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Universidade Federal de Minas Gerais Departamento de Engenharia Elétrica Fault Ride-through Enhancement in DFIG with Control of Stator Flux Using Minimized Series Voltage Compensator Sandro Élisson da Silveira . Sidelmo Magalhães Silva . Braz de Jesus Cardoso Filho Published in: IET Renewable Power Generation, 2018

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Fault Ride-Through Enhancement in DFIG with Control of Stator Flux Using Minimized Series Voltage Compensator Sandro Elisson da Silveira 1, Sidelmo M. Silva 2, Braz J. Cardoso Filho 3 1,2,3

Graduate Program in Electrical Engineering - Federal University of Minas Gerais, Belo Horizonte, Brazil 1 [email protected] , [email protected] , [email protected]

Abstract: Wind energy systems based on doubly fed induction generators (DFIG) are very sensitive to grid disturbances, mainly voltage sags, which can cause rotor and stator overcurrents and rotor overvoltage, resulting in turbines shutdown or even damage to the converter connected to the rotor. Besides, the transmission system operators (TSOs) have been issuing strict grid codes, which require the wind energy conversion system (WECS) to keep operating during grid disturbances and supplying reactive power to the system, if necessary. Due to difficulties to access the offshore DFIGs, avoiding damages and shutdowns in these WECS is paramount. In order to overcome this problem this article proposes the control of the generator stator flux through a series voltage compensator (SVC) with minimized components. The proposed SVC draws power from the grid through a transformer with a single turn in the primary side (Single Turn Primary Transformer - STPT) and injects power in the system through a LC filter, without any series transformer. The control of the generator stator flux reduces considerably the stator and rotor current as well as the rotor voltage, allowing the generator to ride-through the grid disturbances. 1. Introduction Among renewable sources, the wind energy has been experiencing the most noticeable growth. In 2015, 4% of the worldwide electrical power was generated by wind energy conversions systems (WECS). The forecast is that 25% of the worldwide electricity will be supplied by wind power in 2050 [1]. Regarding offshore WECS, there is nowadays more than 14GW of installed wind power capacity [2]. The doubly fed induction generator (DFIG) [3], presented in Fig. 1, is one of the most widespread technologies for wind energy applications, reaching about 50% of the market share [4]. As for offshore windfarms, the participation of DFIG in the market share is more than 50% [5]. The great advantage of the DFIG is the fact that this technology operates the WECS with variable speed using a converter with 30% of the generator rated power. In addition, the possibility of operating the converter in four quadrants allows the control of the active and reactive power supplied to the grid. An important issue in DFIG-based WECS is their great sensitivity to disturbances in the electrical system, especially voltage sags and voltage swells. Abrupt voltage sags produce overcurrents and overvoltages in the generator windings that can cause the shutdown of WECS or even destroy the converter or the generator [6, 7]. In order to improve the grid stability, many countries have approved strict grid codes that require wind turbines to remain connected to the grid during disturbances. Some grid codes also demand that the generator injects reactive power during the voltage sag [8]. The usual approach to mitigate the effects of the electrical disturbances in the generator is to connect a crowbar in the rotor windings. The crowbar limits the rotor current inserting resistances in the rotor circuit, keeping the generation system working during the disturbance. However,

the crowbar does not fulfil some strict grid codes, once it does not allow the injection of reactive power into the electrical system during its activation [7, 9, 10]. Other alternative to reduce the effects of voltage sags in the generators is to install a chopper in the converter’s d.c. link [11, 12]. The main problem with this solution is the fact that high rotor currents circulate in the rotor side converter (RSC) during the disturbances, requiring high current rating antiparallel diodes in the RSC to conduct the rotor transient overcurrents when the converter switchings are disabled. The solution proposed by [11] allows the reduction of the overcurrents in the RSC. However, rotor and stator currents can still reach magnitudes as high as twice the rated current during a severe voltage disturbance. Some works proposes to insert impedances in series with the DFIG to limit the fault current in the stator during grid disturbances. The active superconducting fault current limiter (SCFL) is effective to limit fault currents but demands extra hardware to compensate voltage sags [13, 14, 15]. Other proposals to enhance the fault ride through using extra hardware like STATCOMs and parallel capacitors have been proposed extensively [16, 17, 18]. Another alternative proposed to mitigate this problem is the installation of a Series Voltage Compensator (SVC) in series with the stator of the generator [19, 20, 21, 22]. The solutions presented in [20, 21, 22] consist in compensating the voltage sag, keeping rated voltage in the stator windings, which keeps the generator working normally. These SVC based solutions present an important drawback: during the compensation interval, the SVC draws power from the a.c. bus and extra hardware is needed to charge and discharge the energy storage system connected to the d.c. bus. Another issue with these solutions is the association of a series transformer with the generator stator. According to [23], the series transformers must be sized with a power rating of, at

