Nicolaos A. Cutululis DTU Wind Energy
Technical University of Denmark
Wind turbine technologies and controls
EES-UETP HVDC and HVDC Grids for Future Transmission
May 28 – June 1, 2018 Leuven, Belgium
DTU – excellence since 1829
The College of Advanced Technology is founded by Hans Christian Ørsted with two study programmes: Chemistry and Mechanical Engineering. In 1857 Civil Engineering and in 1903 Electrical Engineering.
New Campus in Lundtofte. Official inauguration ceremony in 1974.
Merged with Danmarks Ingeniør Akademi (DIA).
Name change to Technical University of Denmark.
Independent and self-govering university with a Board of Governors and an Executive Board.
Merged with five National Research Institutes, doubling DTU’s staff and expanding the University’s scientific capacity.
Integrated Copenhagen University College of Engineering (IHK).
1829
1962 1994 1995
2001
2013
2007
One university – many locations
DTU Lyngby Campus
DTU Ballerup Campus
DTU Risø Campus
Risø DTU Wind Energy
Risø DTU Wind Energy
Learning objectives
• After this lecture, you should be able to:
–Describe the wind turbine types and concepts –Formulate the aerodynamic and electric power –Understand the basic wind turbine control loops –Explain the main wind turbine control concepts
It’s big!
Source: https://www.ge.com/renewableenergy/wind-energy/turbines/haliade-x-offshore-turbine
Wind Turbine Types
GB ASG
QC TR
Type 1
GB ASG
QC TR
Type 2 VRR
ASG: Asynchronous generator GB: Gearbox QC: Reactive power compensation TR: Transformer VRR: Variable rotor resistance
GB ASG
TR
Type 3
=
~
~
=
CH C L
CR GSC LSC
GSC: Generator side converter LSC: Line side converter CR: Crowbar C: DC link capacitor CH: Chopper L: Series inductance SG: Synchronous generator
SG/ASG
GB
TR
Type 4
=
~
~
=
CH C L
GSC LSC
Source: P. Sørensen, Wind Power Summer School, Control of Wind Power Plants
Wind turbine concepts
Pitch angle control
Rotor speed control wtrω
θ
Fixed speed wind turbines (FSWTs) o Speed fixed to the grid frequency
Variable speed wind turbines (VSWTs) o Decoupled from the grid frequency o Power electronics
Fixed pitch wind turbines Variable pitch wind turbines
o Pitch control wind turbines (pos. angles) o Active stall control wind turbines (neg. angles)
o Passive stall control wind turbines
Source: A.D.Hansen, DTU Master Course 46230 – Power system Balance with large Wind Power
Electrical power – power curve
Wind speed [m/s] 0 5 10 15 20 25
1
2
power limitation zone
power optimization zone
cut-out wind
cut-in wind rated wind speed
rated power
aerodynamic power 3UP ∝
Power curve provides steady state relation (measured as 10 min averages) between wind speed and power
Source: A.D.Hansen, DTU Master Course 46230 – Power system Balance with large Wind Power
vtip
ϕ
U
Top view
Aerodynamic power – power coefficient
• P : aerodynamic power [W]
• U : wind speed
• ρ : air density [kg/m3]
• A : rotor (swept) area
• Cp : power coefficient
• ϕ : blade pitch angle
• λ : tip speed ratio
( )ϕλρ ,21 3
pCAUP =
UR
Uv ⋅
==ωλ tip
A
vtip
ω
Front view
U
Side view
Source: P. Sørensen, Wind Power Summer School, Control of Wind Power Plants
Aerodynamic efficiency
( )θλ,pp CC =
( )θλ,pC
λ θ1θ nθ2θ
1λ
2λ
nλ
θ
λ
-90
-45
0
45
905
1015
200.0
0.1
0.2
0.3
0.4
0.5
Cp
Pitch angle [deg]
Tip speed ratio
Source: A.D.Hansen, DTU Master Course 46230 – Power system Balance with large Wind Power
Wind turbine control
Why control wind turbines?
Fixed speed wind turbines
λ θ1θ nθ2θ
1λ
2λ
nλ
kθ
fixed pitch θ
( )kpC θλ,U
Rwtr ⋅=ωλ
fixed ωwtr
fixed
optpoptopt CUAP 3
21 ρ=
-90
-45
0
45
905
1015
20
0.0
0.1
0.2
0.3
0.4
0.5
Cp
Pitch angle [deg]
Tip speed ratio
Source: A.D.Hansen, DTU Master Course 46230 – Power system Balance with large Wind Power
optpC optλ
RUoptopt
wtr
⋅=λ
ω
Variable speed wind turbine
max3
21
max pC CUAPp
ρ=U
Rwtropt
⋅=
ωλ
optθmaxpC
λ θ1θ nθ2θ
1λ
2λ
nλ
θ
kλλopt
θopt
variable
-90
-45
0
45
905
1015
20
0.0
0.1
0.2
0.3
0.4
0.5
Cp
Pitch angle [deg]
Tip speed ratio
maxpC
Source: A.D.Hansen, DTU Master Course 46230 – Power system Balance with large Wind Power
Variable speed wind turbine (VSWT) control loops
Source: P. Sørensen, Wind Power Summer School, Control of Wind Power Plants
VSWT performance
P [pu]
U [m/s]
P [pu]
ngen [rpm]
A
B
C DPrated
ω [pu]
A
B C Dωnom
λ [rad/s]A B
C
D
λopt
U [m/s]
U [m/s]
A
B
C, D
Cp A BC
D
U [m/s]
U [m/s]
θ [deg]
A B C
D
nnomUrated
Power curve
AB: variable BCD: fixed
ωω
optλRotor speed adjusted to keep
ω
Control concept
Efficiency decreases in power limitation
Active pitch control in power limitation
Constant pitch angle in optimization
Source: A.D.Hansen, DTU Master Course 46230 – Power system Balance with large Wind Power
Electrical control – MPPT
max3
21max
pC
wtr CUAP p ρ=
3
3
3
max5
max
max
21
gear
gen
C
pCwtrwtrgeargen N
CRPN
p
pω
λπρωω =⇒=
3
max35
21max
opt
pwtr
Cwtr
opt
wtrwtropt
CRPRU
UR p
λωπρ
λωωλ =⇒
⋅=⇒
⋅=
wtrgen PP ≈Assuming:
3max
genC
wtr constP p ω⋅=
genω
3max
genC
genpP ω∝genP
3max
genC
genpP ω∝
Source: A.D.Hansen, DTU Master Course 46230 – Power system Balance with large Wind Power
Electrical control – MPPT
Control concept
3genoptP ω∝
nomgenω
Prated
A
B
AB – optimization with variable speed
B’
C,
BC – optimization with fixed speed
D
CD – power limitation zone
Control design
nomgenω pu
genω
pugenP
B A
1
3gen
pugen constP ω⋅=1
C,D Prated 2
2 1=pugenP
3
3 1)(1 '_3 +−= puC
genpu
vectgenslopeP ωω
C’
?
