06596516

2162 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 28, NO. 4, OCTOBER 2013

Comparative Stability Analysis of Offshore Wind andMarine-Current Farms Feeding Into a Power Grid

Using HVDC Links and HVAC LineLi Wang, Senior Member, IEEE, and Mi Sa Nguyen Thi

Abstract—This paper presents the comparative stabilityanalyzed results of integration of a doubly fed induction gen-erator-based offshore wind farm (OWF), a PMSG-based OWF,and a squirrel-cage induction generator-based marine-currentfarm (MCF) feeding into a power grid through a high-voltagealternating-current line and two high-voltage direct-current(HVDC) links. One of the HVDC links is based on a voltage-sourceconverter (VSC) while the other is a multiterminal configurationthat uses three VSCs at the converter station and a VSC at theinverter station. A power oscillation damping (POD) controllerfor the MT-HVDC system is designed, and the design steps includethe selection for the POD controller based on the total effectson the remaining system. A frequency-domain approach basedon a linearized system model using calculated eigenvalues and atime-domain scheme based on a nonlinear system model subjectto disturbances are systematically performed to compare thedamping characteristics contributed by the three transmissionschemes. It can be concluded from the simulation results that theproposed MT-HVDC link is capable of rendering better dampingcharacteristics to stabilize the integrated OWFs and MCF feedinginto a power grid under a severe fault than the HVAC line and theVSC-HVDC link.

Index Terms—Eigenvalues, high-voltage direct-current (HVDC)link, marine-current farm (MCF), nonlinear model simulations,offshore wind farm, voltage-source converter (VSC).

NOMENCLATURE

General and Abbreviation

Offshore wind farm.

Marine-current farm.

High-voltage direct current.

High-voltage alternating current.

Wind turbine.

Manuscript received July 11, 2012; revised December 16, 2012; acceptedJuly 20, 2013. Date of publication September 12, 2013; date of current ver-sion September 19, 2013.This work was supported by the National Science ofCouncil (NSC) of Taiwan under Grant NSC 102-3113-P-006-009. Paper no.TPWRD-00736-2012.L. Wang is with the Department of Electrical Engineering and the Research

Center for Energy Technology and Strategy, National Cheng Kung University,Tainan City 70101, Taiwan (e-mail: [email protected]).M. S. Nguyen Thi is with the Department of Electrical Engineering, National

ChengKungUniversity, Tainan City 70101, Taiwan (e-mail: [email protected]).Color versions of one or more of the figures in this paper are available online

at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/TPWRD.2013.2278039

Marine current turbine.

Multiterminal.

Doubly-fed induction generator.

Permanent-magnet synchronous generator.

Squirrel-cage induction generator.

Gear box.

Voltage-source converter.

Line-commutated converter.

Power oscillation damping.

Rotor-side converter.

Grid-side converter.

Per unit.

Differential operator with respect to.

Per-unit quantities of ac, dc voltage.

Per-unit quantities of ac, dc current.

Per-unit quantities of resistance, reactance.

Per-unit quantities of rotor speed.

Modulation index and phase angle of VSC.

Eigenvalue, wind speed, marine-currentspeed.

Gains of PI controller.

Washout-term time constant of PIcontroller.

Subscripts

- and -axis quantities

Stator and rotor winding quantities ofgenerators.

Quantities of OWF.

Quantities of MCF.

Quantities of reference.

Quantities of maximum and minimum.

0885-8977 © 2013 IEEE

WANG AND NGUYEN THI: COMPARATIVE STABILITY ANALYSIS OF OFFSHORE WIND AND MARINE-CURRENT FARMS 2163

I. INTRODUCTION

T HE RENEWABLE energy topic is one of the hottestissues in the entire world today due to the fast and huge

consumption of fossil fuels in recent years. Renewable energycan be derived from different sources, such as solar, wind,ocean waves, water flow and tides, geothermal heat, biologicalsources, and so on [1]. Among these sources, wind power isnow a very mature and commercialized renewable resourcethroughout the world. The use of wind power is increasing atan annual rate of 20%, with a worldwide installed capacity of238 000 MW at the end of 2011 [2]. However, other renewablepower sources, such as marine current, also have significant po-tential. Marine current is a largely untapped renewable energyresource, with the advantage of having high energy densityamong various renewable energies [3]. The development of themarine-current energy technology grew rapidly, particularlyin oceanic countries, such as Ireland, Denmark, Portugal, theU.K., and the U.S. [4]–[6].Since oceans cover more than 70% of the earth’s surface

