40220140507006

International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 5, Issue 7, July (2014), pp. 56-66 © IAEME
INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING
TECHNOLOGY (IJEET)
ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
Volume 5, Issue 7, July (2014), pp. 56-66
© IAEME: www.iaeme.com/IJEET.asp
Journal Impact Factor (2014): 6.8310 (Calculated by GISI)
www.jifactor.com
56

IJEET
© I A E M E
MODELING ANALYSIS OF AGC IN MULTI SOURCE DEREGULATED
POWER SYSTEMS
K. Hari Krishna1, Dr. K. Chandra Sekhar2
1(E.E.E., Assoc. Prof., Kallam Haranadhareddy Institute of Technology, Guntur,
Andhra Pradesh, INDIA)
2(E.E.E., Prof. H.O.D., R.V.R.J.C. College of Engineering Technology, Guntur,
Andhra Pradesh, INDIA)
ABSTRACT
This paper presents a new AGC simulation model for deregulated power systems, which
simplifies the design of the controller by concentrating mainly on load disturbances due to contract
violation of DISCOs in the system. In each area of the proposed AGC model thermal, hydro and gas
generators are considered to be part of generation control. Frequency variation due to the bilateral
contract loads is also studied with the help of DPM (DISCO participation matrix) concept. The
MATLAB/SIMULINK model of the proposed model is presented for the contracted load and UN
contracted load. Performance of the designed controller in controlling the frequency of the system
under contracted load and UN contracted load deviation is analyzed using simulation results.
Keywords: Deregulated Power Systems, DISCO Participation Matrix, Automatic Generation
Control, Thermal Generation, Hydro Generation.
1. INTRODUCTION
In the traditional power systems, the generation, transmission and distribution are owned by a
single entity called a vertically integrated utility (VIU), which supplies power at regulated rates.
Such VIUs are interconnected by tie lines to other VIU’s to enhance reliability. Following a load
disturbance within a VIU, the frequency of that VIU experiences a transient change, and the
feedback mechanism comes into play and generates an appropriate rise/lower signal to the turbine to
make the generation follow the load. In steady state, the generation is matches with the load, driving
the tie line power and frequency deviations to zero.

57

As deregulation in electric industry is a fast approaching reality, the operation and regulation
of the power system in this new type of environment will be different from as it was in the regulated
scheme. Under deregulation the power system structure changed in such a way that would allow the
evolving of more specialized industries for generation (GENCO), transmission (TRANSCO) and
distribution (DISCO). In the context of open access, increased competition two questions have been
consistently rising; (i) how can system reliability and security be maintained and (ii) how can be
economic efficiency maintained?. As a result, the concept of independent system operator (ISO) as
an unbiased coordinator to balance reliability with economics has emerged [2-3]. However, the
common operational objectives, i.e. restoring the frequency and the net interchanges to their desired
values for each control area remain. In the vertically integrated power system structure, some
generation units are equipped with secondary control and frequency regulation requirements, but in
an open energy market, even such GENCOs may or may not participate in the AGC. A deregulated
power system consists of generation companies (GENCO), distribution companies (DISCO),
transmission companies and Independent System model for the deregulated environment should
possess. In the section 3 we proposed a new model which incorporates this Operator (ISO). In this
open market based in bilateral contracts, DISCOs have the freedom to contract with any of the
GENCO in the own area or other area and these contracts are made under supervision of ISO. ISO is
also responsible for managing the ancillary services like AGC etc. Same as DISCOs, ISO will also
have freedom to get power from the same or other area to provide ancillary services to the system.
Therefore, in system with an open access policy, there is a need for an AGC model which can be
used for analysis as well as development of a efficient control strategies. Attempts have been made in
recent past to study AGC issues in deregulated environment. Most of the studies essentially use a
model proposed by M.A. Pai [1] for AGC in deregulated power systems. Varieties of models have
been developed over the last few decades considering different types of generation in each area. But
all the generation in an area is of the same type of (reheat/non reheat or hydro) generation [2]-[15].
In real situations, each control area may have various types of generation such as hydro, thermal, gas,
nuclear etc. The results in [6] are an attempt to study the performance of AGC with thermal, hydro
and gas generations in the same area. But, it does not distinguish the generator participation between
meeting the area load and AGC.
In view of this the main aim of this work are: (1)to develop a realistic AGC model under
open market system, to take into account the effect of bilateral contracts on the system, to include the
concept of DISCO Participation matrix in a two area AGC system, to consider the three types of
generators to be part of AGC (Thermal, Hydro, Gas) and optimize the gain of integral controller
under deregulated environment.This paper is organized as follows, In section 2 we first briefly
present the AGC model proposed in [1] and which is used by several other researchers. We highlight
its limitations and indicate the desirable features that an AGC features and includes three types of
generating stations to be part of AGC. Simulation results are given in section 5, to highlight the
difference between the proposed model and existing AGC models. We also demonstrate design of a
simple control strategy which can be adopted in the deregulation scenario. However this control is
available for any of the well known alternate control strategies.
2. CONVENTIONAL AGC MODEL FOR DEREGULATED POWER SYSTEMS
2.1 Conventional Model
The conventional model, that’s being used by several researchers [1-15], is essentially a
simple extinction of traditional Elgerd model [1]. In this AGC model, the concept of disco
participation matrix (DPM) is included to the conventional AGC model to incorporate the bilateral

