Investigation of the control voltage and reactive power in wind farm load bus by STATCOM and SVC

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1 Scientific Reearch and Eay Vol. 5(5), pp , 4 Augut, 200 Available online at ISSN Acadeic Journal Full Length Reearch Paper Invetigation of the control voltage and reactive power in wind far load bu by STATCOM and SVC Ali Ozturk * and Kenan Dooglu Departent of Electric Education, Faculty Technical Education, Duzce Univerity, 8620-Bec/Yorukler, Duzce, Turkey. Accepted 5 July, 200 In thi tudy, the voltage tability of the bu load in variou tatic and dynaic load yte that are fed by a wind far ha been exained. In the control of load voltage and reactive power, 0 MVAr tatic ynchronou copenator (STATCOM) and tatic var copenator (SVC) i ued. In the wind far exained, double feed induction generator (DFIG) i ued. In voltage and reactive power control, the reult of tie repone and daping ocillation have been found uing MATLAB / Siulink. The reult achieved have proved that SVC and STATCOM yield good reult when ued in ter of voltage tability of the yte. Key word: Wind far, STATCOM, SVC. INTRODUCTION One of the renewable energy ource, wind turbine have been ued widely in recent year. The otive behind thi coon ue of wind turbine can be the low cot and it being environent friendly. However, when wind turbine are produced with large power, oe proble arie in connecting it to power yte. One of the reaon for thi i that the change in load deand of the yte ake the yte untable. Thi intability in the power yte bring about the voltage and reactive power proble of the yte. In Power yte, voltage and reactive power control proble are iportant for continuou cae tability. Thee proble have been olved through power electronic driver included in Flexible AC Traniion yte (FACTS). Parallel FACTS driver uch a SVC and STATCOM have been ued widely in tranient voltage control due to their high perforance (Wei, 2006). When the load connected to a bu load in STATCOM controlled wind far which i intalled into the circuit, the effect of terinal voltage, reactive power and peed regulation have been exained in ter of rotor *Correponding author. E-ail: aliozturk@duzce.edu.tr. Tel: Fax: tability perforance, and STATCOM control ha been oberved to yield good reult (Paulo Ficher de Toledo, 2005). The oent-lip characteritic of Induction Generator operating under low voltage in the yte to which wind far i connected were exained. It wa found that with the ue of SVC and STATCOM, the reult can be iproved in cae of an unexpected condition in the yte (Jon are Suul, 2008). By uing SVC and STATCOM, failure analyi wa done in DFIG at different tie, and it wa oberved that SVC and STATCOM yielded tie repone quickly in the control of voltage, reactive power and peed characteritic (Foter, 2007). Daping ocillation at the bifurcation point and at the tie of overload in the power yte wa exained in ter of voltage tability; and it wa oberved that ocillation da-ping can extinguih in a horter pan of tie when STATCOM and SVC are ued (Mithulananthe, 2003; Rahi, 2003) STATCOM and the intallation of variou load value at different tie were perfored with the ue of Proportion Integrate and Fuzzy Logic in bu load voltage and reactive power control (Kenan and Alta, 2008). Generic STATCOM ha been deigned in order to iprove wind far tability that i fored in fixed peed induction generator. PV curve in bu load with and without STATCOM were exained. It wa hown that the tability point of thi generic