and the wind energy above the sea surface can be used togenerate large electric power, an offshore wind farm (OWF)and a marine-current farm (MCF) can be extensively developedin the entire world in the near future. The reason for havingthese two different forms of generation close to each other isdriven by geographical conditions: infrastructure and planningpermission. Currently, ocean energy and wind energy havebeen combined together in many countries, especially in theU.K. [7]–[11]. However, integration of large-capacity windand ocean energy into a power grid is confronted with severalchallenges, including reduction or elimination of power fluctu-ations, securing power quality (PQ), connection of large OWFsand MCFs to weak grids, prediction of wind/wave-power vari-ations, changes in operating strategies of conventional powerplants, and so on. To conquer the mentioned obstacles of inte-grating large-capacity wind power and oceanic power feedinginto a power grid, a high-voltage direct-current (HVDC) linkcan be used to integrate various forms of high-capacity renew-able energy resources, such as OWFs and MCFs due to theirhigh-power and fast-modulation control capability. HVDCtransmission systems are also one of the solutions to increasethe distance between offshore power generations and onshoredistribution grids. HVDC technologies are mature and in op-eration in existing interconnected systems [12]. Most of themare for point-to-point transmissions [13]–[18]. However, whenhigh-capacity OWFs and MCFs are connected to a commonac bus, the point-to-point HVDC transmission scheme hasdifficulty controlling each farm that is independently operated.To form a supergrid and to achieve independent control func-

tions, HVDC systems with multiple points of connection, whichare referred to as multiterminal (MT)-HVDC systems, are re-quired. Linking more than two HVDC terminals to form anMT-HVDC system can have several advantages. The first par-allel MT-HVDC system based on a line-commutated converter(LCC) was proposed in [19] while a series MT-HVDC systemwas discussed in [20] and [21]. The voltage-source converter(VSC)-based HVDC systems are more suitable to the MT con-figuration than the LCC-based HVDC systems. The reasons of

using the VSC-HVDC systems include independent control ofreactive power and active power, black-start capability, no com-mutation failure, and no voltage polarity reversal needed to re-verse power [22], [23]. The VSC-based MT-HVDC systems forconnecting wind farms were reported in [24] and [25]. An OWFwith 100 WTGs connected to a large power grid through anMT-HVDC link using 25 VSCs was proposed in [26]. The con-trol of VSC-based MT-HVDC transmission for offshore windpower was examined in [27]. A detailed analysis of differentMT-HVDC topologies was discussed in [28]. The steady-statemodels of converters used in VSC-based MT-HVDC systemswere investigated for power-flow analysis [29].With these significantly large-scale integration systems,

the strategies for power fluctuation mitigation and dampingimprovement have vital importance. Among these aspects, thePID or PI damping controller using the pole-placement tech-nique is the first choice. However, one of the most importantstages in designing the power oscillation damping (POD) con-troller is the selection of input/output (I/O) signals. The PODcontroller’s output of an MT-HVDC system can be properlyadded to the reference signal of the VSC station. The feedbacksignal can be the deviation of rotor speed or active power ofthe generator closest to the corresponding converter which isessentially most effective to damp out the critical oscillationmodes.In this paper, three POD controllers of three corresponding

VSCs of the MT-HVDC system for connecting two OWFsand one MCF are designed using the pole-placement scheme,respectively. The objective is to choose an effective controlscheme to damp out the critical modes of the studied systemwithout having negative impacts on the other modes of thestudied system. The results of the proposed MT-HVDC systemare also compared with the ones of a conventional VSC-basedHVDC link and an HVAC scheme on a technical basis.

II. CONFIGURATION OF THE STUDIED SYSTEM

Fig. 1 shows the configuration of the studied system. Adoubly fed induction generator (DFIG)-based OWF (OWF #1),a permanent-magnet synchronous generator (PMSG)-basedOWF (OWF #2), and a squirrel-cage induction generator(SCIG)-based MCF are feeding into a power grid throughthree transmission systems, that is, a four-terminal VSC-basedHVDC system (the green block), an VSC-HVDC link (theyellow block), and an HVAC line (the blue block). The fourconnection points , shown in Fig. 1, are used to properlyconnect the two OWFs and the MCF to the power grid. Thecharacteristics of the 80-MW OWF #1 are represented by anequivalent aggregated wind DFIG driven by an equivalentaggregated variable-speed WT through an equivalent-aggre-gated gearbox (GB) while an equivalent aggregated windPMSG driven by an equivalent aggregated variable-speed WTis used to simulate the performance of the 60-MW OWF #2.The 40-MW MCF is simulated by an equivalent aggregatedSCIG driven by an equivalent aggregated variable-speed MCTthrough an equivalent aggregated GB. The output terminals ofthe two OWFs and the MCF are connected to associated localloads through a 0.69/24-kV stepup transformer and an underseacable.


Fig. 1. Configuration of the studied OWFs and MCF fed to a power grid through an MT-HVDC link (top), an VSC-HVDC link (bottom left), and an HVAC line(bottom right).

