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CHAPTER 2

LITERATURE REVIEW

2.1 FACTS

More literature is available on the topic beginning with Gotham and

Heydt (1998) who integrated 3 main generic types of FACTS device. Here,

the modeling of Flexible AC Transmission System (FACTS) devices for

power flow studies and the role of that modeling in the study of FACTS

devices for power flow control are discussed. FACTS devices are solid-state

power converters that have the capability of controlling of various electrical

parameters in transmission circuits. A number of power flow study programs

were developed in order to model various types of FACTS devices. Three

main generic types of FACT devices are suggested and the integration of

those devices into power flow studies. Studies relating to wheeling and

interchange power flow controls are illustrated.

The epoch making American Electric Power (AEP) with the first

commercial unit of UPFC by Ye and Kazerani (2000) pointed to a new

direction in power engineering. The successful incorporation of FACTS

control in the power systems require a clear understanding of all possible

approaches and their operating limits. In this paper, first a systematic study of

the operating constraints of 1-converter FACTS devices based on series

voltage and shunt current injection is conducted. Then, the power ratings of

the series voltage and shunt current injection devices performing the same job

of reactive power compensation or power flow control are compared and the

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conditions under which each approach becomes more economical are derived.

The results can be generalized to FACTS devices with more than one

converter such as UPFC

Using the concept of maximum power transferring capability of the

lines and buses, the optimum location for FACTS devices was identified by

Moghavvemi and Faruque (2000). He presents a study of FACTS devices

mainly Static Var Compensator (SVC) and Controlled Series compensator

(CSC). Their steady-state modeling and effects on power system performance

have been also studied. It also includes the studies on static stability

improvement of a power system and hence power flow improvement in the

network. Standard stability evaluation technique has been used to identify the

optimum place for the implementation of Flexible AC transmission System

(FACTS) devices and the effects of FACTS on system loadability has been

studied and presented here. The technique to identify the optimum location

for the placement of FACTS devices is based on the concept of maximum

power transferring capability of the lines and buses. The study has been

carried out on the IEEE 24 and 118 bus test systems. The Study reveals that

incorporation of FACTS devices significantly enhances system stability as

well as power transfer capability of the system.

Dash et al (2000) designed a controller using an incremental fuzzy

logic controller in a nonlinear manner. He presents a simple hybrid fuzzy

logic proportional plus conventional integral controller for FACTS devices in

a multi-machine power system. This controller is designed by using an

incremental fuzzy logic controller in place of a proportional term in a

conventional PI controller and provides a wide variation of controller gains in

a nonlinear manner. This controller is well suited to series connected FACTS

devices like UPFC, TCSC and TCPST, etc., in damping multi-modal

oscillations in a multi-machine environment. Digital simulations of a multi-

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machine power system subjected to a wide variety of disturbances validate the

efficiency of the new approach.

Xu and Agelidis (2002) proposes that the series converter injected a

voltage with controller magnitude and phase, to control the active/reactive

power flow in a transmission line. A unified power flow controller (UPFC)

based on the flying capacitor (FC) multilevel voltage-source converter (VSC)

topology with phase-shifted sinusoidal pulse-width modulation (PWM)

control is presented. This converter allows higher power handling, potentially

lower power loss, lower harmonic distortion and hence less filtering

requirements when compared with the typical two-level counterpart. The

shunt converter absorbs/ supplies active power demanded by the series

converter to maintain a constant DC link voltage, also providing independent

reactive support to the network. A complete model of the proposed UPFC

system is shown and the control circuits are described in the synchronous d-q

frame. Finally, simulation results are provided to confirm the robustness of

the proposed system.

Menniti et al (2002) proposes that the IPFC employs two DC/AC

inverters with a common DC-link, each to provide series compensation for a

selected line of the transmission system. Because of the common DC-link,

any inverter within IPFC is able to transfer real power to any other. Naturally,

each inverter is able to provide reactive compensation. The main purpose of

this paper is to extend the nonconventional controller previously proposed by

the authors for unified power flow controller to interline power flow

controller. The proposed controller is used to arrange the controls of the series

inverters, in order to take into account, by approximated reasoning, the system

nonlinearity and inverters' interactions. Some simulation cases are considered

to compare the performance of the proposed controller with respect to that of

other conventional controllers. For this investigation ATP-Electromagnetic

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Transients Program is used as the study tool. A mathematical model of the

IPFC is presented and the model is used to investigate the flexibility of power

flow control Diez-Valencia et al (2002) , he investigates the steady state

operation of the interline power flow controller (IPFC), in the presence of

operating constraints of the IPFC. Some case studies are presented to illustrate

the analysis and the possibility of using improved control strategies is

discussed.

Mishra et al (2002) elaborated an integrated approach of radial

basis function neural network (RBFNN) and Takagi-Sugeno (TS) fuzzy

scheme with a genetic optimization of their parameters has been developed in

this paper to design intelligent adaptive controllers for improving the transient

stability performance of power systems. At the outset, this concept is applied

to a simple device such as thyristor-controlled series capacitor (TCSC)

connected in a single-machine infinite bus power system and is then extended

to interline power-flow controller (IPFC) connected in a multi machine

power system. The RBFNN uses single neuron architecture and its parameters

are dynamically updated in an online fashion with TS-fuzzy scheme designed

with only four rules and triangular membership function.

The rules of the TS-fuzzy scheme are derived from the real - or

reactive-power error and their derivatives either at the TCSC or IPFC buses

depending on the device. Further, to implement this combined scheme only

one coefficient in the TS-fuzzy rules need to be optimized. The optimization

of this coefficient as well as the coefficient for auxiliary signal generation is

performed through genetic algorithm. The performance of the new controller

is evaluated in single-machine and multi machine power systems subjected to

various transient disturbances. The new genetic-neuro-fuzzy control scheme

exhibits a superior damping performance as well as a greater critical clearing

time in compared to the existing PI and RBFNN controller with updating of

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its parameters through the extended Kalman filter (EKF). Its simple

architecture reduces the computational burden, thereby making it attractive

for real-time implementation. Index Terms-Damping modal oscillations,

FACTS, fuzzy, genetic, intelligent controller, neural, power system and

stability.

From Xiao et al (2002) viewpoint of operational planning, this

paper focuses on the evaluation of the impact of FACTS control on Available

Transfer Capability (ATC) enhancement. Technical merits of FACTS

technology on ATC boosting are analyzed. An optimal power-flow-based

ATC enhancement model is formulated to achieve the maximum power

transfer of the specified interface with FACTS control. For better study of the

capability of FACTS control, a power injection model of FACTS devices,

which enables simulating the control of any FACTS devices, is employed.

Studies based on the IEEE 118-bus system with all categories of FACTS

devices demonstrate the effectiveness of FACTS control on ATC

enhancement.

