Application of Grid-Converter to Direct-Driven Wind Turbine Technology

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1 Advaned Siene and Tehnology Letters Vol.73 (FGCN 014), pp Appliation of Grid-Converter to Diret-Driven Wind Turine Tehnology Gu Cailian 1, Ji Jianwei 1, u Aoran and hang Liu 1 Shenyang Agriultural University, Shenyang, China Shenyang Institute of Engineering, Shenyang, China gul@sie.edu.n Astrat. For diret drive synhronous wind power generation syste, the onverter of diret drive otor is onneted to the stator side of peranent agnet synhronous generator side, through ontrolling the onverter, the axiu wind energy an e aptured. Main iruit design of the diret-drive grid-onverter is studied. Firstly, power grid side filter is designed and alulated, LCL filter is used instead of traditional L type filter, in this way, the value of the indutane the volue and ost are redued effetively, and its inhiitory effet on high frequeny signal is ore ovious. Not only eet the vetor triangle, ut also grid onnetion haroni urrent is restrained. Seondly, the filter of otor side is also designed, aout the prole of voltage refletion for long ale drive otor PWM onverter on the otor side, the solution is to redue the output value of the du/dt and inrease the pulse rise tie, at the sae tie the refleted voltage of the otor side is also redued. Finally,Brake unit is researhed, at the instant of the power grid voltage dips is deteted, hopper ontrol is started to IGBT of rake unit, aking the ahine side power in addition to the net fro the side of the part, the rest are onsued in the rake unit, to ensure that the equipent an grid-onneted operated. The last ut one, the pre-harging iruit is inluded. Keywords: diret-driven wind turine syste; line-side LCL filter; generatorside du/dt filter 1 Introdution In reent years, China's eletri power syste proposed onstrution of a strong, sart grid onept Therefore, the developent of new energy tehnologies has eoe a hot spot. Conneted for diret-drive synhronous wind power systes, diret-drive otor-side onverter and peranent agnet synhronous generator stator side, its ontrol, to ahieve axiu wind energy apture [1]. Full power onverter is an iportant part of the grid through the onverter an e issued y the generator energy etter. Diret-drive wind power onverters, there are any key tehnologies need to e studied []. Diret-drive wind turine and inverter theoretial analysis to alulate the paraeters of the ain iruit, and the ahine side and network side onverter ontrol ethod arried out researh, and the use of siulation and experient to prove the thesis proposes developent of the feasiility of the ethod. ISSN: ASTL Copyright 014 SERSC

2 Advaned Siene and Tehnology Letters Vol.73 (FGCN 014) Perforane analysis of onverter of diret-drive wind power generation syste the Diret-drive wind power syste is one of the ost popular wind power systes at present [3], in order to failitate analysis, the urrent transforer unit of grid side is usually referred to as grid side onverter, the urrent transforer unit of generator side is alled generator side onverter. Under noral irustanes, the urrent transforer is onneted to grid with unit power fator [4]..1 Struture analysis Power of wind power syste, generated y the generator is transitted into grid y onverter, The onverter not only need to eet the relevant requireents that the grid is onneted to a generator, ut also produe the right PWM voltage to drive the otor, and then stator urrent and rotor speed an e ontrolled[5]. The onrete struture is as follows:.1.1 Diode retifier +Boost onverter +DC/AC inverter:firstly AC voltage generated y Peranent agnet diret drive otor is transfored y diode retifier into diret urrent, and then the DC voltage is iproved y the Boost onverter onverts to the appropriate voltage level in order to e used y inverter ehind of it. And then through the inverter, the high quality AC is transfored and fed into the grid [6].fewer IGBT devie is eployed with the struture and has ertain advantages. However, the power quality of peranent agnet otor side is poor, the effiieny and the power fator of the otor are also e affeted [7]..1. Bak-to ak onverter: Two-level and three-level ak-to-ak onverters, an perfet to ahieve grid side and otor side ontrol, and to failitate the realization of LVRT funtion. Aong the, apaitor size of three level H ridge ak-to-ak onverter is redue effetive however, openings winding is needed y otor and transforer windings to inrease the weight and loss of the otor and transforer. Higher level voltage, saller du/dt and ore output level nuer an e realized y five-level H Bridge, volue and loss of the indutane is further redued [8]. However, the prole of us neutral point voltage flutuation and inner and outer pipe loss unalaned DC is still existing, openings winding otor and transforer are still needed. Multilevel asaded H ridge ak-to-ak onverter, an ahieve higher voltage ore than five level H ridge onverter, e used in grid voltage to l0kv~0kv voltage grade [9-10]. But eah ak-to-ak unit needs a high-frequeny transforer isolation of the otor and the power grid.. Analysis of tehnial onditions For the diret drive wind power grid-onneted onverter, generally the grid side onverter works in three-phase syste with 690V voltage and then the value is iproved through the transforer to 10kV grid. Using IGBT as the swithing devie, in order to ensure the drive signal well anti-interferene harateristi, the optial drive is adopted. Beause diret drive onverters ainly work in the sea or harsh 100 Copyright 014 SERSC

