CHAPTER 3 ENHANCING VOLTAGE STABILITY AND LOSS...

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CHAPTER 3

ENHANCING VOLTAGE STABILITY AND LOSS

MINIMIZATION USING ANN AND GA WITH UPFC

3.1 INTRODUCTION

Modern power system networks are being operated under highly

stressed conditions due to continuous increase in power demand. This has

imposed the threat of maintaining the required bus voltage and thus the

systems have been facing voltage instability problem. A system enters a state

of voltage instability when a disturbance, increase in load demand, or change

in system condition causes a progressive and uncontrollable decline in

voltage.

Techniques for voltage stability analysis are P-V Analysis, Q-V

Analysis and Time-Domain Analysis as in (Kundur 1994). FACTS devices

can regulate the active and reactive power control and adaptive to voltage

magnitude control by their fast control characteristics and so reduce flow of

heavily loaded lines and maintain voltages in desired level ( Galiana 1996).

FACTS have made the power systems operation more flexible and secure.

They have the ability to control, in a fast and effective manner and also it is

possible to control the phase angle, the voltage magnitude at chosen buses

and/or line impedances of transmission system as in Hingorani and Gyugyi

(2001) .

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UPFC is the most versatile member of FACTS devices family and

can be applied in order to control all the power flow parameters. Power flow

can be controlled and optimized by changing power system parameters using

FACTS devices. So optimal choice and allocation of FACTS devices can

result in suitable utilization of power system. UPFC helps to maintain a bus

voltage at a desired value during load variations. FACTS controllers

enhance the voltage profile and the load ability margin of power systems as in

Sode-Yome et al (2005). The heuristic and intelligent algorithms help to find

the proper places and sizes of FACTS devices as in Gerbex et al (2001). To

maintain the stability of the system, finding the location for fixing the FACTS

controller and also the amount of voltage and angle to be injected is more

important.

The hybrid technique includes

Artificial Neural Network and

Genetic Algorithm.

The proposed hybrid method using MATLAB for different systems

such as IEEE 14, 30, 57 and 118 bus systems has been carried out and the

performance evaluation is presented.

3.2 PROBLEM STATEMENT

The enhancement of voltage stability of the power system is one of

the most challenging problems in power system. The method of enhancing the

voltage stability and loss minimization using artificial neural network and

Genetic algorithm with UPFC is presented. The load flow analysis is carried

out with Newton-Raphson method using MATLAB software package. The

parameters of UPFC are modelled into power flow equation and thus it is

used to determine the power injection in terms of voltage and power angle.

The ANN is used for identifying the optimal location for fixing UPFC and the

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Genetic algorithm computes the amount of voltage and angle to be injected.

The total power loss of the system in normal case, sudden increase in load

power case and after connecting UPFC are noted and compared. The total

power loss of the system without UPFC gets increased, whereas for the

system with UPFC, it gets reduced. The results obtained using proposed

method are found to provide minimum real power loss when compared to

Newton-Raphson based load flow method, thus enhancing the voltage

stability of the power system.

The objective function is to minimize the real power losses under

several constraints.

Real Power Losses

The real power loss is calculated using the Equation (3.1):

N

jiijmmloss BYjViVConjalP

1,**)(*)(Re (3.1)

where, mV is the voltage magnitude,

ijY is the Y-bus matrix, and

B is the base MVA value.

Problem Constraints

The equality constraints are the load flow Equations (3.2) and (3.3)

given by,

PGi-PDi = Pi (3.2)

QGi-QDi = Qi (3.3)

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where,PGi and QGi are generated real and reactive powers at bus i,

respectively. PDi and QDi are real and reactive power loads at bus i,

respectively.

Voltage Constraints

Voltage magnitude at each node should be within their permissible

range (Vmax and Vmin) and Equations (3.4) given by,

Vimax Vi Vi

min (3.4)

where, Vmin, Vmax are the minimum and maximum limits for the voltage

magnitude.

Reactive Power Constraints

Reactive power at each node should be within their permissible

range (Qmax and Qmin) and Equations (3.5) given by,

Qimax Qi Qi

min (3.5)

where, Qmin, Qmax are the minimum and maximum limits for the Reactive

power

3.3 POWER FLOW CALCULATION USING NEWTON-

RAPHSON METHOD

In the power system, one of the most important processes is load

flow calculation. There are different methods available for load flow

calculation. Among them the Newton-Raphson method is the most commonly

used. By using Newton-Raphson load flow analysis method, the active and

reactive power flow in all the buses and the corresponding line losses are

calculated. For that, first the bus voltages, angle, active and reactive power,

reactance, inductance values are given as inputs and then power flow in each

46

bus is calculated. The real and reactive power flow in the bus is calculated

using the Equations (3.6) and (3.7) respectively.

N

kikikikikkii BGVVP

1sin*cos** (3.6)

N

kikikikikkii BGVVQ

1cos*sin** (3.7)

where, i is the sending end bus, k is the receiving end bus, N is the total

number of bus, iV & kV are the voltage at i & k bus respectively, ik is the

angle between i & k bus, and ikG & ikB are the conductance and

susceptance values respectively.

Using the above Equations (3.6) and (3.7), the real and reactive

power flow between the buses is computed.

Assigning initial guess in the Newton Raphson method is only to

initialize the dataset to move towards the optimal solution in the search space.