Fardanesh and Schuff (2003) reports on the results of studies

performed to ensure satisfactory dynamic performance of the New York

electric system with the unified power flow controller (UPFC) and interline

power flow controller (IPFC) configurations of the Marcy convertible static

compensator (CSC). A brief description of the CSC and its operating modes

are provided as well. Fardanesh (2004) describes a method for optimal

dimensioning of multi converter voltage sourced converter-based FACTS

controllers. This general method allows comparisons of the steady-state

performance and effectiveness of all single-, two-, and three-converter

controllers in achieving specific power system operating objectives. The

controllers includes the generalized unified power flow controller and its sub

devices, i.e., the static compensator, the static synchronous series

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compensator, the unified power flow controller, and the interline power flow

controller. The effects of various shunt and series converter size

modularizations in multi converter FACTS controllers are demonstrated.

Sensitivities to power system topology related issues such as system strength,

parallel paths, and compensated line impedances, as well as system loading,

have been analyzed. An Optimal Power Flow (OPF)-type formulation with

embedded effective impedances and/or current injections is utilized to provide

a single framework for representing all single- and multi converter FACTS

controllers considered. A small power system model is utilized in this study

mainly focusing on the FACTS controller utilization and performance.

Realistic constraints representing various converter limits have been

implemented. MATLAB optimization routines are utilized.

Wei et al (2004) suggested the maximum dispatch benefit of an

interline power flow controller (IPFC) often occurs when it operates at its

rated capacity and line flow set point regulation is no longer possible. This

paper uses injected voltage sources to directly model an IPFC and impose the

rating limits in a Newton-Raphson load flow algorithm. A dispatch strategy is

proposed for an IPFC operating at rated capacity, in which the power

circulation between the two series converters is used as the parameter to

optimize the voltage profile and power transfer. Voltage stability curves for

two test systems are shown to illustrate the effectiveness of this proposed

strategy.

Zanetta and Vasquez-Arnez (2004) proposed the Interline Power

Flow Controller (IPFC) as one of the newest devices within the FACTS

group. By utilizing this device, an enhanced controllability over independent

transmission systems or those lines whose sending-end are connected to a

common bus can be obtained. As an extended version of the UPFC (Unified

Power Flow Controller), the IPFC appears as an excellent solution for the

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control of multiline systems, but it also presents its own complexities whilst

operating under certain system conditions. The steady-state response and

performance of a generalized IPFC controlling two independent AC systems,

is evaluated. None-the-less, the study can be extended to systems having more

than two transmission lines. In order to observe its dynamic behavior and

simultaneously validate the previous steady-state analysis, an IPFC model

was also built in the ATP program. The results obtained validates the IPFC

model built and ratifies its capability for controlling the power flow over the

compensated transmission lines.

Eldamaty et al (2005) presents a new control method based on

fuzzy logic technique to control a unified power flow controller (UPFC)

installed in a single-machine infinite-bus power system. The objective of the

fuzzy logic based UPFC controller is to damp power system oscillations.

Phillips-Herffron model of a single-machine power system equipped with a

UPFC is used to model the system. The fuzzy logic based UPFC controller is

designed by selecting appropriate controller parameters based on the

knowledge of the power system performance. Simple fuzzy logic controller

using mamdani-type inference system is used. The effectiveness of the new

controller is demonstrated through time-domain simulation studies. The

results of these studies show that the designed controller has an excellent

capability in damping power system oscillations.

Pengcheng Zhu et al (2005) suggested the voltage balance, real

power balance and reactive power balance of a UPFC system are analyzed. It

is interesting to find that when the UPFC bus voltage is stable as power flows

changing any increase/decrease in the transmission line reactive power due to

in-phase component of the series voltage injected by the series converter

causes an equal increase/increase in the shunt converter reactive power. In

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short, the shunt converter supplies increase/decrease reactive power in

transmission line. So there are two methods to control the UPFC. One is the

series converter output voltage control the real/reactive power flows, the

shunt converter is controlled to make the DC link voltage stable and generate

reactive power to make the UPFC bus voltage constant, the other is that the

series converter output voltage is controlled to manage the real power flow

and maintain the UPFC bus voltage stable while the shunt converter control

the DC link voltage and the reactive power flow. Based on the analysis, a

comparison of the proposed one with the conventional one is carried out with

experiments. It is found that with the proposed control scheme the UPFC can

get a better reactive power flow control performance with as small bus

voltage ripple as the conventional one. However both control schemes can

realize effective power flow control with constant UPFC bus voltage.

Vasquez-Arnez and Zanetta (2005) dealt with the operational

analysis and the limitations of a generalized interline power flow controller

(GIPFC), whilst interacting with the network. The GIPFC is one of the newest

devices within the FACTS technology. By utilising this device, an enhanced

controllability over independent transmission systems, can be obtained. The

steady-state analysis of a GIPFC controlling two balanced independent AC

systems, is initially evaluated. The model and the analysis developed are

based on the d-q orthogonal co-ordinates, which seems to be a quite an

appropriate and easy method for assessing the GIPFC response towards the

system's operation. Yet, to observe its dynamic behaviour and simultaneously

validate the previous steady-state analysis, a phase-shift VSI-based GIPFC

model was also built in the ATP program. Whereever applicable, a

comparative evaluation between the GIPFC and the IPFC, is also presented.

Liang Zhong Yao et al (2005) discuss the efficient utilization of the

existing networks with high penetration of wind power needs more

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sophisticated control schemes using advanced power flow and voltage control

resources, namely power electronic controllers (FACTS) while enhancing

voltage security and voltage stability control. In this paper, the application of

static series synchronous compensator (SSSC) for the purpose of congestion

management and transfer capability of power systems with high penetration

of wind power has been studied. A transfer capability computation approach

for congestion management of systems with wind farms using series

compensation FACTS i.e. SSSC is proposed in this paper. The approach

proposed can simultaneously take voltage, thermal and voltage stability limits

into consideration, and may also consider any electricity transaction

constraints.

Numerical results based on the modified IEEE 30 bus system

with/without the SSSC demonstrates the feasibility as well as the

effectiveness of the SSSC for congestion management with high penetration

of wind power in the network. The results using SSSC to improve system

transfer capability and congestion management is encouraging. With the large

integration of wind generation into power transmission networks, it can be

anticipated that FACTS controllers including the SSSC may be increasingly

applied in effective management of transmission network power flows.

Vasquez-Arnez and Zanetta (2005) deals with the operational

analysis and the limitations of a generalized interline power flow controller

(GIPFC), whilst interacting with the network. The GIPFC is one of the newest

devices within the FACTS technology. The steady-state analysis of a GIPFC

controlling two balanced independent AC systems is initially evaluated. The

model and the analysis developed are based on the d-q orthogonal

co-ordinates, which showed to be a quite an appropriate and easy method for

assessing the GIPFC response towards the system's operation. Yet, to observe

its dynamic behaviour and simultaneously validate the previous steady-state

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analysis, a phase-shift VSI-based GIPFC model was also built in the ATP

program. Where applicable, a comparative evaluation between the GIPFC and

the IPFC,is also presented.