pugenP
pugenω
puCgen
'ω
Source: A.D.Hansen, DTU Master Course 46230 – Power system Balance with large Wind Power
Pitch Control
Power optimization: It keeps the pitch angle at its optimal value
Power limitation: It s active limiting the power to the rated value
optθ
P [pu]
A
B
C DPrated
Cp A BC
D
U [m/s]
U [m/s]poweroptimisation
powerlimitation
A B C
D
U [m/s]
θ [deg]θ [deg]
Source: A.D.Hansen, DTU Master Course 46230 – Power system Balance with large Wind Power
Pitch Control
Pitch controller Actuator refθ θrefω
ω
typically PI controller speed error as input
hydraulic or electric reference pitch angle as input
θ
Actuator
servosT+11
,maxθ maxθ
minθ,minθ
refθ+
-
minθ
ω
refω
Pitch controller
maxθ
ω∆PI controller
θ
θ
Source: A.D.Hansen, DTU Master Course 46230 – Power system Balance with large Wind Power
Fault-ride-through (FRT)
• Fault-ride-through (FRT) is the capability of electric generators to stay connected in short periods of abnormal electric network voltage
• If FRT not present, generators are susceptible of tripping (disconnect) when a fault occurs, leading to loss of generation frequency collapse blackout
• The concept – FRT – applies equally to all generators, but the power electronic interface makes the FRT behavior of wind power fully dependent on control
• The capability is required for both under-voltage (LVRT) or over voltage (OVRT)
Source: N. A. Cutululis, DTU Master Course 46W27 – Grid connection and integration of wind power
Under-voltage FRT
Source: Til Kristian Vrana et al. Wind Power within European Grid Codes: Evolution, Status and Outlook, 2017
FRT for VSWT
Source: A. D. Hansen & G. Michalke, Multi-pole permanent magnet synchronous generator wind turbines’ grid support capability in uninterrupted operation during grid faults, IET Renewable Power Generation, 2009
FRT for VSWT
Source: A. D. Hansen & G. Michalke, Multi-pole permanent magnet synchronous generator wind turbines’ grid support capability in uninterrupted operation during grid faults, IET Renewable Power Generation, 2009
FRT for VSWT
Source: A. D. Hansen & G. Michalke, Multi-pole permanent magnet synchronous generator wind turbines’ grid support capability in uninterrupted operation during grid faults, IET Renewable Power Generation, 2009
Grid voltage
Grid power
Generator power
FRT for VSWT
Source: A. D. Hansen & G. Michalke, Multi-pole permanent magnet synchronous generator wind turbines’ grid support capability in uninterrupted operation during grid faults, IET Renewable Power Generation, 2009
Mechanical torque
Generator speed
DC voltage
Active power control functions
“A wind power plant must be equipped with active power control functions capable of controlling the active power supplied by a wind power plant in the Point of Connection using activation orders with set points” “In case of frequency deviations in the public electricity supply grid, the wind power plant must be able to provide frequency control to stabilise the grid frequency (50.00 Hz)” “A wind power plant must be equipped with constraint functions, i.e. supplementary active power control functions”
*Technical regulation 3.2.5 for wind power plants above 11 kW – Energinet.dk, Denmark
Active power constraint functions
1 - Absolute power constraint “An absolute power constraint is used to limit active power from a wind power plant to a set point-defined maximum power limit in the Point of Connection.”
2- Delta power constraint (spinning reserve) “A delta power constraint is used to constrain the active power from a wind power plant to a required constant value in proportion to the possible active power.” 3- Ramp rate constraint “A ramp rate constraint is used to limit the maximum speed by which the active power can be changed in the event of changes in wind speed or active power set points.”
*Technical regulation 3.2.5 for wind power plants above 11 kW – Energinet.dk, Denmark
Active power constraint functions
*Technical regulation 3.2.5 for wind power plants above 11 kW – Energinet.dk, Denmark
2
1
3
Conclusions
Wind turbines are (very) controllable devices …but the controllability can vary a lot, depending on turbine concept: - fixed / variable speed - fixed / variable pitch Control can: - optimize production - reduce structural loads - support grid integration