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ISSN 2348–2370

Vol.07,Issue.07,

July-2015,

Pages:1194-1202

Copyright @ 2015 IJATIR. All rights reserved.

Improve Performance on AC Fault Ride through in Multiterminal HVDC Grids K. AJAY KUMAR

1, CH. PRATHYUSHA

2

1PG Scholar, Vaageswari College of Engineering, Ramakrishna Colony, Karimnagar(Dt), Telangana, India.

2Assistant Professor, Vaageswari College of Engineering, Ramakrishna Colony, Karimnagar(Dt), Telangana, India.

Abstract: A totally operational multi terminal dc (MTDC)

grid can play the strategic position for mainland ac

techniques interconnection and to integrate ocean going

wind plants. The incredible importance of such structure

requires the compliance using fault trip through (FRT)

capability in case of mainland air conditioning unit faults.

In order to provide FRT ability in MTDC grids,

communication-free innovative control functionalities

exploiting a couple of local control rules with the converter

channels and wind generators are determined. The

suggested control functionalities are responsible for

mitigating this dc voltage surge effect resulting from the

lowering of lively power treatment into onshore air

conditioning unit systems through grid mistakes. The

suggested strategies envision an easy control in the wind

wind turbine active power output like a function in the dc

grid voltage surge and make up alternative options to

prevent the using classical solutions while using

installation of chopper resistors from the MTDC grid. The

feasibility as well as robustness in the proposed techniques

are exhibited and discussed from the paper within different

circumstances.

Keywords: Fault Trip Through (FRT), HVDC, VSC,

MTDC.

I. INTRODUCTION The development of additional electrical interconnect-

ions is presently being planned by sea exploiting offshore

grids, as it is documented in the European project

―Twenties‖ and in the Intelligent Energy Europe projects

―OffshoreGrid‖ and ―TradeWind‖. In both cases, offshore

interconnections are expected to provide two main

requirements: the support to exchange power between ac

areas and offshore wind power integration. The ac

transmission of bulk power over long distances in

offshore interconnections is technically limited by the

high capacitance of shielded power cables. High-voltage

direct current–voltage-source converter (HVDC–VSC)

technology seems to be the most promising solution for

offshore dc connections since it uses small harmonic

filters, it allows the independent control of active and

reactive power, bidirectional power flows, voltage

support and it is able to provide black-start capability .

Regarding HVDC transmission, multiterminal dc

(MTDC) grids are foreseen as an alternative solution to

point-to-point connections, providing higher flexibility,

increased redundancy and reduction of maximum power not

supplied to onshore grids in case of dc disturbances.A fully

operational MTDC grid with offshore wind farms (WF) can

be regarded as a large (virtual) power plant capable of

providing ancillary services to mainland ac grids [1].

In this sense, it is expected that MTDC grids also provide

fault ride through (FRT) capability for faults occurring in the

mainland ac grid, in line with grid code requirements for

onshore wind generators [2]. The analysis and performance

evaluation of different control solutions for the provision of

FRT requirements in point-to-point HVDC systems

equipped with VSC. In any case, the dc voltage rise due to

the onshore VSC power transfer reduction during the ac grid

fault is the major concern for the development of any control

strategy. the authors propose five methodologies to

dissipate/accommodate dc grid power in order to control the

dc voltage rise. Excepting the solution based on the

installation of dc chopper resistors, the other methodologies

rely on a fast communication channel between onshore and

offshore converter/wind turbine and involve: active power

reduction output through offshore converter current control,

wind turbine power set-point adjustment, offshore grid

frequency adjustment and offshore ac grid voltage controlled

reduction. the authors propose a strategy to control the dc

voltage rise during the ac grid fault by de-loading the

offshore WF proportionally to the dc voltage rise. However,

this strategy assumes the use of a communication link

between the offshore converter and each wind turbine. Also,

the installation of dc grid chopper resistor has been

contemplated as an alternative.

