Research Article Application of Multipoint DC Voltage Control in VSC-MTDC System

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1 Hinawi Publishing Corporation Journal of Electrical an Computer Engineering Volume 213, Article ID , 7 pages Research Article Application of ultipoint DC Voltage Control in VSC-TDC System Yang Xi, Ai Qian, Huang Jiantao, an An Yiran Department of Electrical Engineering, Shanghai Jiaotong University, SEIEE 1-22, 8 Dongchuan RD, inhang District, Shanghai 224, China Corresponence shoul be aresse to Ai Qian; aiqian@sjtu.eu.cn Receive 4 arch 213; Revise 13 ay 213; Accepte 29 ay 213 Acaemic Eitor: Yong Fu Copyright 213 Yang Xi et al. This is an open access article istribute uner the Creative Commons Attribution License, which permits unrestricte use, istribution, an reprouction in any meium, provie the original work is properly cite. The voltage-source-converter- (VSC-) base multiterminal VSC-HVDC power transmission system (VSC-TDC) is an ieal approach to connect win farm with power gri. Analyzing the characteristics of oubly fe inuction generators as well as the basic principle an the control strategy of VSC-TDC, a multiterminal DC voltage control strategy suitable for win farm connecte with VSC-TDC is propose. By use of PSCAD/ETDC, the propose control strategy is simulate, an simulation results show that using the propose control strategy the conversion between constant power control moe an constant DC voltage control moe can be automatically implemente; thus the DC voltage stability control an reliable power output of win farm can be ensure after the fault-cause outage of converter station controlle by constant DC voltage an uner other faults. The simulation result shows that the moel can fulfill multiterminal power transmission an fast response control. 1. Introuction Win energy is one of the most wiely use renewable energy sources with its large potential capacity [1]. By the en of 212, more than installe win power units are built in China an the installe capacity reaches W [2]. But rising capacity also brings much negative influence on the gri stability an power quality[3]. With fast evelopment of power electronic technology an voltage source converter high voltage DC transmission technology (VSC- HVDC), HVDC system has been use in long istance transmission lines or cables [4]. VSCs provie continuous an inepenent control of real an reactive powers an have a better ynamic performance compare to current source converters [5]. The literature [6, 7]points out that win farm integration technology base on the VSC-HVDC cannot only solve the negative influence on gri safety an power qualitywhenwinfarmsconnecttogri,butalsoimprove the transmission capacity, which helps to make flexible win power flow controlcome true [8]. The literature [9] proposes that VSC-HVDC system enables fast control of active an reactive power inepenently. As mentione above, HVDC light technology is a goo way to transport biirectional power between win farms an gri [1]. In aition, the VSC-HVDC system can fee power into passive networks without local power generation [11]. When one terminal of the VSC-base HVDC system fails or exits, win farm connecte with single terminal will be out of operation. But the application of VSC-base multiterminal system (VSC-TDC) characterize by high requirements on reliability an quality is able to solve the problem. VSC- TDC has lots of potential avantages compare with classic HVDC, such as short circuit current reuction an rapi control of active an reactive power [12 14]. Control strategies are stuie after moeling [15, 16] an VSC-base TDC has attracte much attention [17, 18], especially for win farm integration. At present, the common use VSC-TDC control strategies are voltage rop characteristic metho [19] an master-slave metho [2, 21]. But now all these strategies are still in the stage of theoretical research or simulation experiment. The literature [22] eals with power flow calculation (PFC) of hybri AC/DC power systems where several asynchronous AC systems are interconnecte via a common multiterminal VSC-HVDC system an proposes

2 2 Journal of Electrical an Computer Engineering aunifieac-dcapproachforpfcofahybriac/dc power system. The literature [23] proposes a stochastic multiobjective optimization algorithm for simultaneous active an reactive power ispatch in electricity markets with win power volatility. The literature [24] proposes a new unifie metho for power flow calculation in AC gris with embee multiterminal HVDC systems base on voltage source converter. 