Intelligent based methods require the dataset for training which was obtained

by several methods by incorporating the fundamental features available in the

system. In the proposed methods, ANN based training is used to make the

system viable to understand the bus information at various stages which is

directly coupled to the techniques such as GA, PSO and BA. In this context

the search direction is determined by the concept of evolution, bird flocking

and food foraging by ant. Based on this the movement towards the optimal

solution is determined without the requirement of initial guess. The initial

solution is obtained by the fitness function evaluation by the respective

algorithms.

The overall process takes place in the proposed method as in

Figure 3.1.

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Figure 3.1 Overall process takes place in the proposed method

Start

Computing Power flow between the buses using Newton Raphson method

UPFC Modelling

Training NN using generated dataset

Training ANN to obtain the optimal location for fixing UPFC

GA to compute the amount of voltage and angle to be injected to reduce power loss

Stop

Generating training dataset for fixing UPFC

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3.4 FACTS DEVICES

FACTS devices have the ability to control the phase angle, the

voltage magnitude at chosen buses and line impedances of transmission

system. In order to meet the growing power demand, utilities have an interest

in better utilization of available power system capacities, existing generation

and existing power transmission network, instead of building new

transmission lines and expanding substations. UPFC is the most versatile

among variety FACTS devices which can be used for power flow control,

enhancement of transient stability and voltage regulations. UPFC has been

proved to be an effective means for regulating voltage profile and power flow

in modern power systems.

3.4.1 General Representation of UPFC

A combination of Static Synchronous Compensator (STATCOM)

and Static Synchronous Series Compensator (SSSC), which are coupled via a

common DC link, allows bidirectional flow of real power between the series

output terminals of the SSSC and the shunt output terminals of the

STATCOM. They are controlled to provide concurrent real and reactive series

line compensation without an external electric energy source. The UPFC, by

means of angularly unconstrained series voltage injection, is able to control,

concurrently or selectively, the transmission line voltage, impedance and

angle or alternatively, the real and reactive power flow in the line. The UPFC

also provides independently controllable shunt reactive compensation.

Among the available FACTS devices, the UPFC is the most

promising and powerful FACTS device. A major function of the UPFC during

steady state is to redistribute power flow along transmission lines and

transients state. It can be used to improve the damping of low frequency

49

oscillations. To perform these, UPFC needs to be equipped with power flow

controller, a DC voltage controller and a damping controller. The UPFC is the

most versatile and complex power electronic equipment that has emerged for

the control and optimization of power flow in electrical power transmission

systems. Traditional power transmission concepts, the UPFC is able to

control, simultaneously or selectively, all the parameters affecting power flow

in the transmission line. Alternatively, it can independently control both the

real and reactive power flow in the line unlike all other controllers.

Figure 3.2 General representation of UPFC

An UPFC combines a STATCOM and a SSSC as shown in

Figure 3.2. The UPFC is capable of both supplying and absorbing real and

reactive power and it consists of two voltage source converters: series and

shunt converter, which are connected to each other with a common DC link.

One of the two converters is connected in series with the transmission line

through a series transformer and the other in parallel with the line through a

shunt transformer. These two voltage source converters share common

capacitor, which provides DC voltage for the converter operation. The power

balance between the two converters is a prerequisite to maintain a constant

voltage across the dc capacitor. Series converter or SSSC is used to add

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controlled voltage magnitude and phase angle. It can exchange real power

with the transmission line and thus improves the power flow capability of the

line as well as its transient stability limit. The shunt converter exchanges a

current of controllable magnitude and power factor angle with the power

system.

Applying the forcing function viewpoint of flow control, the

functional capabilities of the UPFC can be put into a different and from the

standpoint of practic al applications, more meaningful perspective. That is, the

inherent two-dimensional control capability (manifested by the independent

magnitude and angle control of the injected compensating voltage) implies

that the UPFC is able to control directly both the real and reactive power flow

in the line. From this view point, the conventional terms of series

compensation and phase shifting become irrelevant: the UPFC simply

controls the magnitude and phase angle of the injected voltage so as to force

the magnitude and angle of the line current, with respect to a selected voltage

(e.g. the receiving end), to such values which establish the desired real and

reactive power flow in the transmission line. The representation of UPFC

model in a transmission line is shown in Figure 3.3.

Sending end bus i

Receiving end bus

VSC VSC

R+jX

Shunt transformer

Series transformer

DC link

Figure 3.3 Representation of UPFC in a transmission line

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3.4.2 UPFC Modelling

The power injection in terms of voltage and power angle, due to the

insertion of UPFC is given in the Equations (3.8) to (3.11).

injknew

injiinjnew

injkinjkinjki

GVVVG

BGVVP

cos****2*

sin*cos**2 (3.8)

qiinjinew

injinew

ki IVBGVQ *cos*sin** (3.9)

injinew

injiinjkk BGVVP sin*cos** (3.10)

injiinjiinjkk BGVVQ cos*sin** (3.11)

where, iP , kP , iQ , kQ are the real and reactive injecting powers

from bus i and bus k respectively,

injV and inj are the injecting voltage and angle respectively.

GGG iknew ,

BBB iknew .

Here newG and newB represent the combined conductance and susceptance of

the UPFC and the line to which it is connected.

The amount of voltage and angle to be injected and the optimal

location for fixing UPFC in the system are identified using the hybrid

52

technique. The next step is identifying the location for fixing UPFC using

ANN.