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(a)

(b)

(c)

(d)

Fig. 1. (a) Doubly Fed Induction Generator – DFIG, (b) Minimized SVC to enhance Fault Ride Through – SCC with STPT, (c) Minimized SVC to enhance Fault Ride Through – SCC with Shunt Transformer, (d) Block diagram of the Stator Flux Control least, twice that of the SVC, seriously impacting the overall size and cost of the system. The solution proposed in [19] consists in mitigating the generator overcurrent and overvoltage through the control of the generator stator flux, reducing its oscillation during the voltage disturbance. The SVC presented stores its energy in the d.c. link of the DFIG converter and the SVC is connected to the grid through a series transformer. This work proposes the control of the generator stator flux using a minimized series voltage compensator as presented in Fig. 1. In order to control the generator stator flux in case of a disturbance, the SVC supplies a fraction of the generator voltage during a short time. Therefore, the proposed SVC requires a low energy storage capacity. The proposed technology is comprised by: an independent storage energy system; a converter responsible for charging the SVC d.c. link (Series Charger Converter - SCC) that, differently from other solutions, is connected directly to the grid through a transformer with a single turn in the primary side (Single Turn Primary Transformer - STPT); a converter responsible for controlling the generator stator flux (Control Stator Flux Converter - CSFC), that is connected to the grid using a LC filter, without any series transformer, as presented in [24]. This paper is organized as follows: Section II explains the strategy to control the generator stator flux during grid voltage disturbances; Section III outlines the SVC topology and discuss its advantages; Section IV is devoted to present the control strategies implemented in the CSFC and SCC; Section V shows the DFIGs performance

with SVC proposed when the DFIG is subjected to different kinds of disturbances; Finally, the conclusion is drawn in Section VI. 2. Generator Stator Flux Control The fundamentals of the stator flux control strategy are thoroughly explained in [19]. During normal operation, the converter connected to the rotor (Rotor Side Converter – RSC) and the converter connected to the grid (Grid Side Converter - GSC) are controlled in a similar way as in a typical DFIG system. The grid voltage oriented vector control of the RSC allows a decoupled control of torque and reactive power at the stator terminals. Similarly, the grid voltage oriented vector control of the GSC controls the DFIG d.c. link voltage, as well as the system reactive power. As for the CSFC, it does not operate and the grid current is bypassed by the static switch, composed by anti-parallel thyristors. During a voltage sag, the SVC is activated and controls the stator voltage in order to transition the total stator flux to a new level compatible with the new wind farm voltage. The development of the voltage sag detection logic is described in the following paragraphs. The relation between the stator flux variation and the wind farm voltage )*+* is given by the equation +*

,-.( 0 )*+* 1 )2+* 1 3.+* . 5.( 1 678 -+* .( ,/

&'

"#$% "(

(2) 2

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+*

where )2 is the voltage applied by the SVC, 3. is the stator current, 5.( is the stator resistance, 78 is the grid voltage frequency. The superscript vf indicates that all variables are wind farm voltage oriented, with the angle obtained by a Phase-Locked Loop (PLL) [25]. During "#

&'

normal operation condition $% is zero. When a disturbance "( occurs, the equilibrium observed in (1) is disrupted and the "#

