A control strategy for output maximisation of a PMSG-based variable-speed wind turbine

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University of Wollonon Research Online Faculty of Enineerin an Information Sciences - Papers: Part A Faculty of Enineerin an Information Sciences 009 A control stratey for output maximisation

E., Muttai, K. M. & Nenevitsky, M. (009). A control stratey for output maximisation of a PMSG-base variable-spee win turbine.

1 University of Wollonon Research Online Faculty of Enineerin an Information Sciences - Papers: Part A Faculty of Enineerin an Information Sciences 009 A control stratey for output maximisation of a PMSG-base variable-spee win turbine M E. Haue University of asmania K M. Muttai University of asmania, kashem@uow.eu.au M Nenevitsky University of asmania, michael.nenevitsky@utas.eu.au Publication Details Haue, M. E., Muttai, K. M. & Nenevitsky, M. (009). A control stratey for output maximisation of a PMSG-base variable-spee win turbine. Australian Journal of Electrical an Electronics Enineerin, 5 (), Research Online is the open access institutional repository for the University of Wollonon. For further information contact the UOW Library: research-pubs@uow.eu.au

2 A control stratey for output maximisation of a PMSG-base variablespee win turbine Abstract his paper presents a control stratey for output maximisation of a irect rive permanent manet synchronous enerator (PMSG)-base small-scale variable-spee win turbine. he control topoloy uses a sinle switch three-phase switch-moe rectifi er an the enerator torue, an power is controlle by controllin the switch uty cycle of the switch. o extract maximum power from the win, the torue reference of the PMSG is calculate from enerator spee an win turbine characteristics. From this torue reference, a current reference is calculate usin measure DC link voltae an enerator spee. he current error is then use to control the uty cycle of the switch-moe rectifier an thereby torue of the enerator is reulate throuh a proportionalinteral reulator. he operational characteristics of the eneratin system are investiate uner varyin win spee throuh extensive simulations an the results confi rm that the propose control stratey can maximise the output power uner fluctuatin win spees. Keywors turbine, control, stratey, output, maximisation, pms, variable, spee, win Disciplines Enineerin Science an echnoloy Stuies Publication Details Haue, M. E., Muttai, K. M. & Nenevitsky, M. (009). A control stratey for output maximisation of a PMSG-base variable-spee win turbine. Australian Journal of Electrical an Electronics Enineerin, 5 (), his journal article is available at Research Online:

3 1 A Control Stratey for Output Maximization of a PMSG Base Variable Spee Win urbine M. E. Haue, Member, IEEE, K. M. Muttai, Senior Member, IEEE, an M. Nenevitsky, Senior Member, IEEE Abstract-- his paper presents a control stratey for output maximization of a irect rive permanent manet synchronous enerator (PMSG) base small scale variable spee win turbine. he control topoloy uses a sinle switch three-phase switch-moe rectifier an the enerator torue an power is controlle by controllin the switch uty cycle of the switch. o extract maximum power from the win, the torue reference of the PMSG is calculate from enerator spee an win turbine characteristics. From this torue reference, a current reference is calculate usin measure c link voltae an enerator spee. he current error is then use to control the uty cycle of the switch-moe rectifier an thereby torue of the enerator is reulate throuh a PI reulator. he operational characteristics of the eneratin system are investiate uner varyin win spee throuh extensive simulations an the results confirm that the propose control stratey can maximize the output power uner fluctuatin win spees. Inex erms Output maximization, permanent manet synchronous enerator, switch-moe rectifier, variable spee win turbine I. INRODUCION ecently, there is a first rowin interest on win power Reneration ue to environmental concern an hiher oil price. Many countries are affluent in renewable enery resources; however they are locate in remote areas where power ri is not available. Local, small scale stan-alone istribute eneration system that can utilize these renewable enery resources when ri connection is not feasible. Permanent manet synchronous enerator is suitable for such applications because of their property of self excitation, which allows an operation at a hih power factor an hih efficiency. Also, the irect rive PMSG is much more promisin than other enerators because of hiher enery ensity, smaller size, an low losses [1,]. o extract maximum power from the fluctuatin win, variable spee operation of the win turbine enerator is necessary. his reuires a sophisticate control stratey for the enerator. Optimum power/torue trackin is popular control stratey as it helps to achieve optimum win enery utilization [-7]. Some of these control strateies use win velocity to obtain the esire shaft spee to vary the enerator spee. However, anemometer base control stratey increases cost an reuce the reliability of the overall system. hese control strateies are not suitable or too expensive for a small scale win turbine. Sensorless control metho for maximum power point trackin is reporte in the literature [5,6]. In [6], the current vector of an interior type PMSG is controlle to optimize the win turbine operation at various win spee, which reuires six active switches to be controlle. Switchmoe rectifier has been investiate for use with automotive alternator with permanent manet synchronous machines [8,9]. he switch-moe rectifier has also been investiate for small scale variable spee win turbine [10, 11]. In this paper, a control stratey for output maximization of a PMSG base small scale win turbine is evelope. he metho has the followin features: he enerate ac power from PMSG is converte to c power thouh a simple uncontrolle ioe brie rectifier. It reuires only one active switchin evice (IGB), which is use to control the enerator torue to extract maximum power. It is suitable for small scale win turbine. It is a simple, low cost solution. he structure of the paper is as follows. he moel of the win turbine-enerator system is iscusse in section II. he control topoloy an the win power eneratin system are presente in section III. In section IV, simulation results are presente an iscusse. Finally conclusions are mae in section V. II. MODELING OF URBINE-GENERAOR SYSEM he moels of PMSG an win turbine are presente in the followin sub-sections: A. PMSG Moel he - an - axes voltaes of the PMSG can be iven by: v v i R p (1) s s i R p () where, an are the - an - axes stator flux linkaes an are iven by the followin euations. L i () M L i (4) he torue euation of an interior permanent manet synchronous enerator is iven by [1], e P( i i ) P M i ( L L ) ii (5)