3.5 ANN TO OBTAIN LOCATION FOR FIXING UPFC

Artificial Neural Network is a mathematical model or

computational model that is inspired by the structure and/or functional aspects

of biological neural networks. In the proposed method, ANN is used to

identify the optimal location for fixing UPFC to maintain the stability of the

system. ANN consists of two stages: training stage and testing stage. In the

training stage, neural network is trained based on the training dataset and in

the testing stage, if the input variable is given, it gives the corresponding

output variables.

3.5.1 Learning ANN to obtain Bi and Bj

In the training stage, ANN consists of three layers, namely input

layer, hidden layer and output layer. In the proposed method, input layer

consists of two variables; hidden layer consists of variables and output layer

consists of two variables. The input variables are the fault occurred bus

number and power error while the output variables are the bus locations

where UPFC is to be connected. By considering this condition, neural

network is trained. For training the neural network, back propagation

algorithm is used. The structure of neural network used in the proposed

method is shown in Figure 3.4.

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Figure 3.4 Structure of neural network used in the proposed method

The steps for training the neural network are,

Step 1: Initialize the input weight for each neuron.

Step 2: Apply a training sample to the network. Here, eB and eP are the

input to the network and iB and jB are the output of the network.

)(1

12 ryWBn

rri (3.12)

)(1

22 ryWBn

rrj (3.13)

where,)exp(1

1)(11 eer BVw

ry (3.14)

Equations (3.12), (3.13) and (3.14) represent the activation function

performed in the input and output layer respectively.

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Step 3: Adjust the weights of all neurons.

Step 4: Determine the location for fixing UPFC.

3.5.2 Testing ANN to obtain iB and jB

In the testing stage, if the fault bus and power error are given as

input, the neural network gives the output as the location for fixing UPFC in

the system. After connecting the UPFC in the above obtained locations, the

next process is computing the voltage and angle values injected in UPFC.

3.6 GENETIC ALGORITHM

A Genetic algorithm is based on the mechanism of natural

selection. It is a powerful numerical optimization algorithm to reach an

approximate global maximum of a complex multivariable function over a

wide search space. It always produces high quality solution because it is

independent of the choice of initial configuration of population.

Genetic algorithm is initially developed by John Holland,

University of Michigan during 1970’s. It is an iterative procedure, which

maintains a constant size population of candidate solutions. During each

iteration step, genetic operators such as crossover and mutation are performed

to generate new populations and the chromosomes of the new populations are

evaluated via the value of the fitness. Based on these genetic operators and the

evaluations, better new populations of candidate solution are formed. If the

search goal has not been achieved, again GA creates offspring strings through

the operators and the process is continued until the search goal is achieved.

The flow chart of the GA procedure is shown in Figure 4.2.

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Figure 4.2 Flow chart of the GA procedure

Start

Specify the parameters for GA

Generate an initial particle of voltage and angle nv,2v,1viV & n,2,1i

Evaluation function for each particle

from the Equation (3.15)

Output of best chromosomes

Stop

The best individual is

found

Apply GA operatorscross over

and mutation

I=i+1

No

Yes

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3.6.1 GA to Compute Vi and Qi

A Genetic algorithm is a search heuristic that mimics the process of

natural evolution. In the proposed method, genetic algorithm is used for

computing the voltage and angle to be injected in the system. GA consists of

5 major stages: 1) Generation of initial chromosomes 2) Fitness evaluation 3)

Crossover 4) Mutation and 5) Termination.

Generation of initial chromosomes

The initial process that takes place in genetic algorithm is the

generation of initial chromosomes. In the proposed method, two

chromosomes are generated. The initial chromosomes are Vn = {V1, V2, ... Vn}

and n = { 1, 2, ... n} ; where, n is the number of genes in the chromosome.

The initial chromosomes are generated between the minimum and maximum

values of the entire chromosome. After generating the initial chromosomes,

the next step is to compute the fitness function.

Fitness function

Fitness function is one of the most important processes in genetic

algorithm, applied to identify the best chromosome. In the proposed method,

the voltage and angle injecting values generated in the above stage are

injected to the system and after injecting the values, the power loss is

computed. This total power loss is considered as the fitness function and the

Equation (3.15) is given by,

N

jiijmmloss BYjViVConjalP

1,**)(*)(Re (3.15)

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where, mV is the voltage magnitude, ijY is the Y-bus matrix, and B is the base

MVA value. By using Equation (3.15), the total power loss in the system is

computed.

Crossover operation

The crossover operation is performed between two chromosomes to

obtain a new chromosome. The crossover operation is done based on the

crossover rate rC 0.8. Based on this crossover, the genes are selected and a

new child chromosome is generated. After generating a new chromosome, the

fitness function is applied to this new child chromosome. Then mutation

follows the completion of crossover operation.

Mutation operation

The mutation operation is performed based on the mutation

rate rM 0.02. The mutation is done by mutating the genes randomly based on

the given mutation rate. After the completion of mutation operation, the next

step is termination.

Termination

In the termination stage, the best chromosome is selected based on

the fitness function. The above process is repeated until it reaches maximum

number of iterations. After the completion of termination process, the best

voltage and angle injecting values are obtained based on the fitness function.

By fixing the UPFC in the optimal locations identified using the

neural network and then by injecting the voltage and angle values computed

using the proposed method, the system will remain stable.