&'

term "($% can be used to activate the SVC stator flux control. The stator flux is controlled in a synchronously rotating dq reference frame, with the d-axis oriented along the position of the stator flux space vector, and the q-axis oriented along the position of the wind farm voltage space vector [26, 27]. From these considerations, it is developed the stator flux control block diagram presented in Fig. 1, that computes the voltage to be added to the machine stator terminals to properly control the stator flux. The d-axis component of the reference stator flux is +* given by (2), where )9* is the q-axis component of the wind farm voltage. +* +* )9* 1 5.( . 39. +*∗ (2) -". 0 678 The d-axis component of the stator flux is given by +* (3), where )9.( the q-axis component of the stator terminals voltage. +*

+*

+*

-". 0 ;0

[email protected] A 2

(4)

Where E is the total energy supplied by the SVC, C is the total SVC capacitance and V is the voltage in the SVC d.c. link. The calculations above show the stator flux control to enhance the DFIG fault ride through can be achieved with small d.c. link capacitances. As the energy required from the SVC to keep working properly a 2MW DFIG generator is rather low, the SVC can use a simple converter topology to charge its d.c. link. The d.c. link can be charged either through a STPT connected to the SCC, as presented in Fig. 1, or through a shunt transformer, as seen in Fig. 1. The STPT necessary to charge the SVC has a ratio of 2500:12.5A and a voltage drop of 5V in the primary winding when conducting rated current (see Fig. 4). Therefore, the SVC can be equipped with a 12.5kVA split core STPT to simplify the installation. The SVC injects the necessary voltage to control the stator flux through an LC filter, thus eliminating the costly and bulky series transformer. As the SVC operates during short intervals, some hundreds of milliseconds, at most, the power converter of the CSFC can have small heatsinks, or even no heatsink. During the normal operation of the DFIG the CSFC is bypassed by the static switch. When a disturbance occurs, the bypass is turned off and the CSFC is connected to the grid. As aforementioned, the main components of the proposed SVC present a reduced size and power rating, which makes this SVC an attractive solution to enhance the fault ride-through of new DFIGs, that need to comply with strict grid codes, as well as already installed DFIGs that need to fulfil new code requirements. This solution is especially useful in offshore DFIGs, since they need to be thoroughly protected against overcurrents and overvoltages due to the inherent difficulties to reach these generators.

Fig. 2. (a) Generator stator flux during sag without SVC, (b) Rotor current during sag without SVC, (c) Stator current during sag without SVC 3

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Fig. 3. (a) Wind farm voltage sag down to 20% – Phase to neutral, (b) Voltage supplied by the SVC, (c) Voltage supplied by the SVC – Zoom

4. Series Voltage Compensator Control The block diagram of the CSFC voltage control is indicated in Fig. 5. The CSFC control guarantees that the capacitor voltage @C of the LC filter will follow the voltage reference @C∗ generated by the stator flux control. Both SCC and CSFC considered here were designed assuming a switching frequency of 8kHz with a three-level output voltage. The LC filter was designed with a 3.3kHz cutoff frequency, and its main parameters are presented in TABLE I. The control gains of the CSFC were calculated to achieve a good dynamic stiffness for the system. TABLE I also includes the control parameters of the system. The poles in the dynamic stiffness plot in Fig. 5 were adjusted for 2900Hz, 1450Hz and 750Hz. These frequencies were chosen to increase the bandwidth of the outer voltage control loop. The proposed control scheme is successful to make the capacitor voltage @C to track the reference @C∗ , as shown in Fig. 5. The d.c. link voltage of the SVC (@DD E is controlled by the SCC. The block diagram of the SCC control is depicted in Fig. 6. The RL filter was calculated to guarantee a maximum current ripple of 10A. The calculated parameters are presented in TABLE II. The control gains were calculated through the dynamic stiffness characteristic and are presented in TABLE II. The poles of the dynamic stiffness curve in Fig. 6 were tuned for 100Hz, 10Hz and 1Hz. A notch filter (NF) intended to block the doublefrequency ripple from disturbing the output current was implemented. Different from [30], the notch filter was implemented in the feedback path. The notch filter has a transfer function given by

FGH IJE 0

J A K 47 A J A K 4ξ7J K 47 A

The used NF is centered ω=2.π.50 rad/s and has a damping voltages applied to the STPT are whose angles are obtained through (PLL).

