A Decoupled Control Strategy Of PMSG for Variable Speed Wind Power Application

Transcription

1 ISSN (Onlne) : ISSN (Prnt) : Internatonal Journal of Innovatve Research n Scence, Engneerng and Technology Volume 3, Specal Issue 3, March Internatonal Conference on Innovatons n Engneerng and Technology (ICIET 14) On 21 st & 22 nd March Organzed by K.L.N. College of Engneerng, Madura, Taml Nadu, Inda A Decoupled Control Strategy Of PMSG for Varable Speed Wnd Power Applcaton Swagat Pat #1, Narendra Kumar Jena #2, Santosh Acharya #3 #1 Department of Electrcal Engneerng, Sksha O Anusandhan Unversty,Bhubaneswar, Oha, Inda #2 Department of Electrcal Engneerng, Sksha O Anusandhan Unversty,Bhubaneswar, Oha, Inda #3 Department of Electrcal Engneerng, Sksha O Anusandhan Unversty,Bhubaneswar, Oha, Inda ABSTRACT Speed control of permanent magnet wnd turbnes. But wth advancement n power synchronous machnes for relable speed wnd energy electronc converters, varable speed wnd power systems has always been a challengng task. But wth the generaton has become possble. Varable speed wnd development of vector control strateges the speed control WECS conssts of two measure blocks. They are process has been easly achevable. In ths paper the (1) Control of the generator for transent and steady control of speed and torque of a PMSG s cussed. state performance mprovement [1-6]. Vector control strateges have been mplemented for the (2) Control of the Grd-sde converter for supplyng PMSG control. The PMSG s modeled n synchronous power at constant voltage and frequency [1-6]. rotatng reference frame. The whole control scheme s The choce of generator for a WECS s very modeled usng Matlab/Smulnk and the results are vtal task. Inducton generator are used extensvely n cussed WECS for ther advantages that they are robust, effcent and cheaper. But they suffer from a drawback KEYWORDS Permanent magnet synchronous that they can t generate flux for power generaton.so generator(pmsg), Vector control scheme, PI controllers. ether they have to be grd connected or a capactor bank s needed to make the machne self excted. Agan as they draw reactve power from the grd they have a I. INTRODUCTION low workng power factor [11, 12].Although nducton In the advent of the advanced and profcent generators are the man work horse of WECS, but to technologes the wnd Energy Converson System acheve hgh power densty PMSG are used. In PMSG (WECS) has penetrated well n the energy market. the rotor s provded wth permanent magnet so there s Although Inducton Generators are the work horse of the no need of rotor wndng, so no rotor loss occurs n the WECS, but to acheve hgh power densty wth reducng machne. To mantan a constant ar gap flux there s no sze, Permanent Magnet Synchronous Generators (PMSG) need of magnetzng current hence the workng power are used. The drawbacks of these machnes are more factor of PMSG s hgh. Although these machnes have expensve and prone to demagnetzaton. PMSG based drawbacks that they are costly and less effcent than WECS are of two types, such as drect drven and ndrect nducton machnes and they are prone to drven. As n synchronous generator multple pole desgn demagnetzaton, but can provde a promsng and hgh s possble, hence t s employed n the gearless operaton. qualty power to the grd. In case of drect drven PMSG, t nee less mantenance As mentoned earler n varable speed wnd because there are no gear drves. In the recent years t has power generaton the control of the generator plays a become a promsng source of Clean and renewable vtal role n maxmum power extracton from wnd[11, Energy. But WECS has a major drawback that the wnd 12].Many control structures have been recently behavor s hghly changng, so constant voltage and developed for the control of PMSG, such as Vector control[7-1],drect Torque control, Drect power frequency generaton s not possble wth fxed speed control, In vector control the actve and reactve power Copyrght to IJIRSET 22 M.R. Thansekhar and N. Balaj (E.): ICIET 14

