ANALYSIS AND ACTIVE/REACTIVE POWER CONTROL OF DOUBLY FED INDUCTION GENERATOR (DYNAMIC MODELLING)

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1 International Journal of Engineering Reearch and Application (IJERA) ISSN: ANALYSIS AND ACTIVE/REACTIVE POWER CONTROL OF DOUBLY FED INDUCTION GENERATOR (DYNAMIC MODELLING) Dr.K.Chandra Sekhar, Y.Sumanth, P.Suneel Raju, N.Dharani Kumar R.V.R & J.C College of Engineering: Chowdavaram: Guntur ABSTRACT: Increaing ize of wind farm require power ytem tability analyi including dynamic model of the wind power generation. Nowaday, the mot widely ued generator type for unit above 1 MW i the doublyfed induction generator. In thi paper doubly-fed induction generator the tator i directly connected to the grid and active/reactive power control i done through rotor-ide converter. Active/ reactive power to the DFIG are controlled by injecting the proper rotor voltage derived from controller o a to maintain contant terminal voltage. Thi paper i propoed to implement on MATLAB/SIMULINK platform. KEYWORDS: Doubly fed induction generator, Variable peed wind turbine, Pitch control, Dynamic modeling. NOMENCLATURE V = Stator voltage, [V] V r = Rotor voltage, [V] V, Stator d and q winding voltage, [V] d V q I, Stator d and q winding current, [A] d I q V, Rotor d and q winding voltage, [V] dr V qr I, Rotor d and q winding current, [A] dr I qr V o = Stationary reference voltage, [V] V = Rotor reference voltage, [V] r o I = Stationary current, [A] Ir = Rotor current, [A] T = Electromagnetic torque, [N-m] e T = Mechanical torque, [N-m] m Q = Stator reactive power, [p.u] Q r = Rotor reactive power, [p.u] P = Stator active power, [p.u] P = Rotor active power, [p.u] r f o = Bae frequency, [Hz] L = Magnetizing inductance [H] Vignan Lara Intitute of Technology and Science Page 35 m L, Stator and rotor per phae L r winding inductance, [H] L, Stator and rotor per phae l L lr Leakage inductance, [H] R, Stator and rotor per phae R r Winding reitance, [] = Rotor mechanical peed, [rad/] m = Bae peed, [rad/] o I. INTRODUCTION IN RECENT year, there ha been an increaed attention toward wind power generation. Conventionally, gridconnected cage rotor induction machine are ued a wind generator at medium power level. When connected to the contant frequency network, the induction generator run near ynchronou peed drawing the magnetizing current from the main, thereby reulting in contant peed contant frequency (CSCF) operation. However, the power capture due to fluctuating wind peed can be ubtantially improved if there i flexibility in varying the haft peed [1]. In uch variable peed contant frequency (VSCF) application rotor ide control of grid-connected wound rotor induction machine i an attractive olution. In the ytem under conideration, the tator i directly connected to the three phae grid and the rotor i upplied by two back-to-back PWM converter (Fig. 1). Such an arrangement provide flexibility of operation in ubynchronou and uper-ynchronou peed both in the generating and motoring mode [2]. The rating of the power converter ued in the rotor circuit i ubtantially lower than the machine rating and i decided by the range of operating peed. Of the two converter, the function of the line ide converter i to regulate the dc bu voltage and act a unity power factor interface to the grid for either direction of power flow [3-5]. The machine ide converter

2 International Journal of Engineering Reearch and Application (IJERA) ISSN: ha to control the torque and flux of the machine or alternatively the active and reactive power. The preent work i concerned with the control of the active/reactive power of DFIG. Fig.1 Doubly Fed Induction Generator Wind Turbine Thi paper i divided a per the following ection. Section-I give the overview of the total paper. Section-II preent decription about the doubly fed induction generator. Section-III preent the dynamic imulation of doubly fed induction generator in term of dq winding. Section-IV preent the control trategy adopted for the doubly fed induction generator. Then in Section-V, VI, VII preent the reult, concluion and future cope repectively. The employment of DFIG for thi type of application i jutified by many factor: the induction