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3.7 SIMULATION RESULTS

The proposed algorithm is applied to IEEE 14, 30, 57 and 118 bus

systems whose data have been given in Appendix 1, 2, 3 and 4. The

simulation studies are done for different scenarios. The first scenario is the

normal operation of conventional NR method. The second scenario is after a

sudden increase power in bus. The third scenario is the one after the UPFC

installed in the proposed method (ANN and GA). The proposed method is

used to place UPFC in the optimal location to enhance the voltage profile and

reduce the power losses of the system. The simulation parameters considered

for the test cases are shown in Table 3.1.

Table 3.1 GA parameters

Parameter Chosen Value

Population s size 20

Crossover rate 0.8

Mutation rate 0.02

3.7.1 IEEE 14 Bus System

The test system consists of 5 generator buses (bus no. 1, 2, 3, 6 and

8), 9 load buses (bus no. 4, 5, 7, 9, 10, 11, 12, 13 and 14) and 20 transmission

lines. The base MVA considered is 100 MVA. In bus number 5, the optimal

location for connecting UPF using the proposed method is buses 4 and 5. A

comparison of the voltage profile and real power loss of IEEE 14 bus system

for different loading conditions is shown in Figures 3.6 and 3.7 respectively.

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Table 3.2 Voltage profile of IEEE 14 bus system for different load

conditions

Bus Number

Voltage at each bus using

Conventional NR Method

(p.u)

After sudden increase in

power in bus 5 (p.u)

Proposed Method with UPFC

connected in buses 4 & 5 (p.u)

1 1.0600 1.0600 1.0600

2 1.0450 1.0350 1.0460

3 1.0100 1.0100 1.0100

4 1.0132 1.0038 1.0157

5 1.0166 1.0056 1.0177

6 1.0700 1.0600 1.0700

7 1.0457 1.0358 1.0487

8 1.0800 1.0700 1.0800

9 1.0305 1.0205 1.0315

10 1.0299 1.0198 1.0311

11 1.0461 1.0361 1.0465

12 1.0533 1.0431 1.0533

13 1.0466 1.0365 1.0472

14 1.0193 1.0090 1.0213

Table 3.2 shows the voltage profile of all the 14 buses for normal

load condition, after sudden increase in the power in bus 5 and voltage

obtained UPFC connected in buses 4 and 5.

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Figure 3.6 Voltage profile of IEEE 14 bus system for different scenarios

From Figure 3.6, it appears clear that two different load conditions

are tested: voltage at normal condition and sudden load increase in bus 5. The

voltages obtained after the increase in load and after connecting UPFC using

the proposed method are compared. It is clear that after the sudden increase in

load power, the voltage profile gets decreased while comparing it with normal

load case. After connecting UPFC using the proposed method, the voltage

profile in most of the buses gets enhanced.

Table 3.3 shows the real power loss in the system in normal case,

sudden increase in load power case and after connecting UPFC using

proposed method.

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Table 3.3 Real power loss of IEEE 14 bus system for different load

conditions

S.NoBus No


(MW)

Sudden Increase in

Power (MW)

Proposed Method

UPFC Bus Connection

ANN and GA

(MW)

1 4 13.593 16.859 3--4 12.050

2 5 13.593 16.354 4--5 11.859

3 7 13.593 16.886 7--8 12.154

4 9 13.593 16.938 9--10 12.213

5 10 13.593 17.203 10--11 12.532

6 11 13.593 17.158 10--11 12.385

7 12 13.593 17.698 12--13 12.639

8 13 13.593 17.484 12--13 12.476

Figure 3.7 Comparison of real power loss of IEEE 14 bus system for

different scenarios

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From Figure 3.7, it is clear that the real power loss occurred for

normal load condition is 13.593 MW. After sudden increase in the load power

in bus 5, the real power loss is increased to 16.354 MW. Then, using the

proposed method with UPFC, the real power loss gets reduced to 11.859 MW.

Table 3.4 Comparison of real power loss of IEEE 14 bus system for the

other methods

Method Real power loss (MW)

Benabid et al (2009) NSPSO 13.460

Bagriyanik et al(2003) GA 12.600

Senthilkumar and Renuga (2010) BF 12.500

Proposed method ANN with GA 11.859

Table 3.4 makes it clear that proposed method obtains 11% of loss

reduction compared to NSPSO value reported in Benabid et al (2009), 5.8 %

of loss reduction compared to GA value mentioned in Bagriyanik et al (2003)

and 5.1 % of loss reduction compared to BF value indicated in Senthilkumar

and Renuga (2010). This shows the effectiveness of the proposed approach

which minimizes the real power loss compared to the other methods.


The test system consists of 6 generator buses (bus no. 1, 2, 5 , 8, 11

and 13), 24 load buses (bus no. 3, 4, 6, 7, 9, 10, 12, 14 ,15, 16, 17, 18, 19, 20,

21, 22, 23, 24, 25, 26, 27, 28, 29 and 30) and 41 transmission lines. The base

MVA considered is 100 MVA. In bus number 6, the optimal location for

connecting UPF using the proposed method is buses 6 and 8. A comparison of

the voltage profile and real power loss of IEEE 30 bus system for different

loading conditions is shown in Figures 3.8 and 3.9 respectively.

