CHAPTER 2 LITERATURE REVIEW - Shodhganga : a …shodhganga.inflibnet.ac.in/bitstream/10603/24215/7/07... ·  · 2014-09-01systems and using transformer tap changing settings. ...

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CHAPTER 2

LITERATURE REVIEW

2.1 GENERAL

The literature surveyed related to the performance improvement of

power system using computational intelligence technique with optimal power

flow considering FACTS devices are reviewed and presented in this chapter.

Also, comprehensive review of literature on optimal power flow, reactive

power compensation, importance of FACTS in controlling the power flow,

FACTS devices types and benefits are presented.

2.2 REVIEW OF LITERATURE

The development of an optimal solution to network problems was

initiated by the desire to find the minimum of the operating cost for the supply

of electric power to a given load (Kichmayer 1958). The problem evolved as

the so called dispatch problem. The principle of equal incremental cost to be

achieved for each of the control variables or controllers has already been

realized in the pre-computer era when slide rules and the like were applied.

A major step in encompassing not only the cost characteristics but

also the influence of the network, in particular the losses were the formation

of an approximate quadratic function of the network losses expressed by the

active injections. Its core was the B-matrix which was derived from a load

flow and was easily combined with the principle of equal incremental cost

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thus modifying the dispatched powers by loss factors. The formulation of the

problem must be considered as a remarkable improvement as shown by

Squires, Carpentier, however, still there was no effective algorithm available.

At that time the ordinary load flow made considerable progress

(Tinney et al 1967, Scott 1974) and the capabilities of computers showed

promising aspects.

Peschon et al (1968) proposed a method to minimize the

transmission power losses by selecting of reactive power injections in to the

systems and using transformer tap changing settings. They have included a

suitable method to get the solution from a feasible optimal point, but it is

more time consuming.

Dommel and Tinney (1968) presented a method to find the optimal

power flow using a non linear optimization technique. They have used a non

linear objective function of cost or losses using kuhn-tucker conditions, but

control variables are not coordinated due to slow convergence. This is not

suitable for large systems.

Hano et al (1969), proposed a new method of controlling the system

voltage and reactive power distribution in the system. They followed the

sensitivity relation ship between controlled variables and loss sensitivity

indices and the implemented direct search algorithm to minimize the losses.

Narita et al (1971) developed the sensitivity analysis using method

of base optimization technique to minimize the voltage deviation and

minimize the system losses. To obtain successful operation they used voltage

and reactive power regulating devices installed at various points.

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Scott (1974) proposed power flow calculations to perform power

system planning, operational planning and control. the OPF is solved by

varities of methods i.e, successive linear programming method. Minimization

of transmission losses can be achieved by controlling system devices such as

generators, capacitors, reactors and tap changing transformers; it is possible to

minimize the system losses by reactive power redistributions in the system

Mamandur et al (1981) proposed an efficient algorithm to minimize

the transmission loss. Considering the network performance constraints and

the constraints on the control variables, they were applied a dual linear

programming technique to find optimal adjustments to the control variables

satisfying many constraints. This method is used to improve voltage profile

and minimize system losses under operating condition. The result is showing

to zigzagging due to slow convergence.

Shahidehpour et al (1990) discussed an overview of the reactive

power allocation in electric power systems. Optimal reactive power control is

the most important functions giving inadequate reactive power bring up some

problems such as low voltage profile, extra loss and equipment overload.

They have carried out to solve this problem, using nonlinear and linear

programming methods.

Bhatele et al (1985) proposed a mathematical formulation of optimal

power control problem to minimize and control the voltage profile. They have

developed reduced gradient and Fletcher’s update algorithm to solve this

problem. In most of the studies, only they have considered system losses

minimization. They are not considered light load conditions when the

generators are under exited.

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Rama Iyer et al (1983) formulated optimization problem to optimal

allocation of reactive power using the linear programming technique. It is

very fast converge compared to earlier algorithms.

Thukaram et al (1984) described an improved method of reactive

power optimization. In this technique they were avoiding the inverse of large

matrices. They have included voltage-dependency characteristics of loads.

Deeb et al (1988) formulated a mathematical formulation of the

reactive power optimization problem. They were proposed outstanding

features that it does not require matrix inversion, less computation time and

memory space and also it can be utilized for large scale systems. They have

incorporated dependent variables for formulations of equality constraints.

Benders decomposition can be implemented for problem formulation in order

to save computation time and faster convergence.

Huneault et al (1991) presented a literature of published works in

the field of optimal power flow and dispatching. They suggested that

classification of methods based on the optimization technique. They have

compiled more than three hundred publication work. In early 1930’s for

minimizing the fuel cost they were used incremental loading method.