2. The Characteristics of DFIG in Win Farm At present, in win farms, variable frequency technology is the evelopment irection, which can be ivie into irectly riven synchronous generator an oubly fe inuction generator system accoring to structure an operation. Variable electrical constant frequency win generator can realize the ecoupling between rotate spee an power frequency, which helps to reuce the interaction between win power an gri interaction. Especially ouble-fe inuction generator (DFIG) has become the main choice in the win farm evice, as it not only changes the operation of win power system, but also reuces the capacity of the frequency converter of win power generation equipment. Therefore, base on the output characteristics of the DFIG, this paper stuies its relationship with VSC-TDC system coorination control. DFIG changes the input rotor excitation current frequency through the frequency converter to change the magnetic fiel of the rotor rotating spee. So the rotating spee is able to be a constant. At present, the control of DFIG is often mae by constantoutputpower.insuchmoe,activepowerimbalance will lea to a voltage fluctuation, which may estroy the system stability. The mission of the VSC-TDC is to eliver power from the win farm instantaneously to ensure the bus voltage stability. So the aim of the converter control is to keep constant AC voltage an AC active power. The griconnecte win farm an VSC-TDC system structure are shown in Figure VSC-TDC System an Its Control Strategy Applie in Win Farm Inthefollowingpart,thecontrolstrategysuitableforwin farm connecte with VSC-TDC is propose Converter Station Controller Applicable to Win Farm. In Figure 1, the system can guarantee reliable win farm output, as well as the stability of power supply. Converter1 an converter3 are connecte with the power gri, converter2 with a win power fiel, an converter4 with a passive network to provie local loa. Compare with two-terminal VSC- HVDC system, this system is more reliable an substantial. As mentione previously, converter2 controller takes the set of active power an constant AC voltage control strategy, an converter4 connecte to the passive network (VSC4) takes constant AC voltage control strategy, an converters connecte to the network (VSC1 an VSC3) use multiple DC voltage control metho, that is, constant DC voltage control strategy an power control strategy base on DC bias control separately. This paper uses a converter control esign baseonthestrategyabove.theactiveanreactivepower regulation control system an DC voltage control system baseontheinversesystemcanbesimplifieasshownin Figures 2 an 3. Insie the virtual box of Figure 2 is the calculation process of inverse system. ref, ref,ane sref are active power, reactive power, an voltage reference values an,, E s are VSC output active power, reactive power, an VSC DC voltage measurement. Their ifferences are ajuste through proportional integral unit ();, D respectively for pulse with moulation epth an phase ifference; A, B as intermeiate variables. The main equation (1) is shown as follows. In this paper, converter loss is ignore. =E I P c, A= U2 s cos α, U s Y B= U 2 s Y sin α, U s Y arctan ( B ) α π, A A, B, = { arctan ( B ) α π, A A, B, { arctan ( B { A )α, = 2A U cos (δα). A>, 3.2. ultipoint DC Voltage Control. VSC1 uses a constant DC voltagecontrolstrategyshowninfigure 3, whichisresponsible for maintaining the balance of active power an DC voltage stability. DC voltage will rise or escen accoring to the irection of power flow. When the active power in VSC-TDC system is insufficient, VSC1 sens active power to DC network by the power gri this time. When VSC1 exits, the active power in the system is insufficient, an DC voltage ecreases; when the VSC-TDC system active power is superfluous, VSC1 sens active power back to the gri. At this moment, VSC1 exits, active power in the system becomes superfluous, an DC voltage rises. To improve the reliability of VSC-TDC system DC voltage control, except VSC1 which uses the DC voltage control, DC voltage bias control is introuce to VSC3, that is, multipoint DC voltage control strategy base on the irect voltage eviation control. The basic principle is as follows VSC3 is in the reactive rate inepenent control state when VSC1 is in the normal working state; while the VSC1 occurs a fault an exits, DC voltage nees to be etecte. When DC voltage excees the allowable range, DC voltage control will take the place of constant power control automatically, keeping active power in balance an maintaining the DC voltage constant. The control system is shown in Figure 4. (1)

3 Journal of Electrical an Computer Engineering 3 DIFG U s1 U c1 I c1 I c2 U c2 U s2 Power gri U s3 AC DC Converter1 U I c3 c3 DC AC Converter2 I c4 U c4 U s4 Win farm AC DC DC AC Power gri Converter3 Converter4 Z Figure 1: Configuration of VSC-TDC with win farm. Inverse system computer metho ref U s ref Formula 3 Formula 2 ΔB Limiting amplitue Limiting amplitue B A Formula 4 Formula 5 PW trigger pulse generating moule Trigger signal ΔA U Figure 2: Structure of PQ control system. U U cref U c I U c I P ref ref Inverse system metho Figure 3: System for constant DC voltage control.