III. HIGH-VOLTAGE, DIRECT CURRENT (HVDC)

A. Introduction

A high-voltage, direct current electric power transmission

system uses direct current for the bulk transmission of

electrical power, in contrast with the more common

alternating current (AC) systems. For long-distance

transmission, HVDC systems may be less expensive and

suffer lower electrical losses. For underwater power cables,

HVDC avoids the heavy currents required to charge and

discharge the cable capacitance each cycle. For shorter

distances, the higher cost of DC conversion equipment

compared to an AC system may still be warranted, due to

other benefits of direct current links. HVDC allows power

transmission between unsynchronized AC transmission

K. AJAY KUMAR, CH. PRATHYUSHA

International Journal of Advanced Technology and Innovative Research

Volume.07, IssueNo.07, July-2015, Pages: 1194-1202

systems. Since the power flow through an HVDC link can

be controlled independently of the phase angle between

source and load, it can stabilize a network against

disturbances due to rapid changes in power. HVDC also

allows transfer of power between grid systems running at

different frequencies, such as 50 Hz and 60 Hz. This

improves the stability and economy of each grid, by

allowing exchange of power between incompatible

networks. The modern form of HVDC transmission uses

technology developed extensively in the 1930s in Sweden

(ASEA) and in Germany. Early commercial installations

included one in the Soviet Union in 1951 between Moscow

and Kashira, and a 100 kV, 20 MW system between

Gotland and mainland Sweden in 1954. The longest HVDC

link in the world is currently the Xiangjiaba–Shanghai

2,071 km (1,287 mi), ±800 kV, 6400 MW link connecting

the Xiangjiaba Dam to Shanghai, in the People's Republic

of China. Early in 2013, the longest HVDC link will be the

Rio Madeira link in Brazil, which consists of two bipoles

of ±600 kV, 3150 MW each, connecting Porto Velho in the

state of Rondônia to the São Paulo area, where the length

of the DC line is 2,375 km (1,476 mi).

B. High voltage transmission

High voltage is used for electric power transmission to

reduce the energy lost in the resistance of the wires. For a

given quantity of power transmitted, doubling the voltage

will deliver the same power at only half the current. Since

the power lost as heat in the wires is proportional to the

square of the current for a given conductor size, but does

not depend on the voltage, doubling the voltage reduces the

line losses per unit of electrical power delivered by a factor

of 4. While power lost in transmission can also be reduced

by increasing the conductor size, larger conductors are

heavier and more expensive. High voltage cannot readily

be used for lighting or motors, so transmission-level

voltages must be reduced for end-use equipment.

Fig1.Schematic diagram of Thury HVDC transmission

system.

C. Offshore Wind Transformers are used to change the voltage levels in

alternating current (AC) transmission circuits. Because

transformers made voltage changes practical, and AC

generators were more efficient than those using DC, AC

became dominant after the introduction of practical systems of

distribution in Europe in 1891 and the conclusion of the War

of Currents competition at the same time in the US between

the direct current (DC) system of Thomas Edison and the AC

system of George Westinghouse. Practical conversion of

power between AC and DC became possible with the

development of power electronics devices such as mercury-

arc valves and, starting in the 1970s, semiconductor devices as

thyristors, integrated gate-commutated thyristors (IGCTs),

MOS-controlled thyristors (MCTs) and insulated-gate bipolar

transistors (IGBT).

D. Power

Offshore wind power refers to the construction of wind

farms in bodies of water to generate electricity from wind.

Stronger wind speeds are available offshore compared to on

land, so offshore wind power’s contribution in terms of

electricity supplied is higher, and NIMBY opposition to

construction is usually much weaker. However, offshore wind

farms are relatively expensive. At the end of 2012, 1,662

turbines at 55 offshore wind farms across 10 European

countries were generating electricity enough to power almost

five million households. Offshore wind power refers to the

construction of wind farms in bodies of water to generate

electricity from wind. Unlike the typical usage of the term

"offshore" in the marine industry, offshore wind power

includes inshore water areas such as lakes, fjords and

sheltered coastal areas, utilizing traditional fixed-bottom wind

turbine technologies, as well as deep-water areas utilizing

floating wind turbines. A subcategory within offshore wind

power can be nearshore wind power.