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Table 3.5 Voltage profile of IEEE 30 bus system for different load conditions

Bus Number



(p.u)





1 1.0600 1.0600 1.06002 1.0330 1.0330 1.04303 1.0135 1.0083 1.02204 1.0028 0.9968 1.01405 1.0000 1.0000 1.01006 1.0005 0.9927 1.01267 0.9924 0.9877 1.00538 1.0000 0.9900 0.99909 1.0305 1.0261 1.0398

10 1.0138 1.0089 1.022711 1.0728 1.0720 1.082012 1.0451 1.0421 1.052013 1.0710 1.0700 1.071014 1.0269 1.0235 1.032715 1.0194 1.0156 1.021616 1.0245 1.0207 1.027417 1.0116 1.0010 1.018818 1.0049 1.0007 1.014819 0.9996 0.9951 1.010020 1.0024 0.9978 1.012521 1.0008 0.9960 1.010722 1.0041 0.9990 1.013123 1.0012 0.9965 1.011724 0.9911 0.9856 1.001025 0.9945 0.9876 1.001526 0.9764 0.9694 0.984527 1.0053 0.9977 1.011328 0.9985 0.9903 1.002029 0.9851 0.9773 0.991530 0.9734 0.9655 0.9802

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load condition, after sudden increase in power in bus 6 and voltage obtained

UPFC connected in buses 6 and 8.


From Figure 3.8, it is seen that two different load conditions are

tested: voltage at normal condition and sudden load increase in bus 6. The






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conditions

S.NoBus No


(MW)

Sudden Increase in

Power (MW)

Proposed Method

UPFC Bus Connection

ANN and GA

(MW) 1 3 17.914 20.288 3--4 16.9412 4 17.914 20.945 4--6 17.0643 6 17.914 21.565 6--8 16.9394 7 17.914 22.206 5--7 17.6565 9 17.914 21.621 9--10 17.1376 10 17.914 21.725 10--21 17.2277 12 17.914 21.214 12--16 17.1018 14 17.914 22.424 14--15 17.5529 15 17.914 22.064 15--23 17.46010 16 17.914 21.920 16--17 17.34811 17 17.914 22.007 10--17 17.45212 18 17.914 22.954 18--19 17.72613 19 17.914 23.067 19--20 17.73514 20 17.914 22.804 19--20 17.53915 21 17.914 22.319 21--23 17.57016 22 17.914 22.405 22--24 17.56617 23 17.914 22.357 23--24 17.45818 24 17.914 22.914 24--25 17.67919 25 17.914 23.024 25--27 17.75720 26 17.914 23.034 25--26 17.74921 27 17.914 22.174 25--27 17.44722 28 17.914 21.862 8--28 17.32923 29 17.914 23.053 29--30 17.72324 30 17.914 23.053 27--30 17.718

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proposed method.


different scenarios

From the Figure 3.9, it is clear that the real power loss occurred for


in bus 6, the real power loss is increased to 21.565 MW and then by using the


Table 3.7 Comparison of real power loss of IEEE 30 bus system for the

other methods


Nikoukar and Jazaeri (2007) GA 17.695

Kalaivani and Kamaraj (2012) GA 17.523

Ajay-D-Vimalraj et al (2008) GA 17.2215


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From Table 3.7, it becomes evident that the proposed method

obtains 4.27 % of loss reduction compared to GA value reported in Nikoukar

and Jazaeri (2007), 3.33 % of loss reduction compared to GA value

rmentioned in Kalaivani and Kamaraj (2012) and 1.64 % of loss reduction

compared to GA value indicated in Ajay-D-Vimalraj et al (2008). This shows

the effectiveness of the proposed approach that minimizes the real power loss

compared to the other methods.


The test system consists of 7 generator buses (bus no. 1, 2, 3, 6, 8, 9

,12) 50 load buses (bus no. 4, 5, 7, 10, 11, 13, 14, 15, 16, 17, 18, 19, 20, 21,

22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42,

43, 44, 45, 46, 47, 48, 49, 50, 51,52, 53, 54, 55, 56, 57) and 80 transmission

lines. The base MVA considered is 100 MVA. In bus number 7, the optimal

location for connecting UPF using the proposed method is buses 7 and 8. A

comparison of the voltage profile and real power loss of IEEE 57 bus system

for different loading conditions is shown in Figures 3.10 and 3.11

respectively.

Table 3.8 Voltage profile of IEEE 57 bus system for different load

conditions

Bus Number



(p.u)





1 1.0400 1.0400 1.04002 1.0200 1.0200 1.0200

3 1.0150 1.0150 1.0150

4 1.0085 1.0085 1.0145

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Table 3.8 (Continued)

Bus Number



(p.u)





5 1.0059 1.0058 1.02146 1.0100 1.0100 1.03007 1.0231 1.0207 1.06268 1.0550 1.0550 1.05509 1.0100 1.0100 1.0100

10 1.0052 1.0051 1.005211 0.9980 0.9979 0.998012 1.0250 1.0250 1.025013 0.9977 0.9975 0.997714 0.9891 0.9888 0.989215 1.0070 1.0068 1.007016 1.0207 1.0202 1.020817 1.0213 1.0208 1.021518 1.0065 1.0064 1.012519 0.9814 0.9813 0.986220 0.9782 0.9781 0.982221 1.0275 1.0272 1.030722 1.0295 1.0292 1.032523 1.0281 1.0277 1.032124 1.0179 1.0166 1.038025 0.9725 0.9709 0.991026 0.9786 0.9777 1.001727 1.0115 1.0093 1.044628 1.0301 1.0274 1.060529 1.0457 1.0425 1.065030 0.9551 0.9537 0.9732

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Bus Number



(p.u)