Tecrathana et al (2005) suggested that Interline power flow

controller (IPFC) is a new concept of the FACTS controller for series

compensation with the unique capability of power flow management among

multiple lines from a substation. As for the ability of controlling power flows

on multiple transmission lines by using DC-to-AC inverters through common

DC link, any inverters within IPFC are able to inject active power to the

connected transmission line independently and thereby facilitate active power

transfer among the lines, together with independently controllable reactive

series compensation of each individual line. This paper proposes the

utilization of this apparatus, for simplicity, which is applied to a test system,

6-machine 22-bus test system with optimal power flow (OPF) control method

to solve overload problem. The OPF control method for a satisfied solution of

the minimum cost and the entire power flow balance is also discussed.

2.2 IPFC AND ITS FUNCTIONALITY

Athamneh and Wei-Jen Lee (2006) explained Transmission system

is the backbone of the electrical power delivery system. It is essential to

maintain safety and efficient operations of the transmission system on both

steady state and transient using different methods to improve the overall

performance of the power system. In addition to construct new transmission

lines, Flexible AC transmission system (FACTS) are effective devices to

increase the transfer capacity, improve different stability aspects, and control

the power flow especially for the interconnected systems. The Mediterranean

Ring, a major international electric power interconnection project initially

conceived of during the 1960s. It plans to connect electric power transmission

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grids among the countries that encircle the Mediterranean Sea. Hashemite

Kingdom of Jordan reigns over a strategic location among the middle-east

countries. It is bordered with Iraq, Syria, Saudi Arabia, Israel, and the

Palestinian Authority Territory. Power transfer capabilities between Jordan

and its neighboring countries play important role in the effectiveness of the

Mediterranean Ring. This paper studies the impact of FACTS on the

performance of Jordanian transmission system under different levels of power

exchange with Egyptian and Syrian power systems. This helps to determine

the appropriate types and locations for FACTS devices to be installed to

improve these limits.

Yankui Zhang et al (2006) Zhang et al. have presented an

innovative power injection model (PIM) of interline power flow controller

(IPFC) for power flow analysis. The series coupling transformer impedance

and the line charging susceptance have been included in this model. In this

circumstance, sparsity technique has been applied because it has been verified

that the original structure and symmetry of the admittance matrix could still

be kept and the Jacobian matrix could keep the block-diagonal properties.

They have achieved the specified control target by adjusting the IPFC state

variables simultaneously with the network state variables. Also, the practical

constraints of IPFC in Newton power flow have been taken into account in

their model.

Zhang Yong-gao et al (2006)) provides a new advanced technology

solution to improve the flexibility, controllability and stability of a power

system. The unified power flow controller (UPFC), as an outstanding part one

for regulating power flow among the FACTS, can control respectively

transmission line real power, reactive power and node voltage. In this paper

operation principle and model of UPFC are introduced, and control strategy of

current feed-forward plus double PI loop for adjusting shunt inverter real

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power is proposed. According to math model of shunt inverter, a simple

model in the synchronous rotating dq coordinates is given and a dq

decoupling double close-loop controller is established and designed. The

simulation results for a case study indicate that DC bus voltage and node

voltage can be controlled efficiently, attest that control scheme and controller

design are viable and effective. This paper has a certain instructive

significance for UPFC application. It settles foundation in both practice and

theory for further manufacturing UPFC laboratory-scale equipment.

Kazemi and Karimi (2006) explains the effect of interline power

flow controller (IPFC) on damping low frequency oscillations which has been

implied in some papers, but has not investigated in detail. This paper

investigates the damping control function of an interline power flow

controller installed in a power system. For this purpose, single machine-

infinite bus model integrated with IPFC is used, and the linearized model is

established. Using this model, Phillips-Heffron model of system for steady

state digital simulations is derived. In this paper, numerical results with

Matlab Simulink toolbox, which show the significant effect of IPFC on

damping inter-area oscillations, are represented.

Jun Zhang and Yokoyama (2006) presents a comparison study

between the applications of the unified power flow controller (UPFC) and the

interline power flow controller (IPFC) in optimal power flow (OPF) control.

The power injection models of the flexible AC transmission systems

(FACTS) devices are reviewed and incorporated in the OPF problem without

active power generation redispatching, which minimizes the overall

generating cost. The FACTS devices are planned for power flow regulation

and their additional degrees of freedom act as additional potential in

optimizing the power system. The performance of the UPFC and the IPFC is

compared from the viewpoint of the total active power losses and their

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necessary capacities through numerical examples. The feasibility of a

gradient-based algorithm, namely sequential quadratic programming (SQP), is

tested, and the importance and some techniques of proper selection of the

initial optimization conditions are also presented.

Zhang (2006) suggested The interline power flow controller (IPFC)

is the latest generation of flexible AC transmission systems (FACTS) devices

which can be used to control power flows of multiple transmission lines. This

paper presents an optimal power flow (OPF) control in electric power systems

incorporating IPFC. The injection models of both the IPFC and the

transmission lines embedded with IPFC, which can be easily incorporated in

load flow programs and optimal power flow programs, are developed.

Numerical examples demonstrated that IPFC can be used for congestion

management and total active power loss minimization in electric power

systems at the same time. The minimum capacity of the IPFC converters is

determined in the optimization process simultaneously.

Vasquez-Arnez and Zanetta Jr, (2006) Arnez et al. have analyzed

Interline Power Flow Controller (IPFC) and the Generalized Interline Power

Flow Controller (GIPFC) which are VSI-based multi-line FACTS controllers

and presented their operational analysis. Kazemi, A. and Karimi, E.,(2008)

have analyzed IPFC and GIPFC being the newest devices within the FACTS

technology have been used to achieve an improved and almost instantaneous

control over independent transmission systems. They have initially modeled

the steady-state analysis of an IPFC and GIPFC controlling two balanced

independent AC systems. Utilization of the instantaneous power theory

together with the d-q orthogonal co-ordinates has been proved to be proper

tools for evaluating the GIPFC response towards the operation of both

controlled systems.

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Namin (2006) explained the test case is made to verify the current

injection model of the UPFC. The UPFC is installed in a sample network.

Then a fault study apply to this network by monitoring active power flow in

the faulted line for the system with and without the UPFC. The parameters of

the UPFC are chosen based on static behavior of the UPFC. With the control

of the variables r and gamma, improvements in damping of the oscillations

are shown obviously. The general form of the UPFC control system has been

proposed. The UPFC should operate in the automatic power flow control

mode keeping the active and reactive line power flow at the specified values.

This can be achieved by the linearizing the line power flow. Figures show the

first preliminary results of the proposed control method if the specified value

of the active and reactive power be chosen.

An alternative control strategy for the UPFC is based on the series

voltage injected by the UPFC. If this injected voltage is instantaneous by the

UPFC, the components can be related to the control variables r and . The

further studies will investigate these control methods with respect to

performance and robustness.

Hossam-Eldin et al (2006) proposed the main objectives of flexible

AC transmission systems (FACTS) are to increase the transmission capacity

of lines and to control the power flow over designated transmission system.

