Converter Protection Scheme for Doubly-Fed Induction Generators during Disturbances

Transcription

1 Converter Protection Scheme for Doubly-Fed Induction Generator during Diturbance 1 Kadam D.P., Dr. Kuhare B.E. 1 Aitant Profeor, K. K. Wagh Intitute of Engineering Education and Reearch Nahik (MS), India. Profeor & H.O.D., K. K. Wagh Intitute of Engineering Education and Reearch Nahik (MS), India. Abtract: With the increaing hare of wind in power generation, the dynamic behavior of the power ytem will change coniderably due to different technologie ued for wind and conventional generator. Thi paper will decribe the utainability of Doubly-Fed Induction Generator during the abnormal condition on grid alo during the fault condition. For the election of the uitable rating of crowbar (chopper reitor) approximation are to be carried out. For imulation tudie taking wind peed variation into account, or when the rotor haft peed deviation become ignificant, the turbine peed and it pitch control ytem have to be conidered. The hort-circuit current contribution of DFIG ha received much attention. Wind turbine with a doubly fed induction generator have a crowbar to protect the power electronic converter that i connected to the rotor winding of the induction generator. A Grid fault ride through capability of Doubly Fed Induction Generator in Wind Energy Tranfer Sytem i determined uing PSCAD / EMTDC Software Simulation. DFIG Rotor ide converter i very much enitive to Grid Fault. A ingle line to ground fault at grid i taken for tudy. Voltage dip occur on tator voltage and current rie intantaneouly, with thi rotor ide current increaed which will reult in damage of rotor ide converter. Keyword: Wind Farm, PSCAD, Doubly-fed induction generator (DFIG), flux linkage, grid fault, wind power generation I. INTRODUCTION The pat decade ha een the emergence of wind a the world mot dynamically growing energy ource. With the increaing hare of wind in power generation, the dynamic behaviour of the power ytem will change coniderably due to different technologie ued for wind and conventional generator. Therefore, WT and wind park have to be conidered in power ytem dynamic tability tudie for which, however, uitable WT model are needed. Thee model have to compromie between accuracy, for conidering relevant dynamic interaction between grid and WT, and implicity required for the imulation of large ytem. WT modelling i a topical reearch currently conducted by many academic intitution and developer. Different publication came out in the recent pat from which, taking into account the apect of large-cale tability tudie, [1] [7] hould be mentioned. Depite the effort made, the WT model till need ome refinement, extenion, and adaptation. In cae of evere grid fault, the DFIG and it aociated converter ytem have to be protected againt damage, for which the crowbar (CB) i a widely ued approach. The CB i a reitance connected to the rotor circuit for a hort period for de-energizing the machine while the converter i diconnected. CB witching i triggered on the bai of rotor current and/or converter dclink voltage value. In normal operating mode, the rotor ide converter control active and reactive current and thu P and Q of the DFIG independently. The correponding controller will be derived baed on the DFIG equation. Simplified model are preented alo for the converter dc-link and line ide converter. For imulation tudie taking wind peed variation into account, or when the rotor haft peed deviation become ignificant, the turbine peed and it pitch control ytem have to be conidered. For thi purpoe, a generic model i propoed. There i need to tudy effect of thee factor to identify the main iue which are reponible for detoriation of power quality, reliability, ecurity and tability of large wind farm grid. Hence, it i neceary to addre thee iue including tability and reliability of grid a well a atifactory operation of generator including ride through capability during normal a well a fault condition. II. INDUCTION GENERATOR The IG conit of a three-phae wound rotor induction machine, mechanically coupled to either a wind or hydro turbine, whoe tator terminal are connected to a contant voltage and contant frequency utility grid. The variable frequency output i fed into the ac upply by an ac dc ac link converter coniting of either a full-wave diode bridge rectifier and thyritor inverter combination or current ource inverter (CSI)-thyritor converter link. One of the outtanding advantage of DFIG in wind energy converion ytem i that it i the only cheme in which the generated power i more than the rating of the machine. However, due to operational diadvantage, the DFIG cheme could not be ued extenively. The high maintenance requirement, low power factor, and poor reliability are the few diadvantage due to the liding mechanical contact in the rotor. Thi