31 0.9346 0.9336 0.949132 0.9582 0.9579 0.966133 0.9560 0.9556 0.963934 0.9771 0.9765 0.979235 0.9851 0.9846 0.986436 0.9953 0.9949 0.996037 1.0046 1.0012 1.005238 1.0329 1.0327 1.033839 1.0027 1.0023 1.003140 0.9924 0.9920 0.992841 1.0208 1.0206 1.021342 0.9913 0.9912 0.992043 1.0346 1.0345 1.034744 1.0369 1.0307 1.037145 1.0558 1.0556 1.055846 1.0805 1.0805 1.081547 1.0538 1.0538 1.054448 1.0478 1.0477 1.047949 1.0569 1.0568 1.057650 1.0443 1.0442 1.044551 1.0728 1.0726 1.072852 1.0088 1.0065 1.047553 0.9954 0.9935 1.025454 1.0238 1.0232 1.031155 1.0610 1.0600 1.061556 0.9925 0.9924 0.993557 0.9886 0.9885 0.9887

70

Table 3.8 depicts the voltage profile of all the 57 buses for normal

load condition, after sudden increase in power in bus 7 and voltage obtained

UPFC connected in buses 7 and 8.


From Figure 3.10, it looks clear that two different load conditions

are tested: voltage at normal condition and sudden load increase in bus 7. The






71


conditions

S.NoBus No


(MW)

Sudden Increase in

Power (MW)

Proposed Method

UPFC Bus Connection

ANN and GA

(MW) 1 4 27.058 29.615 4--6 26.3592 5 27.058 29.670 5--6 26.3403 7 27.058 29.369 7--8 25.9244 10 27.058 30.001 10--12 26.6235 11 27.058 29.876 11--13 26.4706 13 27.058 29.673 13--15 26.4207 14 27.058 29.575 14--15 26.4418 18 27.058 29.727 4--8 26.4549 19 27.058 33.387 19--20 26.95510 20 27.058 32.887 19--20 26.84011 21 27.058 31.523 21--22 26.98212 22 27.058 30.960 22--38 26.78213 23 27.058 31.098 22--23 26.77414 24 27.058 32.370 24--25 26.95315 25 27.058 33.457 25--30 26.90516 26 27.058 32.389 26--27 26.97617 27 27.058 31.171 27--28 26.76918 28 27.058 30.175 27--28 26.65019 29 27.058 29.389 28--29 26.20520 30 27.058 33.643 30--31 26.91321 31 27.058 33.351 30--31 26.94422 32 27.058 32.982 31--32 26.92523 33 27.058 33.551 32--33 26.95824 34 27.058 33.328 34--35 26.87625 35 27.058 33.369 34--35 26.989

26 36 27.058 32.519 36--37 26.756

72


S.No Bus No


(MW)

Sudden Increase in

Power (MW)

Proposed Method

UPFC Bus Connection

ANN and GA

(MW) 27 37 27.058 31.985 37--39 26.82328 38 27.058 30.690 38--49 26.59429 39 27.058 32.248 37--39 26.78530 40 27.058 32.784 36--40 26.95331 41 27.058 31.156 11--41 26.72032 42 27.058 33.707 56--42 26.89233 43 27.058 29.896 11--43 26.40534 44 27.058 30.311 38--44 26.62535 45 27.058 28.818 44--45 25.92736 46 27.058 29.616 46--47 26.40737 47 27.058 30.244 47--48 26.61238 48 27.058 30.381 48--49 26.67139 49 27.058 30.236 48--49 26.58040 50 27.058 31.053 50--51 26.68441 51 27.058 30.029 50--51 26.53642 52 27.058 31.854 52--53 26.92343 53 27.058 32.854 53--54 26.84544 54 27.058 32.721 54--55 26.72145 55 27.058 30.737 54--55 26.65146 56 27.058 33.652 56--41 26.89247 57 27.058 33.517 57--56 26.895



proposed method.

73


different scenarios



in bus 7, the real power loss is increased to 29.369 MW. Then by using the


Table 3.10 Comparison of real power loss of IEEE 57 bus system for the other methods



Ajay-D-Vimalraj et al (2008) GA 27.5595


From Table 3.10, it becomes clear that proposed method obtains

6.86 % of loss reduction compared to GA value reported in Kalaivani and

Kamaraj (2012) and 5.93 % of loss reduction compared to GA value indicated

in Ajay-D-Vimalraj et al (2008). This shows the effectiveness of the proposed

approach that minimizes the real power loss compared to the other methods.

74


The test system consists of 54 generator buses (bus no. 1, 4, 6, 8,

10, 12, 15, 18, 19, 24, 25, 26, 27, 31, 32, 34, 36, 40, 42, 46, 49, 54, 55, 56, 59,

61, 62, 65, 66, 69, 70, 72,73, 74, 76, 77, 80, 85, 87, 89, 90, 91, 92, 99, 100,

103, 104, 105, 107, 110, 111, 112,113, 116) , 64 load buses (bus no. 2, 3, 5, 7,

9, 11, 13, 14, 16, 17, 20, 21, 22, 23, 28, 29, 30, 33, 35, 37, 38, 39, 41, 43, 44,

45, 47, 48, 50, 51, 52, 53, 57, 58, 60, 63, 64, 67, 68, 71, 75, 78, 79, 81, 82, 83,

84, 86, 88, 93, 94, 95, 96, 97, 98, 101,102, 106, 108, 109, 114, 115, 117, 118),

86 transmission lines and bus no. 69 is slack bus. The base MVA considered

is 100 MVA. In bus number 17, the optimal location for connecting UPF

using the proposed method is buses 15 and 17.