In the MT-HVDC configuration, the two OWFs and the MCFare connected to the dc line through individual offshore stepuptransformers of 0.69/24 kV, individual undersea cables, indi-vidual offshore step-up transformers of 24/150 kV, and con-verters , respectively. The output terminals of thesethree converters are connected to the same dc line through in-dividual capacitors and dc lines. The ac terminals of converter

are fed to ac bus through a step-down transformer of150/230 kV and an underground cable. The ac bus is alsoconnected to a power grid (an infinite bus) through a connec-tion line.In the VSC-HVDC link or the HVAC line, the 24-kV common

ac bus is fed to the 230-kV ac bus (bus ) through an offshorestep-up transformer of 24/150 kV, an undersea cable, the VSC-HVDC link or the HVAC line of 150-kV, an onshore step-uptransformer of 150/230 kV, and an underground cable. The pro-posed VSC-HVDC link consists of an ac-to-dc VSC, a -equiv-alent dc cable, and a dc-to-ac VSC. The mathematical modelsof the subsystems shown in Fig. 1 are explained as follows. Thefollowing equations are expressed in per unit (p.u.) except thatthe time variable and base angular frequency are in secondsand radians per second, respectively.

A. Wind and MCT Model

The captured mechanical power by a WT/MCT from wind/marine current is given by

(1)

where is the air/seawater density , isthe blade impact area , is the wind/marine-currentspeed (in meters per second), and is the dimensionlesspower coefficient of the WT/MCT. The cut-in, rated, and cutoutspeeds of the studied WT/MCT are 4/1, 15/2.5, and 24/4 m/s,respectively. When wind/marine-current speed is higher thanthe rated speed, the corresponding pitch-angle control system isactivated to limit the output power of the WT/MCT at the ratedvalue.

B. Mass-Spring-Damper Model

The two-inertia reduced-order equivalent mass-spring-damper model used for simulating the performance of the WTdirectly coupled to the rotor shaft of the wind PMSG of OWF#2 and the WT coupled to the rotor shaft of the wind DFIGthrough a GB of OWF #1 can be referred to in [30]–[32].This mass-spring-damper model can also be applied to the oneof the MCTs coupled to the rotor shaft of the marine-currentSCIG through a GB whose effect can be properly includedin this model. Since the employed turbine model, pitch-anglecontrol system, and mass-spring-damper model of the studiedMCF are similar to the ones employed in the two OWFs, somemathematical models employed in the OWF can be used forthe MCF by slight modification except the parameters.

C. DFIG Model, PMSG Model, SCIG Model, and Operationof Associated Power Converters

The stator windings of the wind DFIG in Fig. 1 are directlyconnected to the low-voltage side of the 0.69/24-kV step-up


transformer while the rotor windings are connected to the same0.69-kV side through a rotor-side converter (RSC), a dc link,a grid-side converter (GSC), and a connection line. The fun-damental axis equivalent-circuit model and the corre-sponding equations based on a synchronously rotating referenceframe can be referred to [33]. For normal operation of a windDFIG, the input voltages of the RSC and the GSC can be ef-fectively controlled to achieve the aims of simultaneous outputactive-power and reactive-power control [34], [35]. The corre-sponding per-unit axis voltage–current equations of thewind PMSG shown in Fig. 1 can be referred to in [36]. The fun-damental control block diagrams of the VSC-based converterand the VSC-based inverter of each wind PMSG can be referredto in [37]. The per-unit axis voltage–current equations ofthe marine SCIG shown in Fig. 1 can be referred to in [38].

D. MT-HVDC Link Model and Its Control Design

The MT-HVDC link model shown in Fig. 1 consists ofthree ac-to-dc VSCs (converters ), four dc lines,and one dc-to-ac voltage-source inverter (converter ). Thebase values for the ac and dc quantities of the MT-HVDC linkshould be properly selected so that the per-unit values of dcquantities remain unchanged when they are converted to thesynchronous reference frame of the ac system [39].The per-unit differential equations of the dc voltages of each

VSC of the proposed MT-HVDC system shown in Fig. 1 can beexpressed by

(2)

(3)

where subscript 1, 2, and 3 represents the order of the threedc cables; , , and correspond to converters

, respectively; is the differential operator with respect totime ; is the base angular frequency; and arethe phase angle and modulation index of the VSC, respectively;

is the phase angle of the ac bus; subscripts and arethe - and -axis quantities of the ac systems, respectively; andsubscript denotes the quantities of the converter station.The relationship between the currents at the sending end and

the DC link shown in Fig. 1 can be given as

(4)

The per-unit differential equations from the output terminalsof converter to the ac grid are given by

(5)

(6)

Fig. 2. Control block diagram of the VSCs connected to OWFs/MCF.