(5)

at double frequency coefficient ξ=0.5. The grid current oriented, a Phase-Locked Loop

Table 1 CSFC Parameters Symbol Lf RL Cf Kpv

Fig. 4. (a) Generator stator flux controlled by the SVC, (b) Energy required from the SVC during the stator flux control, (c) CT primary voltage during voltage sag (d) STPT secondary current during voltage sag

Kiv Kpi Kinv P V I

Parameter

Value

Inductance – LC filter Resistance – LC filter Capacitance – LC filter Proportional Gain – Voltage Control Loop Integral Gain – Voltage Control Loop Proportional Gain – Current Control Loop Proportional Gain – Converter Rated Power / Per Phase Rated Phase Voltage in rms Rated Phase Current in rms

116 µH 1 mΩ 20 µF 0.18Ω

474Ω/s 3.71Ω-1 1 270kVA 150V 1800A

4

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Table 2 SCC Parameters Symbol Lf RL Kpv Kiv Kpi Kinv P V I

Table 3 SVC d.c.-link capacitance per phase

Parameter

Value

Inductance – LR filter Resistance – LR filter Proportional Gain – Voltage Control Loop Integral Gain – Voltage Control Loop Proportional Gain – Current Control Loop Proportional Gain – Converter Rated Power / Per Phase Rated Phase Voltage in rms Rated Phase Current in rms

33.3 mH 10 mΩ 0.75Ω

STPT

Shunt Transformer

Brazil Code

12mF

6mF

UK Code

60mF

25mF

4.3Ω/s 23Ω-1 1 12.5kVA 1000V 12.5A

Fig. 6. (a) Block diagram of the SCC voltage control, (b) Dynamic stiffness for SCC d.c.-link voltage control

Fig. 5. (a) Block diagram of the CSFC voltage control, (b) Dynamic stiffness for CSFC voltage output control, (c) Reference voltage and voltage over the capacitor of the LC filter during stator flux control

5. DFIG Performance with Proposed SVC In order to verify the effectiveness of the proposed SVC, a DFIG system protected by the SVC was simulated, considering the fault ride-through (FRT) requirements of two different grid codes. One grid code chosen was the Brazilian code, that in agreement to other grid codes [8] states that the generators must continue to operate in the event of deep voltage sags. The other grid code chosen was the strict code from UK, a country with many installed offshore DFIGs, whose code demands that the generators must continue working even during zero voltage ride through. Fig. 7 presents the voltage limits required by the grid codes studied. Initially the DFIG system protected by the SVC was subjected to a type A voltage sag down to 20% during 500ms (see Fig. 3), as required by the Brazilian code. The generator stator flux control executed by the SVC was able to maintain the generator working and supplying active and reactive power normally during the sag. The generator and the RSC did not face any stator or rotor overcurrent as shown in Fig. 8. The rotor voltage increased but did not reach the phase to neutral peak limit of 1690V. The generator rotor accelerated and reached a speed of about 1530rpm, a 5% variation, which is well within a typical operating speed range of 30%. In this simulation, no pitch control was implemented to reduce the acceleration, but it is 5

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important to observe that the sag time is too short to allow for an effective pitch control. Through the simulations it was possible to size the d.c. link capacitors of the SVC. The values obtained were summarized in TABLE III. The SVC with STPT was able to control the generator stator flux with a capacitance of 12mF per phase in the d.c. link. Using this capacitance, the d.c. link voltage dropped to about 700V during the stator flux control interval, as shown in Fig. 7. As for the SVC with a shunt transformer, it was able to control the generator stator flux with 6mF per phase in the d.c. link. The d.c. link voltage fell down to 800V during the stator flux control, as seen in Fig. 7. Simulations demonstrated that whenever there is a remaining voltage in the grid during the sag, the capacitance required by the SVC is reduced. Afterwards, the DFIG system protected by the SVC was subjected to a type A voltage sag according to the requirement of the UK grid code (see Fig. 7). The voltage applied has a sag down to 0% during 140ms (7 cycles). The voltage then increases until it reaches 85% of the rated voltage at 2.5s. The generator stator flux varies following the grid voltage. This is observed when the voltage drops abruptly and when the voltage ramps up with a constant rate (see Fig. 9). During the voltage sag, no rotor or stator overcurrent are observed in the generator (see Fig. 10). The reduction of the stator flux leads to rotor acceleration, but the speed varies within the typical operating speed range (see Fig. 10).