4 4 Journal of Electrical an Computer Engineering E refh E refl E E ref State estimation E ref DC voltage control System 1 1 State estimation PW ref Inverse system compute metho 2 2 Figure 4: Block iagram of the DC voltage error metho base on multipoint DC voltage control. U s re f U s ref re f Inverse system metho PW Figure 5: System for constant active power an constant AC voltage control. The control system inclues two controllers to achieve DC voltage an constant power control, respectively (shown in Figures 2 an 3). When VSC1 exits, if VSC1 sens active power to the gri before the fault, the DC voltage will rise; otherwise, the DC voltage will ecrease. Once the DC voltage exceestheratedcvoltageofvsc3,dcvoltagereference value is fixe on the highest reference value (or the lowest reference value) an will not change. At the same time, the converter changes from fixe power control moe to constant DC voltage control moe Initialization of Active Power an AC Voltage Controller on Win Farm Sie. As previously mentione, in orer to keep the instantaneous power transmission from win power an maintain the bus voltage stability of win farm, VSC2 that is connecte to the win farm must use constant active power an AC voltage, using power inepenent control system (shown in Figure 2) to esign the active power an constant AC voltage controller (shown in Figure5). The reactive instruction input value is the sum of the ajuste volume of unit (AC voltage eviation measurements) an the measure reactive power. In Figure 5, U s is the actual measurement of AC bus voltage value; U sref is bus voltage value for reference Passive Network Constant AC Voltage Controller. When the VSC-TDC system supplies power to passive network, to obtain symmetrical sinusoial alternating current, constant AC voltage control must be use to obtain the symmetry of AC voltage. The AC voltage controller is shown in Figure Simulations an Analysis In orer to verify the reliability of the strategy an applicability of VSC-TDC in win farm, PSCAD/ETDC simulation software is use to buil the system moel as shown in Figure 1. In the system, we set the reference power at 1 VA, the reference voltage at 62.5 kv, an the switching frequency at 165 Hz. In the simulation results, U sn, E n,an n (n = 1, 2, 3, 4) are representative of each VSC connection bus AC voltage, VSC DC voltage, active power VSC into VSC- TDC system. There are some cases stuie as follows. Case 1. Simulation of win spee change an fan switch cause by active fluctuations from win farm. At 1 s, active power from VSC2 to VSC-TDC system rises from 5 W to 1 W, an results are shown in Figure 7 (U s4 is the voltage of passive network an U s2 isthewinfarmbus voltage). The results show that the controller can track

5 Journal of Electrical an Computer Engineering 5 re f U s re f U s re f Inverse system metho PW Figure 6: System for constant AC voltage control. U sn (pu) n (W) E n (kv) 2 ref (a) Active power of VSC2 1.2 U s4 U sref4 U.8 s2 U sref (b) AC bus voltage of VSC2 an VSC E 1 E 2 E 3 E (c) DC voltage of current converter Figure 7: Variation of active power in win farm. n (W) E n (kv) U sn (pu) (a) Active power of VSC1-VSC3 E 3 E 2 12 E 1 E U s4 (b) DC voltage of converter U sref4 U s2 U sref (c) AC bus voltage of VSC2 an VSC4 Figure 8: Permanent loss of VSC1 uner conition of absorbing active power from DC sie. thewinchangeswellanensurethestabilityofthesystem effectively. Case 2. Before the fault, 3 = 3 W, 4 = 1 W, VSC1transmitsactivepowertotheDCnetwork.At1s,VSC1 gets a fault an exits, an DC voltage increases; VSC3 is automatically converte to DC