A comparison of the voltage profile and real power loss of IEEE

118 bus system for different loading conditions is shown in Figures 3.12 and

3.13 respectively.

Table 3.11 Voltage profile of IEEE 118 bus system for different

conditions

Bus Number


Conventional NR Method (p.u)



Proposed Method with UPFC connected

in buses 15 &17 (p.u)

1 0.9550 0.9550 0.95502 0.9648 0.9647 0.96483 0.9659 0.9657 0.96594 1.0080 1.0080 1.00805 1.0030 1.0030 1.00306 0.9800 0.9800 0.98007 0.9793 0.9792 0.9793

75


Bus Number







8 0.9850 0.9850 0.98509 1.0016 1.0012 1.001610 1.0200 1.0200 1.020011 0.9801 0.9799 0.980212 0.9800 0.9800 0.980013 0.9609 0.9603 0.960914 0.9726 0.9725 0.972615 0.9600 0.9600 0.960016 0.9708 0.9704 0.972017 0.9787 0.9781 0.978718 0.9630 0.9630 0.963019 0.9720 0.9720 0.972020 0.9606 0.9601 0.962021 0.9579 0.9571 0.958422 0.9664 0.9657 0.966523 0.9953 0.9950 0.995424 1.0020 1.0020 1.002025 1.0200 1.0200 1.020026 0.9650 0.9650 0.965027 0.9580 0.9580 0.958028 0.9508 0.9507 0.950829 0.9528 0.9527 0.952830 0.9526 0.9516 0.952931 0.9570 0.9570 0.957032 0.9730 0.9730 0.973033 0.9612 0.9609 0.961234 0.9840 0.9840 0.9840

76


Bus Number







35 0.9710 0.9709 0.971136 0.9700 0.9700 0.970037 0.9839 0.9838 0.983938 0.9367 0.9360 0.937939 0.9478 0.9476 0.947740 0.9400 0.9400 0.940041 0.9308 0.9306 0.930842 0.9350 0.9350 0.935043 0.9509 0.9502 0.950944 0.9274 0.9263 0.927545 0.9298 0.9288 0.929846 0.9650 0.9650 0.965047 0.9752 0.9751 0.975248 0.9656 0.9654 0.965649 0.9750 0.9750 0.975050 0.9543 0.9540 0.954551 0.9239 0.9233 0.923952 0.9246 0.9239 0.924653 0.9290 0.9284 0.929054 0.9250 0.9250 0.925055 0.9220 0.9220 0.922056 0.9240 0.9230 0.925057 0.9324 0.9322 0.933458 0.9310 0.9310 0.935059 0.9550 0.9550 0.955060 0.9966 0.9966 0.996661 1.0050 1.0050 1.005062 0.9880 0.9880 0.9880

77


Bus Number







63 0.9492 0.9491 0.949264 0.9691 0.9691 0.969165 0.9750 0.9750 0.975066 1.0200 1.0200 1.020067 0.9979 0.9977 0.997968 0.9892 0.9892 0.989269 1.0350 1.0350 1.035070 0.9740 0.9740 0.974071 0.9785 0.9785 0.978572 0.9900 0.9900 0.990073 0.9810 0.9810 0.981074 0.9580 0.9580 0.958075 0.9566 0.9544 0.956776 0.9630 0.9630 0.963077 0.9760 0.9560 0.976078 0.9738 0.9558 0.973879 0.9804 0.9669 0.982480 1.0300 1.0300 1.030081 0.9830 0.9829 0.983082 0.9580 0.9495 0.959083 0.9569 0.9508 0.956984 0.9636 0.9616 0.963685 0.9750 0.9750 0.975086 0.9601 0.9598 0.960187 0.9650 0.9650 0.965088 0.9770 0.9767 0.977089 0.9950 0.9950 0.995090 0.9550 0.9550 0.9550

78


Bus Number







91 0.9700 0.9700 0.970092 1.0000 1.0000 1.000093 0.9801 0.9789 0.980194 0.9719 0.9699 0.972195 0.9603 0.9570 0.961596 0.9704 0.9661 0.971497 0.9943 0.9920 0.994998 1.0044 1.0042 1.004699 1.0000 1.0000 1.0000

100 0.9870 0.9870 0.9870101 0.9772 0.9768 0.9776102 0.9907 0.9905 0.9909103 0.9600 0.9600 0.9600104 0.9610 0.9610 0.9610105 0.9450 0.9450 0.9450106 0.9381 0.9378 0.9387107 0.9320 0.9320 0.9320108 0.9417 0.9416 0.9419109 0.9408 0.9407 0.9409110 0.9430 0.9430 0.9430111 0.9700 0.9700 0.9700112 0.9450 0.9450 0.9450113 0.9830 0.9830 0.9830114 0.9614 0.9612 0.9616115 0.9598 0.9597 0.9599116 0.9950 0.9950 0.9950117 0.9624 0.9620 0.9626118 0.9393 0.9380 0.9398

79


load condition, after sudden increase in power in bus 7 and the voltage

obtained UPFC connected in buses 15 and 17.

Figure 3.12 Voltage profile of IEEE 118 bus system for different

scenarios

From Figure 3.12, it seens clear that two different load conditions

are tested: voltage at normal condition and sudden load increase in bus 17.

