Interline Power Flow Controller (IPFC) NegussieNegash Power Engineering Msc Student at

JIT department of electrical and computer engineering Nov 2014 /15

Interline Power Flow Controller (IPFC)

NegussieNegash

Power Engineering Msc Student at Jimma University, Jima Ethiopia

ABSTRACT

The interline power flow controller (IPFC) is one of the latest

generation and advanced flexible AC transmission systems

controller which can be used for dynamic compensation and

effective power flow management among transmission corridors. It

is VSC-based FACTS controller for Series compensation with the

unique capability of power management among multiline of a

substation. It simultaneously controls the power flow in

multiline systems or sub network. Since IPFC contain converters

with common direct current link, any inverter within the IPFC is

able to transfer real power to another and there by facilitate

real power transfer among the lines of the transmission system.

IPFC may be used to solve the complex transmission network

overcrowding management problems that transmission companies are

now a day facing to transmit a large power. Simplicity and fast

system response are two main characteristics of Interline power

flow controller. From many FACT devices today, IPFC is more

advanced and easy controller to solve the overcrowding of the

power management of the transmission system.

There many researches and journal papers consider interline power

flow controller FACT device, but they do not condense the Review article on interline power controller (IPFC)


operation principles, application, do not explain the advantages

of IPFC over the other FACT devices. This paper going to discuss

the operation principles and advantageous of IPFC like for

transient ,, voltage , rotor angle stability, power system

oscillation control, power flow control , and finally the unique

properties of IPFC over the other FACT devices are investigated.

Key words: direct current link DC FACT devices, IPFC interline

power controller, VSC voltage source converters

Introduction

Over view of FACT devices

As power transfer grows, the power system can become more

difficult to operate,

and the system becomes more insecure with unscheduled power flows

and losses increased. At this time, there is a large demand on

the transmission network, and demands will continue to increase

due to an increasing number of non-utility generators. The

growing transmission capacity can be achieved by either building

new transmission lines or increasing the transfer capability of

Review article on interline power controller (IPFC)


existing transmission facilities[5] [3].But, it is not

economically possible to to develop transmission systems just by

fixing new transmission lines because of variety of environmental

aspects like some regulatory requirements and land uses. land

use. As a result, some transmission lines are heavily burdened

and the power system stability becomes a power transfer-limiting

factor. [18][23]

Today the power systems are can be mechanically controlled. But

it has its own draw back i.e. there is no high-speed control,

cannot be initiated frequently because mechanical device tend to

broke out very quickly related to static electronic devices.

An effective solution is, thus, to consider the use of

transmission controllers (e.g. power electronics based

transmission controllers).The rapid development of self-

commutated semiconductor devices, have made it potential to

design power electronic materials called flexible AC tranimission

controller (FACT) devices. [21] Flexible ac transmission system

(FACTS) controllers have the potential to increase the capacity

of existing transmission networks through functional adaptability

and control flexibility. FACTS controllers have the capability of

direct control of transmission line flows by changing the main



transmission constraints such as magnitude voltage, power angle

of transmission lines impedance of the line.

The generation of flexible ac transmission controller is not rise

at one time rather it passes through gradual changes. As a result

there is a number of FACT devices controller: - shunt controller

like static varcompensator (SVC), static synchronous compensator

(STATCOM) and series controller like thyristor controlled series

capacitor (TCSC), and static synchronous series compensator

(SSSC) and there is third classification called combination of

both series and shunt controller like thyristor controlled phase

shift transformer (TCPST), inter line power flow controller

(IPFC), unified power flow controller (UFPC) and dynamic flow

controller (DFC). Once again FACT devices can be classified based

on the power electronics technology used for the convertors as,

Thyristor based controllers: - SVC, TCSC, TCPST and DFC.

Voltage source based controllers: -SSSC, STATCOM, UFPC AND IPFC.

Generally FACT devices are based on either Voltage or Current

Source Converters (VSC/CSC) can be used to control steady-state

as well as dynamic or transient performance of the power system

[2].

Thus the interline power controller (IPFC) is among the FACTS

devices aimed at simultaneously controlling the power flow in

multiline systems. The interline power-flow controller (IPFC) is



a new and advanced FACTS controller, which can be used for

dynamic compensation and effective power-flow management among

transmission corridors [6].