2 994 Sci. Re. Eay Figure. Syteatic tudy of STATCOM. STATCOM in dynaic yte can pread into a wider area (Qi, 2008). In power yte, the voltage and current change in bu load were exained at different tie. In thi tudy, SVC and Thyritor Controlled Serie Copenator (TCSC) have approached the reference value of tie repone in dynaic load (Einoglu, 2003). The effect of variou dynaic load on the voltage profile of load yte have been exained through SVC; and good reult were obtained in the active and reactive power control of bu load in ter of voltage regulation (Einoglu, 2004). In thi tudy, a 9 MW wind far operate a connected to network. SVC and STATCOM were ued in order to tabilize the voltage and reactive power flow in the bu load of thi power yte when tatic and dynaic power entered the current. In voltage and reactive power control of bu load, the curve of variou tatic and dynaic load tie repone and ocillation daping were drawn. In tie repone and ocillation daping, SVC and STATCOM were copared with one another. STATIC SYNCHRONOUS COMPENSATOR (STATCOM) STATCOM work produce active and reactive power dependent on the tranfor leakage reactance between voltage ource inventor generator and AC voltage ource control (Wang, 2003). The ultiate goal of STATCOM i to produce reactive ipedance that can be adjuted in continuou or gradual anner in order to eet the copenation need of traniion line (Shenghu, 2009). STATCOM voltage ource convertor and tranforer are connected to AC yte in a parallel anner. In STATCOM control yte, d-q reference can uually be defined in frae network voltage ynchroni. It i poible to control d-q current independent of DC voltage and reactive power of STATCOM. The calculation of Re-active Power related to STATCOM DC voltage are expreed a given: 2 Q = V B + kv VB co( θ α ) kv VG in( θ α ) dc Here, V i the traniion voltage, B i the ueptance, k the odulation index, Vdc the capacitor voltage, alpha the thyritor firing angle, theta phae angle of the traniion line, G i the adittance of coupling tranforation. STATCOM circuit odel ha been hown Figure. The voltage produced by STATCOM i beneficial in providing for the network. The leakage reactance ued in tranforation, however, enable the yte to function in a table anner by enabling the unexpected current that coe out when the voltage value i higher than the voltage generated by STATCOM to flow on itelf. Moreover, STATCOM iprove the daping ocillation that coe out in dynaic voltage control with the rie in deand of the load yte. STATIC VAR COMPENSATOR (SVC) The line voltage, in cloed loop AC voltage control, give out reference value and error ignal in the eaureent dc ()

3 Ozturk and Dooglu 995 Figure 2. STATCOM voltage control unit. of the point in which SVC i connected to the network (Shenghu, 2009). SVC ha been deigned for reactive power control againt diipation and fat voltage control. In ot of it application field, SVC ha been deigned for reactive power generation and control. Moreover, it i ued for voltage control. It can be ued for reducing power ocillation, a well. The fundaental function of SVC i to control bu voltage for reactive power control in the area into which it i intalled. SVC circuit odel i a hown on Figure 2. In general, SVC conit of Thyritor Controlled Reactor (TCR) and thyritor witching copenator (TSC) (Maood, 2006). Depending on operating condition of the circuit, the trigger angle of thyritor have been identified and they have been introduced into the circuit. In Forward and backward operation of the circuit, the triggering angle are et during the operation and reactor and capacitor are introduced into the circuit. A capacitive and inductive working ituation upplie the variable of the inductance. Thi inductance value i calculated a follow: π v = = (2) L 2 ( π α ) + in 2α Total equivalent ipedance of the controller can be repreenting a: e = where, c π / rx in 2α 2α + π (2 ) r x (3) c r x = liit of the controller are given by the L firing angle liit, which are fixed by deign (Kaarpohi, 2008). In converter circuit, jut a capacitor, provide voltage for the circuit a a generator, o it can iniize the lo that will coe out a a reult of witching loe of Inulated Gate Bipolar Tranitor and Gate Turn off Thyritor, ued a power electronic eleent. STATCOM AND SVC CONTROLLER With the connection of STATCOM to the yte, the upply of voltage and reactive power control ha been aied in the load bu. STATCOM of voltage control circuit i hown in Figure 3. Here, the eaured value of voltage V to the bu, Vref (reference voltage) and the T and T2 are contant tie, the eaured voltage value of load bu wa copared with the reference value. Specifying the error rate between the, reactive current axiu and iniu value were entered into the odulation index by ean of park tranforation. Thi value and the previou odulation index value were collected o that the yte would have taken the lat odulation index coefficient. The control unit in SVC i ore baic to STATCOM. SVC of voltage control circuit i hown in Figure 4. Error value, the difference between the eaured bu voltage and the reference voltage, i the input of the control unit. The thyritor are fired related to thee value. In thi tudy, the wind far connected to the network running of load bu will be voltage control and reactive power control. 0 MVAr STATCOM and SVC will be ued for Reactive power and voltage control. It i expected that the voltage per bu load and reactive power will decreae oewhere in the reference value through control. The tudy i aied at providing the Proper Proportion Integrate (PI) coefficient o that the repone tie of reactive power and voltage that correpond to reference