Fig. 3. Control block diagram of the VSC connecting to the ac grid.

where is the per-unit electrical angular frequency. The con-trol block diagrams of the MT-HVDC link are shown in Figs. 2and 3. The corresponding differential equations for controllingthe modulation indices and phase-angle convertersand converter of the MT-HVDC link are described by

(7)

(8)

(9)

(10)

where represents the quantities of deviation; subscript ref de-notes the quantities of reference; and are the gains ofthe modulation index control block and the phase-angle con-trol block of the converter, respectively; and and are thetime constants of the modulation index control block and thephase-angle control block of the converter, respectively. Theemployed system parameters of the studied system are listed inthe Appendix for conciseness.

III. DESIGN OF A POD CONTROLLER FOR THE VSC-BASEDMT-HVDC LINK USING MODAL CONTROL THEORY

This section presents a unified approach based on modalcontrol theory to design POD controllers for VSCs of theMT-HVDC link. The design procedures are applied to thethree VSCs connected to OWF/MCF. The feedback signals aredeviations of the active power at the bus connected to OWF #1,OWF #2, or MCF. The POD controller’s output can be addedto the reference signal of the VSC station. The design stepsinclude the selection for the best POD controller for VSC ofthe MT-HVDC system through examining the total effects onthe remaining system. The design steps can be referred to theones listed in [27]–[30].A simple proportional-integral (PI) controller is employed for

the POD controller of the VSC of the MT-HVDC link. The con-


Fig. 4. POD configuration for the VSC connecting the OWF and MCF side.

TABLE IEIGENVALUES (RAD/S) [DAMPING RATIOS] OF THE

DOMINANT MODES UNDER THREE CASES

trol block diagram of the proposed PI damping controller as aPOD controller is shown in Fig. 4. The PI controller consists of awashout termwith a time constant of and a PI function blockwith gains and . The input signal of this controller is thepower deviation of the connected bus at OWF #1, OWF #2, orMCF ( , or ). The output signal is the dampingsignal (or auxiliary signal) to control in order to im-prove the damping of the dominant mode of the DFIG-basedOWF, PMSG-based OWF, and SCIG-basedMCF. The mechan-ical mode of each generator is properly chosen since this modehas the poorest damping compared with that of the other modes.The pole-assignment scheme is employed for the design of

the PI controller. The eigenvalues and damping ratios of thedominant modes in three cases of the studied systemwithout andwith the designed PI controller are listed in the fourth and fifthcolumns of Table I, respectively. It can be clearly observed fromTable I that these dominant modes have been exactly positionedon the desired locations of the complex plane and their dampingratios have been improved by the addition of the designed PIcontrollers.Fig. 5 shows the root-loci plots of the mechanical modes of

DFIG-based OWF, PMSG-based OWF, and SCIG-based MCFof the studied system with and without the designed POD con-troller at the corresponding VSC station when wind/marine-cur-rent speeds increase from cut-in to cut-out values. The changesof wind/marine-current speeds are the random combinations be-tween three quantities: wind speeds at OWF #1, OWF #2, andmarine current speed at MCF.The root-loci results shown in Fig. 5(a) show that both me-

chanical modes move leftward and the corresponding dampingalso increases when converter has the designed POD con-troller. When the designed POD controller is applied to con-verters or as shown in Figs. 5(b) and (c), only the me-chanical mode of PMSG-based OWF #2 or SCIG-based MCFmoves leftward while the remaining onesmove to the right-handside of the complex plane. Thus, the designed POD controller atconverter using the power deviation at bus as the

Fig. 5. Root loci of mechanical modes under different wind/marine-currentspeeds.

input signal can be considered as the most suitable POD con-troller for the studied system to effectively improve system dy-namic stability.

IV. EIGENVALUE ANALYSIS

Table II lists the comparative eigenvalues with their cor-responding damping ratios of the studied DFIG-based OWF,PMSG-based OWF, and SCIG-basedMCF feeding into a powergrid through the MT-HVDC link, the VSC-HVDC link, and theHVAC line under wind speeds of 12 m/s for the two OWFs andthe marine-current speed of 2.5 m/s for the MCF. The designedPOD controller in the previous section is also applied to theVSCs of the proposed MT-HVDC link. The cable length of thethree transmission technologies is properly selected to be thesame.When comparing the eigenvalues listed in Table II, it is found

that the MT-HVDC link, the VSC-HVDC link, or the HVACline have little effect on the eigenvalues of the PMSG-basedOWF or the local load but they have small effects and signif-icant effects on the eigenvalues or stability of the DFIG-basedOWF and the SCIG-based MCF, respectively. It is due to thefact that the stator windings of the equivalent wind DFIG andmarine-current SCIG are directly connected to the common actransmission line through a 0.69/24-kV step-up transformer but