load contracts. The DPM gives the extent of consumption of a DISCO from a particulate GENCO. In
a power system with m DISCOs and n GENCOs, the DPM is given as
cpf cpf cpf cpf

cpf cpf cpf cpf
=

58

11 12 13 14
21 22 23 24
31 32 33 34
41 42 43 44
DPM
cpf cpf cpf cpf
cpf cpf cpf cpf
is the “generation participation factor”, which shows the participation factor of
GENCO i in the load following of DISCO j. The sum of all the entries in a column in this matrix is
unity ( ). Whenever a load demanded by a DISCO changes, it is reflected as a
local load in the area to which this DISCO belongs.
These information signals which are not present in the conventional AGC. In [1] introduction
of these signals are justified arguing that these signals give an indication regarding which generator
has to follow to which DISCO. As there are many GENCOs in each area, AGC signal has to be
distributed among them according to their participation in the AGC. “ACE (Area Control Error)
participation factors (apf)” are the coefficient factors which distributes the ACE among GENCOs. If
there are ‘m’ number of GENCOs then

.In this model, the scheduled value of steady
state tie line power is given as
1 2 , (demand of DISCOs in area II from GENCOs in area I) -
(demand of DISCOs in area I from GENCOs in area II)
sch eduled P − D =
Then the tie line power error 1 2,error P− D
is expressed as
1 2,error 1 2,actual 1 2,scheduled P P P − − − D = D − D
1 2,error P− D
is used to generate the respective ACE signals instead of Ptie in traditional power systems.
ACE of ith area will be given as
1 1 1 1 2tie,error ACE B F P− = D + D
2 2 2 2 1tie,error ACE B F P − = D + D
2.2 Limitations of the Model
As indicated earlier, the introduction of DPM into the conventional AGC model is the most
significant change that has been incorporated in the above model. The other feature is the
requirement that there must be at least one GENCO in each area to provide AGC. Several controllers
have been designed for this model with an inclusion of bilateral contracts by use of DPM. But the
fact is bilateral contracts are known demands and the variation of frequency due to these contracts
need not be included in design of secondary control of AGC. Simulation results for the existing
model which includes bilateral contracts are presented with and without controller in the figure1.
From figure1 it is evident that the performance of the system frequency due to contracted load
demand (bilateral contracts) is same in all possible cases (with and without controller).

0 10 20 30 40 50 60
0
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
-0.09
D = D − D
P cpf P cpf P −
tie scheduled ij Lj ij Lj
= = = =
ACE B f P (3)
ACE B f P (4)
59

(a) (b)
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
Figure 1: Frequency response and Tie line power deviation for the existing model which includes
bilateral contracts with and without controllers
3. PROPOSED AGC MODEL
The two area AGC system considered has two individual areas connected with a tie line. The
deviation in each area frequency is determined by considering the dynamics of the governors,
turbines, generators and loads represents in that area. The tie line deviation between the areas is
computed as the product of the tie line constant and the frequency deviation difference between two
areas. fig. 2 shows the AGC model of the two area system considered. Figure 3 shows dynamic
models of the generators in the modeling of each area. The state space representation of AGC model
is given by
(x = Ax + Bu + Gp + b q 1)
Where x is state vector, u is control vector and p is disturbance vector. A, B and and are
the constant matrices associated with state, control, disturbance and bilateral contract vectors
respectively. The tie line power in two area AGC is given as
12 ( )
D = D − D
12 1 2
(2)
T
P f f
tie
s
The scheduled power on the tie line in the direction from area I to area II is
2 4 4 2
1 2 ,
1 3 3 1
i j i j
From the AGC model, frequency and tie line power error signals are used to generate the ACE signal
in respective area [1]. This ACE of the area is written as
.
1 1 1 12
tie error
= D + D
−
.
2 2 2 21
tie error
= D + D
−
-0.5
dist + cont at begi
cont+dist after delay
only dist at begi
0 10 20 30 40 50 60
-0.1
Only dist
Dist + Contr at Begi
Dist + contr with delay