FACTS can perform all objectives of reactive power control and voltage

control within the transmission and distribution networks and at load

terminals. Several schemes of flexible AC transmission systems FACTS are

either in use today. One of the most important FACTS devices is the Unified

Power Flow Controller (UPFC), which is used to investigate its effect on load

flow and loss reduction in power system. The UPFC is a combination of a

static shunt synchronous series compensator (STATCOM) and a static

synchronous series compensator (SSSC), which are coupled via a common

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DC link. The UPFC is a device, which can control simultaneously all the

three parameters of line power flow which are line impedance, voltage and

phase angle. The UPFC improves terminal voltage regulation, series capacitor

compensation and transmission angle regulation.

The main objectives of this work are to develop a new basic control

scheme and comprehensive analysis for a unified power flow controller

(UPFC) also to develop MATLAB program which simulate the UPFC and its

action on the power system. This developed technique has been proved to be

very effective and will enable engineers to study and investigate how the

UPFC can affect the transmission system using the series voltage and shunt

current injection. It was possible to demonstrate that the UPFC can improve

the system characteristics and gives the best transient and dynamic stability. It

can highly improves the power factor. Many cases are investigated and

studied such as application of the UPFC to control voltage and power flow.

The cases are tested for the same simulated power system but with different

load types and different system voltages. In all cases, the performance of the

system was analyzed, tested and studied to indicate voltages, currents and

power performance and showed to be satisfactory.

Du et al (2007) explained A structure-preserved power-frequency

slow dynamics simulation model and suggest for interconnected ac/dc power

systems with automatic generation control (AGC) consideration, which will

be applied to study relevant emergency control in future so that the bulk

system viability crisis caused by load-frequency slow dynamics can be

released. In the model, the network structure of interconnected power systems

is entirely preserved, and the multi-area dynamic load flow (DLF) is

developed for simulation. The generator speed governor and rotor dynamics,

load-frequency characteristics, simplified models for high voltage direct

current (HVDC) transmission and flexible ac transmission systems (FACTS)

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device thyristor controlled series capacitor (TCSC) suitable for long-term

dynamics are considered with their AGC interfaces kept for future

emergency-AGC study. However, at this stage, the sub-problem of reactive

power and voltage is neglected for modelling simplicity and dc load flow is

thus used for network solution. The concept of area centre of inertia (ACOI)

is used based on the assumption of uniform frequency in each control area

similar to that of the conventional single-area DLF calculation.

The application of ACOI concept is attractive because the signal

can be obtained from Wide-Area Measurement Systems (WAMSs) in real

time and used to enhance long-term frequency stability through advanced

control in future. The computer test results from 2-area 4-machine and IEEE

30-bus power systems demonstrates the validity and effectiveness of the

suggested model and corresponding algorithm.

Karami et al (2007) has proposed a method that simultaneously

enhance voltage security and manage congestion of transmission network by

identifying optimal location and capacity of the Static Synchronous

Compensator (STATCOM) and identifying the capacity of an appropriately

placed IPFC respectively. To this complicated constrained optimization

problem, they have implemented Artificial intelligence as a heuristic

technique. It has been demonstrated that, in addition to solving congestion

management problems, voltage security margin has also been improved by

their proposed method

Grzegorz Benysek (2007) has proposed an innovative probabilistic

method to evaluate the power rating of an IPFC system within a distributed

generation environment. Considerable savage has been achieved by their

proposed system in the design of the IPFC system by reducing the power

ratings requirement of the used inverters and filters. Potential advantages of

their proposed approach in terms of cost savings have been proved by both

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analytical prediction and experimental results. Very remarkably, they have

achieved those assessments with a very high level of confidence, exceeding

99.9%. Thus, their new approach has not compromised the reliability of the

system. With the rapid development of DG-systems and their expected

proliferation in the near future, the important problem of the economy of the

DG-system has been solved by their proposed new approach, unlike this most

other researches have concentrated mainly on other aspects like reliability and

power quality.

Sankar and Ramareddy (2007) proposed a VSC-based FACTS

controller called inter line power flow controller an inter line power flow

controller (IPFC) with the unique capability of power management among the

multi-lines of a substation for Series compensation in power system. By

enabling utilities to get most service from their transmission facilities, the

FACTS technology has been necessary for alleviating some of the difficulties

of the transmission network. FACTS controllers have been capable of

controlling series impendence, shunt impedance, current, voltage and phase

angle. Diverse controller’s circuits have been simulated using PSPICE

software package. In a transmission system, to progress the power flow and to

provide a power balance, IPFC has been used.

Xia Jiang et al (2007) described the use of interline power flow

controller (IPFC) for maximizing voltage-stability limited power transfer and

damping power swings is investigated. An IPFC consist of two voltage-

sourced converters inserted in series in transmission lines, whose DC

capacitors are coupled. This paper discusses the regulation modes of an IPFC

and its control strategies at rated capacity. The rated-capacity operation is

important in determining the maximum power transfer capability under

voltage stability condition. Also, IPFC can improve small-signal stability by

providing damping control supplemental to its regulation control. A modal

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decomposition approach is proposed to select the best damping control input

signals. The results are illustrated on a 20-bus test system.

Padiyar and Prabhu (2007) explained that the interline power-flow

controller (IPFC) is a voltage-source-converter (VSC)-based flexible ac

transmission system (FACTS) controller for series compensation with the

unique capability of power-flow management among the multiline

transmission systems of a substation. The reactive voltage injected by

individual VSCs can be maintained constant or controlled to regulate active

power flow in the respective line. While one VSC regulates the dc voltage,

the others control the reactive power flows in the lines by injecting series

active voltage. This paper presents the modelling of IPFC with 12-pulse,

three-level converters and investigates the subsynchronous-resonance (SSR)

characteristics of IPFC for different operating modes.

The analysis of SSR is carried out based on eigenvalue analysis and

transient simulation of the detailed system. It is illustrated with the help of a

case study on a system adapted from the IEEE Second Benchmark Model.

The analysis uses both D-Q model (neglecting harmonics in the output

voltages of VSCs) and the three-phase model of VSCs using switching

functions. While the eigenvalue analysis and controller design is based on the

D-Q model, the transient simulation considers both models.

Jun Zhang and Yokoyama (2007) described the latest generation of

FACTS devices, namely the interline power flow controller (IPFC), is the

combination of multiple series compensators, which are very effective in

controlling power flows in transmission lines. In this paper, the evaluation of

the impact of the IPFC on available transfer capability (ATC) enhancement is

presented. An ATC computation method based on the optimal power flow

(OPF) control is formulated to evaluate the power transfer capability from the

specified generation unit to the specified load. The IPFC, represented by its

28

power injection model, is incorporated into the OPF control formulation. The

effectiveness of the IPFC control is demonstrated clearly by numerical

simulations on a 2-machine 4-bus system and a 6-machine 22-bus system.

The results are also compared with those of the unified power flow controller

(UPFC) in various aspects.

Sankar and Ramareddy (2007) achieve operational reliability and

financial profitability more efficient utilization and control of the existing

transmission system infrastructure. Mechanical switch based traditional

approaches cannot realize full utilization of transmission system due to the

needed large stability margin. Flexible Alternating Current Transmission

System (FACTS) is a power electronics based real time computer controlled

technology provides needed corrections of transmission functionality in order

to efficiently utilize existing transmission systems and therefore minimizing

the gap between the stability and the thermal levels. Basic principles of the

IPFC simulated using PSPICE and discussed. Simulation results demonstrate

the capability of IPFC to realize power balance in a transmission system with

two identical lines and two non-identical lines.

