reduced inertia response in power systems with high ... 02...reduced inertia response in power ......
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Oleksandra DudurychDepartment of Electric Power Stations
Institute of Power Engineering and Control Systems
Lviv Polytechnic National University, Ukraine
Reduced Inertia Response in Power
Systems with High Penetration Systems with High Penetration
Levels of Wind Energy
Supervisor:
Dr Michael ConlonSchool of Electrical and Electronic Engineering
Dublin Institute of Technology, Ireland
Overview
� Inertia Response and RoCoF
� What is Inertia?
� Why is Inertia important?
� The maths behind Inertia
� WTGs Concepts
� Wind Energy in Ireland� Wind Energy in Ireland
� Study Model using PowerFactory
� Simulation
� Results
� Conclusions
� References
What is Inertia?
� Inertia can be seen as the “resistance to change”
� Inertia of the power system is proportional to the
amount of rotating masses in the system
� It prevents the grid frequency suddenly changing
and results from synchronous generatorsand results from synchronous generators
� Inertia determines the rate of change of frequency
(RoCoF) following a load event
Why is Inertia Important? (1)
� The mechanical and electrical energy must be
balanced during steady state mode
� The balance between the supply and demand power
must be maintained
� The larger the system inertia, the less is the rate of
change of frequency following a power imbalancechange of frequency following a power imbalance
� When a mismatch is between the supply and
demand in the system, the rotors of the connected
generators will release or absorb kinetic energy and
as a result, the rotational speed and frequency will
change
Why is Inertia Important? (2)
� This is known as Inertia Response
� Inertia shows the speed of change of frequency
� This is important because many distribution
generators have their anti-islanding protection
based on RoCoF relay
� If RoCoF is high and there are a lot of distribution� If RoCoF is high and there are a lot of distribution
generators in such system, they will trip and system
will collapse
� Grid Code RoCoF standard is 0.5 Hz per second
The maths behind Inertia
Inertia and Wind Turbine Generators
� The traditional synchronous generators have certain
qualities which are very essential in controlling the
grid frequency
� WTGs currently do not participate in frequency
regulation. They do not increase or decrease their
power output when the frequency deviates from itspower output when the frequency deviates from its
nominal value
� Frequency stability in the power grid is essential for
maintaining security of the supply, this inadequacy
of the WTGs may pose a limit to the level of
penetration of these technologies into the existing
system
WTGs Concepts (1)
� Fixed speed
WTGs – are directly
connected to the
grid, there would notgrid, there would not
be much change in
the inertial and droop
responseWT with IG
WT with DFIG
� Variable speed
WTGs – the power
electronics interface
between the generator
WTGs Concepts (2)
WT with DFIG
WT with fully rated convertor SG
between the generator
and grid results in an
electrical decoupling,
due to which the inertial
and droop capabilities
will be missing
Wind Energy in Ireland (1)
� In Ireland currently all types WTGs are used, mainly
DFIGs
�Changes in transmission System required to facilitate
40% of electricity from renewable sources by 2020
�One of the range of challenges is reduction of inertia
in system with increasing windin system with increasing wind
�Higher values are observed under conditions of high
wind penetration
Wind Energy in Ireland (2)
3000
4000
5000
Po
wer,
MW
System LoadWind Generation
0
1000
2000
01/01/13 20/02/13 11/04/13 31/05/13 20/07/13 08/09/13 28/10/13 17/12/13
Po
wer,
MW
Date
Overall Trace (2013)
3000
4000
5000
Po
wer,
MW
System Load
Wind Generation
Wind Energy in Ireland (3)
0
1000
