower to a 0 kv grid through a 0 km, 5 kv feeder. Wind turbines using a doubly-fed induction generator (DFG) consist of a wound rotor induction generator and an AC/DC/AC GBT-based PWM converter. The stator winding is connected directly to the 60 Hz grid while the rotor is fed at variable frequency through the AC/DC/AC converter. The DFG technology allows extracting maximum energy from the wind for low wind see by otimizing the turbine seed, while minimizing mechanical stresses on the turbine during gusts of wind. Fig.0 Simulation results of detailed model of Wind Energy Conversion System 55 Page

10 n this model the wind seed is maintained constant at 5 m/s. The control system uses a torque controller in order to maintain the seed at. u. The reactive ower roduced by the wind turbine is regulated at 0 Mvar.This model is used to analyse the steady-state oeration of the DFG and its dynamic resonse to voltage sag resulting from a remote fault on the 0-kV system. The simulation results are rovided in figure 0.From the simulation results we observe the DFG wind farm roduces 9 MW.The corresonding turbine seed is..u. of generator synchronous seed.the DC voltage is regulated at 50 V and the reactive ower is ket at 0 Mvar.At t=0.0s the ositive-sequence voltage suddenly os to 0.5.u. causing an oscillation on the DC bus voltage and on the DFG outut ower. During the voltage sag the control system tries to regulate DC voltage and reactive ower at their set oints (50 V,0 Mvar).The system recovers in aroximately 4 cycles. V. Conclusion This aer gives a detailed modelling of the wind energy conversion systems and the imacts of interfacing the wind energy conversion system with the grid. From the simulation results we infer that considerable harmonics in the current are observed on interface of the wind energy conversion system with the grid. However these harmonics can be reduced by emloying control system with torque controller for seed regulation and voltage regulator for voltage regulation. A MATLAB version R009a demo model is taken for analysis of wind energy conversion system. The test results from analysis of wind energy conversion system indicates that design of control system with suitable torque controller and voltage regulator can imrove the erformance of wind energy conversion systems under the fault conditions. V. Scoe Of Future Work This work could be extended for future research by the design of control system with different controllers and by making analysis of its erformance under various fault conditions. References [] UCTE, Union for coordination of transmission of electricity, Wind Power in the UCTE interconnected System, November 004. [] E. Sooner and A.C. Williamson, Direct couled ermanent magnet generators for wind turbine alications, EE Proceeding, Electric Power Alications. Vol. 4, N,.-8, January, 996. [] M.R.Dubois, H.Polinder and J.A. Ferreira, Comarison of generators toologies for direct ive wind turbines, ECM 9, Manchester UK, , 99. [4] Thomas Ackerman, Wind Power in Power Systems, Royal nstitute of Technology Stockholm, Sweden, Edition: John Wiley and sons, Ltd, 005. [5] M.G.Gracia_, M. P. Comech, J.Salla and A. Llombart, Modelling wind farms for grid disturbance studies, Renewable Energy (008)09. [6] T.Petru and T.Thirnger, Modelling of wind turbines for ower system studies, EEE Trans. Energy Convers. Vol. 7, N 4,. -9, Nov. 00. [7] E.S.Abdin and W.Xu, Control design and dynamic erformance analysis of a wind turbine-induction generator unit, EEE Trans. Energy Convers. Vol. 5, N,. 9-96, March [8] G.Saccomando, J. Svensson and A.Sannino, mroving voltage disturbance rejection for variable-wind seed wind turbine, EEE Trans, Energy Convers, Vol. 7, N,. 4-48, June 00. [9] htt:// V47_US.df [0] C.M. Ong, Dynamic Simulation of Electric Machinery using Matlab/Simulink, Prentice-Hall PTR, Uer Saddle River, New Jersey, 998. [] Z.Miao and L.Fan. The art of modeling and simulation of induction generator in wind generation alications using high-order model, Simulation Modelling Practice and Theory Vol. 6,. 9 5, 008. [].Zubia, X. Ostolaza, A.Suserregui and G.Taia, Comlete wind farm electromangetic transient modelling for grid integration studies, Energy Conversion and Management, Vol. 50(), March 009, [] M.Martins, A.Perdana, P.Ledesma, E.Agneholm and O.Carlson, Validation of fixed seed wind turbine dynamics models with measured data, Renewable Energy, Vol.8(8), July 007,.0-6. [4] M.L.Doumbia and A.Traoré, Modélisation et simulation d une machine asynchrone à cage à l aide du logiciel Matlab/simulink, MSAS, Bamako, July 8-, 00; [5] S.Derriche, H. Djebrani and DJ.Djemai, modélisation et simulation d un générateur éolien connecté au réseau à l aide du logiciel MATLAB/SMULNK,Mémoired ingénieur d état de l Université Mouloud Mammeri de Tizi-Ouzou, Algérie, Setembre 008. [6] L.Leclercq, Aort du stockage inertiel associés à des éoliennes dans un réseau électrique en vue d assurer des services systèmes.thèse de Doctorat, Laboratoire d Electrotechnique et d Electronique de Puissance de Lille, Le 4 décembre 004. [7] P.M. Anderson, and Anjan Bose, Stability simulation of wind turbine systems, EEE Transactions on Power Aaratus and Systems, Vol. 0, No., , December 98. [8 ] N. Laverdure, S. Bacha, D. Roye, B. Raison, and F. Dumas, Elements of modeling of wind ower systems with energy management: two structures in comarison, EEE 8th Annual Conference of the ndustrial Electronics Society, Vol., , November 00. [9] L.Krichen, B.Francois and A.Ouali, A fuzzy logic suervisor for active and reactive ower control of fixed seed wind energy conversion system, Electric Power System Research, Vol. 78, , 008. [0] F.oitiers, Etude et commande de génératrice asynchrone our l utilisation de l énergie éolienne, Thèse de doctorat.université de Nantes, France, 9 Décembre Page

MATHEMATICAL MODELLING AND SIMULATION OF INDUCTION GENERATOR BASED WIND TURBINE IN MATLAB/SIMULINK

MATHEMATICAL MODELLING AND SIMULATION OF INDUCTION GENERATOR BASED WIND TURBINE IN MATLAB/SIMULINK Md. Rasel Sarkar, Sabariah Julai, Chong Wen Tong, Ong Zhi Chao and Mahmudur Rahman Department of Mechanical,