Fig2. The world's second full-scale floating wind turbine

(and first to be installed without the use of heavy-lift

vessels), WindFloat, operating at rated capacity (2 MW)

approximately 5 km offshore of Póvoa de Varzim,

Portugal.

Improve Performance on AC Fault Ride through in Multiterminal HVDC Grids

International Journal of Advanced Technology and Innovative Research

Volume.07, IssueNo.07, July-2015, Pages: 1194-1202

IV.MODELING AND CONTROL OF MTDC GRIDS

A. Introduction

The MTDC grid provides the interconnection of ―N‖

offshore WF to ―M‖ mainland collection points. In order to

evaluate the dynamic behavior of the MTDC grid,

including the HVDC–VSC stations and offshore WF, it is

necessary to develop adequate models for simulating the

operational characteristics of the overall system. Modeling

system components will allow the identification of the

most appropriate decentralized control strategies in order to

provide FRT capability in MTDC grids. It is important to

highlight that the major dynamic phenomena to be

analyzed in this paper are associated to faults occurring in

the mainland ac grid. Therefore, a RMS modeling approach

is assumed, where losses, harmonics and fast switching

transients of the converters are neglected. Taking into

account this general consideration, the next sub-sections

present a brief description of the adopted models.

B. DC Grid

The dc grid is assumed to be bipolar (symmetrical

voltages), being the dc cables represented by a

concentrated parameter model (cable resistance, inductance

and capacitance). Following this approach, the dc grid

algebraic and state equations can be derived.

C. HVDC Converters

As previously mentioned, HVDC–VSC technology is

assumed to be used in the MTDC grid, both at the onshore

and offshore converter stations. From the onshore and

offshore ac grid perspective, converter stations can be

regarded as controllable voltage sources. The

corresponding HVDC–VSC models and operational

philosophies are presented hereafter.

Fig3. Internal control loops of the offshore converters.

1. Offshore Converter The offshore WF is assumed to be connected to an ac

grid, whose voltage and frequency are controlled by the

offshore HVDC–VSC station. Simultaneously, the offshore

converter interfaces the WF network with the MTDC grid.

From the ac side, it performs as a slack bus for the ac

offshore grid by collecting all the generated power and

delivering it to the dc grid. The main converter control loops

are presented in Fig3. The converter model is implemented in

the synchronous reference frame. The HVDC–VSC output

voltages and values are set through PI controllers considering

the voltage and current errors in the referred and reference

frame.

2. Onshore Converter

The onshore HVDC–VSC is responsible for interfacing the

MTDC grid to the ac onshore grid and for the control of the

associated dc terminal voltage (which thereafter leads to the

control of active power being injected into the onshore ac

grid). The dc voltage reference can be defined through a local

droop controller [9], [10] that can be expressed by

(1)

where is the active power delivered by the HVDC–VSC to

the onshore ac grid, is a droop that relates the active power

and dc voltage variations and is a configurable parameter that

can be adjusted in order to modify the steady-state power

sharing between converters. This converter was also modelled

in the synchronous reference- frame through its main control

loops,which are depicted in Fig. 4.2. The converter output

voltages and are set through PI controllers associated to the

converter inner current control loops. The converter outer

control loops provide the current reference through the error

generated between the actual dc voltage and the reference dc

voltage ; the current referent is provided by another PI

regulation loop that can be used for setting the converter

reactive power or output voltage. For this specific case, the

regulation was set to control the ac voltage magnitude at the

VSC ac terminals.