2 cheme i not uitable for iolated power generation becaue it need grid upply to maintain excitation. Thi generator ha the advantage of being relatively cheap and robut. On the other hand, it peed cannot be continuouly controlled, and it i a large and rather uncontrollable conumer of reactive power: thi i a major diadvantage with repect to the grid voltage tability. The doubly fed induction generator i a more uitable generator for wind turbine. It i contructed a an induction generator with wound rotor. The tator winding are directly connected to the grid. The rotor winding are connected to the grid through a Thyritor frequency converter. The frequency converter only ha to proce the generator lip power fraction, which i generally no more than 30% of the generator rated power. Thi reduced rating for the frequency converter implie an important cot aving, compared to a fully rated converter. To tart up a machine from zero peed, an additional oft-tarter connected to the tator winding may be needed. Doubly fed induction generator by mean of controlling the rotor current through the frequency converter, the peed and tator reactive power of the generator can be controlled in a mall range around the generator rated value. The extent of thi range depend on the rating of the frequency converter. current become too high, the thyritor are fired and the high current do not flow through the converter but rather into the crowbar reitor. The enabling of the crowbar can be followed by different action. The whole wind turbine can be diconnected from the grid, but it i alo poible to diconnect the converter from the rotor without diconnecting the wind turbine from the grid. The generator then operate a an induction machine with a high rotor reitance. The third poibility i to keep the turbine connected to the grid and the converter connected to the rotor. With thi type of control, it i poible to reume normal operation immediately after clearance of the fault. When the dip lat longer than a few hundred milliecond, the wind turbine can even upport the grid during the dip III. DFIG PROTECTION Thi ection decribe the hort-circuit behavior of doubly fed induction generator and the crowbar protection that i applied to protect the generator. In normal operation, the pace vector rotate at a ynchronou peed with repect to the reference frame. Ignoring the tator reitance, the derivative of the tator flux i directly proportional to the grid voltage. When the voltage drop to zero (in cae of a fault at the generator terminal), the tator flux pace vector top rotating. Thi produce a dc component in the tator flux. The dc component in the rotor flux of the machine i fixed to the rotor and will continue rotating. Thi will thu add an alternating component to the dc component of the tator flux. The maximum value that the current reach depend mainly on the tator and rotor leakage inductance. The peed at which the dc component will decay i mainly determined by the tranient time contant of the tator and rotor. The voltage dip will caue large (ocillating) current in the rotor circuit of the DFIG to which the power electronic converter i connected. A high rotor voltage will be needed to control the rotor current. When thi required voltage exceed the maximum voltage of the converter, it i not poible any longer to control the current a deired. Thi implie that large current can flow, which can detroy the converter. In order to avoid breakdown of the converter witche, a crowbar i connected to the rotor circuit. Thi can, for example, be done by connecting a et of reitor to the rotor winding via bi-directional thyritor. When the rotor Fig. 1.Crowbar reitor in the rotor circuit The value of crowbar (chopper ) reitance can be calculated from maximum current through rotor winding, which i mainly depend on maximum value of tator current that can be flow at the time of fault or abnormal condition. The maximum value of tator current i given in equation (1), thi i found through approximation. 1.8V (1) i, max ' X + R From (1), it can be oberved that the maximum hort-circuit current of the DFIG trongly depend on the value of the crowbar reitance. Thi ection will invetigate how a good value for the bypa reitance can be determined. There are two main requirement that give an upper and a lower limit to the reitance. The reitance hould be high to limit the hort-circuit current. It hould be low to avoid a too high voltage in the rotor circuit. A too high voltage can reult in breakdown of the iolation material of the rotor and the converter. It i further

3 poible that when the voltage become higher than the dc link voltage, large current will flow through the ant parallel diode of the converter, charging the dc link to an unacceptable high voltage. A lower value will reult in higher current in the rotor of the machine. The thermal time contant of the rotor will however be generally high enough to handle the hort-circuit current for a hort period. Therefore, the maximum value i more important than the minimum value. An approximation of the maximum tator current i given by (17). A all parameter are tranferred to the tator ide, the maximum rotor current (reduced on the tator ide) will have approximately the ame value. The voltage acro the bypa reitor, and thu acro the rotor and converter i V r R i () Combining thi equation with (1), the maximum value of the bypa reitor can be determined a ' V X (3) R < 3. V V Where V r,max i the maximum allowable rotor voltage. It i only an approximation, a it i baed on a number of aumption and approximation. IV.RESULTS Simulation i done with PSCAD / EMTDC Software. Single Line to Ground Fault on grid i taken for tudy. Doubly Fed Induction Generator with Fault at 10 ec duration 0.3 ec without bypa reitor Following Reult are obtained without bypa reitor (crowbar) Fig. 3 Rotor Side Voltage Fig. 4 Rotor Side Current Following Reult are obtained with bypa reitor (crowbar) Fig. Generator Stator Current

4 Fig. 5 Generator Stator Voltage & Generator Stator Current Fig. 6 Rotor Side Voltage & Rotor Side Current Fig. 8 Rotor Reitor Current & Rotor Reitor Voltage V. CONCLUSION The neceary condition for deciding the upper and lower limit of reitance are a following The reitance hould be high to limit the hort-circuit current. It hould be low to avoid a too high voltage in the rotor circuit. REFERENCES Fig. 7 Rotor Side Voltage & Rotor Side Current [1] Jin Yang, David G. Dorrell, John E. Fletcher, A New Converter Protection Scheme for Doubly-Fed Induction Generator during Diturbance IEEE Ind. Electronic, Nov 008 [] Johan Morren, Sjoerd W. H. de Haan, Short-Circuit Current of Wind Turbine With Doubly Fed Induction Generator IEEE Tranaction On Energy Converion, Vol., No. 1, March 007 [3] Slavomir Seman, Jouko Niiranen, Sami Kanerva, Antero Arkkio, and Juliu Saitz, Performance Study of a Doubly Fed Wind-Power Induction Generator Under Network Diturbance IEEE Tranaction On Energy Converion, Vol. 1, No. 4, December 006