voltage moe from constant powermoe,anthedcvoltageiscontrollenear13kv. The results are shown in Figure 8. It can be seen that when VSC1 exits, a DC voltage is still able to remain constant an active power from the win farm an bus voltage are stable. Case 3. Before the fault, 3 = 2 W, 1 = 15 W, VSC1 elivers active power to the DC network. At 1 s, VSC1 faults an exits, an DC voltage ecreases; VSC3 is automatically converte to DC voltage moe from constant power moe, an the DC voltage is controlle near 11 KV. The results are shown in Figure 9. It can be seen from the figure that when VSC1 exits, DC voltage is still able to remain constant an active power from the win farm an bus voltage are stable. Case 4. One phase short circuit fault on win farm bus automatically eliminate 1 ms after the fault occurs. The result is shown in Figure 1 that uring the fault, VSC-TDC can guarantee the stability of the DC voltage. When the fault isappears, the system can be quickly returne to the state before the fault.

6 6 Journal of Electrical an Computer Engineering n (W) E n (kv) E 4 E 3 E 2 E (a) Active power of VSC1, VSC2, an VSC3 1.2 (b) DC voltage of current converter U sn (pu).8.4 U s4 U s2 U sref2 U sref (c) AC bus voltage of VSC2 an VSC4 Figure 9: Permanent loss of VSC1 uner conition of injecting active power into DC sie n (W) E n (kv) 12 E 3 E 1 E 4 E (a) Active power of VSC1, VSC2, an VSC3 (b) DC voltage of current converter Figure 1: A single line-to-groun fault on the AV bus of the win farm. 5. Conclusion ultipoint DC voltage controlle VSC-TDC system can switch the operation moe without communication an greatly improves the operation reliability an economy. So it will be wiely use in future transmission an istribution. The large isturbance between stations or communication network has little influence on the output of win farms. One such application is to supply systems characterize by high loaensityanhighrequirementsonreliabilityanquality together with high costs after prouction interruption. The next step in research will concentrate on the optimization of control strategy an coorination control between the converters. Acknowlegment This project is supporte by the National Natural Science Founation of China (517792) an 863 project (211AA5A18). References [1] A. Tapia, G. Tapia, J. X. Ostolaza, J. R. Saenz, R. Criao, an J. L. Berasategui, Reactive power control of a win farm mae up with ouble fe inuction generators. I, in Proceeings of the IEEE Porto Power Tech Conference, Porto, Portugal, September, 21. [2] Statistics of 212 China s installe win power capacity, China Renewable Energy Society,vol.3,pp.1 3,213. [3] J. Jing an A. Qian, Evaluation of construction an operation of win farms in China an their evelopment prospects, East China Electric Power,vol.35,no.8,pp.44 49,27(Chinese). [4] B. Anerson an C. Braker, A new era in HVDC, IEE Review, vol. 46, no. 2, pp , 2. [5] F. Yong, S. Yeleti, an S. Abelwahe, Optimal operation of multi-terminal VSC VDC power istribution system, in Proceeings of the International Conference on High Voltage Engineering an Application, pp. 17 2, Shanghai, China, September 212. [6] K.Sobrinkkh,P.L.Sorensen,P.Cristrensenetal., DCfeeer for connection of a win farm, in Proceeings of the CIGRE Symposium, KualaLumpur, alaysia, [7] K. Sobrink an P. L. Sorensen, Feasibility stuy regaring integration of the 16W win farm using VSC transmission, in Proceeings of the CIGRE Symposium,21. [8] W. Xiaoguang an T. Guangfu, Effect of VSC-HVDC applie on improving winfarm voltage stability, Power System Technology, vol. 31, no. 8, pp , 27 (Chinese).