In order to comply with the zero-voltage ride-through requirement imposed by the UK grid code, the capacitance of the SVC d.c. link needed to be increased. The necessary capacitances to control the generator stator flux are presented in TABLE III. Both topologies of SVC, with STPT and shunt transformer managed to control the d.c. link voltage during the deep voltage sag, as seen in Fig. 9. Finally, the DFIG was subjected to an unbalanced voltage sag. Fig. 11 shows the DFIG behaviour when subjected to a type B voltage sag down to 20%. The generator stator flux oscillation increases continuously during the voltage sag. The stator currents become unbalanced and increase during the sag, reaching a peak of about 20 kA at the end of the sag. The rotor currents also become unbalanced and increase during the sag, reaching a peak of about 8 kA at the end of the sag. When the DFIG is protected by the SVC no stator or rotor overcurrent are observed in the generator (see Fig. 12). The SVC is active during the transients, eliminating the generator stator flux instabilities. After 100ms, the SVC is turned off. The generator stator flux keeps oscillating, what is expected, since unbalanced sags lead to oscillatory behaviour of the generator stator flux.

Fig. 8. (a) Rotor current during Voltage Sag – Voltage down to 20% during 500ms, (b) Rotor voltage during voltage sag, (c) Stator current during voltage sag, (d) Rotor speed Fig. 7. (a) FRT requirements of Brazil and UK grid codes, (b) DC-link voltage – SVC with STPT – Voltage down to 20% during 500ms, (c) DC-link voltage – SVC with Shunt Transformer – Voltage down to 20% during 500ms

6

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Fig. 9. (a) Stator voltage during sag – UK grid code, (b) Generator stator flux controlled by the SVC, (c) DC-link voltage – SVC with STPT – UK code, (d) DC-link voltage – SVC with Shunt Transformer – UK code

Fig. 11. (a) Wind farm unbalanced voltage sag – Phase to neutral – Phase A down to 20%, (b) Generator stator flux during sag without SVC, (c) Stator current during sag without SVC, (d) Rotor current during sag without SVC

Fig. 10. (a) Rotor current during voltage Sag – UK grid code, (b) Stator current during voltage sag, (c) Rotor speed

Fig. 12. (a) Generator stator flux controlled by the SVC – Unbalanced sag – Phase A down to 20%, (b) Stator current during voltage sag, (c) Rotor current during voltage sag

7

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6. Conclusion DFIGs are susceptible to voltage disturbances since their stators are connected directly to the grid. The mitigation of the effects of voltage disturbances and improving the FRT demands extra devices for DFIGs, such as crowbars and choppers. In this context, the proposed SVC presents itself as an efficient, low cost and compact solution to improve the FRT. Since this is a simple add on device, it can be easily connected to existing as well as new WECS. Simulation results demonstrated that the SVC can fulfil strict grid codes requirements while retaining a potential for compactness and low cost. The SVC operation eliminates rotor and stator overcurrents as well as rotor overvoltages in the DFIG, increasing the reliability of the WECS and reducing maintenance and human intervention, that are undesirable in offshore wind farms.

[9] Hu, S., Zou, X., Kang, Y.: 'A novel optimal design of DFIG crowbar resistor during grid faults', Power Electronics Conference - IPEC-Hiroshima - ECCE-ASIA, May 2014, pp. 555-559.

7.

[12] Jalilian, A., Naderi, S.B., Negnevitsky, M., Hagh. M.T., Muttaqi, K.M.: 'Controllable DC-link fault current limiter augmentation with DC chopper to improve fault ridethrough of DFIG', IET Renewable Power Generation, April 2017, Vol.11, pp. 313-324.