2000
01/12/13 06/12/13 11/12/13 16/12/13 21/12/13 26/12/13 31/12/13
Po
wer,
MW
Date
Overall Trace (December 2013)
Wind Energy in Ireland (4)
40%
50%
60%
70%
Co
ntr
ibu
tio
n o
f W
ind
Gen
era
tio
n t
o S
yste
m D
em
an
d,
%
0%
10%
20%
30%
01/01/13 20/02/13 11/04/13 31/05/13 20/07/13 08/09/13 28/10/13 17/12/13
Co
ntr
ibu
tio
n o
f W
ind
Gen
era
tio
n t
o S
yste
m D
em
an
d,
%
Date
Overall Trace % Contribution (2013)
40%
50%
60%
70%
Co
ntr
ibu
tio
n o
f W
ind
Gen
era
tio
n t
o S
yste
m D
em
an
d,
%
Percentage Contribution to Load
Wind Energy in Ireland (5)
0%
10%
20%
30%
01/12/13 06/12/13 11/12/13 16/12/13 21/12/13 26/12/13 31/12/13
Co
ntr
ibu
tio
n o
f W
ind
Gen
era
tio
n t
o S
yste
m D
em
an
d,
%
Date
Overall Trace % Contribution (December 2013)
Wind Energy in Ireland (6)
�Generation output for 2013
System Demand – 25840. 99 MWh
Wind – 4643.09 MWh
%Wind – 17.97%
Capacity factor – 26%
�Wind Generated Electricity
December
Capacity factor – 45%
DIgSILENT PowerFactory
�The appropriate models are required for the analyse and
simulation the electrical power systems
�The calculation program Power Factory, as written
DIgSILENT (DIGital SImuLation and Electrical
NeTwork) is a computer aided engineering tool for the
analysis of transmission, distribution, and industrialanalysis of transmission, distribution, and industrial
electrical power systems
�A graphical model design with PowerFactory is the
mathematical analysed during simulation
Study Model using
PowerFactoryLOAD 1
P=400 MW; Q=110 MVar
LOAD 2
P=100 MW; Q=40 MVar
DFIG
P= 2 MW
FRCG
P= 2 MW
TRF 2.222/20/0.69TRF 2.222/20/0.69
S=2.222 MVA
TRF 125/220/20
S=125 MVA
SG(1)
S=100 MW
TRF 125/220/10.5 (1)
125 MVA
SG(2)
100 MW
TRF 125/220/10.5 (2)
125 MVA
LINE
CL 20 kVStudy Model
Simulation (1)
� The analyse of this
network is used to
analyse frequency
response due to change
of load
� RoCoF is analysed
when increased
penetration levelpenetration level
DFIG, FRCG, and
combined DFIG and
FRCG
Simulation (2)
Simulation with 10 % DFIGs
Simulation (3)
Simulation with 30 % FRCGs
Results (1)
Wind Synchronous
generators
RoCoF
DFIG FRCG DFIG+FRCG
Table 1
Change of RoCoF with increasing of the penetration
level of wind energy
10% 90% 0.069 0.168 0.115
20% 80% 0.076 0.243 0.183
30% 70% 0.085 0.252 0.191
40% 60% 0.094 0.319 0.235
50% 50% 0.106 0.392 0.272
Results (2)
0.2
0.25
0.3
0.35
0.4
0.45
Ro
Co
F, H
z/s
FRCG
DFIG
Change of RoCoF with increasing of the penetration
level of wind energy
0
0.05
0.1
0.15
0% 10% 20% 30% 40% 50% 60%
Ro
Co
F, H
z/s
Wind
DFIG
DFIG+FRCG
Conclusions
� The increasing penetration of wind energy in the power grid
will effectively reduce the overall system inertia and increase the
equivalent system droop
� The change in these two vital system parameters will
adversely affect the frequency regulation capability of the
network, leading to increased peaks and dips in frequency after
every load eventsevery load events
� If the WTGs provide no inertial and droop capabilities in times
of low system frequency, the robustness of the system will be in
danger
� If variable speed WTGs are to be used for integrating wind
energy into the power grid, the hidden inertia and droop
capabilities from these machines can be extracted
References
DIgSILENT PowerFactory
G. Ramtharan, J.B. Ekanayake and N. Jenkins, “Frequency support from
doubly fed induction generator wind turbines”, IET Renew. Power Gen., pp. 3-
9, March, 2007.
H. Knudsen and J. N. Nielsen, “Introduction to the modeling of wind turbines,”
in Wind Power in Power Systems, T. Ackermann, Ed., Wiley, pp. 525–585,
2005.
P. Kundur, Power system stability and control, McGraw Hill, 1994.P. Kundur, Power system stability and control, McGraw Hill, 1994.
Y. Zhang and S. Ula, “Comparison and evaluation of three main types of wind
turbines”, Transmission and Distribution Conference and Exposition
IEEE/PES, Chicago, pp. 1-6. May 2008.
Thank you for attention!