Regulation of the receiving end voltage of a transmission line

terminating at a substation and linked up to the distribution network is at

present implemented using the transformer tap changers, shunt compensators

using elements-Inductor (L) and Capacitor (C) and synchronous condensers.

They are slow with high wear and tear of moving parts. It is proposed to use

IPFC for regulation of the receiving end voltage in series compensation and

shunt compensation modes. IPFC to perform the voltage regulation at the

receiving end of the line which is terminated at a sub-station to feed a

distribution network simulated. Simulation results for both types of

compensators series and shunt obtained. Results confirm the voltage

29

regulation feature of the IPFC. Hence IPFC at a sub-station can function as a

voltage regulator of a line.

Pandey and Singh (2008) presents an optimal power oscillation

damping (optimal POD) controller design with unified power flow controller

(UPFC). A systematic analysis of optimal POD controller has been presented

with state space model developed in a generalized framework for single

machine infinite bus (SMIB) and two area system. The approach is modular

and general enough so as to include any sub system. The controller designed

shows excellent performance for variety of loading conditions. The sample

system has been studied and the results presented are in good agreements to

the existing operational domain of the UPFC.

Dubey (2008) presents the design of fuzzy logic power system

stabilizers using genetic algorithms in multi machine power system. In the

proposed fuzzy expert system, generator speed deviation and acceleration are

chosen as input signals to fuzzy logic power system stabilizer. In this

approach gains, centers of membership functions and the parameters of the

fuzzy logic controllers have been tuned using genetic algorithm. Incorporation

of GA in the design of fuzzy logic power system stabilizer will add an

intelligent dimension to the stabilizer and significantly reduces computational

time in the design process. The problem of selection of optimal parameters of

fuzzy logic power system stabilizer is converted into an optimization problem

and which is solved by genetic algorithm with the integral of squared time

squared error (ISTSE) based objective function. To demonstrate the

robustness of the proposed genetic based fuzzy logic power system stabilizer,

simulation studies on multi machine system subjected to small perturbation

and three-phase fault have been carried out. Simulation results show the

superiority and robustness of GA based fuzzy logic power system stabilizer as

compare to conventionally tuned controller.

30

Aminifar et al (2008) probes the impact of utilizing an IPFC on the

reliability indices of interconnected power systems. First, a concise

presentation of IPFC and its structure are provided and the reliability model of

two unequally-rated parallel transmission lines equipped with IPFC is then

extracted. The assumed IPFC is composed from two parallel converting

bridges associated with each line. Afterwards, based-on equivalent assisting

unit approach, different commonly-used adequacy indices including the loss

of load expectation (LOLE), loss of energy expectation (LOEE) and system

minutes (SM) are calculated. A set of numerical analyses are conducted to

illustrate the sensitivity of these indices with respect to different parameters.

Beekmann et al (2009) explains lot of power systems renewable

energies and especially wind power are main drivers for the actual

restructuring of transmission and distribution systems. Enhanced power

exchange capabilities over long distances will be one of the necessary

transmission system characteristics in order to achieve a higher penetration

level of wind power. Distribution systems change from pure load distribution

to distributed ldquovirtualrdquo renewable power plants. Therefore wind

power must also participate in maintaining the quality of supply, power

system security and stability. Robust fault-ride-through performances, voltage

control and the management of active and reactive power flows are typical

tasks to be resolved.

Today, wind energy converters not only offer power plant

capabilities similar to conventional generators but may exceed their

performance in various aspects. FACTS-like performances can be provided to

power systems by ENERCON wind energy converters (WECs) due to their

full scale inverter system. Field tested and validated performances of the latest

ENERCON wind energy converters, associated data and models address most

advanced grid codes. For normal and stressed system conditions ENERCON

31

WECs with FACTS capabilities can provide STATCOM-like performances

without the need for an external costly device. Flexible setting options allow

the optimisation for the specific needs of transmission and distribution

systems. Measurements in the field for the validation of wind energy

converters and of models for dynamic studies have been carried out by

ENERCON. These test results show a very good accuracy between

simulations based on these models and field measurements carried out with a

full scale wind energy converter. These FACTS capabilities can lead to a win-

win-situation for the wind farm operator and the system operator to minimize

the integration costs for wind power. Furthermore these FACTS Capabilities

strongly support the further increase of wind power connected the power

systems and help to resolve questions and tasks for the optimized

restructuring of power systems.

Segundo and Messina (2009) investigate the use of Flexible ac

Transmission Systems (FACTS) devices to aid damping of low-frequency

inter-area oscillations in longitudinal power systems is presented. A linear

model of VSC-based FACTS devices that takes into account the dynamics of

dc links is developed and incorporated into production-grade software for

small signal analysis of large power systems. Based on this representation, a

unified framework for modal power oscillation flow studies is then developed

to analyze the sensitivity of modal behavior to FACTS control action. With

this method, the transmission corridors and system parameters having a large

contribution to critical system oscillations modes are determined. The method

is particularly well suited for investigating inter-system oscillations in large-

scale power systems with embedded FACTS controllers The utilized

methodology is tested on a practical 45-machine Mexican system that

includes several major static VAR compensators. Control mode

implementations are discussed and tested and comparisons with existing

technologies are presented.

32

Mohamed et al (2009) presents an optimal power flow control in an

electrical power system incorporating interline power flow controller (IPFC)

and uses the particle swarm optimization (PSO) technique. Based on the

steady state model, the sizing of the IPFC controller in the network is

formulated as an optimization problem to minimize the transmission line loss

in the network. The power flow control constraints due to the use IPFC is

included in optimal power flow (OPF) problem in addition to the normal

conventional constraints.

2.3 VARIOUS ANALYSES IN MODELING OF IPFC

Bhowmick et al (2009) investigate Complexities of computer

program codes for Newton-Raphson load flow (NRLF) analysis are usually

enhanced during power flow modeling of an interline power flow controller

(IPFC). This is due to the fact that the contributions of the series converters of

the IPFC are needed to be accounted for while computing bus power

injections and Jacobian matrix elements. Also, the IPFC real power injection

term along with its associated Jacobian matrix call for new codes to be

written. In this paper an advanced IPFC model is proposed to address this

issue, wherein an existing power system installed with IPFC(s) is transformed

into an augmented equivalent network without any IPFC. To obtain the

solution of the original network containing IPFC(s), the augmented network

can easily be solved by reusing the existing NRLF codes, as this network is

now devoid of any IPFC. Consequently, the complexities of the computer

program codes are reduced substantially. Various practical device limit

constraints of the IPFC can also be taken into account by the proposed model.