1.INTERLINE POWER FLOWCONTROLLER (IPFC)

Recent developments of FACTS research have led to a new device:

the Interline Power Flow Controller (IPFC). The IPFC is a series-

series type of FACTS device that is used to exchange reactive

powers in between two or more transmission lines those are

connected to the same bus [21]. This element consists of two (or

more) series voltage source converter-based devices (SSSCs)

installed in two (or more) lines and connected at their DC

terminals. Thus, in addition to serially compensate the reactive

power, each SSSC can provide real power to the common DC link

from its own line. In general the Interline power flow controller



employs a number of DC to AC converters.These converters are

providing a series compassion for each transmission line.

1.1. Basic structure of Interline power flow controller

(IPFC)

Based on structure Interline power controller (IPFC) catagorized

in two parts:-

a set of converters with shunt converter and without shunt

converter

a) with shunt converter

some structre of an Interline Power Flow Controller (IPFC)

consists of a set of both converters that are connected in series

with different transmission lines and shunt converter which is

connected between a transmission line and the ground.

Fig1 Schematic diagram of IPFC contain shunt converter



b) without shunt converter

However some structure of interline power controller

(IPFC) is consists of a set of converters that are

connected in series with different transmission lines

without shunt convertor. [26]

Fig.2 Schematic diagram of IPFC Without shunt converter

As mentioned above IPFC consist a set of converters. The

converters are connected through a common DC link to exchange

active power. Each series converter can supply independent

reactive compensation of own transmission line. If a shunt

converter is involved in the system, the series converters can

also provide independent active compensation; otherwise not all

the series converters can provide independent active compensation

for their own line [2].



1.2. Working principle of interline power flow controller

(IPFC)

The IPFC structure makes it possible to transfer reactive power,

as well as to exchange real power with the line. This active

power can be obtained throgh power exchange through DC connection

between the SSSCs in different lines. On the other hand, the

transmitted powers in each line is a function of the voltage

amplitude of sending and receiving buses, phase shift of sending

and receiving buses and series impedance of the line.

The interline power flow controller works with a number of direct

current to alternative current

converters each providing series compensation for a different

transmission line. For briefly explain let use two back-to-back

voltage-source converters (VSCs), based on the use of gate-

turnoff (GTO) thyristor valves. The voltage source converters

(VSC) produce voltages that vary in magnitude and phase angle.

These voltages are inserted in series with the managed

transmission lines using series transformers as shown in figure

below.



Fig.3 Schematic diagram of two converters IPFC

The real power exchanged at the ac terminal is converted by the

corresponding VSC into dc power which appears at the dc link as a

negative or a positive demand. Consequently, the real power

negotiated by each VSC must be equal to the real power negotiated

by the other VSC through the dc lines [4]. As result interline

power flow controller (IPFC) can maintain the flow of active and

reactive power in multiple line system even when a failure occur

IPFC can switch off failure line and by bass to the set line.

1.3. Advantageous of IPFC

The Interline Power Flow Controller (IPFC) is one of the Voltage

Source Converter (VSC) based facts controllers which can

effectively manage the power flow via multi-line transmission

system.IPFC has different applications. Balancing reactive and

real power flows through compensated transmission lines,

transmitting power from burdened loda lines to other lines that

not heavily loaded, compensation of voltage drops on resistance

through lines and improving the performance of the compensated

system when dynamic disturbances occur, are the main advantageous

of IPFC.[19][17]



Compensation of reactive power by IPFC

The concept of reactive power compensation holds wide and diverse

field of both system and consumer problems, particularly related

with the quality of power, the reason that most of power quality

problems can be solved with an adequate control of reactive power

[47]. The objectives of load compensation are increase the value

of the system power factor, to balance the real power come from

the ac supply, compensate voltage regulation and to reject

current harmonic components produced by large and changeable

nonlinear industrial loads. Reactive power compensation in

transmission systems also improve the stability of the ac system

by increasing the maximum active power that can be transmitted.