TABLE IISYSTEM EIGENVALUES (RAD/S) [DAMPING RATIOS] OF THE STUDIED SYSTEM WITH THREE DIFFERENT TRANSMISSION SYSTEMS.

the wind PMSG is connected to the common ac bus through a0.69/24-kV step-up transformer and a full back-to-back powerconverter that has the ability to decouple the effect of the PMSGand the ac system.It is also noted that the complex-conjugated modes of the

MT-HVDC and VSC-HVDC systems are both far from theimaginary axis of the complex plane and, hence, they are quitestable and have no negative effects on the dynamic stability ofthe studied system compared with the ones of the HVAC line.For the theme of the studied problem, which can render better

stability of using the MT-HVDC system over the VSC-basedsystem, it is not brought out quantitatively here since the statevariables as well as the dominant modes (mechanical mode ofthe OWF/MCF) are quite different. It can only be concluded thatthe MT-HVDC system is clearly better than the VSC-HVDCsystem when considering the effects of different wind/marine-current speeds on the power of the transmission lines in the nextsection.It can be also easily observed from Table II that the

MT-HVDC link, the VSC-HVDC link, or the HVAC line havecertain effects on the local load. It is due to the facts that theterminal bus is feeding the local load whose power consump-tion is represented by an exponential function of bus voltage[40]. These buses are directly connected to the VSC stationin the proposed MT-HVDC link or to the common bus of aconventional VSC-HVDC and an HVAC system.

V. TIME-DOMAIN SIMULATIONS

This section employs the nonlinear model developed inSection II to compare the transient responses of the threetransmission technologies under different disturbances usingMatlab/Simulink. The red lines, green dashed lines, and bluedashed lines shown in this section represent the results of thestudied system with the MT-HVDC link, the VSC-HVDC link,and the HVAC line, respectively. Two studied cases are con-sidered. Case 1 is a three-phase short circuit suddenly appliedto the infinite bus at 1 s and lasting for 0.1 s under theselected base wind speed of 12 m/s and marine-current speedof 2.5 m/s. Case 2 is different wind-speed and marine-currentdisturbances applied to WTs and MCTs. The wind speed andmarine-current speed are modeled as the algebraic sum of basespeed, gust speed, ramp speed, and noise speed [41].

A. Three-Phase Short-Circuit Fault

Fig. 6 shows transient responses of the studied system underCase 1. Figs. 6(a)–(f) show the transient responses of the ac-tive power and the terminal voltage of OWF #1, OWF #2, andMCF, respectively. It is seen that these responses have sharppeaks at 1 s when the system is with the HVAC line. How-ever, the proposed MT-HVDC link and the VSC-HVDC linkcan effectively suppress the sharp peaks after the applied faultis cleared while the quantities of OWF #1, OWF #2, and MCFcan quickly return back to the steady-state values. Besides, the


Fig. 6. Transient responses of the studied system subject to a three-phase short-circuit fault at the power grid.

terminal voltage of OWF #1, OWF #2, and MCF of the studiedsystem with the proposed MT-HVDC link declines less when

compared with the ones of the system with the VSC-HVDC linkand the HVAC line.It can be observed from the transient responses that the pro-

posed MT-HVDC link can offer better damping characteris-tics to the quantities of OWF #1, OWF #2, and MCF than theVSC-HVDC link and the HVAC line. The transient responseof the local-load current shown in Fig. 6(g) demonstrates thatthe MT-HVDC link can have smaller variations compared withthe one of the VSC-HVDC link and the HVAC line. It is dueto the fact that the terminal bus is feeding a local load with itspower consumption represented as an exponential function ofbus voltage as mentioned in the previous section. It can be con-cluded from the transient simulation responses shown in Fig. 6that the studied system with the proposed MT-HVDC link hasthe ability to suppress large variations on the quantities of thesystem when a severe fault is suddenly applied to the powergrid.