Chen Zaiping et al (2009)explain Networked control system (NCS)

is a kind of closed loop control systems where the sensors, the controller and

the actuators exchange data through network. Because the networks, in which

33

the band width is limited, are introduced in the systems, some new issues

appear unavoidably. At present, the research of networked control system

becomes a focus area in control engineering. According to the characteristics

of NCS, incremental predictive functional control (IPFC) strategy with

random long time delay in NCS is proposed in this paper. Based on the

strategy proposed controller design is given, which realized the compensation

of NCS time delay. Simulation experiments are carried out, and simulation

results confirmed that perfect compensation effect is obtained in the long time

delay NCS with the control strategy proposed in this paper.

Talebi and Abedi (2009) discussed the Interline Power Flow

Controller (IPFC) among the Flexible AC Transmission Systems (FACTS) is

one of the most versatile devices, especially for power flow control of

multiline systems. This paper presents a new utilization of IPFC in power

systems. In this paper, IPFC is used as an Automatic Generation Control

(AGC). In order to obtain this objective, Power Injection Model (PIM) among

the other IPFC's models is chosen and implemented into the modified IEEE-

14 bus test system. Power flow of the test system in presence of IPFC is done

using programming with MATLAB software and the results are presented.

The results indicate that IPFC can be utilized as an AGC.

Ajami and Kami (2009) explained a new concept of the FACTS

controller is Interline Power Flow Controller (IPFC) for series compensation

with the unique capability of controlling power flow among multi-lines within

the same corridor of the transmission line. The IPFC employs two or more

Voltage Source Converters (VSC) with a common dc-link. Each VSC can

provide series compensation for the selected line of the transmission system

(master or slave line) and is capable of exchanging reactive power with its

own transmission system. In this paper, a current-source converter topology

based IPFC is proposed. In this structure, the dc-side current is regulated to a

34

value larger than the peak value of the maximum line current. The injected

voltage is controlled according to the desired reactive power compensation

and management active power flow for master line. The decoupled state-

feedback control for the injected voltage with a separated dc current control is

applied to the proposed system. The proposed IPFC has been simulated using

the Matlab/Simulink program.

Manju and Subbiah (2010) explained about control of power flow,

for increasing the transmission capacity and optimizing the stability of the

power system, FACTS devices are used. One of the most widely used FACTS

devices is Unified Power Flow Controller (UPFC). The controller used in the

operation of UPFC has significant effect on power flow control and stability

enhancement. Conventional PI regulators are generally used in the control of

UPFC. This paper investigates control method, using fuzzy logic, for the

unified power flow controller in order to improve the stability of a power

system. FLC was developed by taking into consideration Mamdani inference

system in the decision process and Mamdani's Centroid method in the

defuzzification process. Studies with different operating conditions are

simulated to prove the ability of UPFC in controlling the power flow and the

effectiveness of fuzzy controller in the performance of UPFC. MATLAB /

Simulink is used to simulate the FLC and UPFC models.

Zhihui Yuan et al (2010) presented a new component within the

flexible ac-transmission system (FACTS) family, called distributed power-

flow controller (DPFC). The DPFC is derived from the unified power-flow

controller (UPFC). The DPFC can be considered as a UPFC with an

eliminated common dc link. The active power exchange between the shunt

and series converters, which is through the common dc link in the UPFC, is

now through the transmission lines at the third-harmonic frequency. The

DPFC employs the distributed FACTS (D-FACTS) concept, which is to use

35

multiple small-size single-phase converters instead of the one large-size three-

phase series converter in the UPFC. The large number of series converters

provides redundancy, thereby increasing the system reliability. As the D-

FACTS converters are single-phase and floating with respect to the ground,

there is no high-voltage isolation required between the phases. Accordingly,

the cost of the DPFC system is lower than the UPFC. The DPFC has the same

control capability as the UPFC, which comprises the adjustment of the line

impedance, the transmission angle, and the bus voltage. The principle and

analysis of the DPFC are presented in this paper and the corresponding

experimental results that are carried out on a scaled prototype are also shown.

Roozbeh Asad and Ahad Kazemi (2010) have proposed a new

method for control of IPFC, based on the structure and behavior of IPFC and

also the principles of its control for managing power flow in transmission

lines. A few advantages of their method have been the simplicity and non

necessity of high speed processors due to quick system response and few

calculations. Their method has become an appealing feasible control

technique for IPFC because of these advantages. All the necessary

computations of their method have been performed automatically by the well

designed control circuit with the help of appropriate feedbacks.

2.4 INTER LINE POWER FLOW CONTROLLER AND ITS

MODELING

Mohamad Reza Banaei and Abdel-Rahim Kami (2010) Banaei et

al. have analyzed the stability of the Interline Power Flow Controller (IPFC)

based linearized Phillips-Heffron model power system. For damping the low

frequency oscillations a novel modeling IPFC supplementary controller that

makes use of four alternative damping parameters has been proposed. They

have discussed the design of the IPFC damping controller robust to changes in

system loading and fault in power system, by the selection of effectiveness

36

damping control signal. The presented control scheme has been capable of not

only achieving independent IPFC but also damping the oscillations.

Xia Jiang et al (2010) analyses the dynamic regulation models for

voltage-sourced converter (VSC) based on flexible ac transmission system

(FACTS). Controllers which are described in this paper. The dynamic models

can then be used to analyze these FACTS controller's capability to improve

the capability of a power transfer path. The contributions of this paper

includes showing that the benefits of FACTS controllers are proportional to

the MVA ratings and the benefits of multiple FACTS controllers are

cumulative. Furthermore, the coupling of dc buses allowing active power

circulation between multiple VSC FACTS controllers may offer additional

improvement in transfer capability.

Jangjit et al (2010) deals with improvement the transmission line

loss by using Interline Power Flow Controller (IPFC). The IPFC is a novel

FACTS device which can control power flow in power systems. The IPFC

consists of multi-series converters. The power flow through the line can be

regulated by controlling both magnitudes and angles of the series voltages

injected by an IPFC. This paper used differential evolution to determine the

control parameters on an IPFC. The proposed method is tested on a sample

multi-machine system.

Parimi et al (2010) presents the application of fuzzy logic based

supplementary controller, for Interline Power Flow Controller (IPFC), to

enhance the damping of low frequency oscillations in the Single Machine-

Infinite Bus (SMIB) power system installed with IPFC. The fuzzy logic based

IPFC controller using Mamdani type inference system is designed with

generator speed and rotor angle as its input signals. The proposed method is

applied to control the input signal of IPFC and thus improving the power

37

system stability. The effectiveness of the controller in damping the power

system oscillations is demonstrated with varying operating conditions.

Mohamed et al (2010) proposes three types of particle swarm

optimization techniques, namely basic particle swarm optimization, inertia

weight approach particle swarm optimization and constriction factor approach

Particle swarm optimization is applied to optimal power flow control of an

electrical power system incorporating Interline Power Flow Controller. Based

on the steady state model, the sizing of the controller in the network is

formulated as an optimization problem to minimize the transmission line loss.

The power flow control constraints of the controller are included in optimal

power flow problem in addition to the normal conventional constraints. The

simulation results on standard IEEE 14-bus system minimizing the

transmission line losses show the effectiveness of the variants of particle

swarm optimization. The optimal control parameters of interline power flow

controller are compared.