The voltages obtained after the increase in load and after connecting UPFC

using the proposed method are compared. It is clear that after the sudden

increase in load power, the voltage profile gets decreased while comparing it

with normal load case. After connecting UPFC using the proposed method,

the voltage profile in most of the buses gets enhanced.

80


conditions

S.No Bus No


(MW)

Sudden Increase in

Power (MW)

Proposed Method

UPFC Bus Connection

ANN and GA

(MW) 1 2 146.740 150.563 2--12 144.768

2 3 146.740 150.337 3--5 144.691

3 5 146.740 149.575 5--6 144.591

4 7 146.740 150.267 6--7 144.885

5 9 146.740 149.064 9--10 144.592

6 11 146.740 150.308 5--11 144.671

7 13 146.740 150.884 13--15 144.675

8 14 146.740 150.690 14--15 144.679

9 16 146.740 150.568 16--17 144.838

10 17 146.740 150.129 15--17 144.588

11 20 146.740 151.053 19--20 145.772

12 21 146.740 150.910 21--22 145.659

13 22 146.740 150.550 22--23 144.686

14 23 146.740 149.591 23--32 144.675

15 28 146.740 151.013 27--28 145.692

16 29 146.740 151.184 28--29 145.672

17 30 146.740 149.875 8—30 144.594

18 33 146.740 151.056 15--33 145.396

19 35 146.740 150.743 35--37 145.174

20 37 146.740 150.287 33--37 144.784

21 38 146.740 150.108 37--38 144.780

22 39 146.740 151.828 37--39 145.939

23 41 146.740 152.521 41--42 145.963

24 43 146.740 151.251 34--43 145.767

81


S.NoBus No


(MW)

Sudden Increase in

Power (MW)

Proposed Method

UPFC Bus Connection

ANN and GA

(MW)

25 44 146.740 151.616 44--45 145.853

26 45 146.740 151.325 45--49 145.829

27 47 146.740 149.812 47--69 144.668

28 48 146.740 149.892 48--49 144.718

29 50 146.740 150.214 50--57 144.772

30 51 146.740 151.113 49--51 145.588

31 52 146.740 151.521 52--53 145.609

32 53 146.740 151.572 53--54 145.758

33 57 146.740 150.974 50--57 145.557

34 58 146.740 151.296 56--58 145.582

35 60 146.740 149.031 60--62 144.683

36 63 146.740 149.215 59--63 144.698

37 64 146.740 149.911 64--65 144.671

38 67 146.740 150.874 62--67 145.324

39 68 146.740 149.823 68--81 144.635

40 71 146.740 150.221 71--72 144.591

41 75 146.740 150.574 69--75 145.012

42 78 146.740 149.728 78--79 144.595

43 79 146.740 150.993 79--80 145.532

44 81 146.740 149.875 68--81 144.739

45 82 146.740 149.119 77--82 144.593

46 83 146.740 150.825 83--85 145.243

47 84 146.740 149.203 84--85 144.632

48 86 146.740 150.945 85--86 145.634

82


S.NoBus No


(MW)

Sudden Increase in

Power (MW)

Proposed Method

UPFC Bus Connection

ANN and GA

(MW)

49 88 146.740 149.943 85--88 144.613

50 93 146.740 149.681 92--93 144.723

51 94 146.740 150.416 92--94 144.898

52 95 146.740 150.783 94--95 145.152

53 96 146.740 149.764 80--96 144.734

54 97 146.740 150.084 80--97 144.713

55 98 146.740 149.604 98--100 144.684

56 101 146.740 150.116 101--102 144.593

57 102 146.740 149.262 92--102 144.594

58 106 146.740 149.577 100--106 144.607

59 108 146.740 149.893 108--109 144.617

60 109 146.740 150.037 109--110 144.641

61 114 146.740 150.914 32--114 145.568

62 115 146.740 150.921 27--115 145.573

63 117 146.740 150.987 12--117 145.689

64 118 146.740 151.065 75--118 145.479

Table 3.12 expresses the real power loss in the system in normal

case, sudden increase in load power case and after connecting UPFC using

proposed method.

83


different scenarios


normal load condition is 146.740 MW. After the sudden increase in the load

power in bus 17, the real power loss is increased to 150.129 MW. Then by

using the proposed method with UPFC, the real power loss gets reduced to

144.588 MW.

Table 3.13 Comparison of real power loss of IEEE 118 bus system for

the other method




84

From the table 3.13, it appears clear that the proposed method

obtain 1.64 % of loss reduction compared to GA value reported in Kalaivani

and Kamaraj (2012). This shows the effectiveness of the proposed approach

that minimizes the real power loss compared to the other method.

3.8 SUMMARY

This chapter has demonstrated the following: A hybrid technique is

used to identify the location for fixing UPFC in the system and also to

compute the voltage and angle injecting values for enhancing the voltage

stability of the system. The proposed techniques are implemented in

MATLAB and tested using IEEE 14, 30, 57 and 118 bus systems. The

performances of the proposed techniques are analyzed by increasing the load

power in the system. Due to the sudden increase in load power, the voltage

profile is decreased and also the total power loss in the system gets increased.

By using the suggested procedure, the voltage profile gets enhanced along

with a reduction in power loss compared to the other methods.

CHAPTER 3 ENHANCING VOLTAGE STABILITY AND LOSS...

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