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  1. 1. K. Uday Kumar Reddy, M. Ramasekhara Reddy, Dr. M. Vijaya Kumar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.1900-1905 Modeling and Control of a Permanent Magnet Synchronous Generator Wind Turbine with Energy StorageK. Uday Kumar Reddy1, M. Ramasekhara Reddy 2, Dr. M. Vijaya Kumar3 1 (M. Tech, Department of Electrical & Electronics Engg, JNTUACE, Pulivendula, A.P, India.) 2 (Assistant Professor, Department of Electrical & Electronics Engg, JNTUACE, Pulivendula, A.P, India.) 3 ( Professor, Department of Electrical & Electronics Engg, JNTUACE, Anantapur, A.P, India.)ABSTRACT Wind energy is an important renewable approach to self-sufficient power generation involvessource which is used for power generation for a using a wind-turbine with a storage mechanism tostand-alone as well as grid connected applications. create a stand-alone system. If wind conditions areIn many remote areas, loads are usually connected favorable, these stand-alone wind energy systemsaway from the grid. In such cases, isolated wind usually can provide communities with electricity atenergy systems can be considered as an effective the lowest cost. Stand-alone wind energy systemsway to provide continuous power to electrical often include batteries, because the available windloads. The power conversion unit features a wi nd- does not always produce the required quantities ofturbine-driven PMSG, a d i o d e rectifier, a power. If wind power exceeds the load demand, theb u c k converter, a battery bank, a feed-back surplus energy can be stored in storage systems likecontroller, and a dc/ac inverter. In this paper, an batteries [1-3]. Multiple types of generators are beingisolated wind energy conversion system is used with wind turbines. Small wind turbines areimplemented using a variable speed permanent equipped with DC generators of up to a fractionalmagnet synchronous generator (PMSG) with kilowatt in capacity [6]. The major types of ACPWM rectifier and a battery for storing the excess generators that are possible candidates in windamount of wind energy. To change the duty cycle turbine systems are as follows:of the converter, a controller of DC-DC buck • Squirrel-Cage rotor Induction Generator (SCIG),converter with MOSFET as a switching • Wound-Rotor Induction Generator (WRIG),component is designed using P, PI and PID • Doubly-Fed Induction Generator (DFIG)controller to provide the efficient choice for the • Synchronous Generator (With external fieldselection of the controller. The proposed scheme is excitation),implemented in MATLAB using Simulink & the •Permanent Magnet Synchronous Generator (PMSG).simulation results show that the output voltage of An induction generator (IG) has beenthe converter can be controlled according to the extensively used in commercial wind turbine units.value of duty cycle and the excess power is stored Asynchronous operation of induction generators isin battery to provide balance between the considered an advantage for application in windgenerator and the load. turbine systems, because it provides some degree of flexibility when the wind speed is fluctuating orKeywords: Wind e n e r g y conversion variable [5-6]. The induction generator based ons y s t e m , battery bank, Permanent magnet Squirrel-Cage rotor (SCIG) is a very popular machinesynchronous generator, isolated system. because of its low cost, mechanical simplicity, robust structure, and resistance against disturbance1. Introduction and vibration. The induction generator based on Renewable sources of energy mainly wound rotor is the doubly fed induction generatorincluding wind power offer a feasible solution to (DFIG), which is a kind of induction machine indistributed power generation for isolated which both the stator windings and the rotorcommunities where grids are unavailable. At present windings are connected to the source [7-8].scenario wind power has emerged as the most viable Another type of generator that has beensource of electric power is economically competitive proposed for wind turbines in several research articleswith the non-renewable sources of energy. In such is synchronous generator. This type of generator hascases, isolated wind energy systems can be the capability of direct connection (direct-drive) toconsidered as an effective way to provide continuous wind turbines, with no gearbox [12]. This advantagepower to electrical loads. One of the most promising is favorable with respect to lifetime and maintenance.applications of renewable energy generation lies in Synchronous machines can use eitherthe development of power supply systems for remote electrically excited or permanent magnet (PM) rotor.villages that lack an economically feasible means of The PM and electrically-excited synchronousconnecting to the main electrical grid. For the type of generators differ from the induction generator in thatloads located far from a utility grid, one practical the magnetization is provided by a Permanent 1900 | P a g e