Moghadam et al (2010) advocates the Interline Power Flow

Controller (IPFC) is a voltage-source-converter (VSC)-based flexible ac

transmission system (FACTS) controller for series compensation in a

multiline transmission system of a substation. The common DC link in the

IPFC configuration enables each inverter to transfer real power to another, so

regulation of DC link voltage is an important issue in overall performance of

the system. In this paper, a new method based on Genetic Algorithm (GA) is

presented to regulate DC link voltage. In this method, GA and system

objective function are adopted to choose best PI parameters for the linear

controller of DC link of IPFC. Simulation results in Matlab/Simulink verifies

the effectiveness of optimized choose of PI controller parameters which are

chosen in a try and error manner conventionally.

38

Veeramalla and Sreerama Kumar (2010) propounds the application

of Interline Power Flow Controller (IPFC) in damping of low frequency

oscillations is investigated. An extended Heffron-Phillips model of a single

machine infinite bus (SMIB) system is used to analyze the damping torque

contribution of the IPFC in power systems. The potential of various IPFC

control signals upon the power system oscillation stability is investigated

under various loading conditions. Simulation results demonstrate the

effectiveness of IPFC controllers on damping low frequency oscillations.

Alomoush (2010) develops the Bacterial Foraging (BF)

optimization algorithm imitates the foraging behavior of Escherichia coli (E.

coli) bacteria that exist in human intestine, whose foraging habit is modeled

as a distributed optimization process. This paper applies the BF algorithm to

design optimal controllers of a single-machine-infinite-bus (SMIB) system

equipped with an interline power flow controller (IPFC). The system is

described by a set of nonlinear equations. The BF algorithm is used to tune

the parameters of the IPFC control signals in the nonlinear optimization

process. The controllers are optimally tuned to stabilize the system, increases

system damping, and improve the steady-state response when the system is

subjected to different disturbances. Simulations demonstrate that the optimal

BF-based controllers can significantly stabilize the system and efficiently

damp low frequency oscillations under severe disturbances. The results are

compared to the results obtained using the genetic algorithm (GA) to show the

effectiveness of using BF to attain a global optimal solution of the design

problem.

39

2.5 ARTIFICIAL INTELLIGENT TECHNIQUES IN IPFC

Gomathi et al (2010) enunciates about the flexible AC transmission

systems (FACTS) technique, the power flow in the interconnected power

systems, can be controlled flexibly. This paper is concerned about the state

estimation of system, which contain Flexible AC Transmission System

(FACTS) device. Interline power flow controller (IPFC) is one of the versatile

FACTS device which is considered for estimating the state of the system.

Based on the conventional power system state estimation model, a kind of

model for state estimation with IPFC is introduced in this paper, in which

power injection model is used and the effect of IPFC on the power flow is

transferred to the lines which are connected to it. This method is integrated to

the conventional state estimation program with the consideration of IPFC.

The results demonstrate, that the model is effective for practical use. The

operation and working of Interline Power flow Controller was analyzed and

simulated results using Matlab-Simulink is presented.

Mohamed and Rao (2010) discusses the control parameters of

voltage source converters used in Interline Power Flow Controller (IPFC) are

designed to realize optimal power flow in a power system with modified

Newton-Raphson method. The optimal control parameters are derived to

minimize the transmission line losses employing three intelligent optimization

techniques, namely Particle Swarm Optimization (PSO), Genetic Algorithm

and Simulated Annealing. The selected techniques are employed on IEEE 30-

bus bench mark power system and the optimal parameters of IPFC, the

voltage profile and the transmission line losses of power system are derived

from the simulations. The simulation results validate the efficacy of the three

optimization techniques and PSO technique is proved to be more efficient

compared to the other two techniques.

40

Naresh Babu et al (2010) analyzes about the interline power flow

controller (IPFC) is one of the latest generation flexible AC transmission

systems (FACTS) controller used to control power flows of multiple

transmission lines. This paper presents a mathematical model of IPFC, termed

as power injection model (PIM). This model is incorporated in Newton-

Raphson (NR) power flow algorithm to study the power flow control in

transmission lines in which IPFC is placed. A program in MATLAB has been

written in order to extend conventional NR algorithm based on this model.

Numerical results are carried out on a standard 2 machine 5 bus system. The

results without and with IPFC are compared in terms of voltages, active and

reactive power flows to demonstrate the performance of the IPFC mode

Nagalakshmi and Kamaraj (2011) concerns the optimal location

and control of Flexible AC Transmission System (FACTS) devices using

Differential Evolution (DE) and Particle Swarm Optimization (PSO) for

enhancing loadability in transmission system for pool model in deregulated

electricity market. This approach uses AC load flow equations with the

constraints on power system generation, transmission line flow, magnitude of

bus voltages, and FACTS device settings. For the proposed method three type

of FACTS devices namely Thyristor Controlled Series Compensator (TCSC),

Static VAR Compensator (SVC), and Thyristor Controlled Phase Shifting

Transformer (TCPST) are used. To validate the proposed approach

simulations are performed on IEEE 6 bus system and 39 bus New England

Test Systems. Comparisons are made in terms of solution quality,

computational time, and convergence characteristics. The simulation results

thus obtained indicate that by optimal location and control of FACTS devices,

using DE, enhances the loadability in transmission system with less

computational time and faster convergence than using PSO. This comparative

study concludes that by optimal location and control of FACTS devices using

41

DE will be more effective for loadability enhancement in transmission system

for pool model in deregulated electricity market.

Yao Shu-jun et al (2011) describe based on the basic principle of

Unified Power Flow Controller circuit, give a simple analysis about the

principle of power flow control of UPFC, and a detailed simulation model of

UPFC considering the charging dynamics of its DC link capacitor is provided.

Using the UPFC simulation model established in SIMULINK, a dynamic

simulation tool in MATLAB, take a simple power system with UPFC as an

example. The simulation test has been conducted on a simple system

composed of synchronous generator and infinite capacity bus, the steady state

and transient characteristics of UPFC in this system are researched. In the

process of simulation, the control strategy of UPFC system is also discussed,

its shunt side control the terminal voltage of the system and the firing angle of

converter 1 the shunt part of UPFC, in order to keep the terminal bus voltage

magnitude of UPFC and the DC capacitor voltage as constant, respectively.

its series side control terminal voltage and firing angle of converter 2 the

series part of UPFC, so as to keep the real power and reactive power of the

line with UPFC device as constant or to act as a series compensator. Further

analysis shows that all the active power of the series side is provided or

absorbed by the DC capacitor presented among the two converters. The active

power is provided by the shunt side convertor of the UPFC.

That is to say, both converter is associated with the part of DC link,

therefore, it is very necessary to consider the dynamic situation of the DC

capacitor when establishment the mathematical of UPFC. The results from

simulation and experiments show that by means of UPFC the power flow

distribution among transmission lines can be give back rapidly and

reposefully. The transient experiments proved that UPFC can improve the

42

stability of power grid. Simulation results also confirm that UPFC can restrain

the oscillation of power angle and power flow.