4 For a surface PMSG, which is use in this paper therefore, the torue euation becomes: L L, PM i (6) he enerator torue an rotor spee are relate by m m J Bm (7) t In euations (1-7), v, v, i, i, L an L are the an axes stator voltaes, currents an inuctances respectively, R s is the stator resistance, λ M is the amplitue of the flux linkae (Wb) in the stator ue to permanent manet in the rotor, is the electrical anular velocity in ra/sec, m is the rotor spee, B is the ampin coefficient (Nm.s), J is the moment of inertia (k.m ), an P is the number of pole pairs. p is the operator /t. he torue euation iven in (5) consists of two terms. he first term represents the excitation torue an the secon term is the reluctance torue ue to rotor saliency. B. Win urbine Aeroynamic Characteristics he amount of power capture by the win turbine (power elivere by the rotor) is iven by [1]: 1 Pt Pwin C p (, ) Avw C p (, ) (8) Where, is the air ensity (k/m ), v is the win spee in m/s, A is the blaes swept area, C p is the turbine rotor power coefficient, which is a function of tips pee ratio (λ) an pitch anle (β). he coefficient of performance of a win turbine is influence by the tip-spee to win spee ratio (SR), which is iven by: SR R m (9) vw mr or, vw (10) where, ω m = rotational spee of turbine rotor in mechanical ra/s, an R = raius of the turbine. Fiure 1 shows a typical C p versus characteristics of a win turbine. By substitutin v from euation (10) into euation (8), the turbine power can be written as; mr Pt 0.5AC p (11) III. SYSEM CONFIGURAION Fiure shows the control structure of a PMSG base stanalone variable spee win turbine. However, the sinle switch three-phase switch-moe rectifier an its control alorithm with output power maximization are investiate in this paper. he stanalone system consists of the followin: Win turbine Permanent manet synchronous enerator, which is irectly riven by the earless win turbine. A sinle switch three-phase switch-moe rectifier, which is controlle to extract maximum power from the fluctuatin win. A PWM voltae source IGB-inverter. A. Sinle Switch hree Phase Switch-moe Rectifier he output of a variable spee PMSG is not suitable for use as it varies in amplitue an freuency ue to fluctuatin win. A constant DC voltae is reuire for irect use, storae or conversion to AC via an inverter. In this paper, a sinle switch three-phase switch-moe rectifier is use to convert the ac output voltae of the enerator to a constant c voltae before conversion to AC voltae via an inverter. he sinle switch three phase switch-moe rectifier consists of a three-phase ioe brie rectifier an a DC to DC converter. he output of the switch-moe rectifier can be controlle by controllin the uty cycle of an active switch (such as IGB) at any win spee to extract maximum power from the win turbine an to supply the loas. he averae output voltae of the rectifier consierin the stator resistance an enerator leakae inuctance is iven by: 6 V V LsI I Rs (1) where, freuency, R s = stator resistance, L s leakae inuctance, I rectifier averae output current, V m maximum line to line voltae at the enerator output, V RMS phase voltae at the enerator output. he relationship between the terminal voltae of the enerator an the DC bus voltae can be erive from the balance of power. From the conservation of enery, the power on the AC sie must be eual to the power on the DC sie. Assumin that the rectifier operates in continuous conuction, unity power factor is maintaine at the enerator terminal an losses in power conversion are neliible, the power balance becomes: V I V I (1) From euations (1) an (1), the relationship between the AC enerator rms current I ) an the DC bus current is iven by ( Fiure 1. ypical C characteristics. p I I (14) 6 he output of the sinle switch three-phase switch-moe rectifier as shown in fiure, is iven by V 1 1 D c V (15)

