EES-UETP HVDC and HVDC Grids for Future Transmission · Nicolaos A. Cutululis . DTU Wind Energy . Technical University of Denmark. Wind turbine technologies and controls . EES-UETP

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


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


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


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


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


Variable speed wind turbine (VSWT) control loops


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


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∝


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


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]


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


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


FRT for VSWT


Grid voltage

Grid power

Generator power

FRT for VSWT


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.”


Active power constraint functions


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

EES-UETP HVDC and HVDC Grids for Future Transmission · Nicolaos A. Cutululis . DTU Wind Energy . Technical University of Denmark. Wind turbine technologies and controls . EES-UETP

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