Oleksandra Dudurych
Department 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
Levels of Wind Energy
Supervisor:
Dr Michael Conlon
School 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
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 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 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
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 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)
WT with IG
Fixed
speed
WTGs – are directly
connected to the
grid, there would not
be much change in
the inertial and droop
response
WTGs Concepts (2)
Variable
speed
WTGs – the power
electronics
interface
between the generator
and grid results in an
electrical
decoupling,
due to which the inertial
and droop capabilities
will be missing
WT with DFIG
WT with fully rated convertor SG
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 wind
Higher values are observed under conditions of high
wind penetration
Wind Energy in Ireland (2)
System Load
Wind Generation
5000
Power, MW
4000
3000
2000
1000
0
01/01/13
20/02/13
11/04/13
31/05/13
20/07/13
Date
Overall Trace (2013)
08/09/13
28/10/13
17/12/13
Wind Energy in Ireland (3)
System Load
5000
Wind Generation
Power, MW
4000
3000
2000
1000
0
01/12/13
06/12/13
11/12/13
16/12/13
21/12/13
Date
Overall Trace (December 2013)
26/12/13
31/12/13
Wind Energy in Ireland (4)
70%
Contribution of Wind Generation to System Demand, %
60%
50%
40%
30%
20%
10%
0%
01/01/13
20/02/13
11/04/13
31/05/13
20/07/13
08/09/13
Date
Overall Trace % Contribution (2013)
28/10/13
17/12/13
Wind Energy in Ireland (5)
Percentage Contribution to Load
70%
Contribution of Wind Generation to System Demand, %
60%
50%
40%
30%
20%
10%
0%
01/12/13
06/12/13
11/12/13
16/12/13
21/12/13
26/12/13
Date
Overall Trace % Contribution (December 2013)
31/12/13
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 industrial
electrical power systems
A graphical model design with PowerFactory is the
mathematical analysed during simulation
Study Model using
PowerFactory
Study Model
LOAD 1
P=400 MW; Q=110 MVar
LOAD 2
P=100 MW; Q=40 MVar
DFIG
P= 2 MW
FRCG
P= 2 MW
TRF 2.222/20/0.69
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 kV
Simulation (1)
The analyse of this
network is used to
analyse
frequency
response due to change
of load
RoCoF is analysed
when
increased
penetration
level
DFIG, FRCG, and
combined DFIG and
FRCG
Simulation (2)
Simulation with 10 % DFIGs
Simulation (3)
Simulation with 30 % FRCGs
Results (1)
Table 1
Change of RoCoF with increasing of the penetration
level of wind energy
Wind
Synchronous
generators
RoCoF
DFIG
FRCG
DFIG+FRCG
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)
0.45
0.4
0.35
RoCoF, Hz/s
0.3
0.25
FRCG
0.2
DFIG
DFIG+FRCG
0.15
0.1
0.05
0
0%
10%
20%
30%
Wind
40%
50%
60%
Change of RoCoF with increasing of the penetration
level of wind energy
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 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. 39, 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.
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!