1
Tr.s+1
Thermal Plant
1
Tgh.s+1
Hydero Plant
a
b.s+c
Gas Plant
60

Kps
Tps.s+1
-K2
s
-K2
s
T12
s
Kps
Tps.s+1
B1
B1
Pg1-Pd1-Ptie
Area 1 Generators
[Ptie]
BC of GEN 1
BC of GEN 2
BC of GEN 3
BC of GEN 4
BC of GEN 5
BC of GEN 6
Bilateral Contracts of DISCOMs
GR 2
GR 1
GR 3
BC 1
ACE 1
BC 2
Ptie
BC 3
Ptie
BC 4
BC 5
ACE 2
BC 6
GR 4
GR 6
GR 5
Pg2-Pd2+Ptie
Area 2 Generators
Fig 2: Modified model of AGC in deregulated power systems with Thermal, Hydro and Gas
generators
0.2
Load in Area 1
Kr*Tr.s+1
Tt.s+1
-Tws+1
0.5*Tws+1
-Tcrs+1
Tf.s+1
1
Tg.s+1
TR.s+1
Trh.s+1
X.s+1
Y.s+1
1
Tcd.s+1
BC 1
Fig 3: Sub system of the area 1 generators
1
Pg1-Pd1-Ptie
-1/Rth
apf1
apf2
apf3
GR 1
2
-1/Rhy
-1/Rg
6
4
BC 2
8
BC 3
7 Ptie
ACE 1
GR 2
1
GR 3
3
The two area system in the deregulated case with identical areas can be optimized with
5
respect to system parameters to obtain the best response. The parameter involved in the feedback is
the integral controller (KI). The optimal value of KI depends upon the cost function used for
optimization. The integral of squared error criterion (ISE) is used in this case; the objective of this
controller is achieved by minimizing a performance index (J). Where J is given as
( ) 2 2 2
1 2 tie12 error J f f P dt − = D + D + D
4. SIMULATION RESULTS
Case 1:
Two area AGC model is used to illustrate the performance of the present model. To study this
model, consider a case where all the DISCOs contract with the GENCOs for power as per the bellow
DPM:


D = D = D = D =
0.03; 0.09; 0.09; 0.05;
P P P P
m m m m
D = D =
0.09; 0.05
P P
P =Load of DISCO + Load of DISCO = 0.2 pu MW (no un contracted load)
61

0.1 0 0.2 0
0.2 0.1 0.1 0.5
0.3 0.2 0.3 0.1
DPM=
0.2 0.1 0 0.2
0.2 0.2 0.3 0.2
0 0.4 0.1 0
It is assumed that each DISCO demands 0.1pu power from GENCOs as defined in DPM and
each GENCO participated in AGC as defined by following apfs: apf1=0.33, apf2=0.33, apf3=34,
apf4=0.33, apf5=0.33, apf6=0.34.
For the DPM mentioned above GENCOs generation must be
1 2 3 4
5 6
m m
The total local load in area 1
L1,LOC 1 2
Similarly, the total local load in area 2
L2,LOC 3 4 P =Load of DISCO +Load of DISCO = 0.2 pu MW (no un contracted load)
Tie line power can be calculated by using the formula given in the above section and is given by
0.01pu as shown in the results.
The response of the system is shown in figure 4.
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
0 10 20 30 40 50 60 70 80 90 100
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
(a) (b)
0.1
0.08
0.06
0.04
0.02
0
-0.02
-0.04
(c) (d)
-0.8
Time
Frequency 1
0 10 20 30 40 50 60 70 80 90 100
Time
frequency 2
0.1
0.08
0.06
0.04
0.02
0
-0.02
0 10 20 30 40 50 60 70 80 90 100
Time
GENCO 1
0 10 20 30 40 50 60 70 80 90 100
Time
GENCO 2

12
10
8
6
4
2
0
-2
x 10
-3
0 10 20 30 40 50 60 70 80 90 100
Time
62

0.3
0.25
0.2
0.15
0.1
0.05
0
-0.05
0 10 20 30 40 50 60 70 80 90 100
Time
0.12
0.1
0.08
0.06
0.04
0.02
0
0 10 20 30 40 50 60 70 80 90 100
Time
GENCO 4
(e) (f)
0.1
0.08
0.06
0.04
0.02
0
-0.02
-0.04
0 10 20 30 40 50 60 70 80 90 100
Time
0.3
0.25
0.2
0.15
0.1
0.05
0
-0.05
0 10 20 30 40 50 60 70 80 90 100
Time
GENCO 6
(g) (h)