Zhifeng Qiu et al (2009) discussed a literature survey of OPF

problems in the electricity market context; traditionally classical mathematical

optimization methods have been implemented to solve conventional OPF

problems, due to urgency of a deregulation electricity market and

consideration of dynamic system properties. Conventional mathematical

methods suffer from poor convergence and it is very difficult to get local

optimum and not suitable for large scale system.

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Singh et al (2000) proposed a simple and efficient method to

optimal location of FACTS devices considering congestion management for

controlling the device parameters. They used two step approach one for

location of FACTS devices and other for control parameters fixing. It can be

used to reduce the flow on over loaded lines and to increase utilization of the

alternative path excess capacity. This will lead to increase power transfer

capability in existing transmission lines and distribution systems. However,

due to increase demand and adverse effect between FACTS devices, very

difficult to find the optimal locations in most effective manner and how many

devices to be installed on economic basis is a question of great significance.

Momoh et al (1998) analyzed an integrated approach to study the

optimal power flow (OPF) with phase shifter for alleviating over loads in line

conventional OPF are hourly based but these OPF with phase shifter are daily

based because of discrete nature as well as phase shifting adjustment also

discrete .

Aditya tiwari et al (2012) presented a multi objective optimal power

flow for optimal allocation of FACTS devices using genetic algorithm.

Introduction of FACTS devices reduces the power system losses, reduces the

cost of the generation, improve the stability and increase the power transfer

capability. The main objective of the work is to develop the technique based

on the GA, able to identify the number and location of FACTS devices.

Burchett et al (1984) introduced a successive quadratic

programming based OPF methods. This method simplifies the nonlinear OPF

problem with quadratic objective and linearised constraints. This technique

can be utilized for large number of inequality constraints and gives high

accuracy compared to LP method.

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Sun et al (1984) proposed the Newton’s method for solving the

nonlinear OPF problem as a constrained optimization with equality

constraints only. Then, the Lagrange function can be developed and this

function must satisfy the Kuhn-Tucker condition, which is a set of nonlinear

equations.

Momoh et al (1997) discussed the challenges to OPF. The Newton’s

OPF method is one of the best OPF method. This method can solve highly

nonlinear problems. OPF formulation can be solved using an advanced

optimization techniques such as GA, Interior point method, SA,

decomposition and Newton’s method.

Wu et al (1998) proposed allocation and control of FACTS devices

for stability improvement of large scale system. They introduced modal

analysis, and location index for optimal location of FACTS devices. Several

critical swing modes were taken in to consideration for large scale system

model analysis, which provides information on frequency and damping of

each mode is adopted in this work.

Lu et al (2001) presented an improving system security via optimal

placement of Thyristor controlled series capacitor. Single contingency

sensitivity method has been implemented for branch flows, this can be used to

improve a branch prioritizing index in order to rank branches for optimal

placing of TCSCs.

Paterni et al (1999) introduced a optical location of phase shifter in

the french network by genetic algorithm for controlling the power flows in a

network introduced series FACTS devices such as series capacitors or phase

shifters. This can help the reduced power flows in over loaded lines resulting

in an increasing loadability of the system and reduced cost of production.

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Using multiple phase shifters is complex due to interaction of one another

genetic algorithm. They have chosen last location of phase shifters.

Ge et al (1999) developed a new method to incorporate the power

flow control needs of FACTS in studying the OPF problem. They considered

three FACTS devices namely TCSC, TCPS, UPFC. The proposed method

decomposes into two problems. First one is normal power flow and second

one is optimal power flow problem. The active power OPF is no long a linear

optimization problem. So it is not possible to use the conventional linear

programming based technique directly.

Lehmkoster (2002) presented a security constrained optimal power

flow for an economic operation of FACTS devices in liberalized energy

markers. In this work described the optimization method based on sequential

quadratic programming (SQDO) including models of FACTS devices suitable

for a gradient based optimization.

Al rashidi et al (2009) described the issues related with major

computational intelligence tools which are used to solve optimal power flow

problem. The main computational techniques include EP, GA, ES, ANN, SA,

ACO, FST, and PSO. They have been implemented in a variety of range of

optimization problems.

Chaohua Dai et al (2009) introduced a new algorithm seeker

optimization for reactive power dispatch considering voltage stability.

Optimal reactive power dispatch is well known as a nonlinear multimodal and

multi objective optimization problem where global optimization technique is

used in order to avoid local minima.

In the last decades computation intelligence based technique such as

GA, DE & PSO algorithms etc. in this work a seeker optimization

algorithm(SOA) is described to solve reactive power dispatch.

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Chung et al (2000) proposed a hybrid GA approach for OPF with

consideration of FACTS devices, to minimize the total generation fuel cost

and keep the power flows within the security limits using GA is integrated

with conventional OPF for selecting the best control parameters.