D. HVDC–VSC Current Limiting

From an operation point of view, HVDC–VSC technology

is able to remain connected to the ac grid during low voltage

sags. Nevertheless, power electronic converters have a

maximum current limit associated with the thermal

characteristics of the power electronic switches. However,

short over currents are admissible in the power converters

(around 8% overcurrent capacity is assumed). Considering

that during a fault a certain reactive current component is to

be injected by the converter station, the component can be

defined as . These limits were implemented in the current

control loops of each converter station.

1. Wind Generator Model

Regarding the offshore WF, two most common generator

technologies with FRT capability were considered in order to

demonstrate that the FRT control schemes for the MTDC grid

proposed in this paper are effective. For the first case,

offshore WF were assumed to be equipped with permanent-

magnet synchronous generators (PMSG) interfaced with the

ac offshore grid via an ac/dc/ac full converter. For this case a

lumped model was adopted according to the approach

described in . For the second case, offshore WF were assumed

to be equipped with DFIG, which are modeled according to

the approach presented. The control approach] is able to

K. AJAY KUMAR, CH. PRATHYUSHA

International Journal of Advanced Technology and Innovative Research

Volume.07, IssueNo.07, July-2015, Pages: 1194-1202

effectively reduce the transient rotor and stator currents in

DFIG by allowing a controlled increase of the rotor speed

following voltage sag thus improving its FRT performance.

Fig5. Internal control loops of the onshore converters.

V.PROPOSED APPROACHES FOR FRT

PROVISION IN MTDC GRIDS

A. Introduction

The converter current limits are responsible for reducing

the onshore HVDC–VSC active power injection capability

during voltage sags. Offshore WF commonly operate in a

maximum power extraction philosophy and offshore

HVDC–VSC injects the incoming power into the dc grid.

Therefore, during an ac mainland fault, a significant power

reduction occurs in the HVDC–VSC terminal connected to

the faulted area. Without the use of any specific strategy

(which are addressed hereafter), the offshore WF will

remain operating under a maximum power extraction

strategy. Consequently, the dc power imbalance will result

on dc over voltages in the different MTDC grid nodes

depending on the pre-disturbance active power flows and

on the MTDC grid topology [6]. Nonetheless, dc over

voltages must be controlled in order to avoid equipment

damages and provide the expected flexibility in terms of

FRT capability.

Fig6. Control scheme of onshore dc chopper resistor.

In order to mitigate the dc voltage rise effect, three

control strategies are proposed and tested. The first one

consists on a conventional solution based on dc chopper

resistors installed at onshore VSC-level and is considered

as a reference case. The other two strategies rely on

innovative communication free solutions that exploit the

control flexibility of both offshore HVDC–VSC converter

stations and wind generators to perform fast active power

reduction at the wind generator level. These control strategies

are based on the implementation of local control rules at

offshore converter stations and at wind turbine generators and

are intended to avoid the use of solutions based on dc chopper

resistors.

B. Onshore DC Chopper

A dc chopper consists on a dc resistor controlled through a

power electronic switch and it is installed at the HVDC–VSC

onshore converter station as it is depicted in Fig6. A detailed

sizing of a dc chopper-based solution for FRT compliance in

MTDC grids is out of the scope of this paper (as previously

mentioned, this type of solution is considered only as a

reference case). Nevertheless, it depends on several factors,

namely the MTDC grid power in-feeds (power in-feeds from

offshore WF or from other mainland ac grid areas) as well as

on the mainland grid connection points and its electrical

distance. In this case, a simple approach based on a worst case

scenario was considered. The worst case condition

corresponds to a situation where all HVDC–VSC stations are

operating at the nominal power. In case of a fault, healthy

converters (connected to non-faulted ac mainland grids) are

not able to increase their power injection and power

dissipation in chopper resistors is required in order to mitigate

the dc voltage rise. Based on this assumption, each dc chopper

must be sized to dissipate the nominal power of the HVDC–

VSC to which it is connected.

Fig7. Control scheme for FRT provision based on dc

voltage: (a) AC offshore grid voltage control. (b) AC

offshore grid frequency control.

