Control and simulation of doubly-fed induction generator Control and simulation of doubly-fed induction generator for variable-speed wind turbine systems based on an for variable-speed wind turbine systems based on an
integrated Finite Element approachintegrated Finite Element approach
Qiong-zhong Chen*, Michel DefournyQiong-zhong Chen*, Michel Defourny##, Olivier Brüls*, Olivier Brüls*
*Department of Aerospace and Mechanical Engineering (LTAS), University of Liège, Belgium
# SAMTECH Headquarters, Liège, Belgium
EWEA 2011, Brussels, Belgium
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OutlineOutline
Background
Control of DFIG
Integrated simulation approach
Examples & validation
Conclusions
3
BackgroundBackground
Wind turbine concepts
Evolution of WT size:
Increased flexibility Increased coupling effects
(Data source: A. Perdala, dynamic models of wind turbines, PhD thesis, 2008)
WT types Gen. types
DFIG WTs DFIG
FSWTs SCIG
FCWTs PMSG, SCIG etc.
Other OSIG
Equipped gen. types
(Figure from EWEA factsheets)
4
BackgroundBackground
Computer-aided analysis for WT systems Software specialized in a certain field
Aerodynamics: AeroDyn etc. Structure: ADAMS/WT etc. Electrics: DIgSILENT etc.? Different systems on different simulation platforms?? No detailed coupling analysis
Integrated simulation packages: GH Bladed, Simpack Wind, HAWC2, FAST etc.
? Weak coupling (DLLs or co-simulation) ?? Numerical stability?
Need for integrated optimization tools (Bottasso, 2010)
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BackgroundBackground
Samcef for Wind Turbine (S4WT) Nonlinear FE flexible multibody solver: SAMCEF/MECANO One single platform:
Aeroelastics, multibody, control, electrodynamics etc. Flexibility in blades, shafts, tower etc. Simulation approaches: Weak & strong coupling
An integrated model on S4WT(Courtesy: Samtech)
…
6
Highlights of the paperHighlights of the paper
Improved control strategies of DFIG WTs Grid-synchronization Power optimization
Strongly-coupled approach for mechatronic systems [B. & Golinval 2006]
Integrated structure-control-generator analysis on S4WT
Brüls, O. and Golinval, J. C. The generalized-α method in mechatronic applications. Zeitschrift für angewandte mathematik und mechanik (ZAMM) 86, 10 (2006), 748-758.
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Control of DFIGControl of DFIG
Working process of WT systems
Control of DFIG: soft grid connection power optimization
Gear box
Grid
AC/ DC
DC/ AC
SWs
SWg SWr
Transformer
DFIG
RSC GSC
Wind turbine
A schematic configuration of a DFIG wind turbine
E
A B
C
D
Power Optimization
Power Limitation
Win
d p
ow
er
Wind speed
0
Tu
rbin
e o
utp
ut
pow
er
Rotor speed
0 A
B
C
D, E Power Optimization
Power Limitation
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Grid synchronization controlGrid synchronization control
Objective: Regulate stator voltage, frequency, phase angle
grid before connection
Method: Grid-voltage-oriented reference frame Vector control PI Controller designed based on internal model control
(IMC) method
+
_ Gr(s)
+ + qrVqr_refi qri
l r drs L i
+
DFIG
Cqr(s)
l r drs L i
_
FF term
+
_ Gr(s)
+ + drVdr_refi dri
l r qrs L i
_ DFIG
Cdr(s)
l r qrs L i
+
FF term
D,q-axis rotor current control loops
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Power controlPower control
Objective: Follow a pre-defined power-speed characteristics
profile speed regulation
Method Stator-flux-oriented reference frame
Vector control q-axis rotor current active power d-axis rotor current reactive power
IMC or pole placement method for design of controllers
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Power controlPower control
Power control scheme
Controllers: PI or IP regulators Design of controllers
PI : IMC method (current loop) IP : pole placement method (speed loop)
controller: CTω(s)
+
_
qr_refi
qri
qrvref
e_refT
dr_refi
dri
refQ drv
DFIG
controller: CiT(s)
controller: CiQ(s)
controller: Cvi_qr(s)
controller: Cvi_dr(s)
+
_
+
_
Decoupled speed and reactive power control of DFIG
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Design of controllersDesign of controllers
PI controller for q-axis rotor current i-v transfer function
PI controller on IMC
IMC parameter:
For electrical dynamics, the rise time is set to 10ms
1
( ) 1( )
( )qr
vi_qrqr
rs
I sG s
XV sR s
ω
1 1( ) ( ) rvi_qr qr
s
X RC s G s
s ω s
riseln 9 /= t
+
_ Cvi_qr(s) Gvi_qr(s)
¯ + qrVqr_refiqri
qrE
current control block
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Design of controllersDesign of controllers
IP controller for speed control Close-loop transfer function
Pole placement method