(i)
GE N CO 3
GENCO 5
Tie line power
Figure 4: (a,b) Frequency deviations in area 1 and 2 (Hz), (c,d,e,f,g,h) Generated power of six generators
in two area AGC, (i) Tie line power
Results in the figure 5 shows that, to meet the DISCOs demand each generator is generating
power according to their participation matrix mentioned in the DISCO participation matrix. Due to
power balance between the generated power by the GENCOs and load demand by the DISCOs, the
frequency in each area is settled to its rated value (frequency deviation in the response is settled to
zero). The tie line power is also observed to be at its calculated value is also observed to be at its
calculated value from the simulation results. This testifies that the designed controller is succeeded in
controlling the generation and frequencies of the system to maintain the system balance.


D = D = D = D =
0.08; 0.03; 0.08; 0.05;
P P P P
m m m m
D = D =
0.06; 0.1
P P
P =Load of DISCO + Load of DISCO + load disturbance=0.2 pu + load disturbance
0.23
0.225
0.22
0.215
0.21
0.205
0.2
0 50 100 150 200 250 300 350
63
Case 2: Contract Violation

It may happen that a DISCO violates a contract by demanding more power than that specified in
the contract. This excess power is not contracted out to any GENCO. This Un-contracted power must be
supplied by the GENCOs in the same area as the DISCO. It must be reflected as a local load of the area
but not as the contract demand. Consider that DISCOs in area 1 are violating contracts and demanding an
excess power as shown in figure 6. The response of the system is shown in figure 6 with this contract
violation for the disturbance shown in the figure 5 and for the DPM as follows.
0.1 0 0.3 0.4
0 0.1 0 0.2
0.3 0.4 0.1 0
DPM=
0.2 0 0.2 0.1
0.2 0.3 0 0.1
0.2 0.2 0.4 0.2
Each GENCO participated in AGC as defined by following apfs: apf1=0.2, apf2=0.5, apf3=3,
apf4=0.3, apf5=0.45, apf6=0.25.
For the DPM mentioned above GENCOs generation must be
1 2 3 4
5 6
m m
The total local load in area 1
L1,LOC 1 2
Similarly, the total local load in area 2
L2,LOC 3 4 P =Load of DISCO +Load of DISCO =0.2 pu (no un contracted load)
Fig 5: Contract power violation in the area 1
0.195
time
D is tu rb a n c e P o w e r

64

0.6
0.4
0.2
0
-0.2
-0.4
-0.6
0 50 100 150 200 250 300 350
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
(a) (b)
0.08
0.06
0.04
0.02
0
-0.02
-0.04
(c) (d)
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
(e) (f)
0.3
0.25
0.2
0.15
0.1
0.05
0
-0.05
(g) (h)
(i)
0.12
0.1
0.08
0.06
0.04
0.02
0
0.3
0.25
0.2
0.15
0.1
0.05
0
-0.05
0.08
0.06
0.04
0.02
0
-0.02
-0.04
0.005
0
-0.005
-0.01
-0.015
-0.02
-0.025
Figure 6: (a,b) Frequency deviations in area 1 and 2 (Hz), (c,d,e,f,g,h) Generated power of six generators
in two area AGC, (i) Tie line power
-0.8
time
frequency 1
0 50 100 150 200 250 300 350
time
frequency 2
0 50 100 150 200 250 300 350
time
GENCO1
0 50 100 150 200 250 300 350
time
GENCO2
0 50 100 150 200 250 300 350
time
GENCO3
0 50 100 150 200 250 300 350
time
GENCO4
0 50 100 150 200 250 300 350
time
GENCO5
0 50 100 150 200 250 300 350
time
GENCO6
0 50 100 150 200 250 300 350
time
Tie line power