5 PMSG Position sensor Switch-moe Rectifier i L D V S I c C C c V c DC bus V c IGB Inverter i a, i b v a,v b AC Bus Loa 1 Loa 1 θ m /t ω m I V PWM Switch-moe Rectifier Control with MPP DC Loas Battery storae PWM Voltae & Freuency Control ω Loa 1 Fiure. Control Structure of a PMSG base stanalone variable spee win turbine. Assumin neliible losees in the converter: I I c 1 1 D where, the uty ratio, D on off, s = perio (16) For the case of boost type switch-moe rectifier, the PMSG shoul be chosen with terminal voltae at maximum spee to allow for a small voltae boost in the c-c converter for all situations. B. Control Alorithm for Maximum Power Extraction It is apparent from euation (11) that the win turbine can prouce maximum power when the turbine operates at maximum C p (i.e. at C p _ opt ). So it is necessary to keep the rotor spee at a optimum value of the tip spee ratio, opt. If the win spee varies, the rotor spee shoul be ajuste to follow the chane. he taret optimum power can be written from euation (11) as; m _ opt R m _ opt 0. 5AC p _ opt K opt m _ opt opt P (17) where, 0.5 R K opt A C p _ opt opt (18) opt an m opt _ vw Kwvw R (19) herefore, the taret optimum torue can be iven by m _ opt opt m _ opt K (0) he mechanical rotor power enerate by turbine as a function of the rotor spee for ifferent win spee is shown in fiure. he optimum power is also shown in this fiure. he optimum power curve (P opt ) shows how maximum enery can be capture from the fluctuatin win. he function of the controller is to keep the operatin of the turbine on this curve, as the win velocity varies. It is observe from this fiure that there is always a matchin rotor spee which prouces maximum power for any win spee. If the controller can properly follow the optimum curve, the win turbine will prouce maximum power at any spee within the allowable rane. he optimum torue can be calculate from the optimum power iven by euation (0). For the enerator spee below the rate maximum spee, the enerator follows the euation (0). If the enerator spee excees the rate maximum spee, the win turbine enery capture must be limite by applyin pitch control or rivin the machine to the stall point. he structure of the propose control stratey of the switch moe rectifier is shown in fiure 4. he control objective is to control the uty cycle of the switch S in fiure, to extract maximum power from the variable spee win turbine an transfer the power to the loa. he control alorithm inclues the followin steps: Measure enerator spee, ω. Determine the reference torue (fiure 5) usin the followin euation: * K opt ( ) (1) his torue reference is then use to calculate the DC current reference by measurin the rectifier output voltae, V as iven by: * * I ( ) / V () he error between the reference c current (an measure c current is use to vary the uty cycle of the switch to reulate the output of the switch-moe rectifier an the enerator torue throuh a PI controller. he enerator torue is controlle in the optimum torue curve in fiure 5 accorin to enerator spee. he acceleration or eceleration of the enerator is etermine by the ifference of the turbine torue m an enerator torue. If the enerator spee is less than the optimal spee, the turbine torue is larer than the enerator torue an the enerator will be accelerate. he enerator will be ecelerate if the enerator spee is hiher than the optimal spee. herefore, the turbine torue an enerator torue settle own to the optimum torue point m _ opt at any win spee an the win turbine is operate at the maximum power point.

4 For example (consierin fiure ), if the PMSG operatin at point a an win spee increases from v w1 to v w (point b), the aitional power an hence torue causes the PMSG to accelerate.

A similar situation occurs when the win velocity ecreases. his is also shown in fiure 6 (c).