5 [4] D. Xiang, L. Ran, P. J. Tavner, and Shunchang Yang, Control of a Doubly Fed Induction Generator in a Wind Turbine During Grid Fault Ride-Through IEEE Tranaction On Energy Converion, Vol. 1, No. 3, September 006 [5] A. Peteron, L. Harnefor, and T. Thiringer, Evaluation of current control method for wind turbine uing doubly-fed induction machine, IEEE Tran. Power Electron., vol. 0, no. 1, pp. 7 35, Jan [6] M. S. Vicato and J. A. Tegopoulo, Tranient tate analyi of a doublyfed induction generator under three phae hort circuit, IEEE Tran. Energy Conver., vol. 6, no. 1, pp. 6 68, Mar [7] Erlich and U. Bachmann, Grid code requirement concerning connection and operation of wind turbine in Germany, in Proc. IEEE Power Eng. Soc. General Meeting, Jun. 1 16, 005, pp [8] M. A. Pöller, Doubly-fed induction machine model for tability aement of wind farm, Proc. IEEE PowerTech, Bologna, Italy, Jun. 003, BPT [9] F. M. Hughe, O. Anaya-Lara, N. Jenkin, and G. Strbac, Control of DFIG-baed wind generation for power network upport, IEEE Tran. Power Syt., vol. 0, no. 4, pp , Nov [10] J. B. Ekanayake, L. Holdworth, X. G. Wu, and N. Jenkin, Dynamic modelling of doubly fed induction generator wind turbine, IEEE Tran. Power Syt., vol. 18, no., pp , May 003. [11] Y. Lei, A. Mullane, G. Lightbody, and R. Yacamini, Modeling of the wind turbine with a doubly fed induction generator for grid integration tudie, IEEE Tran. Energy Conver., vol. 1, no. 1, pp , Mar [1] Johan Morren, Sjoerd W. H. de Haan, Ridethrough of Wind Turbine with Doubly-Fed Induction Generator During a Voltage Dip IEEE Tranaction On Energy Converion, Vol. 0, NO., JUNE 005 [13] Rogério G. de Almeida and J. A. Peça Lope, Participation of Doubly Fed Induction Wind Generator in Sytem Frequency Regulation IEEE Tranaction On Power Sytem, Vol., NO. 3, AUGUST 007 [14] Hee Sang Ko, Gi-Gab Yoon, Nam-Ho kyung and Won-Pyo Hong Modeling and Control of DFIG- Baed variable peed wind turbine Electrical Power Sytem Reearch, Volume 78, Iue 11, November 008. a Large Wind Farm, Paper accepted for IEEE PSCE 006 Conference, PP , 006. [16] S. Bozhko, R. Li, R. Blaco-Gimenez, G. M. Aher, J. C. Clare, L. Yao, and C. Sae, STATCOM- Controlled HVDC Power Tranmiion for Large Offhore wind Farm: Engineering Iue Paper accepted for IEEE Conference, PP , 006. [17] Joaquin Eloy-Garcia, Serge Poullain, Abdelkrim Benchaib, Dicrete- Time Sliding-Mode Control of a STATCOM Including Voltage and Current Limitation for Wind Farm Application, Paper accepted for IEEE EPE-PEMC 006 Conference, PP , 006. Prof. Kadam D.P graduated in Electrical Engineering from Govt. College of Engineering, Amaravati in 1997 & hi Mater Degree in Electrical Engineering from Walchand college of Engg., Sangli, Shivaji Univerity, Kolhapur with Power Sytem a a pecialization. He i working a an Aitant Profeor at K.K.W.I.E.E. & R, Nahik, Maharahtra, India.He i puruing Ph.D from Pune Univerity. Hi reearch area include Optimization of Reactive Power, Power Quality & FACTS. Hi total experience pan over 11 year. Prof. Dr. B. E. Kuhare graduated in Electrical Engineering from Govt. College of Engineering, Aurangabad and obtained Gold Medal for Univerity Topper in He completed hi ME Electrical Control Sytem from Pune Univerity in 199 and obtained Ph.D. in Power Quality from Pune Univerity in 006. He i alo a Certified Energy auditor. He Publihed around 100 International and National Paper. He i alo a conultant to variou indutrie in India and abroad. He i working a Profeor & Head of Electrical Engg. Dept. at K.K.W.I.E.E. & R, Nahik, Maharahtra, India. [15] Wei Qiao, Ronald G. Harley, Ganeh K. Effect of FACTS Device on a Power Sytem Which Include