4 996 Sci. Re. Eay Figure 3. Syteatic tudy of the SVC. Figure 4. SVC voltage controller unit. WIND TURBINE Figure 5. Double feed induction generator. value will be hort and daping ocillation will not poe unfavorable effect for the ake of voltage tability of bu load. In thi tudy, the focu i et on the DFIG. DFIG are preferred due to the fact that they can be frequency and voltage control. The tator of DFIG i directly connected to the grid, wherea the rotor winding i connected with voltage ource convertor. By upplying a voltage with variable frequency and variable aplitude to the rotor circuit, the voltage at the tator terinal can be kept contant. Rotor ide converter uually provide active and reactive power of the achine while the line ide converter keep the voltage of the DC circuit contant (Wilch, 2007). Wind Turbine circuit odel i hown in Figure 5. The DFIG wind turbine wa repreented by the odeling of the rotor, drive train, induction generator, and power converter and protection yte. The rotor odel expree the echanical power extracted fro the wind

5 Ozturk and Dooglu 997 by the rotor, given a: 3 P w = PAu C p ( λ, θ ) (4) 2 where, Pw (W) i the aerodynaic power, r (kg/) the air denity, A (2) the rotor dik area, R () the rotor radiu, u (/) the wind peed, and Cp the power coefficient which i a function of the tip peed ratio l (ratio between blade tip peed and wind peed) and y the pitch angle of rotor blade. The electrical differential equation are preented next, expre per unit and uing generator convention, which ean that the current are poitive when flowing toward the grid, and active and reactive power are poitive when fed into the grid. ded = ( e dt T o d ( ) i q i L ) + SWe q W u Lσr + L, (5) deq i L = ( eq ( ) id) + SWe d W u dt T Lσr + L g o T = L ( i i i i ) dr (7) d qr q where u denote voltage, denote current, indexe d and q, the direct and quadrate coponent, indexe and refer to tator and rotor, e and e are the internal voltage coponent of induction generator, W i the ynchronou peed, i the generator lip, T o i the tranient open circuit tie contant, i the tator reactance and i the tranient reactance, expreed a T L + L d q (6) r o = σ (8) Rr W ( L + L ) = σ (9) = = W L σr L 2 + L (0) qr dr With and R and R r the tator and rotor reitance, L σ L σ the tator and rotor leakage inductance and r L the agnetizing inductance (Fernandez L.M., 2007). SYSTEM OF STUDY In thi tudy, 575 V, 60 Hz and 9 MW wind far wa ued.the wind far generator wa powered with the induction generator in it. The wind far produce voltage regulation, which i dependent on the voltage value of the capacitor included in the back to back convertor. With the control of the yte frequency depending on the f convertor, network voltage i aured to be equal. Moreover, thank to a booter tranforer, voltage wa raied fro 575 V to 25 Kv. Network voltage and frequency value are regarded to be 20 Kv, 60 Hz. In the network, the voltage wa reduced fro Kv with the ue of tranforer a in the wind far. In the yte, nuber bu i connected to the network, nuber 2 bu i connected to wind far, and nuber 3 bu ha been exained a the bu that i involved in the area where the network and wind far wa converted to 25 Kv. Variou active and reactive power were connected in load bu. Both dynaic and tatic load eaureent of thee load were conducted at the ae value. In thi iulation tudy, SVC and STATCOM of 0 Mv were ued a parallel to bu load. In control unit of STATCOM and SVC, PI controller wa ued due to the fact that they can react ore quickly and le ocillation, which i aied at voltage and reactive power control are conducted with PI control and the reactive power will be brought to reference value in the nuber 3 load bu of the yte. Kp =, Ki = 500 were adopted for voltage control, how-ever, for reactive power control, Kp=0., Ki= 50 were adopted. In thi tudy, for voltage reference value,.0 p.u wa identified, yet for reactive power reference value, 0.0 ha been identified. Syte circuit odel i a hown in Figure 6. SIMULATION RESULTS On the operation of the yte, the tatic and dynaic load value dependent on load bu have been hown in the table given. Static and dynaic load value reain the ae. Voltage and reactive power control of STATCOM which i connected to the load bu when active load i 4 MW and reactive load i 2MWAr tatic i hown Figure 7 and 8. Voltage and reactive power control of SVC which i connected to the load bu when active load i 4 MW and reactive load i 2 MWAr tatic can be een in Figure 9