The activation of each dc chopper control strategy is based

on a dc voltage threshold that will trigger power dissipation in

the resistor. In terms of RMS system modeling, the dc

chopper active power dissipation is locally regulated based on

a proportional control rule having as input the positive dc

voltage deviation (over voltage magnitude) [5]. The dc

chopper de-activation occurs if: (1) the dc voltage reaches a

Improve Performance on AC Fault Ride through in Multiterminal HVDC Grids

International Journal of Advanced Technology and Innovative Research

Volume.07, IssueNo.07, July-2015, Pages: 1194-1202

value below the threshold activation level (eg.: after fault

clearance) or; (2) the chopper resistor temperature

overreaches the maximum value (thermal protection

tripping), meaning that the resistor maximum energy

dissipation capability has been overreached. This specific

situation is often related to a permanent fault event and

must be handle by additional control schemes to perform

permanent active power reduction at offshore WF-level.

B. FRT Provision through Wind Turbine Power

Regulation

Modern wind turbines connected to ac grids in onshore

applications are FRT compliant, coping with the

requirements of many grid codes [2]. However, MTDC

grids decouple the offshore WF and the onshore ac grid.

Therefore, in order to derive a communication-free solution

to provide FRT in MTDC grids, strategies exploiting the dc

over voltages resulting from onshore ac faults can be

advantageous. The main objective is the implementation of

local controllers at the offshore VSC and at the wind

generators enabling them to perform fast active power

regulation as it is generally depicted in Fig. 4. The

envisioned control strategies exploitMTDC grid voltage

rise in order to control (1) the offshore ac grid voltage or

(2) the offshore ac grid frequency.

C. Local Controls at the Wind Generator Level

As previously mentioned, PMSG and DFIG were

assumed to be used in offshore WF in order to demonstrate

the feasibility and evaluate the performance of the

proposed wind generators’ active power control strategies.

Regarding PMSG, the wind generator local control for fast

active power regulation is set to dissipate active power

proportionally to ac offshore grid voltage (case 1) or

frequency variations (case 2). To achieve a fast response, it

is assumed the power dissipation is made at the wind

generator chopper resistor installed on the dc bus bar of the

ac-dc-ac full converter [2], [6], while having the advantage

of keeping the generator side decoupled from the transient

phenomena. For the DFIG, the active power regulation is

naturally achieved for the ac voltage regulation strategy,

since the controlled voltage sag in the offshore ac grid

leads to the generator de-magnetization, increasing slightly

its angular speed and consequently reducing the injected

power [23]. In this case, inrush currents resulting from the

demagnetization of DFIG are a critical issue due to the

current limits of the HVDC–VSC station connected to the

offshore ac grid. In order to overcome this drawback, the

control strategy presented in [3] is adopted, as it was

previously mentioned. Compared to conventional DFIG

control strategies, it presents the advantage of assuring a

considerable limitation of the stator currents following the

voltage dip, while limiting also the rotor current and

avoiding the need of the crowbar.

The control principle exploits the possibility of allowing

the DFIG rotor speed increase in coordination with the

control of the wind turbine pitch angle in order to limit the

acceleration phase and to avoid stability issues. Regarding

the frequency-based active power regulation strategy in the

DFIG, a supplementary control is used in the speed control

loop implemented in the rotor side converter which allows a

rotor speed increase to achieve a fast reduction of active

power generation.

Fig.8. MTDC grid test system.

VI. SIMULATION RESULT

In order to characterize the transient overvoltage

phenomena in MTDC grids, a 500 ms three-phase fault was

simulated near Area #1 onshore converter ac terminals at 1 s

(see Fig8). The most important results are presented in Fig9 &

10. The time evolution of the active power in each HVDC–

VSC terminal shows that during the fault Area #1 onshore

converter reduces the capability of exporting about 160MW.

In contrast, the onshore converter in Area #2 was able to

increase the power transmission in about 50MW. This

behavior is related with the previously presented dc

voltage/active power droop control which regulates the active

power extraction as a function of the dc voltage variations.