3 Advaned Siene and Tehnology Letters Vol.73 (FGCN 014) onditions, eah oponent ainet internal need to prevent salting out and dust, on the other hand, on aount of larger power for the diret drive onverter, so the requireents of heat dissipation is higher, if the ooling volue will e great, so often ooled y water ooling[11]. The tehnial paraeters are shown in Tale 1. Tale1. Diret-drive wind power grid-onneted prototype paraeters DC voltage(udc) 100V(DC) Power grid voltage Generator side rated apaity 1450kVA Power Grid frequeny %V 47.5~51.5H Variations range of voltage of Generator side Variations range of otor speed vrs Swith frequeny 1.9kH 4-18r/in Drive Method Photi dirve For the voltage type retifier, it is need to eet the ondition of forula 1. UDC>1.41Ul (1) In the paper, 100V> V.therefore, the design eets the onditions. 3 Diret-drive wind power onverter ain iruit design On the asis of tehnology onditions of the diret-drive wind turine onverter, the filter of grid side of onverter ain iruit, the filter of generator side, the rake unit and pre-harging iruit are designed The filter design of grid side Three-phase voltage soure PWM retifier output voltage of the PWM wave to ahieve and the network ust require filtering. Traditional network side of the filter is generally L filter, it has to eet the requireents of vetor ontrol: to eet the vetor triangle, ut also to ahieve the inhiitory effet of the grid urrent haronis. L-type filter is reliale, relatively siple design, whih has een widely used. However, with the power level of inrease, the deline of the swithing devie swithing frequeny, in order to eet the requireents of haroni suppression, the aount of indutane you need to e very large. Large indutane L will not only inrease the volue of the onverter and inrease the ost of the onverter, ut also akes the onverter urrent regulation slows down [1]. LCL filter instead of the traditional L-shaped filter an effetively redue the total value of the indutane, reduing the size and ost, and the inhiitory effet of high frequeny signal is ore pronouned. The line-side onverters in this artile using the LCL filter struture. Where L1 is the onverter side indutane, the CF filter apaitor, L is the transforer leakage Copyright 014 SERSC 101

4 Advaned Siene and Tehnology Letters Vol.73 (FGCN 014) indutane. Where L1 is the onverter side indutane, the CF filter apaitor, L is the transforer leakage indutane. When VSR works in unity power fator, known y the vetor triangle: E ( L I ) U 11 () Where E for the grid phase voltage peak, the peak of the U using SVPWM ontrol strategy for AC output voltage, I is the peak of the AC output urrent. The value of L11 an e alulated: L11 <65 H. When VSR works in ondition of pure apaitive reative power: E L I ) U (3) ( 11 L 11 I 11 (h) I 1 (h) L U 11 (h) I C1 (h)+i 1 (h) U a (h) - CF 1 + U C1 (h) Fig 1. Line-side LCL filter for one phase L 11 <10 H (4) Therefore, the onverter side indutane value ust e less than 10 H. The single-phase filter iruit sheati shown in Fig 1 that only fundaental ontent of the line-side voltage haroni oponent is the short iruit. And the indutor L11 should also eet the following forula: U ( n ) L ax L ( n ) ax, n,3, 11 n I ( n ) (5) U(n) is the n-th haroni of the onverter output voltage, I(n) is the requireents for the grid haroni urrent axiu, ω is the angular frequeny of the fundaental. Values of the filter apaitor CF1 varies depending on the loation of the voltage and urrent sensors. The urrent sensor easureents in this paper are the network-side onverter urrent, the voltage sensor to easure the voltage on the AC filter apaitor CF1. When the onverter with unity power fator onverter parallel operation, is equivalent to an equivalent resistane, the definition of the ipedane of the aseline ipedane : 10 Copyright 014 SERSC