7 Journal of Electrical an Computer Engineering 7 [9] L. Weimers, New markets nee new technology, in Proceeings of the International Conference on Power System Technology (POWERCON ),vol.2,pp ,Perth,Australia,2. [1] H.-F. Liang, G.-Y. Li, G.-K. Li, K. Zhang, an. Zhou, Simulation stuy of VSC-HVDC system connecte to passive network, Power System Technology, vol. 29, no. 8, pp. 45 5, 25 (Chinese). [11] P.. eshram, A. N. Kau, R. N. Nagpure, an K. L. Thakre, VSC-HVDC for improvement of quality of power supply, in Proceeings of the IEEE Region 1 Conference: Analog an Digital Techniques in Electrical Engineering (TENCON 4), pp , Nagpur, Inia, November 24. [12] T. Weizhong an R. H. Lasseter, An LVDC inustrial power istribution system without central control unit, in Proceeing of 31th IEEE Annual Power Electronics Specialists Conference, vol.2,pp ,Piscataway,NJ,USA,2. [13] Z. Chao, Z. Xiaoxin, L. Ruomei et al., Stuy on the steay characteristic an algorithm of power flow for VSC-HVDC, in Proceeings of the Chinese Society for Electrical Engineering (CSEE 5),vol.25,no.6,pp.1 5,25. [14]. Yin, G.-Y. Li, T.-Y. Niu, G.-K. Li, H.-F. Liang, an. Zhou, Continuous-time state-space moel of VSC-HVDC an its control strategy, in Proceeings of the Chinese Society of Electrical Engineering (CSEE 5),vol.25,no.18,pp [15] S. Cole, J. Beerten, an R. Belmans, Generalize ynamic VSC TDC moel for power system stability stuies, IEEE Transactions on Power Systems,vol.25,no.3,pp , 21. [16] C. Zheng, X. Zhou, an R. Li, Dynamic moeling an transient simulation for VSC base HVDC in multi-machine system, in Proceeings of the International Conference on Power System Technology (POWERCON 6), Chongqing, China, October 26. [17] D. Van Hertem an. Ghanhari, ulti-terminal VSC HVDC for the European supergri: obstacles, Renewable & Sustainable Energy Reviews,vol.14,no.9,pp ,21. [18] J. Zhu an C. Booth, Future multi-terminal HVDC transmission systems using voltage source converters, in Proceeings of the 45th International Universities Power Engineering Conference (UPEC 1),pp.1 6,Cariff,UK,September21. [19] L. Weixin, ControlanApplicationofulti-TernimalHVDC Base on Voltage-Source Converter, cgill University, ontreal, Canaa, 23. [2] H. Jiang an Å. Ekström, ultiterminal HVDC systems in urban areas of large cities, IEEE Transactions on Power Delivery, vol. 13, no. 4, pp , [21] K. Sakamoto,. Yajima, T. Ishikawa, S. Sugimoto, T. Sato, an H. Abe, Development of a control system for a highperformance self-commutate AC/DC converter, IEEE Transactions on Power Delivery,vol.13,no.1,pp ,1998. [22]. Baraar,. Ghanhari, D. Van Hertem, an A. Kargarian, Power flow calculation of hybri AC/DC power systems, in Proceeings of the IEEE Power an Energy Society General eeting, San Diego, Calif, USA, July212. [23] A. Kargarian an. Raoofat, Stochastic reactive power market with volatility of win power consiering voltage security, Energy, vol. 36, no. 5, pp , 211. [24]. Baraar,. Ghanhari, an D. Van Hertem, VSC-HVDC in power flow calculation using unifie methoology, in Proceeings of the IEEE PES Innovative Smart Gri Technologies Europe, pp. 5 7, December211.

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