Workshop on Renewable Energies November 14-25, 2005 Nadi, Republic of the Fiji Islands Module 2.2 Module 2.2-2 WIND TURBINE TECHNOLOGY WIND TURBINE TECHNOLOGY Electrical System Electrical System Gerhard J. Gerdes 4-Nov-05 (11:23) e7 / PPA Workshop on Renewable Energies 2 Contents Module 2.2 Contents Module 2.2 J Types of generator systems J Variable and fixed speed J Inverter technologies
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Workshop on Renewable Energies
November 14-25, 2005
Nadi, Republic of the Fiji Islands
Module 2.2Module 2.2--22
WIND TURBINE TECHNOLOGYWIND TURBINE TECHNOLOGYElectrical SystemElectrical System
Gerhard J. Gerdes
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Contents Module 2.2Contents Module 2.2
Types of generator systems
Variable and fixed speed
Inverter technologies
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Converter type Application
induction (asynchronous) generator
applied in a large number of turbines (Danish type)
synchronous generator only used for a small number of small wind turbines, mainly for stand alone systems
asynchronous or synchronous generator with electronic inverter system
a widely used concept for variable speed machines, increasing applications with growing size of wind turbines
Types of generator systemsTypes of generator systems
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0
2
4
6
8
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12
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30 kW - <500 kW 500 kW - <1MW 1 MW - 2 MW
nu
mb
er
of
dif
fere
nt
typ
es
one speed
two speed
variable speed
Generator concepts of todayGenerator concepts of today’’s s
commercially available turbinescommercially available turbines
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ASG
induction generatorGear box
rotor
transformermain switch
fuse
contactor
thyristor startercompensation
system managementwind speed
pitch or stall
Electr. quantities
rotor
speed
Control
grid
Wind turbine with Induction Generator, direct Wind turbine with Induction Generator, direct
control: power control by pitch (seldom stall)speed limitation by pitchspeed control by power regulation of the inverter
system
advantage: smoothing of power output, compensation of wind speed fluctuationscontrollable power generationcontrollable production of reactive poweroperation at optimal power coefficient cp due to variable speedgeneration of voltage and frequency for autonomous energy systems
disadvantage: expensive constructiongeneration of harmonics,higher level of maintenance
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Wind turbine with variable speed Wind turbine with variable speed
rotor rotor
power – rotor
speed curve =
always in
aerodynamic
optimum
source: DEWI
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Advantage variable speedAdvantage variable speed
fluctuations of wind speed
converted into torque
fluctuations
high mechanical strain on
the drive train
fluctuations of wind speed
converted into rotor speed
increase
rotor stores energy
smoothens output
source: DEWI
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6 pulse rectifier 6 pulse rectifier –– inverter systeminverter system
rectifier
6-pulse
inverter transformer
source: DEWI
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12 pulse rectifier 12 pulse rectifier –– inverter systeminverter system
I1
and
I2
before
and after the
transformer
two 6-pulse
inverters in parallel
special transformer
(three windings, with star/
triangle configuration)
source: DEWI
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Harmonic distortionHarmonic distortion
6-pulse inverter with high level of
harmonic distortion
requires high efforts for filtering
12-pulse inverter normally two 6-
pulse inverter in parallel
one inverter with star-star, the
other with star-triangle
connection
special three-winding transformer
harmonic distortion greatly
reduced
12-pulse inverter more complex,
requires less efforts for filtering
6-pulse inverter
12-pulse inverter
source: DEWI
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Inverter with pulseInverter with pulse--widthwidth--
modulation PWMmodulation PWM
rectifier inverter
with
IGBT
transformer
source: DEWI
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Function of PWM inverterFunction of PWM inverter
the condenser between rectifier and PWM inverter acts
like an ideal DC voltage source
Insulated Gate Bipolar Transistors (IGBT) switch at
high frequencies (up to 10 kHz) to create a sine wave
practical no harmonic distortion up to ordinal number
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harmonics with higher ordinal numbers exist, but have
no effect on the grid, because
inductance of the grid blocks higher frequencies
capacitance of grid acts like a short-cut for high
frequencies
ideal for modern variable speed wind turbines
power output can be controlled (power gradient)
no harmonic distortion
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Output of a PWM inverter with Output of a PWM inverter with IGBTsIGBTs
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Power switch cabinet Power switch cabinet
(300 kW) with (300 kW) with IGBTsIGBTs
((EnerconEnercon))
DC in
AC out
IGBT modules
IGBT control
board (MPU)
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Frequency analysis of a wind with pulse width modulated inverter
frequency resolution: 6,25 Hz
0.0
0.5
1.0
1.5
2 3 4 5 6 7 8 9 10
Frequency, kHz
Cu
rre
nt/
no
min
al c
urr
en
t, %
Sampling frequency of the PWM inverter
2. harmonic3. harmonic
Frequency analysis of a wind with Frequency analysis of a wind with
PWM inverter PWM inverter
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Double fed induction generatorDouble fed induction generatorvariable speed with pulse width modulated invertervariable speed with pulse width modulated inverter