Chansareewittaya and Jirapong (2011) explains evolutionary

programming (EP) with optimal maximum number of FACTS controller and

search space managing methods are proposed to determine the optimal

allocation of FACTS controllers to enhance power transfer capability of

power transactions between generators and load buses. Particular optimal

allocation includes optimal locations and parameter settings. Two types of

FACTS controllers including thyristor-controlled series capacitor (TCSC) and

static var compensator (SVC) are used individually in this study. The

objective function is formulated as maximizing total transfer capability (TTC)

and minimizing power losses. Power transfer capability determinations are

calculated based on the optimal power flow (OPF) technique. Split and non-

split search space managing methods are used. Test results on IEEE 118-bus

system and the practical Electricity Generating Authority of Thailand (EGAT)

58-bus system showed that EP with optimal maximum number of FACTS and

the proposed split search space managing method gave higher TTC and less

maximum number of FACTS controllers than those from non-split method.

Therefore, the installation of FACTS controllers with optimal maximum

number and optimal allocation are beneficial for the further expansion plans.

Moghadam et al (2011) investigates the Interline Power Flow

Controller (IPFC) as a voltage-source-converter (VSC)-based flexible ac

transmission system (FACTS) controller for series compensation in a

multiline transmission system of a substation. The capability of injecting

series voltages with controllable magnitude and phase angle makes it a

powerful tool for better utilization of existing transmission lines in a multiline

transmission system. IPFC is used to regulate active and reactive power flow

in a multiline system, usually. In this paper, a control method for IPFC is

43

proposed to control magnitude and phase angle of one sending bus of a

substation. All degrees of freedom of IPFC and decoupled synchronous frame

concept are used in the proposed control structure. Simulation results in

Matlab/Simulink are presented to show the capability of IPFC in

compensating the bus voltage.

Sreejith et al (2011) presents a mathematical model of IPFC,

termed as power injection model (PIM). The model is incorporated in a

MATLAB power flow program based on Newton-Raphson (NR) algorithm to

study the power flow control in transmission lines in which IPFC is placed.

By utilizing this device (IPFC), an enhanced controllability over independent

transmission systems or those lines whose sending-end are connected to a

common bus, can be obtained. The power flow through the line can be

regulated by controlling both magnitudes and angles of the series voltages

injected by an IPFC. Generally, the IPFC employs multiple dc-to-ac inverters

providing series compensation for a different line respectively. A program in

MATLAB has been written and numerical results are carried out on a

standard 2 machine 5 bus system and IEEE 30 bus system. The results

without and with IPFC are compared in terms of voltages, active and reactive

power flows to demonstrate the performance of the IPFC model.

Bharathi and Rajan (2011) deals with an advanced FACTS

controller for power flow management in transmission system using IPFC.

Regulator uncertainty, cost, and lengthy delays to transmission line

construction are just a few of the barriers that have resulted in the serious

deficiency in power transmission capacity that currently prevails in many

regions. Solving these issues requires innovative tool on the part of all

involved. Low environmental-impact technologies such as flexible AC

transmission system (FACTS) and dc links are a proven solution to rapidly

enhancing reliability and upgrading transmission capacity on a long-term and

44

cost-effective basis. Interline power flow controller (IPFC) is a new concept

of FACTS controller for series compensation with the unique capability of

power flow management among multi-line of a substation. In this work

mainly concentrated on choosing a suitable voltage source converter, to

employ it in the IPFC. A 48 pulse multilevel inverter has been developed by

cascading several units of three level diode clamped multilevel inverter

(NPCI) with the help of phase shifting transformer. A simple and typical test

system model has been developed to check the performance of IPFC an

advanced FACTS controller. A closed loop controller has been developed to

maintain the voltage profile of the test system.

Shan Jiang et al (2011) presents the dynamic behaviour of two

different Flexible AC Transmission System (FACTS) devices, the Interline

Power Flow Controller (IPFC) and the Unified Power Flow Controller

(UPFC) in a benchmark system. The small signal model of the Interline

Power Flow Controller (IPFC) is developed and validated using detailed

electromagnetic transients simulation. Using this validated model, the

damping capabilities of the IPFC and the UPFC are compared and

rationalized. From a small signal dynamics point of view, it is shown that the

series branches of these devices essentially segment the network creating a

new structure. This structure change may be used to effectively improve

system damping without requiring the design of a tuned feedback controller.

The IPFC's two series branches in contrast to the UPFC's single series branch

permit more opportunities for network segmentation. Hence the IPFC has a

greater potential for improving the systems dynamic performance.

Belwanshi et al (2011) emphasizes that Fuzzy logic based

supplementary controller is installed with Interline Power Flow Controller

[IPFC] to damp low frequency oscillations. IPFC is a new concept of the

Flexible AC Transmission system controller for series compensation with the

45

unique capability of power flow of multiple transmission lines. For the

analysis Modified linearized Philips - Heffron model of Single Machine

Infinite Bus system is established with a IPFC. The simulation results are

presented to show the effectiveness and robustness of the proposed control

schemes like Power Oscillation Damping [POD] controller, Power System

Stabilizer [PSS] controller and Fuzzy logic controller by selecting effective

control signals. Investigations reveal that coordinated tuning of IPFC with

Fuzzy logic controller provide the robust dynamic performance. Eigen value

analysis validates the performance of various controllers.

Parimi et al (2011) overviews the nonlinear dynamic model of a

typical multi-machine power system incorporated with Interline Power Flow

Controller (IPFC) has been developed. The oscillation modes with low

damping ratio are identified from the eigenvalue analysis of the linearized

Phillips-Heffron model. A power oscillation damping controller has been

designed for the IPFC using phase compensation technique to enhance the

transient stability of the system. Additional power flow controllers have also

been incorporated into the system to control the power flow demand in the

transmission lines on which the IPFC is connected. The performance of the

designed IPFC controllers has been assessed by simulation studies on a multi-

machine system for power flow demand control as well as overall power

system damping.

Chengaiah and Satyanarayana (2012) takes up the planning and

operation of interconnected large power systems is becoming complex. The

power transfer capability of long transmission lines is usually limited by large

signals ability. Economic factors such as the high cost of long lines and

revenue from the delivery of additional power give strong intensive to explore

all economically and technically feasible means of raising the stability limit.

The development of effective ways is to use transmission systems at their

46

maximum thermal capability. In this paper a Simulink Model is considered

with UPFC model to evaluate the performance of a single and double

transmission line systems (6.6/22) kV. The UPFC model is a member of the

FACTS family with very attractive features and it is a solid state controller

which can be used to control active and reactive power flow in a transmission

line. In the simulation study, the UPFC model facilitates the real time control

and dynamic compensation of AC transmission system. It provides the

necessary functional flexibility required for solving the problems faced by the

utility industry. It should be considered as real and reactive power

compensation, capable of independently controlling voltage profile as well as

the real and reactive powers in the line. The simulation model is tested for

single and double transmission line systems with and without UPFC model in

MATLAB / SIMULINK environment