2 A Decoupled control strategy of PMSG for varable speed wnd power applcaton are decoupled and controlled ndependently[7-1].drect Torque control strategy concentrates on the control of the stator flux vector wth respect to the rotor flux, such that desred operatng conons can be met[9,1]. In ths paper the modelng and dynamc behavor of drect drven varable speed medum power based PMSG has been proposed. For controllng the PMSG the generator sde converter s controlled whch results n the control of speed/torque of the generator and also the control of the actve and reactve power flow to the grd. For the control of machne sde converter vector control strategy employng PI controllers s mplemented. The whole system s smulated usng Matlab/Smulnk envronment and results are analyzed. II. SYSTEM OVWRVIEW The wnd energy converson system, as shown n Fg.2 comprses of wnd turbne, PMSG, PWM converter and converter control system. The output of PMSG s not sutable for use because t generates power at varable voltage and frequency due to varable wnd speed. So t s converted to constant DC voltage at the DC lnk to be drectly used as a dc source or for storage or further nverted nto AC and synchronzed to a grd. A vector controlled IGBT based nverter s used to regulate the speed, actve power and reactve power of the PMSG durng the wnd speed varaton And the torque equaton for generator can be gven as 3 3 T e n p n p ( Ld Lq ) 2 2 n =Par of poles p The rotors of wnd turbne and generator are connected drectly,so they can be expressed as dg J Te Tm Bmg (5) Where T = electromagnetc torque, e T = load torque, m J = rotor nerta ncludng turbne., = mechancal speed of the generator. g B m =dampng coeffcent The actve and reactve power taken by the machne can be represented by the followng equatons P V Q V V V IV. INVERTER MODEL (7) (8) III. MODELLING OF PMSG Generally machne models are expressed n d-q reference frame, because f t s modeled n abc reference frame then the equatons descrbng the machne,nvolves varyng nductances, so t s complex to solve by any analytcal method. To allevate ths shortcomngs,by park s transformaton the varyng machne equatons are transferred to nvarant( dc)equatons n a synchronously rotatng frame. In ths paper d-q reference based equatons have been descrbed. d v ra Ld - Lω (2) d v ra L Lω a b c T1 T3 T4 T6 INVERTER Fg.1 Inverter Structure T5 T2 cdc Where v =stator voltage n d-axs v = stator voltage n q-axs = stator current n d-axs d = stator current n q-axs L = L = L =Stator Inductance q s =synchronous speed of stator =Rotor s magnetc flux lnkage A voltage source nverter s used n order to get the varable voltage varable frequency alternatng current supply. A smplfed PWM nverter model dagram s shown n the Fg.1 Va [2sa sb sc ] (11) 6 Vb [2sb sa sc ] (12) 6 Vc [2sc sa sb ] (13) 6 Copyrght to IJIRSET 23 M.R. Thansekhar and N. Balaj (E.): ICIET 14

3 A Decoupled control strategy of PMSG for varable speed wnd power applcaton Where, V a, V b, V c are the phase voltages, V = DC lnk voltage s a s b s c dc 2T1 1 2T 3 1 2T 5 1 Where T1,T3,T5 are the swtches. V. CONROL STRUCTURE To get rd of the demerts of Scalar control, vector control s used profusely. In ths paper the d-axs component of current s algned wth flux vector and q-axs component current s 9 degree ahead of t. The d-axs current controls the reactve power and q-axs current controls the actve power. So the actve and reactve power are decoupled and can be controlled easly and ndependently. Bascally n ths paper two current control loops has been demonstrated as shown n the Fg.2. whch are controlled by conventonal PI controller. Here the rotor angle θ and rotor speed ω has been traced from the generator and converted to ts electrcal equvalent. The error sgnal of the measured speed and reference speed s processed through a PI controller to get current reference s set to,.the d-axs generator =. Fnally the d-q component of the voltage vector whch controls the d-q current of generator s passed through PI controllers. The PI controllers are desgned accordng to the followng equaton u ( t) K e ( t) K e ( t) n pn n n n (15) where u n (t) s the controller output, en s the error, K pn and K n are the proportonal and ntegral gans of the PI controllers respectvely,where n vares from 1 to 3. The gan parameters are tuned manually to get near optmum results and the parameters are gven n table-1 TABLE I Controller no. K p K PI_ PI_ PI_ Wnd Turbne PMSG abc Machne- sde PWM converter cdc V dc d/ abc/dq PWM Generator dq/abc ( L d * ) * rs L * * * r q s _ PI_1 e1 PI_2 PI_3 e2 _ e3 _ Fg.2 Wnd energy converson system wth control scheme Copyrght to IJIRSET 24 M.R. Thansekhar and N. Balaj (E.): ICIET 14

