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!