generator become able to both import and export reactive power, the control of the rotor voltage and current allow the machine to remain ynchronized with the grid while the wind peed varie, thirdly the cot of the converter i lower than in all other application becaue only 25-3% of the mechanical power i fed to the grid through the converter, the ret i delivered directly from the tator. The power flow through the two converter depend on the peed of the machine, to allow the power flow in both direction, The grid ide control trategy ha the main objective to keep contant the DC voltage and to keep the reactive power flowing in the rotor a much near zero a poible in order to minimize the power ize of the converter and. The rotor ide one ha the goal to control the electric torque in order to control the electric torque and maximize the extraction of the power and to have the power unity factor. II. DESCRIPTION OF THE SYSTEM There are two baic option of wind power converion fixed peed and variable peed operation. In fixed operation, the aero turbine can be operated at a contant peed by blade-pitch control of the wind turbine even under varying wind peed. Thi option wa very common becaue of the cot involved with the power converter needed in the variable peed generation to convert the variable frequency to match the contant grid frequency. In variable peed operation, the aero turbine rotational peed can be allowed to vary with wind to maintain a contant and optimum tip peed ratio. The variable peed operation by active pitch control allow optimum efficiency operation of the turbine over a wide range of wind peed, reulting in increaing power output [7].For variable peed generation, an induction generator i conidered attractive due to it flexible rotor peed characteritic in contrat to the contant peed characteritic of ynchronou generator. DFIG configuration i bet uited for variable peed generation ince it can be controlled from rotor ide a well a tator ide. Thi i poible ince rotor circuit i capable of bidirectional power flow. The doubly-fed machine can be operated in generating mode in both ub-ynchronou and uperynchronou mode[8].the rotor will oberve lip power from the in ub-ynchronou operation and can feed lip power back to grid in uperynchronou operation. The rotor converter need thu only to be rated for a fraction 25% (Slip Power) of the total output power. All thee advantage make the DFIG a favorable candidate for variable peed operation. A commonly ued model for induction generator converting power from the wind to erve the electric grid i hown in Figure. 2. Fig.2. Baic configuration of DFIG Wind Turbine The tator of the wound rotor induction machine i connected to the low voltage balanced three-phae grid and the rotor ide i fed via the back-to-back IGBT voltage-ource inverter with a common DC bu. The network ide converter control the power flow between the DC bu and the AC ide and allow the ytem to be operated in ubynchronou and uper ynchronou peed. The proper rotor excitation i provided by the machine ide power converter. III. DYNAMIC SIMULATION OF DFIG IN TERMS OF DQ-WINDINGS Vignan Lara Intitute of Technology and Science Page 36

3 International Journal of Engineering Reearch and Application (IJERA) ISSN: A commonly ued model for induction generator converting power from the wind to erve the electric grid i hown in Fig.1.The tator of the wound rotor induction machine i connected to the low voltage balanced threephae grid and the rotor ide i fed via the back-to-back IGBT voltage-ource inverter with a common DC bu. The network ide converter control the power flow between the DC bu and the AC ide and allow the ytem to be operated in ub-ynchronou and uper ynchronou peed. The proper rotor excitation i provided by the machine ide power converter and the general model for wound rotor induction machine i imilar to any fixedpeed induction generator a follow. 