Acknowledgments The authors thank the Graduate Program in Electrical Engineering (PPGEE-UFMG) for supporting this research and the government agencies CAPES and CNPQ for their financial support. 8. References [1] Global Wind Energy Outlook-2016, 'Global Wind Energy Outlook Scenarios' (Global Wind Energy Council, 2016), pp. 15-29 [2] Global Wind Report – Annual Market Update-2016, 'Offshore Wind' (Global Wind Energy Council, 2016), pp. 58-65 [3] Pena, R., Clare, J.C., Asher, G. M.: 'Doubly fed induction generator using back-to-back PWM converters and its application to variable speed wind-energy generation', IEE Proceedings - Electric Power Applications, May 1996, Vol. 143, No 3, pp. 231-241 [4] Liserre, M., Cárdenas, R., Molinas, M., Rodríguez, J.: 'Overview of Multi-MW Wind Turbines and Wind Parks', IEEE Transactions on industrial electronics, April 2011, Vol. 58, No. 4, pp. 1081-1095 [5] Keysan, O.: 'Future Electrical Generator Technologies for Offshore Wind Turbines', IET Engineering & Technology Reference, December 2014, pp. 1-11 [6] Pannell, G., Atkinson, D., Kemsley, R., et al.: 'DFIG Control Performance Under Fault Conditions for Offshore Wind Applications', IET Proc. 18th International Conference on Electricity Distribution, Turin, Italy, June 2005 [7] López, J., Gubía, E., Olea, E., Ruiz, J., Marroyo, L.: 'Ride Through of Wind Turbines with Doubly Fed Induction Generator Under Symmetrical Voltage Dips', IEEE Transactions on industrial electronics, October 2009, Vol. 56, No. 10, pp. 4246-4254 [8] Tsili, M., Papathanassiou, S.: 'A Review of Grid Code Technical Requirements for Wind Farms', IET Renewable Power Generation, July 2008, Vol. 3, No. 3, pp. 308-332

[10] Sava, G.N., Duong, M.Q., Leva, S., et al.: 'Coordination control of active crowbar for doubly fed induction generators', International Symposium on Fundamentals of Electrical Engineering (ISFEE), November 2014, pp. 1-5. [11] Naderi, S.B., Negnevitsky, M., Muttaqi. K.M.: 'A modified DC chopper for limiting the fault current and controlling the DC link voltage to enhance ride-through capability of doubly-fed induction generator based wind turbine', IEEE Industry Applications Society Annual Meeting, 2017,pp, 1-8.

[13] Guo, W., Xiao, L., Dai, S., Li, Y., Xu, X., Zhou, W., Li, L.: 'LVRT Capability Enhancement of DFIG with Switch Type Fault Current Limiter', IEEE Transactions on Industrial Electronics, January 2015, Vol.62, pp.332-342. [14] Chen, L., Zheng, F., Deng, C.; Li, Z., Guo, F.: 'Fault Ride-Through Capability Improvement of DFIG-Based Wind Turbine by Employing a Voltage-Compensation-Type Active SFCL', Canadian Journal of Electrical and Computer Engineering, Spring 2015, Vol.38, pp. 132-142. [15] Sahoo, S., Mishra, A., Chatterjee, K., Sharma C.K.: 'Enhanced fault ride through ability of DFIG-based wind energy system using superconducting fault current limiter', 4th International Conference on Power, Control & Embedded Systems, March 2017, pp. 1-5. [16] Abobkr, A.H., El-Hawary, M.E.: 'Fault ride-through capability of doubly-fed induction generators based wind turbines', IEEE Electrical Power and Energy Conference, October 2015, pp. 8-15. [17] Chhor, J., Tourou, P., Sourkounis, C.: 'Evaluation of state-based controlled STATCOM for DFIG-based WECS during voltage sags', IEEE International Conference on Renewable Energy Research and Applications, November 2016, pp. 463 - 471. [18] Huchel, Ł., El Moursi, M.S., Zeineldin, H. H.: 'A Parallel Capacitor Control Strategy for Enhanced FRT Capability of DFIG', IEEE Transactions on Sustainable Energy, April 2015, Vol. 6, pp. 303-312. [19] Flannery, P.S., Venkataramanan, G.: 'Evaluation of Voltage Sag Ride-Through of a Doubly Fed Induction Generator Wind Turbine with Series Grid Side Converter', IEEE Power Electronics Specialists Conference, Florida, USA, July 2007, pp. 1839-1845. 8

