Robust Maximum Power Point Tracking Control of Permanent Magnet Synchronous Generator for Grid Connected Wind Turbines

Transcription

1 Robut Maximum Power Point Trackin Control of Permanent Manet Synchronou Generator for Grid Connected Wind Turbine Amir Khazaee Dept. Electrical and Computer Enineerin Ifahan Univerity of Technoloy Ifahan, Iran Hoein Abutorabi Zarchih Faculty of Electrical Enineerin Ferdowi Univerity of Mahhad Mahhad, Iran Mohammad Ebrahimi Faculty of Electrical Enineerin Ifahan Univerity of Technoloy Ifahan, Iran Abtract In thi paper a cla of PI-lidin mode controller i preented in order to implement maximum power point trackin (MPPT) alorithm for permanent manet ynchronou enerator (PMSG) baed wind turbine. The principle of lidin mode and linear PI controller are combined to enure hih performance operation. The propoed method provide a robut, fat and accurate peed trackin without penalty of hih chatterin which uarantee maximum power point trackin in a wind turbine. Comparative reult demontrate bet performance of tranient and teady tate operation of propoed technique. The imulation reult verify that the preented control tratey i accurate, quick and tronly robut. Keyword-Permanent manet ynchronou drive Slidin mode controller MPPT variable peed wind turbine I. INTRODUCTION Due to reduction of foil fuel and environmental pollution, renewable enerie are currently raiin a reat attention for obtainin electric power []. Wind enery i the mot economical and promiin reource in the world, it i renewable, infinite and environmentally clean []. There are mainly two type of wind turbine: fixed peed operation and variable peed operation []. Variable peed concept i more attractive becaue of it ability of operation at it maximum power coefficient, which reult in larer enery capture from the wind. There are mainly two kind of enerator, ued in variable peed wind turbine: Doubly fed induction enerator (DFIG) and permanent manet ynchronou enerator (PMSG). At preent DFIG [4] i the mot ued enerator in variable peed wind turbine. The advantae of DFIG i that the rated power of converter i only about % of rated turbine power. In thi method variable peed operation i limited in only % of ynchronou peed. In comparion with DFIG, PMSG ha everal advantae uch a the ability of operation over full rane of enerator peed, le weiht, mall in ize, earle drive, lowerin maintenance expene and improvin low voltae ride throuh (LVRT) capability [5]. Baed on thee reaon the uae of PMSG baed direct driven wind turbine are increain widely in power ytem. The power converter ued in thi method i fully rated converter (FRC), caue more expene and more witchin loe. Variou converter confiuration have been propoed in [6]-[8]. Reference [6], [7] preent a confiuration, that uin combination of a diode rectifier and a boot chopper in enerator ide converter. With thi confiuration, enerator power factor i uncontrollable, which reduce enerator efficiency a well a exitence of hih harmonic ditortion current. In [8], control of a variable peed permanent manet enerator with a back to back inverter i dicued. In thi method both active and reactive power are controllable, which make it an attractive choice. Several control trateie have been propoed for enerator ide converter in order to track the reference of enerator peed. In [8] a conventional PI controller i dicued. Thi method i imple but doen t have a atifactory robutne becaue of nonlinearity of the ytem, pecially, with repect to tochatic inherent of wind that increae uncertaintie. In lidin mode approach robutne to uncertaintie i improved but it ha the drawback of chatterin effect, which miht be harmful for the ytem. The preent paper deal with dein of a PI-lidin mode controller for PMSG driven by a back to back converter. The propoed method provide a robut, fat and accurate peed trackin without penalty of hih chatterin which uarantee maximum power point trackin in a wind turbine. The whole ytem includin wind turbine, permanent manet ynchronou enerator, back to back converter, AC rid and control ytem of each converter ha been imulated in MATLAB/SIMULINK to validate the propoed control tratey. II. SYSTEM MODELLING The variable peed wind turbine i a complex electromechanical ytem, conit of wind turbine, permanent manet ynchronou enerator and back to back converter []. (See Fi. ) Fiure. Wind power ytem component