5 Advaned Siene and Tehnology Letters Vol.73 (FGCN 014) ( E / ) E / P (6) P E:the gird side of the line voltage peak P:the rated power of the syste. Suggesting 1 = ωl1, 11 = ωl11, = 1/ωCF1, the equivalent resistane looking at fro the grid side is: grid j j 1 1 j j ( j ( j ) j )( j ( j ) ) (7) ( 1 1 B ) j To ensure that the network side equivalent ipedane into resistane harateristi, ust request the equal zero, the availale apaitane. Generally the leakage indutane of the transforer is regarded as L1 of LCL filter, and for diret drive grid-onneted onverter, the leakage indutane of the transforer is deterined, so it is not need to e designed. MATLAB siulation software is used to design LCL filter. Fourier analysis (FFT) is also used to deopose a phase urrent of the grid side, the haronis are ainly distriuted around the swithing frequeny fs1 =.1kHz around, That THD equals 3.9% eets haroni requireents of the grid-onneted. In wind power appliations, the onverter is loated in the otto, while the generator is installed in the tower, inverter-driven generator stator require a longer ale PWM drive pulse transitted to the generator terinals. Motor-side onverter output for high-frequeny PWM wave, due to the distriution harateristis of the long ale, naely, the existene of the leakage indutane and oupling apaitane, high frequeny differential ode du/dt of the PWM output voltage will ause voltage refletion at the otor end, aking the otor side over-voltage an e up to twie that of the original value [13]. Refletion over-voltage will destroy the insulation of the otor, and otor oon-ode du/dt, voltage is intensified. 3. The filter design of otor side For PWM onverter long-ter drive otor in the otor side of the voltage refletion [14], the solution of this paper is to redue the output of du/dt values, so that the pulse rise tie inreases, so an redue the otor side refleted voltage. In general, the RLC iruit filter, its struture is shown in Fig. Copyright 014 SERSC 103

6 Advaned Siene and Tehnology Letters Vol.73 (FGCN 014) otor-side onverter L Long ale PMSG C R Fig. A du/dt filter iruit of generator-side Aording to the voltage refletion theory tells us, when tt< tr/3, line voltage peak value is: V p lv N ln d V V (1 ) d d (8) vt vt r r tt is the required tie output pulse transission fro the inverter to the generator side;tr is the tie of output pulse rising; N is terinal refletion oeffiient (with the ale harateristi ipedane is approxiately equal to 1); v is the speed of pulse transission; l is ale length (assuing the ale length 90 ).The du/dt of wind generator is 800V/us, aording to previous forulas tr and Vp are alulated respetively 1.375μs and 060V. Line voltage of the generator terinal voltage is 060V peak. Fro the aove alulation, the generator-side onverter output pulse rise tie ust e greater than 1.375us, generally tie of IGBT swithing is 100ns, oviously if requireents annot e eet, the total refletion of voltage ours in the otor side. RLC resonane is eployed to redue the rate of hange of voltage when the IGBT fast swithing, the resistane R plays a daping role. LC resonant yle is generally set to the following equation: L C t (9) Considering the resonant over-voltage, need to set the daping resistane, dap resistane is larger, over voltage suppression effet is etter, and an also liit the apaitor urrent pulse peak, ut too ig daping resistane will redue suppression effet of du/dt, generally restrited to near ritial resistane, resistane is set for: r L (10) R C 104 Copyright 014 SERSC