However, it is notorious that active power dynamics in the

Area #2 converter is slower than the corresponding time

constant observed in the active power reduction in Area #1

converter.

Fig9. Active power flows on HVDC–VSC.

K. AJAY KUMAR, CH. PRATHYUSHA

International Journal of Advanced Technology and Innovative Research

Volume.07, IssueNo.07, July-2015, Pages: 1194-1202

Fig10. DC voltage profile at the MTDC grid terminals.

In order to mitigate the dc over voltages, it is necessary

to exploit control mechanisms that are able to effectively

provide active power balance within the dc grid. In order to

establish a comparative analysis, the same test case and

fault condition is considered in the simulation results that

are presented next.

Fig11. DC voltage profile at the MTDC grid terminals

with onshore chopper resistors.

Fig12. Onshore converter and dc choppers active

power.

A. Onshore Chopper Resistors

In order to define a reference case, the first analysis

consisted on evaluating the behavior of MTDC grid, namely

regarding dc voltage profile and active power flows, when the

FRT capability is to be assured through the use of two dc

choppers installed on each dc onshore terminal. The obtained

results are depicted in Figs.10 and 11, where it is possible to

observe that a small dc overvoltage took place during fault

occurrence It is important to note that for this specific set of

simulations, offshore WF have not change their power

injection since, as aforementioned, the dc grid decouples the

interconnected ac areas and the dc power balance is achieved

through external solutions in relation to the WF.

Fig13. AC voltage profile at offshore network and DFIG

speed.

B. Offshore Wind Turbine Power Regulation Strategies

The two regulation mechanisms for wind turbine power

reduction in the moments subsequent to a mainland ac fault

(ac offshore voltage reduction and ac offshore frequency

increase) are illustrated in two distinct scenarios: 1) both WF

equipped with PMSG and 2) both WF equipped with DFIG. A

detailed analysis of other operating conditions as well as on

the stress regarding converter stations and wind turbines is

presented in Section V.

1. Offshore AC Voltage Reduction:

The results obtained through offshore ac voltage control

for wind turbine power reduction are depicted in Figs. 5.8, 5.9

and 5.10. In Fig. 5.8 it is possible to observe that the offshore

ac voltage reduction is successfully achieved for both

scenarios (WF equipped with PMSG and with DFIG).

However, a difference on the ac voltage behavior is also

noticeable. This fact is related with the natural response of

each generator regarding the voltage reduction. The PMSG

Improve Performance on AC Fault Ride through in Multiterminal HVDC Grids

International Journal of Advanced Technology and Innovative Research

Volume.07, IssueNo.07, July-2015, Pages: 1194-1202

quickly dissipates active power on its own dc chopper

(previously referred as wind turbine chopper).

2. Offshore AC Frequency Increase:

The alternative scheme for power reduction at offshore

level is based on the WF ac grid frequency control

proportionally to the dc voltage increase. This strategy was

also tested for WF equipped with PMSG and DFIG. The

major results are presented on Figs15, 16 and 17. The

results depicted in Fig.15 allow concluding that frequency

increase has been successfully accomplished on the

offshore WF ac grid for both cases. It is also observable by

the frequency behavior that DFIG-based WF has a bigger

settling time comparing to the PMSG-based WF.

Fig14. Active power flow at dc grid terminals (PMSG

and DFIG).

Fig15. DC voltage profile at the MTDC grid terminals

(PMSG and DFIG).

Fig16. Frequency and DFIG speed at offshore WF (PMSG

and DFIG).

Fig17. Active power flow at the MTDC grid terminals

(PMSG and DFIG).

Fig18. DC voltage profile at the MTDC grid terminals

(PMSG and DFIG).