2 Fiure. Power curve when pitch anle i zero A. Aerodynamic Model The mechanical power extracted from the wind i iven below [9] P wind.5ac p (, ) v Where i air denity (k/m ), A i blade wept area (m ), Cp i the power coefficient, i pitch anle (de) (in thi paper ), v i wind peed (m/) and i tip peed ratio, defined a follow R r v () () Where r i turbine rotor peed (rad/) and R i blade radiu (m). The wind turbine power curve for variou wind peed when are hown in Fi.. It i oberved that, for each wind peed, there exit a pecific point in the wind turbine output power veru rotatin-peed, where the output power i maximized. At thee point opt where opt i a contant value for each turbine. So the reference value for enerator peed, in which, output power i maximized, can be obtained a below. [See Fi. ] r R opt v B. Permanent Manet Synchronou Generator Model () In order to et a dynamical model for enerator that would be ueful to dein the enerator control ytem, the equation of the enerator are tranformed to ynchronou reference frame. The dynamic model of the urface-mounted permanent manet enerator in ynchronou reference frame could be tated a follow [9] did R ud id Piq (4) L L diq R uq iq Pid P (5) L L L S Fiure. MPPT control ytem Where u d and u q are repectively d axi and q axi voltae, i d and i q are repectively d axi and q axi current, L, R are repectively enerator inductance and reitance, i the manet flux and i enerator peed. The electromanetic torque i iven by Te.5P iq Where P i the pole pair number. Equation (6) how that electrical torque can be directly control by quadrature current component. The mechanical dynamic equation i iven below d Te Tl B J Where J i rotor inertia, B i friction contant and T l i the torque produced by wind turbine. III. CONTROL STRATEGY A. Linear and Variable Structure Control A block diaram of linear and variable Structure control (LVSC) method that implemented on enerator ide converter i hown in Fi. 4.a. The controller include a witchin part and a linear one, and ha dual behaviour. Thi i a flexible control cheme that take advantae of the bet feature of linear control, mooth and chatterin free operation, and of lidin mode controller, robutne to uncertaintie. An SVM unit i ued to produce witchin inal baed on voltae reference []. The lidin urface define a below: Where Sw e ( t) cw e ( ) d ref t (6) (7) (8) e ( t) i the enerator peed control error. Dein contant, c i elected to achieve the deired lidin dynamic.

3 In order to track current reference Field oriented control tratey i ued. Thi i a common control tratey in PMSG control ytem (See Fi. 4.b). A deeper tudy of thi control tratey may be found in []. (a) (b) Fiure 4. a) PI-Slidin mode controller b) Field oriented current loop The control law that produce the reference value of torque can be tated a T e ( K P KI )( e K SMC n( S )) Where i Laplace operator and K P and K I are the PI controller ain and K SMC i the lidin mode control (SMC) ain. Adequate balance between the linear PI controller and witchin behaviour of the SMC can be achieved by proper ain election of both controller. For the tranient repone, the linear component i dominant, and the PI ain are elected o a the linear control achieve the deired dynamic repone. In the teady tate operation, the lidin mode component i dominated and the ripple manitude depend on the K SMC ain. It can be proved that lare enouh value for K will fulfill the tability condition S w S w. SMC The lidin mode controller ain K SMC i elected a lare a enouh to obtain the deired performance in term of teadytate robutne and chatterin free operation. (9) B. Grid ide inverter Control dein The dynamic model of the rid connection when electin a reference frame rotatin ynchronouly with the rid frequency i iven below: did ud uid Rid L Liq diq uq uiq Riq L Lid () () Where L and R are the rid inductance and reitance, repectively and u id and u iq are inverter voltae component. If the reference frame i oriented alon the upply voltae, the rid voltae vector i u u d Then active and reactive power may be expreed a j P udi Q udi d q () (4) Active and reactive power are controllable by controllin direct and quadrature current component repectively. The control of thi converter i quite imilar to enerator ide one. Fi. 5 how the block diaram of rid ide converter control. There are two control loop, are ued to control the active and reactive power into the rid. An outer dc voltae control loop i ued to aure that all of the power comin from the enerator i intantaneouly injected to the rid by the inverter. The reactive power can be directly control by reulatin q-axi current component. The current controller make a voltae reference for the inverter that can be implemented by SVM witchin technique. With repect to Equation (6), the reference value of i q can be directly obtained by reference value of electromanetic torque a: i q T e.5 P () The reference value of direct-axi current component can be et to zero to minimize current for a iven toque and therefore minimize reitive loe []. Fiure 5. Field oriented control of rid ide inverter