  2. 2. K. Uday Kumar Reddy, M. Ramasekhara Reddy, Dr. M. Vijaya Kumar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.1900-1905Magnet pole system or a dc supply on the rotor, the natural laws of electromagnetic scaling, there is anfeaturing providing self-excitation property. Self- excitation penalty involved in small PM machines.excitation allows operation at high power factors and As the geometrical size is decreased, thehigh efficiencies for the PMSG [13]. A comparison cross-sectional area available for copper conductorbetween the variable speed wind turbine and the decreases with the square of the linear dimensions.constant speed wind turbine shows that variable The need for the magneto-motive force decreases withspeed reduce mechanical stresses, gusts of wind can the linear dimension, being primarily determined bybe absorbed, dynamically compensate for torque and the length of the air-gap [14]. During the highpower pulsations caused by back pressure of the temperatures, the current may be sufficient enough totower. This backpressure causes noticeable torque demagnetize the magnets providing excitation.pulsations at a rate equal to the turbine rotor speedtimes the number of rotor blades [3-8]. 3. T o p o l o g i e s for isolated operation of a variable speed wind driven PMSG2. Permanent Magnet Generator Figure 1 shows the cross-section of a typical Variable speed use is good for extractingPermanent Magnet Generator (PMG). The l os s more prime mover power as in wind turbine or forfr e e e x c i t a t i on pr ovi d e d b y p e r m a n en t providing optimum efficiency for the prime mover bym a gn e t t h er e for e i n cr e a s e s i n r e l a t i ve increasing its speed with power. Variable speed alsova l u e a s t h e m a ch i n e si z e i s d e c r e a s e d . allows for a more flexible generator system. For wind turbines, a battery may be added to store the extra wind energy that is not momentarily needed for the existing loads or local power grids [10-11]. At variable speed, the DC link voltage is maintained constant by exchanging power with the storage device, battery as shown in Fig. 2.Fig.1 Cross-section of typical c onventionalPermanent Magnet GeneratorThe main features of the permanent magnetsynchronous machine are as follows:1. Robust, compact and less weight.2. Copper loss due to the current flow which is thelargest loss in case of induction machine isapproximately half that of induction motor.3. High efficiency in case of permanent magnet Fig.2 PMSG with PWM rectifier with battery forsynchronous machine compared to induction storing the extra wind energymachine. The merits of permanent-magnet synchronous 4. Modeling of proposed systemmachines [6-8] over electrically excited machines 4.1. Modeling of System[14] can be as follows: This section includes modeling of supply1. No additional power supply for the magnet system (PMSG), load, controller etc. The relevantfield excitation, mathematical analysis is illustrated as follows.2. No sliding contacts, so it requires less 4.2. M o d e l i n g of Permanent Magnet Synchronousmaintenance. Machine.3. Higher reliability due to the absence The permanent magnet synchronous machineof mechanical components like slip rings. block operates in generating or motoring modes. The4. No field winding, no field copper loss. operating mode is dictated by the sign of theThe demerits of PMSM are as follows: mechanical power (positive for generating, negative1. The power factor of operation cannot be controlled for motoring). The electrical part of the machine isdue to the absence of the field winding, represented by a sixth-order state-space model [15].2. Demagnetization of PM at high temperature. The model takes into account the dynamics of the In recent years, the use of PMs is more stator and damper windings.attractive than before [14], because the performance of The equivalent frame (d-q frame) is used forPMs is improving and the cost of PM is decreasing. developing the equations for the model of the PMSG.The permanent magnet synchronous machines can be The following equations are used to express themajorly applied in direct-drive traction motors. Due to 1901 | P a g e