3.1 Voltage equation Stator Voltage Equation: V p r i q q d q V p r i d d q d Rotor Voltage Equation: V p ( ) r i qr qr r dr r qr V p ( ) r i dr dr r qr r dr 3.2 Flux linkage equation Stator flux equation: --- (1) -- (2) q l m q m qr q m qr d l m d m dr d m dr Rotor flux equation qr lr m qr m q qr m q dr lr m dr m d r dr m d 3.4 Torque Equation T (3 / 2)( p / 2)[( i i )] em qr dr dr qr T (3 / 2)( p / 2)[( i i )] em d q q d T (3 / 2)( p / 2) L [( i i i i )] em m dr q qr d IV. CONTROL STRATEGY (3) - (4) -- (5) Fig.3. Rotor ide Converter control trategy Doubly Fed Wound Rotor Induction Machine i an attractive olution for variable peed high power generation. In variable peed contant frequency application, o called lip power recovery cheme i common practice where the power due to rotor lip below/above ynchronou peed i recovered to /upplied from power ource i.e. grid. In DFIG, electrical power output from the tator i at contant frequency irrepective of the rotor peed. To obtain ub and uper-ynchronou peed operation, the rotor mut be able to handle the lip power in both direction. Among the three power port, i.e. tator terminal, rotor terminal and the rotor haft, rotor terminal act a the energy regulating power port balance. In order to achieve a decouple control of active and reactive power; tator flux oriented vector control cheme i adopted. Baed on the previou reearch the following aumption are conidered: 1. Stator voltage drop acro reitance ha been neglected a the effect of tator reitance i quite low compared to the grid voltage [5]. 2. The DFIG i connected to a tiff grid, i.e., the frequency and amplitude of the tator or grid voltage i aumed contant [7]. 3. Magnetizing current of the tator i aumed to be determined by the grid [7]. 4. The q-axi i 9 ahead of the d-axi and rotating at ynchronou peed in the direction of rotation [8]. 5. The tator flux vector i aligned with the d-axi of the tator [8]. The above aumption lead to the following Vd Vq V (6) d q And equation (3) & (4) become Vignan Lara Intitute of Technology and Science Page 37

4 Rotor Active Power Stator Voltage Stator Reactive Power Stator Active power International Journal of Engineering Reearch and Application (IJERA) ISSN: L i d m dr L i q L i m qr dr rr dr m d L i qr rr qr m q --- (7) The active and reactive power produced in the tator, the rotor fluxe and voltage can be written in term of the rotor current a [9] Lm P V * iqr L --- (8) 2 V VL m Q * idr L L Thu from (8), the q-axi current vector component, i qr can be ued to regulate the active power generated by the tator of DFIG while, i dr can be ued to control the reactive power produced by the tator. Eentially, control of the active and reactive power i decoupled and a decoupler i not neceary. A block diagram of the control ytem i preented in Fig Generated Stator Active power (P) Fig 5.2: Stator Active Power (Generated) Stator Reactive Power V.5 Stator Reactive Power (Q) V. RESULTS AND DISCUSSION Fig 5.1 how three phae open circuit voltage V a,v b,v c which are diplaced by 12 electrical degree apart Stator voltage v Va Vb Vc -.5 Fig 5.3: Stator Reactive Power (Generated) Fig 5.4 how the active power aborbed by the rotor in ub-ynchronou mode of operation. Hence the plot ay that from 1 ec onward the rotor i aborbing the active power. Fig 5.5 how the rotor reactive power aborbed in ub-ynchronou mode of operation. Depending on et value of the reactive power the reactive power i limited..4 Rotor Active Power v Rotor Active Power (Pr) Fig 5.1 Stator Open Circuit Voltage.1 The figure 5.2 how the active power generated at the tator terminal. A we are applying negative torque after 1ec therefore from 1 ec onward the generating action will tart. Fig 5.3 how that the reactive power i generated. Hence it ay that depending on the reactive power et value reactive power i limited Fig.5.4: Rotor Active Power (Aborbed) Vignan Lara Intitute of Technology and Science Page 38