B. Different Wind Speeds and Marine-Current Speeds Appliedto OWFs and MCF

In this subsection, the wind speed of the two OWFs and ma-rine-current speed of the MCF change differently. The selectedwind speed and marine-current speed are modeled as the alge-braic sum of base speed (12 m/s for DFIG, 13 m/s for PMSG,and 2.5 m/s for SCIG), gust speed, ramp speed, and noise speed[41]. Fig. 7(a) shows the time-domain responses of the studiedwind speed and marine-current speed that are applied to the tur-bine blades of the twoOWFs andMCF. The remaining ones plotthe comparative dynamic responses of the studied system withthe proposed MT-HVDC link, the VSC-HVDC link, and theHVAC line subject to the applied wind speed and marine-cur-rent speeds shown in Fig. 7(a). Figs. 7(b)–(j) show the transientresponses of the active power, the terminal voltage of OWFsand MCF, the voltage at bus , and active and reactive powerat the infinite bus, respectively. It can be seen that the wind andmarine-current speed in one OWF/MCF will not affect the re-sponses of the other OWF/MCF in the MT-HVDC link whencompared with the ones using the VSC-HVDC link and theHVAC line shown in Fig. 7(b)–(g). In Fig. 7(h) and (j), the acgrid quantities, such as the voltage at bus and the active andreactive power at infinite bus are not also affected when theMT-HVDC and the VSC-HVDC link are employed. In otherwords, the proposed MT-HVDC link can offer better perfor-mance to effectively mitigate the variations of the OWFs/MCFunder different wind and marine-current speeds. The interac-tions between the OWFs and the MCF can be effectively re-duced.

VI. CONCLUSION

This paper has presented the comparative stability analyzedresults of large hybrid DFIG-based OWF, PMSG-based OWF,and SCIG-based MCF feeding into a power grid through anMT-HVDC link, an VSC-HVDC link, and an HVAC line. Theeigenvalue technique has been employed to show the compar-ative damping characteristics contributed by three transmissiontechniques. The comprehensive design of the power oscillation


Fig. 7. Comparative transient responses of the studied systems subject to dif-ferent wind/marine-current speeds.

damping (POD) controller for this MT-HVDC system is pro-posed. The effectiveness of the proposed POD controller hasbeen evaluated by a systematic approach using the eigenvalue

technique and root-loci plot. Transient responses of the studiedsystems subject to a severe three-phase short-circuit fault at thepower grid have demonstrated that the proposed MT-HVDCsystem can effectively suppress large variations on the quan-tities of the studied system. The effect of different speeds ap-plied to two OWFs and the MCF has shown that the proposedMT-HVDC link has little affect on the OWFs and the MCF thanthe VSC-HVDC link and the HVAC line.

APPENDIX

SYSTEM PARAMETERS:System Bases: 24/150/230 kV, 80

MVA

Single WT-DFIG of the 80-MW OWF With Control Sys-tems: 2 MW, 690 V, 0.00706 p.u., 0.171p.u., 0.005 p.u., 0.156 p.u., 2.9 p.u., 3.5s, , , , ,

, , , ,, , , , ,

, , , , ,.

Single WT-PMSG of the 60-MW OWF With Control Sys-tems: , , ,

, , , ,, , ,

, , , ,, , , ,, , , ,, , , .

Single MCT-IG of the 40-MW MCF With Pitch ControlSystem: , , ,

, ,, , ,

, , ,, , , ,.

MT-HVDC Link With Control System:, ,

, , ,, , , ,, , , ,, , , ,, , , ,, , ,, , ,

, .Transmission Lines and Local Load:

, ,, , ,, , ,, .

Step-up Transformers:

.


Constants of Power Coefficients of DFIG WT:, ,

.Constants of Power Coefficients of PMSGWT: ,

, , , , ,, , .

Constants of Power Coefficients of SCIGMCT: ,, , , , , ,, .

REFERENCES[1] U. Bossel, “On the way to a sustainable energy future,” in Proc. 27th

Int. Telecommun. Conf., Sep. 2005, pp. 659–668.[2] REN21 Steering Committee, Renewables 2011 Global Status Rep.

Paris, France, REN21, 2011.[3] A. Clément et al., “Wave energy in europe: current status and perspec-

tives,” Renew. Sustain. Energy Rev, vol. 6, no. 5, pp. 405–431, Oct.2002.

[4] Ocean Power Technologies, Completed Projects. May 2011. [Online].Available: http://www.oceanpowertechnologies.com/

[5] Wavebob, Wavepower. May 2011. [Online]. Available: http://www.wavebob.com/home/

[6] Wavestar, General Consideration–Minimizing Scaling Risks. 2011.[Online]. Available: http://wavestarenergy.com/

[7] S. E. B. Elghali, R. Balme, K. L. Saux, M. E. H. Benbouzid, J. F. Char-pentier, and F. Hauville, “A simulation model for the evaluation of theelectrical power potential harnessed by a marine current turbine,” IEEEJ. Ocean. Eng, vol. 32, no. 4, pp. 786–797, Oct. 2007.

[8] W. M. J. Batten, A. S. Bahaj, A. F. Molland, and J. R. Chaplin, “Hy-drodynamics of marine current turbines,” Renew. Energy, vol. 31, no.2, pp. 249–256, Feb. 2006.

[9] E. D. Stoutenburg, N. Jenkins, andM. Z. Jacobson, “Power output vari-ations of co-located offshore wind turbines and wave energy convertersin california,” Renew. Energy, vol. 35, no. 12, pp. 2781–2791, Dec.2010.

