luis layo (sp) session 4 – block 3 – selected paper - question 6 barcelona 12-15 may 2003 1...

1Luis Layo (SP) Session 4 – Block 3 – Selected Paper - Question 6

Barcelona 12-15 May 2003

Analysis of the effects of wind farms dynamic behaviour on

distribution networks

DFIM Wind Farms Voltage Control CIRED Barcelona 12-15 May 2003

Luis Layo (SP) Session 4 - Block 3

IBERDROLA



Index• Voltage control strategy on DFIM Wind Farms• Models developed for simulations • Reactive power control tests of a wind farm

from a distribution control centre• Voltage control operation procedure• Question 6: Are there now cost effective

solutions for all the voltage control challenges of renewable generators?



Introduction

• Wind energy has turned out to be one of the most important and promising sources of renewable energy

• This energy source will represent a significant proportion of total installed power in the Spanish power system

• The expected amount of wind power establishes important challenges to distribution and transmission network planning and operation

• Problems related to reactive power management in wind farms and to their connection to the electric network



DFIM Model

• This kind of wound rotor machine has to be fed both from stator and rotor sides

• Asynchronous generator which behaves as a synchronous with variable speed. Varying rotor input signal:

– Amplitude: reactive power control

– Phase: active power control

– Frequency: rotor speed control

RotorRotor

GG

ACAC

DCDC

DCDC

ACAC

Switch GearSwitch GearNetworkNetwork

Asynchronous Generator

Asynchronous Generator

DFIM

Doubly Fed Induction Machine

DFIM

Doubly Fed Induction Machine



• Reactive power can be controlled while maintaining active power generation

• Distributes the required reactive power of the farm in a proportional way among all the operative generators:

– Each machine will work with a different power factor

– Machines tend to reach the saturation state at the same time

Control strategy: general features

imaxn

iimax

refi q

q

Qq *

1



Qref

Pe2 PenPe1 Pe3

Wind Farm Control Centre

Distribution Network Control Centre

qn maxq2 max q3 maxq1 max

imax qmax Q imax q

maxQrefQ

ispq .

q2sp q3spq1sp qnsp

Control strategy: model



Control strategy: requirements• Wind generators

– Control loop changes to receive local set point

• Wind Farm Control Centre:– Active power of each machine – P-Q capacity curve

• Distribution network Control Centre– OPF: maximum reactive power available– Communications

• Cost-effective– Take advantage of exiting control capacity



Security Control: voltage monitoring

Qe

V

Vmax normal

Vmin normal

Vmin triggerVmin admisible

Qe=0 , V= 1 P.U.

Control trigger off

Qe free control

Qe free control

Qe emergency control

Qe emergency control

Control trigger off

Vmax admisible

Vmax trigger



0 5 10 15 20 25-800

-600

-400

-200

0

200

Tiempo [seg]

Pote

ncia

Act

iva

[kW

]

Evolución de las Potencias Activas Generadas por cada Máquina

Pot

enci

a ac

tiva

en

kW

Evolución de las potencias activas por máquina

Active power performance of each generator (wind gusts)

0 5 10 15 20 25-400

-300

-200

-100

0

100

200

300

400

Tiempo [seg]

Pote

ncia

Rea

ctiv

a [k

VA

R]

Evolución de las Potencias Reactivas de cada MáquinaEvolución de las potencias reactivas por máquina

Pot

enci

a re

acti

va e

n kV

AR

Reactive power performance of each generator

Reactive Power Control Simulations

0 5 10 15 20 250.900

0.925

0.950

0.975

1

0.975

0.950

0.925

Indu

ctivo

Capa

citiv

o

Tiempo [seg]

Comportamiento del Sistema de Control de cos(phi)

Indu

ctiv

o

C

apac

itiv

o

Comportamiento del Sistema de Control de cos

Power factor performance of the wind farm



Salajones Wind Farm data• 23 MW: 35 wind generators• In service since 1999• Doubly fed induction

generators DFIM• 660 kW machines• 66 kV network connection• Wind farm -> generators:

radio link• Control centre -> wind farm:

optical fibre link

Control Centre OPF -> Q set point



Q control test in a real Wind Farm



Voltage control secondary service

Transmission NetworkTransmission Network Transmission NetworkTransmission Network

Distribution NetworkDistribution NetworkDistribution NetworkDistribution Network

Q’Q’P’P’

Wind FarmWind Farm

Power Factor

0………1

Power Factor

0………1PP QQ

tg =tg =PPQQ

P-P’P-P’ Q+Q’Q+Q’

tg’ =tg’ =P-P’P-P’Q+Q’Q+Q’

• P.O. 7.4: establishes power factor limits (Q generation and absorption bands) in the transmission-distribution border points



Voltage Control Proposal• Required service as normal generators

• Softer conditions in distribution networks

• Perform the voltage control service based in power factor bands according to the periods of the day – Peak: reactive power generation– Off-peak: reactive power absorption– Medium: power factor of unity



Conclusions• Wind farms made up with DFIMs constitute an

important tool from the voltage regulation point of view

• DFIMs are strongly recommended for the new wind farms from the power system viewpoint, especially in areas with a large wind generation concentration

• Wind farms with voltage control capacity will have a better position to be accepted in the system, in terms of planning, installation and operation

• The DFIM technology allows to perform voltage control in a very cost-effective way

luis layo (sp) session 4 – block 3 – selected paper - question 6 barcelona 12-15 may 2003 1...

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