6 998 Sci. Re. Eay Figure 6. Syte circuit odel..5. Bu Voltage(V) Tie() Figure 7. STATCOM voltage controller. and 0. Voltage and reactive power control of STATCOM which i connected to the load bu when active load i 4MW and reactive load i 2 MWAr dynaic have been hown Figure and 2. Voltage and reactive power control of SVC which i connected to the load bu when active load i 4 MW and reactive load i 2 MVAr dynaic i hown in Figure 3

7 Ozturk and Dooglu Reactive Power(Q) Tie() Figure 8. STATCOM reactive power controller...05 Bu Voltage(V) Tie(n) Tie () Figure 9. SVC voltage controller. and 4. CONCLUSIONS In the wind far which operate a connected to the network, the control of the decreae in voltage a a reult of the connection of load to load bu wa exained through STATCOM and SVC. The Proportion Integrate tie table ued to control voltage and reactive power were taken to be the ae for different tatic and dynaic load. Voltage reference value in the bu wa given a p.u while reactive power change value in the bu wa given a 0 p.u. In thi iulation tudy, it wa oberved that both STATCOM and SVC have ade the voltage and reactive power change cloer to reference

8 2000 Sci. Re. Eay 0.5 Reactive Power(Q) Tie(n) Tie () Figure 0. SVC Reactive power controller..5. Bu Voltage(V) Tie() Figure. STATCOM voltage controller. value and ade the table. It wa found that STAT- COM yielded better reult in ter of tie repone than SVC in voltage control. Reactive power wie, it wa found that STATCOM becoe table in a horter tie pan relative to SVC. Taking the yte into conideration in ter of daping ocillation, the fluctuation in SVC i le than STATCOM. On the operation of the yte, the tatic and dynaic load value dependent on load bu have been hown on the Table. The reult of voltage and reactive power control in load bu with 4MW and 2 MVAr load value voltage and reactive control have been hown Table 2.

9 Ozturk and Dooglu Reactive Power(Q) Tie() Figure 2. STATCOM reactive power controller...05 Bu Voltage(V) Tie(n) () Figure 3. SVC voltage controller.