[10] L. Wang and C. -T. Hsiung, “Dynamic stability improvement of anintegrated grid-connected offshore wind farm and marine-current farmusing a statcom,” IEEE Trans. Power Syst., vol. 26, no. 2, pp. 690–698,May 2011.

[11] D. A. Halamay, T. K. A. Brekken, A. Simmons, and S. McArthur, “Re-serve requirement impacts of large-scale integration of wind, solar, andocean wave power generation,” IEEE Trans. Sustain. Energy, vol. 2,no. 3, pp. 321–328, Jul. 2011.

[12] I. M. d. Alegria, J. L. Martin, I. Kortabarria, J. Andreu, and P. I. Ereno,“Transmission alternatives for offshore electrical power,” Renew. Sus-tain. Energy Rev., vol. 13, no. 5, pp. 1027–1038, Jun. 2009.

[13] P. Bresesti, W. L. Kling, R. L. Hendriks, and R. Vailati, “HVDCconnection of offshore wind farms to the transmission system,” IEEETrans. Energy Convers., vol. 22, no. 1, pp. 37–43, Mar. 2007.

[14] C. Du, E. Agneholm, and G. Olsson, “Use of VSC-HVDC for industrialsystems having onsite generation with frequency control,” IEEE Trans.Power Del., vol. 23, no. 4, pp. 2233–2240, Oct. 2008.

[15] C. Du, E. Agneholm, and G. Olsson, “Comparison of different fre-quency controllers for a VSC-HVDC supplied system,” IEEE Trans.Power Del., vol. 23, no. 4, pp. 2224–2232, Oct. 2008.

[16] A. Jaén, E. Acha, and A. G. Expósito, “Voltage source converter mod-eling for power system state estimation: Statcom and VSC-HVDC,”IEEE Trans. Power Syst., vol. 23, no. 4, pp. 1552–1559, Nov. 2008.

[17] M. Yin, G. Li, M. Zhou, and Y. Liu, “Analysis and control of wind farmincorporated VSC-HVDC in unbalanced conditions,” in Proc. IEEE/Power Eng. Soc. Transm. Distrib. Conf, Aug. 2005, pp. 1–6.

[18] A. R. Watson, “Comparison of VSC based HVDC and HVAC inter-connections to a large offshore wind farm,” in Proc. IEEE Power Eng.Soc. Gen. Meeting, Jun. 2005, vol. 1, pp. 1–8.

[19] E. Uhlmann and P. Danfors, “Some aspects of tapping of H.V.D.C.transmission systems,”Direct Current, vol. 8, pp. 124–129, May 1963.

[20] J. Reeve and J. Arrillaga, “Series connection of converter stations in anHVDC transmission system,”Direct Current, vol. 10, no. 2, pp. 72–78,1965.

[21] D. Jovcic, “Offshore wind farm with a series multi-terminal CSIHVDC,” Elect. Power Syst. Res., pp. 747–755, Apr. 2008.

[22] V. F. Lescale, A. Kumar, L.-E. Juhlin, H. Bjorklund, and K. Nyberg,“Challenges with multi-terminal UHVDC transmissions,” in Proc.IEEE Power India Conf. Powercon, New Delhi, India, Oct. 2008, pp.1–7.

[23] J. Liang, T. Jing, O. Gomis-Bellmunt, J. Ekanayake, and N. Jenkins,“Operation and control of multiterminal HVDC transmission foroffshore wind farms,” IEEE Trans. Power Del., vol. 26, no. 4, pp.2596–2604, Oct. 2011.

[24] W. Lu and B. T. Ooi, “Premium quality power park based on multi-terminal HVDC,” IEEE Trans. Power Del., vol. 20, no. 2, pt. 1, pp.978–983, Apr. 2005.

[25] W. Lu and B. T. Ooi, “Optimal acquisition and aggregation of offshorewind power by multiterminal voltage-source HVDC,” IEEE Trans.Power Del., vol. 18, no. 1, pp. 201–206, Jan. 2003.

[26] D. Jovcic, “Interconnecting offshore wind farms using multiterminalVSC-based HVDC,” Proc. IEEE Power Eng. Soc., pp. 1–7, Jun. 2006.

[27] J. Liang, O. Gomis-Bellmunt, J. Ekanayake, and N. Jenkins, “Controlof multi-terminal VSC-HVDC transmission for offshore wind power,”in Proc. 13th Int. Eur. Power Electron. Conf. Exhibit., Barcelona,Spain, Sep. 8–10, 2009, pp. 1–10.

[28] O. Gomis-Bellmunt, J. Liang, R. King, J. Ekanayake, and N. Jenkins,“Topologies of multiterminal HVDC-VSC transmission for large off-shore wind farms,” Elect. Power Syst. Res, vol. 81, no. 2, pp. 271–281,Feb. 2011.