65

The simulation results in figure 6 shows that the disturbance in area 1 causes frequency variation
in area 1 to be more than the same area 2. From the response of the generators it is clear that, as a primary
action generators in both the areas are responding at the beginning for the disturbance in area 1. But when
the secondary control comes in to action, generators in area 1 are only responding for the disturbance in
the corresponding area and remaining generators are ineffective in steady state. The tie line power is also
unchanged in the steady state because there is no contribution of area 2 generators for the disturbance in
area1.
5. CONCLUSIONS
Simulation model for automatic generation control in deregulated power systems is presented by
focusing mainly on the UN contracted load demands. Frequency variation due to bilateral contracts also
been studied with the help of DISCO participation matrix. Dynamic models of most commonly used
generating plants (Thermal, Hydro and Gas) are included in the AGC. Controller is also designed and
analyzed to control the frequency and tie line power errors in multi area AGC in deregulated power
systems. Simulation results shows that for a contracted load generators in both area will respond and
generate the power according to the bilateral contracts but when the load disturbance comes the
generators in the respective area only will compensate the disturbance in the steady state.
APPENDIX
Steam Turbine model parameters
Tg = 0.08; Tt = 0.3; Tr = 10; Kr = 0.3; Rth = 2.4.
Hydro Turbine model parameters
Tw = 1; TR = 5; Trh = 28.75; Tgh = 0.2; Rhy = 2.4;
Gas turbine model parameters
X = 0.6; Y = 1.0; a = 1; b = 0.05; c = 1; Tf = 0.23; Tcr = 0.01; Tcd = 0.2; Rg = 2.4;
Power system parameters
Kps = 120; Tps = 20;
6. REFERENCES
[1] R. Christie and A.bose, “Load-frequency control issues in power system operations after
deregulation,” IEEE transactions power systems, Vol.11, pp.1191-1200, Aug. 1996.
[2] Christie RD, Bose A.Load frequency control issues in power system operations after
deregulation. IEEE Transactions on Power Systems 1996;11 (3):1191–200.
[3] KumarJ, NgKah Hoe, Sheble G. AGC Simulator for price based operation part 1: a model.
IEEE Transactions on Power Systems 1997;12(2):527–32.
[4] Kumar Jayant, NgKah Hoe, Sheble Gerald. AGC simulator for price-based operation part- I:
case study results. IEEE Transactions on Power Systems 1997;12(2):533–8.
[5] Bakken BH, Grand OS. Automatic generation control in a deregulated power system. IEEE
Transactions on Power Systems 1998;13(4):1401–6.
[6] Donde V, Pai M A, Hiskens IA. Simulation and optimization in an AGC system after
deregulation. IEEE Transactions on Power Systems 2001;16(3): 481–9.
[7] Delfino B, Fornari F, MassuccoS. Load-frequency control and in advertent interchange
evaluation in restructured power systems. IEE Proceedings- Generation, Transmission and
Distribution 2002; 149(5):607–14.
[8] Shayeghi Hossein, Shayanfar HeidarAli. Design of decentralized robust LFC in a competitive
electricity environment. Journal of Electrical Engineering 2005;56(9-10):225–36.

66

[9] Shayeghi Hossein, Shayanfar Heidar Ali, Jalili Aref. Multistage fuzzy PID load frequency
controller in a restructured power system. Journal of Electrical Engineering 2007; 58(2):
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[10] Shayeghi H. A robust decentralized power system load frequency control. Journal of
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[11] Hosseini, Etemadi. Adaptive neuro fuzzy inference system based automatic generation
control. Electric Power Systems Research 2008; 78:1230–9.
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[13] Debbarma S, Saikia LC, SinhaN. AGC of a multi-area thermal system under deregulated
environment using non-integer controller. Electrical Power Systems Research 2013; 95:
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[14] Bhatt P, RoyR, GhoshalSP. Optimized multi area AGC simulation in restructured power
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0976-6545, ISSN Online: 0976-6553.
AUTHORS’ INFORMATION
K. Hari Krishna1 received B.Tech M.Tech degrees in Electrical Electronics
Engg. From Jawaharlal Nehru Technological University Acharya Nagajuna
University in 2003 2006 respectively. He is having 10 years of teaching
experience and pursuing Ph.D. from A.N.U. Currently he is an Associate Professor
in the Department of E.E.E., Kallam Haranadha Reddy Institute of Technology,
Guntur. His teaching and research interest include power system operation and
stability.
Dr. K. Chandra Sekhar2 received his B.Tech degree in Electrical Electronics
Engineering from V.R.Siddartha Engineering College, Vijayawada, India in 1991
and M.Tech with Electrical Machines Industrial Drives from Regional
Engineering College, Warangal, India in 1994. He Received the PhD, degree from
the J.N.T.U, Hyderabad, India in 2008. He is having 19 years of teaching and
Research experience. He is currently Professor Head in the Department of
Electrical Electronics Engineering, R.V.R J.C. College of Engineering
Guntur, India. His Research interests are in the areas of Power Electronics,
Industrial Drives FACTS Controllers.

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