4 phase voltage power factor torque P & Q speed A Decoupled control strategy of PMSG for varable speed wnd power applcaton VI. SIMULATION AND RESULT ANALYSIS A. Dynamc response wth the step change n reference speed. The speed versus characterstc has shown n Fg. 3. The oscllaton damps out wthn.4 sec.the system has been subjected to a step change n speed from 314rad/sec(electrcal) to 2rad/sec(electrcal) at 3 secon Fg.3 Speed response durng step change n reference speed Durng ths speed varaton the mechancal torque has been kept constant. As t s a medum power machne, - 25 Nm mechancal torque has been provded. And t has been observed that varaton of torque s for a transent perod of and agan the torque regans ts prevous set value of -25Nm after a of.4 second as shown n Fg Fg.4 Torque response durng step change n reference speed From the Fg.5 t can be seen that when the speed was 314rad/sec (electrcal).e. the machne runs at synchronous speed the ar gap flux s same as the flux of the rotor. But when the reference speed command s reduced to 2rad/sec (electrcal) at 3 sec, the ar gap) flux nee to be ncreased to reduce the speed. The rotor s n capable of ncreasng the ar gap flux. So the machne draws reactve power from the grd for generaton of extra ar gap flux for reducng the speed. Ths s clear from the Fg.5, the reactve power before 3 sec s zero, but after 3 secon the reactve power becomes postve s: reactve power s drawn from the grd. Agan as the speed reduces the torque remans constant so actve power also reduces from - 15 watts to -65 watts Fg.5 Actve and reactve power durng step change n reference speed As the speed decreases the reactve power becomes postve so the power factor reduces from unty to.998 as llustrated n the Fg Fg.6 Power factor durng step change n reference speed Fg.7 & Fg.8 show that the nverter phase voltage and phase current of PMSG respectvely. And from these fgures t s evdent that the nverter frequency s reduced when the speed s reduced at the 3 sec Fg.7 Phase voltage response durng step change n reference speed Copyrght to IJIRSET 25 M.R. Thansekhar and N. Balaj (E.): ICIET 14

5 phase voltage torque Power Factor speed current P & Q A Decoupled control strategy of PMSG for varable speed wnd power applcaton P Q Fg.8 Phase currents response durng step change n reference speed B. Dynamc response wth step change n turbne Torque. Agan ths system has been subjected to a step change n turbne torque at 3 sec and the performance of the system s smulated.the turbne torque s changed from - 25Nm to -4Nm at 3 sec.the speed response of the system can be seen from the Fg.9.It s evdent from the fgure that the speed devates from ts reference valuefor,3 sec due to the sudden changen turbne torque,but agan settles down at the reference value Fg.9 Speed response durng step change n turbne torque The electromagnetc torque response of the PMSG has been llustrated n the Fg.1 and torque vares from - 25Nm to -4Nm Tme Fg.11 Actve and reactve power durng step change n turbne torque ncreases t ten to accelerate the machne but the machne has to be kept the reference speed. Ths s possble by ncrement n the ar gap flux, so the PMSG draws extra reactve power from the grd to generate the extra flux and to mantan the speed at ts reference value. So the reactve power ncreases, whch can be seen from the Fg.11. The Fg.12 gves the power factor of the PMSG durng varable torque conons. Intally the power factor was unty but as the turbne torque ncreased the reactve power ncreased so the power factor decreased to a value less than unty Tme Fg.12 power factor durng step change n turbne torque The phase voltage and phase current of nverter s shown n the Fg.13 & Fg.14.From the Fg.14,t s evdent that the current ncreases as the torque ncreases and from the Fg.13 t s clear that the frequency of the supply voltage remans constant wth the varaton of torque keepng the speed constant Fg.1 Torque response durng step change n turbne torque The excurson of actve and reactve power has shown n the Fg.11.As the torque ncreases the actve power fed to the grd ncreases. When the turbne torque Fg Fg.13 Phase voltage response durng step change n turbne torque Copyrght to IJIRSET 26 M.R. Thansekhar and N. Balaj (E.): ICIET 14