K. AJAY KUMAR, CH. PRATHYUSHA

International Journal of Advanced Technology and Innovative Research

Volume.07, IssueNo.07, July-2015, Pages: 1194-1202

With respect to the dc voltage profiles depicted in Fig18,

the implemented control strategies assure that both WF

respond to the frequency increase in their own grids in

order to reduce the power production. The simulation

results also demonstrates that the WF active power

regulation strategies do not require the adoption of

additional equipment at the MTDC grid level such as the

chopper resistors, thus constituting an alternative solution

to it.

Fig19. DC grid test system for sensitivity analyses.

VII. CONCLUSION

This specific report gives a dialogue for the id along

with growth connected with communication-free command

strategies for FRT provision on MTDC grids

interconnecting offshore WF together with hvac mainland

grids. The suggested command strategies for endowing

MTDC grids together with FRT potential write about a

typical quality: this accommodation/dissipation connected

with productive energy by offshore WF in order to abate

this dc voltage surge consequence. The established option

good using onshore chopper resistors is an efficient option

which might be very easily put in place due to the fact the

command will depend on nearby measurements. Despite

the fact that using these kinds of method fully decouples

offshore WF in the principal along with hvac mistake,

that's benefic in connection with lowered strain problems

for that wind turbines, the dimensions of the desired dc

chopper resistors my personal impede the request by a

cost-effective point of view.

Alternative methods for that mitigation connected with

MTDC in excess of voltages use productive energy

lowering on the generator amount through the exploitation

of a communication-free command method which in turn

will depend on some nearby controllers for being installed

on the offshore converter train station along with on the

turbine amount. The suggested approaches work well

relating to productive energy legislation in order to

guarantee FRT submission by MTDC grids. The attained

final results make it possible for deciding in which

suggested command approaches are generally strong

underneath extremely nerve-racking problems, are

generally independent of the dc grid topology along with

with the pre-disturbance dc grid energy dispatch. This is a

key qualification on the interoperability connected with

solutions by various suppliers. The significant benefit of these

types of approaches relies on a smaller amount expenditure in

connection with implementation with the necessary command

functionalities. Even so, these types of approaches lead to a

few strain in excess of DFIG regarding velocity different

versions (similarly from what happens within wind turbines

linked with onshore grids). In addition, modest in excess of

currents are generally observed in this linked HVDC–VSC

along with should be considered within the style period.

VIII.REFERENCES

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[4] Inteligent Energy Europe. Tradewind Project, 2012.

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[5] T. Ackermann, ―Transmission systems for offshore wind

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[6] N. B. Negra, J. Todorovic, and T. Ackermann, ―Loss

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[8] O. Gomis-Bellmunt, J. Liang, J. Ekanayake, R. King, and

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Author’s Profile:

K.Ajay Kumar, received Diploma in

Electrical and Electronics Engineering from

S.R.R.S Govt Polytechnic, Sircilla,

Karimnagar Dist, SBTET, A.P, B.Tech

Degree in Electrical and Electronics

Engineering from Jyothishmathi Institute of

technology and sciences Nusthulapoor,

karimnagar, A.P. And currently pursuing M.Tech In Electrical

& Electronics Engineering as Power Electronics is

specialization at Vaageswari College of Engineering

Ramakrishna colony, Karimnagar Dist, JNTUH, T.S. My

Improve Performance on AC Fault Ride through in Multiterminal HVDC Grids

International Journal of Advanced Technology and Innovative Research

Volume.07, IssueNo.07, July-2015, Pages: 1194-1202

areas of interest are Power Electronics, Electrical Machines

& HVDC Transmission.

Ch.Prathyusha working as Assistant

Professor in Vageeswari college of

Engineering, Ramakrishna colony,

Karimnagar, T.S. She received the

B.Tech Degree in Jyothishmathi

Institute of technology and sciences

Nusthulapoor, Karimnagar, A.P and

she received P.G. In Electrical & Electronics Engineering

as Power Electronics is specialization at Vaageswari

College of Engineering Ramakrishna colony, Karimnagar

Dist, JNTUH, A.P, she has a teaching experience of 4

years. Her areas of interest are Power Systems, Power

electronics Control Systems, Networks.