4 IV. SIMULATION RESULTS The performance of propoed control tratey i evaluated with the imulation tudy uin MATLAB/SIMULINK. The performance of linear and lidin mode control ytem i compared with conventional PI controller and Slidin Mode controller. Table how the wind turbine and enerator parameter. Wind Speed(m/) (rpm) (rpm) (rpm) Fiure 6. Wind peed (ref) (a) Chatterin Effect (ref) (b) Fiure 7. Speed trackin in a) PI controller (ref) b) Slidin mode controller c) Variable trcture controller Table. Generator and wind turbine parameter PERMANENT MAGNET SYNCHRONOUS GENERATOR Rated Power = KW Pole Pair = Rated voltae = V Stator flux =.5 L = 55 mh WIND TURBINE R =.8 Ohm Blade Radiu =. m C p max =.46 Gear Ratio =.9 Rated Wind Speed = 6 m/ The reult are iven for a wind peed, hown in Fi. 6. A comparion of three control trateie of enerator converter i hown in Fi. 7. Fi 7.a how performance of a conventional PI peed controller, Fi 7.b how performance of the lidin mode peed controller. The operation of peed tracker improved but the chatterin effect exit that miht be harmful. Finally Fi 7.c how proper performance of PI- Slidin mode controller propoed in thi paper. Thi comparion i obtained under uncertaintie of enerator parameter and the inherent fluctuation of wind condition, which reult in torque perturbation on the haft. Finally imulation reult of a propoed variable tructure controller are hown in Fi Generator Speed (rpm ) (ref) id & id(ref) - Fiure 8. Speed trackin in whole rane Fiure 9. Direct-axi current control performance

5 (Slidin mode Surface) Cp (Power Coefficient) ia(a) iq & iq (ref) iq iqref Fiure. Quadrature-axi current control performance Time () Fiure. Phae current (i a) in time rane Fiure. Slidin urface V. CONCLUSION A robut PI-lidin mode technique for maximum power point trackin control of PMSG baed wind turbine wa propoed and evaluated. The control tratey combine lidin mode controller and linear PI principle to achieve a imple and robut hih performance drive. In the teady tate, lidin mode controller i dominated. Durin tranient operation the propoed approach how ood dynamic repone and tron robutne with repect to inherent fluctuation of wind. Thi imple, quick, accurate and robut control tratey uarantee proper performance of MPPT alorithm implementation and therefore bet enery capturin from wind turbine. REFERENCES [] T. Ackermann, Wind Power in Power Sytem, Wet Suex: John Wiley & Son, 5, p. 8. [] O. Anaya-Lara, Wind Enery Generation Modellin and Control, Wet Suex: John Wiley & Son, 9. [] K. Tan, and S. Ilam, Optimum Control Strateie in Enery Converion of PMSG Wind Turbine Sytem without Mechanical Senor, IEEE Tran. Enery Converion, vol. 9, NO., pp 9-99, June 4. [4] L. Helle, Modelin and Comparion of Power Converter for Doubly Fed Induction Generator in Wind Turbine, Ph.D. diertation, Dept. Enineerin and Science at Aalbor Univ, Denmark, 7. [5] H. Li, and Z. Chen, Overview of Different Wind Generator Sytem and Their Comparion, IET Renewable Power Generation, vol., No., pp. 8, Auut 7. [6] R. Morale, R. Ordonez, M. A. Morale and V. Flore, Control Sytem Dein and Simulation of an AC/DC - DC/DC - DC/AC Power Converter for a Permanent Manet Wind Power Generator in Rural Power Generation, in Proc. 9 International Conference on Electrical, Communication, and Computer., pp [7] H. Zhan, C. Fan, R. Tan and J. Zhu, Hih Performance Rectifier with Wide Speed Rane for Direct-Drive Wind Enery Sytem, in Proc. International Conference on Electrical and Control Enineerin., pp [8] M. Chinchilla, S. Arnalte, and J. C. Buro, Control of Permanent- Manet Generator Applied to Variable-Speed Wind-Enery Sytem Connected to the Grid, IEEE Tran. Enery Converion, vol, NO, pp -5, MARCH 6. [9] J. Hui, An Adaptive Control Alorithm for Maximum Power Point Trackin for Wind Enery Converion Sytem, Mater diertation, Dept. Electrical and Computer Enineerin Queen Univ, December 8. [] C. Lacu, I. Boldea and F. Blaabjer, Direct Torque Control of Senorle Induction Motor Drive: A Slidin-Mode Approach, IEEE Tran. INDUSTRY APPLICATIONS, vol 4, NO, pp 58-59, April, 4. [] S. Wu, A Generalized Inverter Control Method for a Variable Speed Wind Power Sytem under Unbalanced Operatin Condition, Mater diertation, Dept. Electrical and Computer Enineerin Cleveland State Univ., April,. [] A. Cimpoeru, Encoderle Vector Control of PMSG for Wind Turbine Application, Mater diertation, Intitute of Enery Technoloy Aalbor Univ., June, Fiure. Maximum power point trackin performance