For over-damped systems:
For mechanical dynamics, the settling time is set to 1s, DFIG alone 2.5s, with WT system
+
_ Ki/s 1/(Js)
+ + e_refTref
Kp
+
_
mT
r
2
( )
( ) ( )ir
ref p i
K /Js=
s s + K /J s+ K /J
2
2p d nd
i nd
K = J
K = J
5.8nd sd= /t
Speed control block
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Integrated simulation approachIntegrated simulation approach
Strongly-coupled representation for mechatronic systems
Extended generalized-α solver Coupled 1st / 2nd order systems Second order accuracy Unconditional stability More details can be referred to [B. & Golinval 2006]
qMq Φ ( λ Φ) g(q,q, ) L y 0
Φ(q) 0
x f (q,q,q,λ, x, y, ) 0
y h(q,q,q,λ, x, y, ) 0
T ak p t
k
t
t
Mechanism
Control system
y ( , , , )q q q
Coupling in a mechatronic system
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Mechatronic Modelling on SAMCEFMechatronic Modelling on SAMCEF
Considerations for the Mechatronic modelling: Functional system decomposition Modularized, parameterized components
E.g. DFIG, PI, PID modules etc. Nodes are introduced for
Mechanical DOFs State variables Outputs
On a general-purpose use User-friendly Reusable
A uniform tangent matrix for Newton iteration
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Examples & validationExamples & validation
2MW DFIG parameters:
WT parameters:
Base voltage (line-to-line): Vbase= 690 V;Base power: Pbase= 2 MW;Grid frequency: fs= 50 Hz;Number of poles: np= 4;Stator resistance: Rs= 0.00488 p.u.;Rotor resistance : Rr= 0.00549 p.u.;Stator Leakage inductance: Lsl= 0.09241 p.u.;Rotor leakage inductance: Lrl= 0.09955 p.u.;Mutual inductance: Lm= 3.95279 p.u..
Inertia of the generator rotor: 100kg·m2
Blade length: 41m;Tower height: 75m;Gearbox ratio: 106Etc.
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Ex. 1:DFIG with defined input torqueEx. 1:DFIG with defined input torque
Simulation situation Synchronization process starts at 0.8
p.u. of the rotating speed
Reactive power reference: 0 p.u.
Speed (active power) control situation: Reference speed:
Input torque:
1 p.u., time 4sec
0.9 p.u., 4sec time 6sec
1.1 p.u., time 6sec
s
1 p.u., time 8.5sec
0.5time 5.25 p.u., 8.5sec time 9.5sec
0.5 p.u., time 9.5sec
mT
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ResultsResults
Grid synchronizationSynchronization starts
Synchronization finishes
A-phase grid voltage A-phase stator voltage
Grid synchronization process
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ResultsResults
Power controlSpeed response
Reactive power response
Rotor current response
iqr
idr
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Ex. 2: DFIG with WT structure modelEx. 2: DFIG with WT structure model
WT models on S4WT wind
8 m s, time 8sec
11 m s, time 8sec
/
/
Integration of DFIG with WT structure model on S4WT
Simulation situation: Initial WT speed:
1.1rad/s (0.74p.u.) Grid synchronization
starts at 0.8p.u. of generator speed
Reactive power reference: 0
Active power control according to wind speed:
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ResultsResults
Grid synchronizationSynchronization starts
Synchronization finishes
A-phase grid voltage A-phase stator voltage
Grid synchronization process
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ResultsResults
Power control
Active power
Reactive power
Schematic power-speed characteristics
Speed response
Power response
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ResultsResults
Influence of structural flexibility
With more rigid structure With more flexible structure
Generator torque
With more rigid structure With more flexible structure
Speed response
Blade Rigi. Flex.
Young’s module (Gpa) 100 30
Damping (N/m/s) 4.55e-2 4.55e-3
Shaft Rigi. Flex.
Bending stiffness (Nm/deg) 86.92 43.46
Bending damping (kg·m2/s) 0 0
Torsional stiffness (Nm/deg) 55.85 27.93
Torsional damping (kg·m2/s) 7858 785.8
Other applied elements: Flexible tower Simple gearbox, bedplate
elements etc.
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ConclusionsConclusions
Improved control strategies for DFIG Grid synchronization & power control Solution to the difficulty in the configuration of the
controllers’ coefficients
Integrated FE approach with strong coupling instead of weak coupling Unconditional stability, less intricacy Could be less efficient
Modular models of the generator/control systems for S4WT package (on a general purpose)
Integrated variable-speed DFIG WT system model analysis and validation
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In acknowledgement of DYNAWIND (grant number: 850533)
funded by Wallonia government, Belgium
Thank you for your Attention!