6 Current(Iabc) A Decoupled control strategy of PMSG for varable speed wnd power applcaton Tme Fg.14 Phase current response durng step change n turbne torque VII. CONCLUSION The PMSG and vector control strateges has been successfully modeled n ths paper. The tunng of PI controllers has been done manually whch means that the outputs shown are near optmum results. The perfect decouplng between speed and torque s acheved by the vector control strategy whch shows that the vector control strategy s an effcent and fast scheme whch s capable for enhancng the performance of PMSG based wnd energy converson system. The workng power factor of the PMSG based wnd energy converson system s better than that of nducton machne based WECS, whch makes PMSG an effcent alternatve for nducton machne, for wnd energy converson system applcatons. [5] Shao Zhang, Student Member, IEEE, Kng-Jet Tseng, Senor Member, IEEE, D. Mahnda Vlathgamuwa, Senor Member, IEEE, Trong Duy Nguyen, Student Member, IEEE, and Xao-Yu Wang, Member, IEEE Desgn of a Robust Grd Interface System for PMSG-Based Wnd Turbne Generators IEEE Transactons On Industral Electroncs, Vol. 58, No. 1, January 211. [6] Md. Enamul Haque, Member, IEEE, Mchael Negnevtsky, Senor Member, IEEE, and Kashem M. Muttaq, Senor Member, IEEE A Novel Control Strategy for a Varable-Speed Wnd Turbne Wth a Permanent-Magnet Synchronous Generator IEEE Transactons On Industry Applcatons, Vol. 46, No. 1, January/February 21 [7] H. Huang C. Mao J. Lu D. Wang Small-sgnal modellng and analyss of wnd turbne wth drect drve permanent magnet synchronous generator connected to power grd Publshed n IET Renewable Power eneraton Receved on 23rd November 21 Revsed on 2nd August 211. [8] Y. Erram, Student Member IEEE, M. Ouassad, Member, IEEE Modellng and Control Strategy of PMSG based Varable Speed Wnd Energy Converson System. [9] Derong Luo, Yanzhao Sun,Shoudao Huang, Keyuan Huang College of Electrcal &Informaton Engneerng, Hunan Unversty, Changsha, 4182, Chna Control of rect-drve Permanent-Magnet Wnd Power System Connected to Grd [1] Z. Xu, P. Ge, Danguo Xu and C.H.Zhang Senor Member, IEEE Harbn Insttute of Technology 151Harbn, Chna Drect Torque and Flux Control of the Converters for a Permanent Magnet Wnd Power Generaton System. [11] A.Tapa, G.Tapa, J.Ostolaza, Modelng and Control of a Wnd Turbne Drven Doubly Fed Inducton Generator, IEEE Trans on Energy Conv.Vol-18,No-2,June-23. [12] R. Cardenas, and R. Pena, Sensorless vector control of nducton machnes for varable speed wnd energy applcatons, IEEE Trans. Egy.Conv., vol. 19, no. 1, pp , Mar. 24. APPENDIX Poles (P) = 4 Rated KW : 6 Rated Current: 12 A Rated voltage: 34 V Rated speed, N=6rpm Stator resstance, R s =.425 Ω Rotor flux =.433 wb Inerta of rotor, J=.2kgm Stator Inductance, Dampng Factor, Ld =Lq =.84 H B= N-rad/sec REFERENCES [1]. Shuhu L, Senor Member, IEEE, Tmothy A. Haskew, Senor Member, IEEE, Rchard P. Swatlosk,and Wllam Gathngs Optmal and Drect-Current Vector Control of Drect-Drven PMSG Wnd Turbnes IEEE Transactons On Power Electroncs, Vol. 27, No. 5, May 212. [2]. S. M. Muyeen, Member, IEEE, Ron Takahash, Member, IEEE, Toshak Murata, and Junj Tamura, Senor Member, IEEE A Varable Speed Wnd Turbne Control Strategy to Meet Wnd Farm Grd Code Requrements IEEE Transactons On Power Systems, Vol. 25, No. 1, February 21 [3] Yang Lyong, Yuan Pee, Chang Zhenguo, Chen Zhgang, L Zhengx College of Mechancal Electroncal and Engneerng North Chna Unversty of Technology Shjngshan, Bejng, Chna A Novel Control Strategy of Power Converter Used To Drect Drven Permanent Magnet Wnd Power Generaton System 29 2nd Internatonal Conference on Power Electroncs and Intellgent Transportaton System. [4] M. Sngh1 V. Khadkkar2 A. Chandra1 Grd synchronsaton wth harmoncs and reactve power compensaton capablty of a permanent magnet synchronous generator-based varable speed wnd energy converson system Publshed n IET Power Electroncs Receved on 13th May 29 Revsed on 6th November 29. Copyrght to IJIRSET 27 M.R. Thansekhar and N. Balaj (E.): ICIET 14