5 Speed Rotor Reactive Power International Journal of Engineering Reearch and Application (IJERA) ISSN: Rotor Reactive power v Rotor Reactive power (Qr) 3-phae fault of little cycle duration a the power converter i very enitive to grid diturbance Fig.5.5: Rotor Reactive Power (Aborbed) Speed v Reference peed Generated peed VIII. REFERENCES [1] Zhao, Y., Zou, X.D., Xu, Y.N., Kang, Y., Chen, J. Maximal Power Point Tracking under Speed-Mode Control for Wind Energy Generation Sytem with Doubly Fed Introduction Generator, Proceeding of the IEEE International Power Electronic and Motion Control Conference 26, Shanghai; China, Vol: 1, pp.1 5, 26. [2] Cardena, Roberto., Pena, Ruben., Senorle Vector Control of Induction Machine for Variable-Speed Wind Energy Application, IEEE Tranaction on Energy Converion, Vol: 19, No: 1, pp , Fig.5.6: Speed of the Generator (Sub-ynchronou) Fig 5.6 how the peed of the generator in ubynchronou mode. From the figure it ay that when we apply negative torque to the turbine uddenly, the peed of the rotor raie abruptly and again come to the tudy tate. VI. CONCLUSION Dynamic modeling i firt developed in ynchronouly rotating reference frame and the control i implemented to the rotor in line voltage oriented reference frame. Independent control of active and reactive power i proved. The oppoite ign of power flow in the rotor verifie both, ub ynchronou peed and uper ynchronou peed mode of operation. Stator voltage i maintained contant at 1 p.u. The d-q component of tator current alo confirm the vector/decoupled control of active and reactive power. VII. FUTURE SCOPE 1) Develop a controller, which can effectively improve the dynamic tability, tranient repone of the ytem during faulty grid condition. 2) To develop a protection ytem for power converter and DFIG for large diturbance like [3] Li, H., Chen, Z., Pederen J.K., Optimal Power Control Strategy of Maximizing Wind Energy Tracking and Converion for VSCF Doubly Fed Induction Generator Sytem, Proceeding of the IEEE International Power Electronic and Motion Control Conference 26, Shanghai; China, Vol: 3, pp [4] Senjyu, T., Sakamoto, R., Uraaki, N., Funabahi, T., Fujita, H., Sekine, H., Output power leveling of wind turbine Generator for all operating region by pitch angle control, IEEE Tranaction on Energy Converion, Vol: 21, No: 2, pp , 26. [5] Mohamed, M.B., Jemli, M., Goa, M., Jemli, K., Doubly fed induction generator (DFIG) in wind turbine modeling and power flow control, Proceeding of the IEEE International Conference on Indutrial Technology 24, AL; USA, Vol: 2, pp , 24. [6] Siegfried, Heier. Grid Integration of Wind Energy Converion Sytem, John Wiley & Son Ltd, 1998, ISBN X [7] He, Yikang., Hu, Jiabing, Zhao, Rende. Modeling and control of wind-turbine ued DFIG under network fault condition, Proceeding of the International Conference on Electrical Machine and Sytem 25, China, Vol: 2, pp , 25. [8] Holdworth, L., Wu, X.G., Ekanayake, J.B., Jenkin, N., Comparion of fixed peed and doubly-fed induction wind turbine during power ytem diturbance, Proceeding of the IEE Generation, Tranmiion and Ditribution, Vol: 15, Iue 3, pp , 23. [9] Toufik, B., Machmoum, M., Poitier, F., Doubly fed induction generator with active filtering function for wind Vignan Lara Intitute of Technology and Science Page 39

6 International Journal of Engineering Reearch and Application (IJERA) ISSN: energy converion ytem, Proceeding of the European Conference on Power Electronic and Application 25, Dreden; Germany, pp. 1-9, 25. Dr.K.Chandra Sekhar preently working a a Head Of the Department, Profeor of Electrical & Electronic Engineering, R.V.R.&J.C. College of Engineering,Guntur. He ha R&D,teaching Experience of 17 yearr.he alo ha a Indutrial Experience of 2 year. He received hi Ph.D. degree from JNTU-H in the year 28.He received hi M.Tech degree in Electrical Machine & Indutrial Drive From REC, Warangal in the year 1994.He received hi B.Tech degree from V.R. Siddhartha Engineering College, Vijayawada in the year Y.Sumanth preently working a a Aitant Profeor in R.V.R.&J.C. College of Engineering,Guntur. He received hi M.Tech degree from KLCE, in the year 21.He received B.Tech degree from Nalanda Intitute of Technology and Engineering, in the year 28. P.Suneel Raju preently working a a Aitant Profeor in R.V.R.&J.C. College of Engineering,Guntur. He received hi M.Tech degree from National Intitute of Technology, Rourkela, in the year 212.He received B.Tech degree from R.V.R.& J.C. College of Engineering,Guntur, in the year 29. N.Dharani Kumar preently working a a Aitant Profeor in R.V.R.&J.C. College of Engineering,Guntur. He received hi M. Tech degree from R.V.R & J.C College of Engg, in the year 21.He received B.Tech degree from Nalanda Intitute of Technology and Engineering, in the year 28. Vignan Lara Intitute of Technology and Science Page 4