Leung et al (2006) developed a new GA method to solve optimal

power flow incorporating FACTS devices.(UPFC) unlike other FACTS

devices it has great flexibility to control the real power, reactive power and

voltage simultaneously. To minimize the total generation fuel cost GA is

coupled with full AC power flow. But recently many other intelligence has

been developed.

Gerbex et al (2001) presented a GA based optimal location of multi

type FACTS devices to increase the loadability of the system. Three

parameters were considered to optimize the problem they are location of the

device their type and their values. Four different types of FACTS devices are

used and modeled for study state analysis namely, TCSC, TCPST,

TCVC&SVC to maximize the power transmitted by the network in

controlling the power flows.

Singh et al (2001) presented a new approach for placement of

FACTS devices in open power markets. FACTS devices can be an alternative

to reduce the flows in heavily loaded lines resulting in an increased

loadability , low system loss ,improve the stability limit and reduced cost of

production.

Mori et al (2000) proposed a parallel tabu search based method for

determining optimal allocation of FACTS in power system for maximizing

the available transfer capability.

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Flexible ac transmission systems (FACTS) have been developed to

improve the performance of weak ac systems and enhance transmission

capabilities over long ac lines. FACTS controllers can be used in all the three

states of the power system, namely: steady state, transient and post transient

steady state. FACTS devices can regulate the active and reactive power as

well as voltage-magnitude (Baghaee et al 2009; Shahgholian, et al 2008).

Dynamic application of FACTS controllers includes transient stability

improvement, oscillation damping (dynamic stability) and voltage stability

enhancement. Facts controller can control shunt impedance, series impedance,

voltage, current and phase angle. FACTS devices types and categories are

presented in (Hingorani 2000) series controllers such as thyristor controlled

series capacitor (TCSC) and static synchronous series compensator (SSSC) ,

(El-Zonkoly et al 2006), shunt controllers such as static var compensator

(SVC)( Amin et al 1999), STATCOM(Shahgholian et al 2008) and

STATCOM with energy-storage system (Kuiava et al 2009), combined series-

shunt controllers such as unified power flow controller (UPFC) (Collins

et al 2006) and combined series-series controllers such as interline power

controller (IPFC) (Mishra et al 2002).

A good number of methods are available on modeling, simulation,

operation and control fundamental of the FACTS devices. Simulation of

FACTS controllers is mainly done in the following two ways: (a) detailed

calculations in 3 phase systems and (b) steady state and stability analyses

(Povh 2004). Shunts FACTS devices are used for controlling transmission

voltage, power flow, reducing reactive loss, and damping of power system

oscillations for high power transfer levels. STATCOM is a kind of dynamic

reactive power compensator, which has been developed in recent days. The

optimization of location of FACTS devices depends on the amount of local

load, the location of the devices, their types, their sizes, improvement

stability, the line loading and system initial operating conditions(Gerbex et al

2003, Sidhartha et al 2009 and Panda et al 2007). There are several methods

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for finding optimal locations of FACTS devices in both vertically integrated

and unbundled power systems. In (Cai et al 2004) an algorithm for find the

best location for the FACTS devices in multi-machine power systems using

genetic algorithm is proposed. In (Gerbex et al 2001) three criteria are

considered for FACTS optimal allocations: available transfer capability

criterion, steady state stability criterion and economic criterion. An alternative

model that can optimize the placement of FACT devices based on multiple

time periods with losses considered proposed in (Yu et al 2004). In (Sharma

et al 2007) the optimal location of a shunt FACTS device is investigate for an

actual line model of a transmission line having series compensation at the

center to get the highest possible benefit. Consequently, evolutionary

algorithms because of their independency from the type of objective functions

and constraints have been used by many researchers in recent years (Niknam

et al 2005, Niknam et al 2010).

2.3 FACTS DEFINITION

Flexible AC Transmission Systems (FACTS) are the name given to

the application of power electronics devices to control the power flows and

other quantities in power systems.

IEEE Definition:

FACTS: AC transmission systems incorporating the power electronic-based

and other static controllers to enhance controllability and increase power

transfer capability.

2.3.1 FACTS History

In its most general expression, the FACTS concept is based on the

substantial incorporation of power electronic devices and methods into the

high-voltage side of the network, to make it electronically controllable. Many

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of the ideas upon which the foundation of FACTS rests evolved over a period

of many decades. Nevertheless, FACTS, an integrated philosophy, is a novel

concept that was brought to fruition during the 1980s at the Electric Power

Research Institute (EPRI), the utility arm of North American utilities

(Hingorani and Gyugyi 2000). FACTS looks at ways of capitalizing on the

many breakthroughs taking place in the area of high-voltage and high current

power electronics, aiming at increasing the control of power flows in the high

voltage side of the network during both steady-state and transient conditions.

