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VÄRLDENS SKILLNAD

Grid Code Testing of Wind Turbines by

VSC-based Test Equipment

Nicolás Espinoza, PhD Student

nicolas.espinoza@chalmers.se

CHALMERS UNIVERSITY OF TECHNOLOGY

Gothenburg, Sweden.

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Project Description • Aim of the project

– To develop methods for grid code testing of wind turbines using

VSC-based test system.

• Activities

– Grid code analysis for interconnection of wind parks.

– Control theory of WT and VSC.

– Mathematical model for stability analysis.

• Results

– Simulation of the WT and the VSC-based test equipment (TE).

– Laboratory experiment at Power System Lab in Chalmers.

– Field test of full power 4 MW WT with 8 MW HVDC system in

Göteborg harbor has started!

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Wind Power Increase • World total installed capacity is 318 GW (117 GW are inside EU)

• 40 GW per year in the last 5 years, approximately.

Year

GW installed

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Grid code development • Regulates the interconnection of the generating plant.

• Special requirements for wind parks.

• Steady state: voltage, power and frequency ranges.

• Dynamic: LVRT and reactive current injection (if allowed).

• Grid code harmonization: ENSTO, Nordic.

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Low Voltage Ride Through (LVRT) • Voltage dip representation at the connection point

0

0 1

0.3

0.4

0.5

0.6

0.2

0.1

0.7

Sy

stem

Vo

ltag

e [p

u]

Time [s]

E.ON (Germany)

Energnet.dk (Denmark)

Red Eléctrica España (Spain)

0.8

0.9

1

2 30.50.25 0.75 1.25 1.5 1.75 2.25 2.5 2.75

Svenska Kraftnät (Sweden)

Nordel

EirGrid (Ireland)

National Grid (U.K.)

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Wind Turbine Topologies

G

Output

transfomer

Full Power Converter

Coupling

inductor and

filtersAC

DC AC

DC

AC Grid

Gearbox/

Gearless

Control system

Wind turbine

Protection by DC crowbar

Generator

Full-size converter WT

• Grid synchronization

• Current during fault is fully

controlled.

• LVRT control.

DFIG WT

• Stator connected to the grid.

• High transient current during fault.

• VSC rated in 1/3 P nominal.

• Poor LVRT capability.

Output

transfomer

1/3 Power Converter Coupling

inductor and

filtersAC

DC AC

DC

AC Grid

Gearbox

Control system

Wind turbine

Protection by DC crowbar

DFIG

Protection by AC crowbar

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Wind Turbine Modelling

Assumptions

• Physical decoupling between

Generator and grid.

• Mechanical transients are slow

compare to electromagnetic

transients.

wfR ,

wu wti , we

wfL , wfC ,

DC

AC

wDCu ,wDCi ,

wDCC ,

WT-VSC

si

GENP

crbR

To Test

equipment

crbsw

TWgwe , gwi ,

G

Output

transfomer

Full Power Converter

Coupling

inductor and

filtersAC

DC AC

DC

AC Grid

Gearbox/

Gearless

Control system

Wind turbine

Protection by DC crowbar

Generator

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Grid Code Testing Equipment

Test Equipment: VSC in back-to-back

AC voltage

control for

LVRTInterface

impedance

AC

GridInterface

impedance

AC

DC AC

DCPCC

Coupling

transfomer

Coupling

trasnformer

DC voltage

control

• Impedance-based

• VSC-based

Z series

Z faultAC

Impedance-based

Test equipment

Grid impendace

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Stability Analysis • Analytical model based on physical equations and control equations.

• Study of interactions between WT and Test Equipment

wfR

,

wu

wti

, we

wfL

, wfC

,

DC

AC

wDCu

,wDCi

,

wDCC

,

WT-VSC

si

AC

DC

PCC

eg

i ut

i

fC

fR

fL

Interface impedance Collector-VSC

eqR

eqL

CL vs OL voltage CTRL

Blue: P-based controller

Red: PI-based controller

Black: Open-loop Well damped area

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Laboratory Setup

utie

1,1, , ff RL

DCu

DCC

Grid Emulator DC machine360 V

DS1103

2,2, , ff RLfC

AC voltage control for LVRT

AC

DC AC

DCwtu , wti ,

AC grid, 400 V, 50

Hz

lR

wDCC ,

wDCu ,

crbR

DS1103

Wind Turbine Model AC-link

wtwt QP ,

• Placed at the Power System Lab. at Chalmers University of Technology.

• Consisting of 2 DC-sourced VSC interfaced by an AC-link.

• 200 V, 10 kVA.

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Field Test Results

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Turbine

VSC

AC

DCAC

Utility Grid

Flexible VSC-based Testing Equipment

Grid VSC

DC

AC

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Conclusions and Future Work

Conclusions

• Need for regulations for renewable energy sources.

• VSC-based T.E. is flexible

• Development of PCC voltage control and control algorithms.

Future Work

• To develop control strategies for testing of:

– Voltage control

– Power oscillation damping

– Frequency control

• Characterization of wind turbines

• To include wind turbine mechanical system

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Thanks for your attention

Nicolás Espinoza, PhD Student

nicolas.espinoza@chalmers.se

CHALMERS UNIVERSITY OF TECHNOLOGY

Gothenburg, Sweden.