  3. 3. K. Uday Kumar Reddy, M. Ramasekhara Reddy, Dr. M. Vijaya Kumar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.1900-1905model of the PMSG as: 4.3. M o d e l i n g of Supply system Vd = Rsid + pd – wr q (1) The supply system consists of three-phase Vq = Rsiq + pq + wr d (2) (PMSG) system, diesel engine and governor blocks. V‟fd = R‟fdi‟fd + p‟fd (3) The model of Permanent magnet synchronous V‟kd = R‟kdi‟kd + p‟kd (4) generator (PMSG) is realized by considering fixed V‟kq1 = R‟kq1i‟kq1 + p‟kq1 excitation of an alternator. The mathematical (5) representation of all these are given above. V‟kq2 = R‟kq2i‟kq2 + p‟kq2 (6) 4.4. Design of a P, PI & PID controller d = Ld id + Lmd ( i‟fd + i‟kd) (7) To change the duty cycle of the converter q = Lq iq + Lmq i‟kq (8) the constants involving in P, PI and PID controller ‟fd = L‟fd i‟fd + Lmd ( id + i‟kd) (9) can be calculated separately by using a suitable trial ‟kd = L‟kd i‟kd + Lmd ( id + i‟fd) (10) and error technique. The controllers are used for ‟kq2 = L‟kq2 i‟kq2 + Lmq iq (11) providing suitable signals for DC-DC buck converter Where the subscripts used are defined as: d, is designed.q: d and q axis quantity, r, s: Rotor and stator 4.5. Wind Turbine Modelingquantity, l, m: Leakage and magnetizing inductance, This block implements a wind energyf, k: Field and damper winding quantity. Rs conversion system. The inputs are actual and desiredrepresents stator resistance, Lls stator leakage speed and the output of the block is mechanical power (Pω) [14]. The amount of power harnessed from theinductance, Lmd and Lmq represent d-axis wind of velocity v is as follows.and q-axis magnetizing inductances. Rf‟ denotesfield resistance and Llfd‟ leakage inductance both P=0.5ρAC ν3 (14)referred to the stator. Damper d-axis resistance Rkd‟ Whereand leakage inductance Llkd‟, Damper q-axis Pω = wind power in wattsresistance Rkq1‟ and leakage inductance Llkq1‟ andthe q-axis resistance Rkq2‟ and leakage Inductance ρ = air density in kg/m3Llkq2‟. All these values are referred to the stator. A= swept area in m2All rotor parameters and electrical quantiti es are Cp=power coefficient of wind turbineviewed fr om the stator and are identified by ν= wind speed in m/sprimed variables. The simplified synchronous 5. Matlab Simulation model of the proposedmachine block implements the mechanical system topologydescribed by: The MATLAB Simulation of proposed∆w (t) = ∫(Tm – Te) dt / (2H) – Kd∆w (t) (12) topology [9] has been shown in the Fig.2. The matlabw(t) = ∆w (t) + wo (13) Simulink tool box simpower has been used for getting `the required results 1902 | P a g e
  4. 4. K. Uday Kumar Reddy, M. Ramasekhara Reddy, Dr. M. Vijaya Kumar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.1900-1905Fig. 3. MATLAB Simulated model of PMSG connected to local Load6. S i m u l a t i o n Results The MATLAB Simulation of proposedtopology has been shown in the Fig.3. The MATLABSimulink tool box Simpower System has been usedfor getting the required results.6.1 Performance of PMSG with PWM rectifier withbattery for storing the extra wind energy: The wind driven PMSG is run at 300 rpm.The output voltage is 200 V at 60 hertz. This variablevoltage and variable frequency o u t p u t i scon ver t ed t o con st an t volta g e an dconstant frequency source. The Fig.4 to 8 shows theVariation of speed for the wind Turbine, Variation of Fig.6. Variation of battery power and battery currentload power, generated power, battery power, batterycurrent & d c-link voltage using P, PI and PIDcontrollers. The rating of the PMSG is given in theappendix Fig.7. Variation of DC-link voltage using a P- controller The change in the level of power varies with Fig.4. Variation of Speed for the wind turbine respect to the change in load demand. The maximum power generated at the rotor-side of PMSG is 3200 watts and later the change in the level of generated power varies with respect to the variation in load demand at different time instants. The battery energy storage mechanism used in the system regulates the system from severe imbalances by exchanging the energy from generator and the battery. The response of dc-link voltage using a proportional-controller is shown in fig. 7. In fig. 7 though the peak –overshoot is less but the output oscillates around 200 volts. Fig.5. Variation of Generated power and Load sidepower The load perbutations are made to occur att=0.5 sec and there is a sudden increase in the level ofload side current to 3 amps which draws more currentfrom the generator. After certain period, t=1 sec thecurrent in the load side again reaches to 2 amps. Thesudden increase in the current implies that the morecurrent is drawn from the generator and the systembalance is obtained by suitable battery energy storagesystems. Fig.8. Variation of DC-link voltage using a PI controller 1903 | P a g e