The new reality of making the power network electronically controllable has

started to alter the way power plant equipment is designed and built as well as

the thinking and procedures that go into the planning and operation of

transmission and distribution networks. These developments may also affect

the way energy transactions are conducted, as high-speed control of the path

of the energy flow is now feasible. Owing to the many economical and

technical benefits it promised, FACTS received the un instinctive support of

electrical equipment manufacturers, utilities, and research organizations

around the world (Song and Johns 1999).

Several kinds of FACTS controllers have been commissioned in

various parts of the world. The most popular are: load tap changers, phase-

angle regulators, static VAR compensators, thyristor controlled series

compensators, interphase power controllers, static compensators, and unified

power flow controllers.

2.3.2 Why FACTS?

2.3.2.1 Connection of generation

Some of the power plants (large hydro and thermal plants) can be

located near the load and can be connected by relatively short AC lines to the

grid. But some of them have to be located very far from the grid (particularly

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hydro plants and coal plants) and the transmission has to be carried out by AC

with FACTS.

2.3.2.2 Connection of isolated loads

Isolated loads are meant as loads that due to geographical or other

conditions are not connected to a major grid but have to rely on local

generation. The local generation is often expensive and not environmentally

sound. If the isolated loads are connected to the main grid, the cost of

electricity goes down. The FACTS devices can be used for this purpose.

2.3.2.3 Interconnection

It is increasingly economical to interconnect with neighboring grids

to benefit from the pooling of resources. FACTS can be used to interconnect

grid with same frequency and also with different frequencies while the

network can maintain their separate frequencies.

2.3.3 Types of FACTS Controllers

Figure 2.1 Types of FACTS controllers

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In general, FACTS Controllers can be divided in to four categories

which are shown in Figure 2.1.

Series controllers

Shunt controllers

Combined series –series controllers

Combined series-shunt controllers

Series controller: the series controller could be variable impedance,

such as capacitor, reactor, etc., or power electronics based variable source of

main frequency, sub synchronous and harmonic frequencies to serve the

desired need. In principle, all the series controllers inject voltage in series

with the line. Even variable impedance multiplied by the current flow through

it, represents an injected series voltage in the line. As long as the voltage is in

phase quadrature with the line current, the series controller only supplies or

consumes variable reactive power.

Shunt Controllers: - As in the case of series controllers, shunt

controllers may be variable impedance, variable source or a combination of

these. In principle all shunt controller inject current into the system. Even

variable shunt impedance causes a variable current injection into the line. As

long as injected current is in phase quadrature with the line voltage it supplies

or consumes variable reactive power. Any other phase relationship will

involve real power exchange also.

Combined series-series controller: - This could be a combination of

separate series controllers, which are controlled in a coordinated manner, or it

could be a unified controller. The series controllers could provide independent

series reactive compensation but also could transfer real power among the

lines via the power link (D.C link). The real power transfer capability of the

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unified series-series controller, referred to as interline power flow controller,

makes it possible to balance both the real and reactive power flow in the lines.

And there by maximize the utilization of the transmission system. Note that

the term “unified” here means that the DC terminals of all controller

converters are all connected together for real power transfer.

Combined series-shunt controller: - This is a combination of series

and shunt controllers which are controlled in a coordinated manner or a

unified power flow controller with series and shunt elements. In principle

combined shunt and series controller inject current in to the system with the

shunt part of the controller and voltage in series in the line with the series part

of the controller. However when the shunt and series controllers are unified,

there can be a real power exchange between the series and shunt controllers

via the power link.

2.3.4 Benefits of FACTS technology

The following benefits will be met with the help of FACTS devices

Solve Power Transfer Limit & Stability Problems

Thermal Limit

Voltage Limit

Stability Limit

Transient Stability Limit

Small Signal Stability Limit

Voltage Stability Limit

Control of power flow as ordered

Increase the system security

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Reduce reactive power flows, thus allowing the lines to carry

more reactive power

Reduce loop flows

Increase utilization of lowest cost generation

Increase (control) power transfer capability of line

Power quality improvement

Load compensation

Limit short circuit current

Increase the loadability of the system

2.4 SUMMARY

It is evident from the above review of literature that exhaustive

research work has already been done by several researchers to improve the

performance of power system.

However, no contributions have been made so far to apply hybrid

algorithms for solving optimal power flow with FACTS devices. Hence,

certain approaches have been made in the present work to improve the

performance of power system performance using computational intelligence

techniques such as, New hybrid PSO technique for optimal location of

FACTS devices considering optimal power flow, modified bacterial foraging

algorithm based Optimal Power Flow to minimize losses and fuel cost

function using shunt devices, Optimal Location of FACTS devices for solving

multi objective OPF using improved shuffled leaping Frog algorithm ,

Solving Optimum Power Flow in Static and Dynamic Environments using

Dynamic Bacterial Foraging Algorithm to solve optimal power flow using

FACTS devices.