Emulated inertial response with wind turbines (Jan Van de Vyver, UGent)

1. Emulated inertial response with wind
turbines
Jan Van de Vyver
Ghent University
Faculty of Engineering and Architecture (FEA)
Department of Electrical Energy, Systems and Automation (EESA)
Electrical Energy Laboratory (EELAB)
INGEN
IEURSWETENSCH
APPEN
ARC HITEC T U UR
Jan.VandeVyver@UGent.be Emulated inertial response with wind turbines 1 / 9

2. Introduction
Who provides ancillary services?
Current situation:
Conventional generation → majority of services
Future situation:
Renewable electricity generation
⇒ conventional electricity generation
Problem:
Renewable = variable, decentralized
⇓
More ancillary services needed:
- additional power reserves
- frequency control
Less conventional generators to provide them:
- increased costs
- reduced life cycle
Solution:
⇒ provide ancillary services with wind turbines
Jan.VandeVyver@UGent.be Emulated inertial response with wind turbines 2 / 9

3. Frequency control
Overview of frequency control
Electric power system
• Power production has to be adapted to consumption at any point in time
• Rotational speed Ω of generators is proportional to grid frequency f
• Grid frequency f can be used as a measure:
- production = consumption ⇒ f = 50 Hz
- production > consumption ⇒ f
- production < consumption ⇒ f
• Grid frequency f is a global parameter
⇒ f can be used to balance production and consumption: primary frequency control
Jan.VandeVyver@UGent.be Emulated inertial response with wind turbines 3 / 9

4. Frequency control Inertial response
Inertial response in the conventional power system
Inertial response
Natural inertial response of directly coupled synchronous generators on disturbances:
Jf0
df
dt
= Pelec − Pload
- f : release of kinetic energy of rotating inertia
- f : absorb kinetic energy in rotating inertia
⇒ stabilising effect
Importance of inertial response
Low system inertia J:
• high ROCOF
• low frequency nadir
• less time for primary controller
to change power output of
generator
0 5 10 15 20 25 30 35
49
49.2
49.4
49.6
49.8
50
J
Time t [s]
f[Hz]
Jan.VandeVyver@UGent.be Emulated inertial response with wind turbines 4 / 9

5. Frequency control Inertial response
Natural inertial response with wind turbines
Modern wind turbines are connected to the grid by means of power-electronic converter:
• Doubly fed induction generator (DFIG)
• Full scale converter (FSC)
⇒ rotational speed Ω of the turbine is decoupled from the grid frequency f
⇒ little or no inertial reponse from variable speed wind turbines
⇒ system inertia J decreases ⇒ f varies more rapidly
Jan.VandeVyver@UGent.be Emulated inertial response with wind turbines 5 / 9

6. Frequency control Inertial response
Emulated inertial response with wind turbines
Solution: Emulation of inertial response with additional control loop in converter
Synthetic inertia:
Mimicking of the inertial response of a
synchronous generator:
Pin = −Kin
df
dt
− Kdroop∆f
Temporary power surge:
Power increase in case of a frequency dip
0 5 10 15 20 25 30 35 40 45 50
0.7
0.75
0.8
0.85
Time t [s]
Pref[pu]
∆POP
tOP
Pref,0
t
Pref
⇒ inertial behaviour of wind turbine ≈ directly coupled synchronous generator
Jan.VandeVyver@UGent.be Emulated inertial response with wind turbines 6 / 9

7. Frequency control Inertial response
Emulated inertial response with wind turbines
Differences with a conventional generator:
• Recovery period is needed to regain normal operation
• Energy yield losses arise due to suboptimal operation during inertial response
Tuning of the control parameters is crucial:
• Depends on the system composition (gas turbines vs. steam-based turbines)
• Can improve frequency response tremendously
• But: also risk of poor frequency response if not properly tuned
Kin[MWs
Hz ]
Kdroop[MW
Hz]
+
-
no WT →
-
0 1 2 3 4 5 6 7
0
0.5
1
1.5
2
2.5
fmin[Hz]
49.58
49.6
49.62
49.64
49.66
49.68
0 10 20 30 40 50 60 70 80 90 100
0.72
0.75
0.78
0.81
Time t [s]
Pwind[p.u.] 0 10 20 30 40 50 60 70 80 90 100
0.8
0.82
0.84
0.86
Ω[p.u.]
— Pwind
- - Ω
0 5 10 15 20 25 30 35 40 45 50
49.5
49.6
49.7
49.8
49.9
50
Time t [s]
f[Hz]
— No WT
- - WT without SI
— WT with SI
Jan.VandeVyver@UGent.be Emulated inertial response with wind turbines 7 / 9

8. Conclusions and outlook
Conclusions and outlook
• Technically, wind turbines can provide ancillary services
• Emulated inertial response and even enhanced frequency control (primary frequency control)
with wind turbines are possible
Outlook
• Development of control strategies with a limited impact on the lifetime of the wind turbines
• Field tests are important to demonstrate the positive impact
Jan.VandeVyver@UGent.be Emulated inertial response with wind turbines 8 / 9

9. Questions
Questions?
Contact details:
Jan Van de Vyver
Electrical Energy Laboratory (EELAB), Department of Electrical Energy, Systems and Automation
(EESA), Ghent University
Technologiepark-Zwijnaarde 913, 9052 Gent
Jan.VandeVyver@UGent.be
Jan.VandeVyver@UGent.be Emulated inertial response with wind turbines 9 / 9