6 4 For example (consierin fiure ), if the PMSG operatin at point a an win spee increases from v w1 to v w (point b), the aitional power an hence torue causes the PMSG to accelerate. he acceleratin torue is the ifference between the turbine mechanical torue an the torue iven by the optimum curve. Finally, the enerator will reach the point c where the acceleratin torue is zero. A similar situation occurs when the win velocity ecreases. his is also shown in fiure 6 (c). In the propose metho, the win spee is not reuire to be monitore an therefore, it is a simple output maximization control metho without win spee sensor (anemometer). Fiure. Mechanical power enerate by turbine as a function of the rotor spee for ifferent win spee. orue reference calculation (e. ) ω m Reference current calculation (e. 4) V * I + I PI 1 error ime.5 - x 10 comparator PWM Gate rive & isolation o switch S in fiure Fiure 4. Control stratey of the switch-moe rectifier. Fiure 5. Generator torue reference versus spee. IV. RESULS AND DISCUSSIONS he moel of the PMSG base variable spee win turbine system of fiure is built usin Matlab/Simpower ynamic system simulation software. he simulation moel is evelope base on a Kollmoren 5.5 kw inustrial permanent manet synchronous machine. he parameters of the urbine an PMSG use are iven in able I. he power converter an the control alorithm are also implemente an inclue in the moel. he samplin time use for the simulation is 0 µs. Base on the torue reulation of the variable spee win turbine the operation can be subivie in three moes as follows: Moe I (win spee Cut in spee): If the win spee is below the cut in spee (Moe I in fiure 5), the power prouce by the win turbine is too low an it is not worth to work with it. So turbine shoul be shut own. Moe II (win spee between cut in spee an rate spee): In this moe, the propose control stratey is applie an enerator follows the torue reference which is iven by the euation (1). he blae pitch anle is set to zero to extract maximum power from the win. Fiure 6 shows the response of the system for a step chane of win spee from 1 m/s to 9 m/s an to 1 m/s. It is seen from fiure 6 (c) that the enerate torue reference follows the optimum mechanical torue of the turbine uite well. he enerator electromanetic torue also track the reference torue as shown in fiure 6(). Fiure 6(e) shows the reference c current an measure DC current. It is observe that the measure DC current follows the reference DC current an reulate the turbine torue to extract maximum power from the win turbine. Fiure 6(f) an 6() show the DC link voltae an c output power, respectively. Fiure 7 shows optimum torue versus spee as well as enerator torue versus spee. urbine mechanical input power an electrical output powers are shown in fiure 8. It is observe that the torue an power follow the optimum curves up to the rate spee. he simulation results emonstrate that the controller works very well an shows very oo ynamic an steay state performance. he control alorithm can be use to extract maximum power from the variable spee win turbine uner fluctuatin win. Moe III (win spee rate spee): If the enerator spee excees the rate spee, the win turbine enery capture must be limite by applyin pitch control, stall reulation control or ump loa. he excess win enery can also be utilize by usin controlle enery storae evices. In this paper, pitch control is use to reulate the turbine spee when the turbine spee is hiher than the rate spee. In this operatin reion, the enerator torue can not follow the optimum torue curve; however the available maximum output can be enerate as shown in fiure 8.

7 5 b a c Fiure 8. urbine mechanical input power an Electrical output power. V. ACKNOWLEDGMEN In this paper, a simple control stratey is propose to extract maximum power from a PMSG base variable spee win turbine uner fluctuatin win spees. he moelin of PMSG an win turbine is presente. he variable spee win turbine system an the control alorithm are iscusse an implemente usin MALAB/Simpower ynamic system simulation software. he simulation results emonstrate that the controller works very well an shows very oo ynamic an steay state performance. he controller is capable to maximize output of the variable spee win turbine uner fluctuatin win. he eneratin system with the propose maximum power extraction stratey is suitable for a small scale win turbine installation for remote area power supply. Fiure 6. Response of the system for a step chane of win spee from 1 m/s to 9 m/s to 1 m/s. orue, opt & (Nm) opt Moe II Moe III Generator spee, ω (ra/sec.) Fiure 7. Optimum torue an enerator torue. VI. ACKNOWLEDGMEN his work is supporte by the Australian research Council ARC) an Hyro asmania Linkae Grant, K he authors reatly acknowlee the support an cooperation of hyro asmania personnel in proviin ata an avice on the operation of remote area power supply system. able I: Parameter of the urbine-generator system Win turbine Density of air 1.5 K/m Area swept by blaes, A 1.06 m Optimum coefficient, K opt Nm/(ra/s) Base win spee 1 m/s PMSG No. of poles 10 Rate spee 184 ra/sec Rate current 9 A Armature resistance, R s 0.45 Ω Manet flux linkae 0.4 Wb Rate torue 0 Nm Rate power 5.5 KW