10 2002 Sci. Re. Eay Table. Different load. Active load (P) (MW) Reactive power (Q) (MVAr) Table 2. Meaureent value. Copenator type and load Ve Qe Tie repone () Daping ocillation between STATCOM tatic load ( ) SVC tatic ( ) STATCOM dynaic ( ) SVC dynaic ( ) The reult of voltage and reactive power control in load bu with 5MW and.5 MVAr load value have been voltage and reactive control. Table 3. Meaureent value. Copenator type and load Ve Qe Tie Repone () Daping ocillation Between STATCOM tatic ( ) SVC tatic ( ) STATCOM dynaic ( ) SVC dynaic ( ) The reult of voltage and reactive power control in load bu with 3MW and 2. MVAr load value have been voltage and reactive control. Table 4. Meaureent value. Copenator type and load Ve Qe Tie Repone () Daping ocillation Between STATCOM tatic ( ) SVC tatic ( ) STATCOM dynaic ( ) SVC dynaic ( ) The reult of voltage and reactive power control in load bu with 5MW and.5 MVAr load value voltage and reactive control have been hown Table 3. The reult of voltage and reactive power control in load bu with 3MW and 2. MVAr load value voltage and reactive control have been hown Table 4. ACKNOWLEDGEMENT Thi work wa preented at the" ELECO' TH International Conference on Electrical and Electronic Engineering" 5-8 Noveber 200, Bura, Turkey. REFERENCES Einoglu U, Ayaun S, Yalcnöz T (2004). Application of SVC on dynaic Load for different Load type Matlab, the 39th International Univeritie Power Engineering Conference, 2: Einoglu U, Yalcnöz T, Herde S (2003). Analyi of FACTS Device for dynaic load uing Matlab, The 38th International Univeritie Power Engineering Conference, 2: Fernandez LM, Jurado F, Saenz JS (2007). Aggregated dynaic odel

11 Ozturk and Dooglu 2003 for wind far with doubly fed induction generator wind turbine, Renewable Energy, pp Foter S, u L, Fox B (2007). Grid Integration of Wind Far uing SVC and STATCOM, Univ. Power Eng. Conference, : Jon AS, Tore U (2008). Low Voltage Ride through of Wind Far with Cage Generator: STATCOM veru SVC, IEEE Tranaction on, 23: Kaarpohi MA, Alinezhad M, Leani H, Talebi N (2008).Coparion of SVC, STATCOM, TCSC and UPFC Controller for tatic Voltage Stability Evaluated by Continuation Power Flow Method, EEE Electrical Power Conference, pp. -8. Kenan Y, ail HA (2008). Reactive Power of Control Load Control with STATCOM Fuzzy Logic, VII. National Clear Energy Conference, pp Maood T, Aty Edri A, Aggarwal RK, Qurehi SA, Jabber Khan A, Al Mulla YY (2006). SVC Modeling and Analyi Technique by MATLAB, PSC, pp. -7. Mithulananthan N, Claudio A, Canizare S, John R (2003). Fellow and Grahan J.Roger, Fellow, Coparion Of PSS,SVC and STATCOM Controller for Daping Power Syte Ocillation, Power Syte IEEE Tranaction on,8: Paulo F, de T, Hailian (2005). Wind Far in Weak Grid Copenated with STATCOM, Int. of Energy Tech., Aaborg Univerity. Qi L, Langton J, Steurer MS (2008). Applying a STATCOM for Stability Iproveent to an Exiting Wind Far with Fixed-Speed Induction Generator, IEEE Power and Energy Society General Meeting, pp Rahi AHMA, Baiyat SAAL, Kandlawala MF (2003). Parallel FACTS Device for Power Syte Stability Enhanceent, IEEE GCC Conference, Article 42. Shenghu Li, Ming D, Jingjing W, Wei Z (2009). Voltage Control capability of SVC with var dipatch and lope etting, Electric Power Syte Reearch 79: Wang HF (2003). Interaction and ultivariable deign of STATCOM AC and DC voltage control, Electrical Power and Energy Syte, pp Wei Qiao, Ganeh KV, Ronald H (2006). Real Tie Ipleentation of a STATCOM on a Wind Far Equipped with Doubly Fed Induction Generator, IEEE Ind. Application Conference, 2: , Wilch M, Pappala VS, Singh SN, Erlich I (2007). Reactive Power Generation by DFIG Baed Wind Far With AC Grid Connection, EEE Power Tech, pp