  5. 5. K. Uday Kumar Reddy, M. Ramasekhara Reddy, Dr. M. Vijaya Kumar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.1900-1905 [3] Ghosh and G. Ledwich, Power Quality Enhancement Using Custom Power Devices. Kulwer Academic, 2002. [4] Gipe, P. Wind power‟, Chelsea Green Publishing Company, Post Mills, Vermount, USA,1995. [5] Rai, G.D. (2000) „Non conventional energy sources‟, Khanna Publishers, 4th Edition, New Delhi (India) [6] Bansal, R.C., Bhatti, T.S., and Kothari, D.P. „On some of the design aspects of wind energy conversion systems”, Int. Journal of Energy Conversion and Management, Nov.Fig.9. Variation of DC-link voltage using a PID Vol. 43, No. 16, pp. 2175- 2187,2002.controller [7] Singh, B. „Induction generator-a The PI-controller offsets or eliminates the prospective‟, Electric Machines and Powersteady state oscillations that are occurred using a Systems, Vol. 23, pp. 163-177, 1995.proportional-controller and the system stability is [8] Zouaghi, “Variable Speed Drive modelingimproved as shown in fig.8. In fig.9, the output of Wind Turbine Permanent Magnetvoltage using PID controller got changed by reducing Synchronous Generator,” ICREP‟04the peak-overshoot & the time of response got International Conference on Renewabledecreased to a certain extent. Hence for economical Energy and Power Quality, Barcelona,savings; PID controller serves better purpose apart Spain, 2004.from the other controllers proposed in this design. So, [9] C. Ong "Dynamic Simulation of ElectricPID controller serves the efficient choice for the Machines Using MATLAB/Simulink"selection of the controller. Editorial "Prentice Hall", 1998. [10] D.C. Aliprantis, S.A. Papathanassiou, M.P.7. Conclusion In the proposed scheme, battery energy Papadopoulos, A.G. Kaladas, “Modelingstorage system provides power balance between the and control of a variable-speed wind turbinegenerated power and the load. The power mismatch is equipped with permanent magnetabsorbed by the BESS. From the obtained results it is synchronous generator,” Proc. Of ICEM, Vol.3, pp.558-562, 2000.clearly observed that the oscillations free output can [11] Mukhtiar Singh, A. Chandra,“ Powerbe obtained by using a PID-controller and PID- Maximization and Voltage Sag/Swell Ride-controller improves the stability of the system and Through Capability of PMSG basedhence is the best choice for the selection of the Variable Speed Wind Energy Conversioncontroller. System” in proc. of 34Th Annual conf. of APPENDIX IEEE Indus. Electronics Society,Permanent Magnet Synchronous Generator: IECON‟08, Orlando, Florida, USA ,2008.3-Phase, 300 V, 60 Hz, 3000 rpm, 4-pole [12] C. Jauch, J. Matevosyan, T. Ackermann andElectromagnetic Torque : 0.8 Nm S. Bolik. 2005. International comparison ofStator Resistance (RS) : 18.7 Ω requirements for connection of windInductance: Ld (H) = Lq(H) : 0.02682 H turbines to power systems. Wind Energy. 8:Flux induced by magnets : 0.1717 Wb. 295-306.References [13] C. Jauch, P. Sorensen and B. Bak-Jensen. [1] R. Mittal, Sandhu, Jain, “Battery energy 2004. International review of grid storage system for a wind driven variable- connection requirements for wind turbines. speed permanent magnet synchronous In: Nordic wind power conference. generator for wind energy conversion Goteborg, March. system”, International Journal of [14] S.N. Bhadra, S. Banerjee, D. Kastha Innovation, Management and Technology, (2005),„Wind electrical systems,„ Oxford Vol. 1, No. 3, August 2010, ISSN: 2010- University Press, 2005, ISBN : 0195670936 248 [15] Bhim Singh and Gaurav Kumar Kasal, [2] Bhim Singh and Gaurav Kumar Kasal, “Solid-State Voltage and Frequency “Voltage and Frequency Controller for a 3- Controller for a stand-alone wind power Phase 4-Wire Autonomous Wind Energy generating system,” IEEE Trans. Power Conversion System” accepted for Electronics, vol. 23, no.3, pp.1170–1177, publication in IEEE Trans. on Energy 2008. Conversion. 1904 | P a g e