8 6 VII. REFERENCES [1]. F. Chan, L. L. Lai, "Permanenet-manet machines for istribute eneration: a review," in proc. 007 IEEE power enineerin annual meetin, pp [] H. Poliner, F. F. A. van er Pijl, G. J. e Viler, P. J. avner, "Comparison of irect-rive an eare enerator concepts for win turbines," IEEE rans. on enery conversion, vol. 1, no., pp. 75-7, Sept [] A. M. De Broe, S. Drouilhet, an V. Gevorian, A peak power tracker for small win turbines in battery charin applications, IEEE rans. Enery Convers., vol. 14, no. 4, pp , Dec [4] R. Datta an V.. Rananathan, A metho of trackin the peak power points for a variable spee win enery conversion system, IEEE rans. Enery Convers., vol. 18, no 1, pp , Mar [5] K. an an S. Islam, Optimal control strateies in enery conversion of PMSG win turbine system without mechanical sensors, IEEE rans. Enery Convers., vol. 19, no., pp. 9 99, Jun [6] M. Chinchilla, S. Arnaltes, an J. C. Buros, Control of Permanent- Manet Generators Applie to Variable-Spee Win-Enery Systems Connecte to the Gri IEEE rans. on Enery Conver., vol 1, no. 1, March 006. [7] D.J. Perreault an V. Caliskan, Automotive Power Generation an Control, IEEE ransactions on Power Electronics, Vol. 19, no., pp , May 004. [8] W.L. Soon an N. Erturul, Inverterless hih-power interior permanent-manet automotive alternator, IEEE ransactions on Inustry Applications. Vol.40, no.4, pp , July 004. [9] D. M. Whaley, W. L. Soon, N. Erturul, Investiation of switchemoe rectifier for control of small-scale win turbines, in proc. IEEE Inustry applications society annual meetin, pp , 005 [10] E. Muljai, S. Drouilhet, R. Holz, V. Gevorian, Analysis of permanent manet enerator for win power battery charin, in proc. IEEE 1996 Inustry applications society annual meetin, pp [11] P.C Krause, O. Wasynczuk an S. D. Suhoff, Analysis of electrical machinery an rive system, IEEE Press, 00. [1] G. M. Masters, Renewable an efficient electric power systems, John Wiley an Sons, 004. VIII. BIOGRAPHIES M. Enamul Haue (IEEE Stuent M 97, M 00) was born in Banlaesh in He rauate in electrical an electronic enineerin from Banlaesh Institute of echnoloy (BI), Rajshahi, Banlaesh, in He receive the M.En. eree in electrical enineerin from University echnoloy in 00. He has worke as an Assistant Professor for Kin Sau University, Saui Arabia an Unite Arab Emirates University for four years. Dr. Haue is currently workin as a Research Fellow in the school of Enineerin of University of asmania, Australia. His research interests inclue power electronics an DSP base variable spee machine rives, Renewable power eneration an associate controls, Win/Solar remote area power supply system, power uality an EMC/EMI issues. K. M. Muttai receive the Ph.D. eree from Multimeia University, Malaysia, in 001. Currently, he is a Senior Lecturer at the School of Enineerin an Deputy Director of the Centre for Renewable Enery an Power Systems at the University of asmania, Australia. He was associate with the Queenslan University of echnoloy, Australia as a Postoctoral Research Fellow from 000 to 00. Previously, he also worke for Multimeia University as a Lecturer for three years. His special fiels of interests inclue istribute eneration, renewable enery, istribution system automation, power system plannin, hyroelectric turbine, win turbine an artificial intellience. Michael Nenevitsky (IEEE M 95-SM 07) receive the B.S.E.E. (Hons.) an Ph.D. erees from the Byelorussian University of echnoloy, Minsk, Belarus, in 1978 an 198, respectively. Currently, he is Chair Professor in Power Enineerin an Computational Intellience an Director of the Centre for Renewable Enery an Power Systems at the University of asmania, Hobart, Australia. From 1984 to 1991, he was a Senior Research Fellow an Senior Lecturer in the Department of Electrical Enineerin, Byelorussian University of echnoloy. After arrivin in Australia, he was with Monash University, Melbourne, Australia. His interests are power system analysis, power uality, an intellient systems applications in power systems. Dr. Nenevitsky is a Chartere Professional Enineer, Fellow of the Institution of Enineers Australia, an a Member of CIGRE AP6 (Electromanetic Compatibility), Australian echnical Committee. Malaysia in 1998, an Ph.D. eree in electrical enineerin from he University of New South Wales, Syney, Australia,

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