[29] X.-P. Zhang, “Multiterminal voltage-sourced converter based HVDCmodels for power flow analysis,” IEEE Trans. Power Syst., vol. 19, no.4, pp. 1877–1884, Nov. 2004.

[30] D. J. Trudnowski, A. Gentile, J. M. Khan, and E. M. Petritz, “Fixed-speed wind-generator and wind-park modeling for transient stabilitystudies,” IEEE Trans. Power Syst., vol. 19, no. 4, pp. 1911–1917, Nov.2004.

[31] S. M. Muyeen, M. H. Ali, R. Takahashi, T. Murata, J. Tamura, Y.Tomaki, A. Sakahara, and E. Sasano, “Transient stability analysisof wind generator system with the consideration of multi-mass shaftmodel,” in Proc. Int. Conf. Power Electron. Drives Syst., Jan. 16–18,2006, vol. 1, pp. 511–516.

[32] P. Cartwright, L. Holdsworth, J. B. Ekanayake, and N. Jenkins, “Co-ordinated voltage control strategy for a doubly-fed induction generator(DFIG)-based wind farm,” Proc. Inst. Elect. Eng., Gen. Transm. Dis-trib., vol. 151, no. 4, pp. 495–502, Jul. 2004.

[33] Task Force .01.10, , “CIGRE Modeling new forms of generation andstorage,” 2000, 5th draft.

[34] F. M. Hughes, O. Anaya-Lara, N. Jenkins, and G. Strbac, “Control ofDFIG-based wind generation for power network support,” IEEE Trans.Power Syst, vol. 20, no. 4, pp. 1958–1966, Nov. 2005.

[35] F. Wu, X.-P. Zhang, K. Godfrey, and P. Ju, “Small signal stability anal-ysis and optimal control of a wind turbine with doubly fed inductiongenerator,” IET Gen., Transm. Distrib., vol. 1, no. 5, pp. 751–760, Sep.2007.

[36] L. Wang and C.-N. Li, “Dynamic stability analysis of a tidal powergeneration system connected to an onshore distribution system,” IEEETrans. Energy Convers., vol. 26, no. 4, pp. 1191–1197, Dec. 2011.

[37] L. Wang and J.-H. Liu, “Dynamic analysis of a grid-connected marine-current power generation system connected to a distribution system,”IEEE Trans. Power Syst., vol. 25, no. 4, pp. 1798–1805, Nov. 2010.

[38] L. Wang, W.-J. Lee, J.-R. Wu, S.-J. Chen, J.-H. Kang, C.-Y Lin, andY.-S. Huang, “Performance analysis of a large-scale hybrid offshorewind and marine-current farm connected to a power grid via an HVDClink,” in Proc. North Amer. Power Symp., Sep. 2010, pp. 1–8.

[39] K. R. Padiyar, “HVDC power transmission systems,” in New Delhi:New Age Int., 2nd ed. India: Nisha Enterprises, 2002.

[40] K. A. Ellithy and M. A. Choudhry, “Effect of load models on AC/DCsystem stability and modulation control design,” IEEE Trans. PowerSyst., vol. 4, no. 2, pp. 411–418, May 1989.

[41] L. Wang, K. Wang, W. Lee, and Z. Chen, “Power-flow control andstability enhancement of four parallel-operated offshore wind farmsusing a line-commutated HVDC link,” IEEE Trans. Power Del., vol.25, no. 2, pp. 1190–1202, Apr. 2010.


Li Wang (S’87–M’88–SM’05) received the Ph.D.degree in electrical engineering from NationalTaiwan University, Taipei City, Taiwan, in 1988.He has been anAssociate Professor and a Professor

in the Department of Electrical Engineering, NationalChengKungUniversity, Tainan City, Taiwan, in 1988and 1995, respectively. He was a Visiting Scholar inthe School of Electrical Engineering and ComputerScience, Washington State University, Pullman, WA,USA, from 2003 to 2004. He was a Research Scholarof the Energy Systems Research Center (ESRC), the

University of Texas at Arlington, Arlington, TX, USA, from 2008 to 2009. Hiscurrent research interests include power system dynamics, power system sta-bility, ac machines analysis, and renewable energy.

Mi SaNguyen Thiwas born in Da Lat City, Vietnam,on April 24, 1984. She received the B.S. andM.S. de-grees in electrical and electronics engineering fromthe University of Technical Education, Ho Chi MinhCity, Vietnam, in 2007 and 2009, respectively, andthe Ph.D. degree in electrical engineering from Na-tional Cheng Kung University, Tainan City, Taiwan,in 2013.Her research interests are simulations of wind en-

ergy conversion systems connected to the power grid.

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