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[20] Wessels, C., Gebhardt, F., Fuchs, F.W.: 'Fault Ride Through of a DFIG Wind Turbine Using Dynamic Voltage Restorer', IEEE Transactions on power electronics, March 2011, Vol. 26, No. 3, pp. 871-882

9. Appendices Table 4 Simulation Parameters Symbol

[21] Yao, J., Li, H., Chen, Z., et al.: 'Enhanced Control of a DFIG-Based Wind-Power Generation System with Series Grid-Side Converter Under Unbalanced Grid Voltage Conditions', IEEE Transactions on Power Electronics, July 2013, Vol. 28, No. 7, pp. 3167-3181

We Pn VS

[22] Gkavanoudis, S.I., Demoulias, C.S.: 'FRT Capability of a DFIG in Isolated Grids with Dynamic Voltage Restorer and Energy Storage', IEEE 5th International Symposium on Power Electronics for Distributed Generation Systems (PEDG), Galway, Ireland, June 2014.

TN J

[23] Silva. S.M.: 'Estudo e projeto de um restaurador dinâmico de tensão', MSc thesis, UFMG, Belo Horizonte, Brasil, 1999. [24] Silva, S.M., da Silveira, S.E., Reis, A.S., Cardoso Filho, B.J.: 'Analysis of a Dynamic Voltage Compensator with Reduced Switch-Count and Absence of Energy Storage System', IEEE Transactions on Industry Applications, October 2005, Vol. 41, No. 5, pp. 1255-1262 [25] Rodriguez, P., Pou, J., Bergas, J., et al.: 'Decoupled Double Synchronous Reference Frame PLL for Power Converters Control'. IEEE Transactions on Power Electronics, 2007, Vol. 22, No. 2, pp. 584-592

IS

VR u Rs Lσs Lm R’r L’σr Rr Lσr Ls Lr

σ-

Parameter Synchronous speed at 50Hz Rated Power Rated stator voltage – Line-toline nominal stator voltage in rms Each phase nominal stator current in rms Nominal Torque Moment of Inertia Stator connection Pair of poles Rated rotor voltage – Line-to-line nominal rotor voltage in rms Rotor connecion Ratio Stator Resistance Stator leakage inductance Magnetizing inductance Rotor Resistance Rotor leakage inductance Rotor Resistance referred to the stator Rotor leakage inductance referred to the stator Stator inductance: Ls= Lm + Lσs Rotor inductance: Lr= Lm + Lσr SVC stator flux controller gain

Value 1500 RPM 2MW 690V 1760A

12,7kNm 650kgm2 Star 2 2070V Star 0.34 2,6mΩ 87µH 2.5mH 26mΩ 783µH 2,9mH 87µH 2.587mH 2.587mH

2.π.50

[26] Abad, G., López, J., Rodríguez, M.A., Marroyo, L., Iwanski, G.: 'Doubly Fed Induction Machine - Modeling and Control for Wind Energy Generation' (IEEE Press, 2011) [27] Novotny, D.W., Lipo, T.A.: 'Vector Control and Dynamics of AC Drives' (Clarendon Press-Oxford, 1996) [28] Bollen, M.H.J.: 'Understanding power quality problems: Voltage sags and interruptions' (IEEE Press, 2000) [29] Akagi, H., Watanabe, E.H., Aredes.: M.: 'Instantaneous power theory and applications to power conditioning' (IEEE Press, 2007) [30] Khajehoddin, S.A., Ghartemani, M.K., Jain, P.K, Backshai, A.: 'DC-Bus Design and Control for a SinglePhase Grid-Connected Renewable Converter With a Small Energy Storage Component', IEEE Transactions on Power Electronics, July 2013, Vol. 28, No. 7, pp. 3245-3254

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