7 Advaned Siene and Tehnology Letters Vol.73 (FGCN 014) 3.3. The rake unit design Diret drive inverter raking unit struture as shown in Fig 6, whih onsists of a swith tue T1,a resistor R1(raking power resistor, through alulation and test seletion 1.0Ω) and diode D1. Swith tue used for hopping ontrol, resistane energy onsuption unit, in order to prevent the hopper proess urrent utations produe over voltage, diode D1 is applied to the freewheeling role. In order to struture of unity, general swithing tue T1 and a diode D1are sae as power odule. Upon detetion of the voltage sag oent, start on the raking unit IGBT hopper ontrol, so that the ahine side eitted power exept to network side part, the rest eing onsued in the rake unit, to ensure noral operation of grid onneted inverter devie. rake unit T 1 PMSG R 1 D 1 Fig 6. Brake unit struture 3.4. Pre-harging iruit design Converter just started on the iddle of the DC filter apaitor voltage is zero, then losed the grid side of the ain iruit reaker, the grid voltage diretly through the network side IGBT anti-parallel diode added to the iddle of the DC filter apaitor, the apaitor voltage on the utation, the apaitor will have a ig ipat on urrent, this ipulse urrent will redue the life of the apaitor. Thus the ain reaker is losed to the interediate DC filter apaitor harging. Pre-harge iruit struture is shown in Fig 7. K ontator is losed efore the losure of the ain iruit reaker Q1, the LCL filter apaitor ranh; do not put the ase for pre-harging. the interediate DC filter apaitor is harged y the grid voltage through pre-harge resistor R (alulated and experiental) to harging. Copyright 014 SERSC 105

8 Advaned Siene and Tehnology Letters Vol.73 (FGCN 014) U L Q 1 L 1 C d R K C Fig 7. Ciruit of the pre-harge 4 Conlusion This paper presents the design and developent of the 1.5MW diret drive wind turine generator and onverter prototype ross feed power experients, ut also due to experiental onditions, only to ahieve a 1MW. Hope to e ale to do full-power experients, and hope that it an eet the requireents of the otor drag experient and wind field experients. Referenes 1.. J. eng, H. T. hang, Y. Li, L. G. Pang,. Yang. Proeedings of the CSEE. 30, 15 (010). F. Blaajerg,. Chen, S. Kjaer. IEEE Trans. Power Eletronis. 19, 1184 (004) 3. H. Li,. Chen. Renewale Power Generation., 13 (008) 4. M. Liserre, R. Cardenas, M. Molinas, J. Rodriguez. IEEE Trans. Indus. Eletron. 58,1081 (011) 5. F. Blaajerg, M. Liserre, K. Ma. IEEE Trans. Power Eletronis. 48, 708 ( 01) 6. S. Kouro, M. Malinowski, K. Gopakuar, J. Pou, L. G. Franquelo. IEEE Trans. Power Eletron. 57, 553 (010) 7. J. M. Carraso, L. G. Franquelo, J. T. Bialasiewiz. IEEE Trans. Indus. Eletron. 53, 100 ( 006). 8. J.. hang, M. Cheng. Pith angle ontrol for variale speed wind turines.the Third International Conferene on Eletri Utility Deregulation and Restruturing and Power Tehnologies, (008) April 6-9; Nanjing, China. 9. D. S. Oliveira, M. M. Reis, C. Silva. IEEE Trans. Power Eletron. 5, 677 (010) 10. M. Malinowski, K. Gopakuar, J. Rodriguez, M.A.Peerez. IEEE Trans. Indus. Eletron. 57, 197 (010) 11. R. Teihann, M. Malinowski, S. Bernet. IEEE Trans. on Indus. Eletron. 5, 471 (005) 1. Y. hang, S.. Duan, Y. Kang. Proeedings of the CSEE. 6, 45 (006). 13.H. F. Ma, D. G. u,. Y. Chen. Chinese Journal of ehanial gineering. 11, 109 (001) 14.A.Jouanne, P. N. Enjeti. IEEE Trans. on Indus. Appl. 33, 1138 (1997) 106 Copyright 014 SERSC