Traditionally, rotating synchronous condensers and fixed or

mechanically switched capacitors or inductors have been used for

reactive power compensation. [24] However, static VAR

compensators using thyristor switched capacitors and thyristor

controlled reactors to provide or absorb the required reactive

power have been developed in recent year. Fact devices now a day

the common for compensation of reactive by switching within DC

link capacitor. The IPFC has a capacity to carry out a whole

real and reactive power compensation of the total transmission

system this capability makes it possible to equalize both active

and reactive power flow between the transmission lines. The

vector control method is used to control the IPFC converter. It



increases the effectiveness of the compensating system against

dynamic disturbances.

Interline power flow controller (IPFC) for voltage Stability

Improvement

Voltage stability is concerned with the ability of a power system

to maintain steady voltages at all buses in the system under

normal conditions. Instability happens in the form of a

progressive fall or rise of voltage of some buses.[46] The

possible consequence of voltage instability is loss of load in

the area where voltages reach very low values, or a loss of

reliability of the power system. The main factors considered as a

cause of voltage stabiliy are the voltage drop that occurs when

reactive and real power flow through inductive reactance’s

associated with the transmission networ. The voltage intability

is affect the power flow system.

Voltage stability of a system affected by reactive power limit of

the system, FACT devices improve the reactive power flow in the

transmission line system there by improving voltage stability.



Interline power flow controller (IPFC) with energy storage

system, the series connected volte source converters (VSC) can

inject a voltage with controllable magnitude and phase angle at

the fundamental frequency, at the same time DC link voltage can

be maintained at desired level irrespective of the applied

different active power. The AC voltage is controllable in both

magnitude and phase with interlines power flow controller (IPFC).

Active power can be exchanged when energy source is added at DC

lin k terminals. Controlling the reactive power is ralated

controlling the voltage stability because the main cause of

voltage ijnstability is the variation of reactive ppower [47].

Interline power flow controller (IPFC) for rotor angle Stability

Rotor angle stability can be defined as the ability of

interconnected synchronous machine of a power to remain in

synchronous stage during disturbance and normal operating

condition.It depends on the ability to keep equilibrium between

electromagnetic torque and mechanical torque of each synchronous

machine in the system. The increasing of angular swings of some

generators leading to their loss of synchronism with other

generators. This type of instability is called roto angle

instability.



The speed of generators and motrs is easily controlled by power

electronic devices. As a result it can control the rotor angle

stability. IPFC is one of the power electronics devices which

contain converters within DC link. Therefore it can allow

reactive and active power to flow in the multiline

simultaneously; the problem of oscillation is easily removed by

dc link. [47]

Interline power flow controller (IPFC) for Damping Low Frequency

Oscillations

The common DC link in the IPFC configuration enables each

inverter to transfer real power to another, so control of DC link

voltage is an essential issue in overall performance of the

system. Before the introduction of fact devices power System

Stabilizer (PSS) has been used as a econicomical, effective and

simple, option to improve power system oscillation stability.

However, PSS may not be able to suppress oscillations resulting from high disturbances, such as three phase faults at generator end.

Interline power flow controller (IPFC), can be applied for

damping oscillations because it can improve the small signal

stability of power systems by adding a supplementary signal for



main control loops. It is a new concept of the FACTS controller

for series compensation with the unique capability

ofcontrollingpower flow among multiline.

The basic control function within IPFC, voltage control ofthe DC

link capacitor interacts negatively with the system and thus

damages the system oscillation stability. This is eliminated by

optimal design of IPFC damping controller and feeding an

additional supplementary feedback control signal from the damping

controller.

Interline power flow controller (IPFC) to increase transient

stability of power system

Transient stability of a power system is its ability to maintain

synchronous operation of the machines when subjected to a large

disturbance. This large disturbance come from fail of corrective

action, large excursions of the system machine rotor angles and

loss of synchronism results among machines. [40]

The Interline Power Flow Controller (IPFC) is a novel device

which can increase transient stability of power system. Transient

stability improvement is one of the important aspects in modern

power system. Since interline power flow controller (IPFC)

consists of Voltage Source Converter (VSC) and dc link which

converts ac to dc and compensate the reactive power, as result

the synchronous operation of the machines subjected to large

disturbance decreases that leads to the excursion of the systemReview article on interline power controller (IPFC)


machines rotor angles and failer of corrective action reduce.

This generally leads to the improvement of transient stability.

That why the swing curve of system without an IPFC get increased

monotonically and thus the system can be considered as unstable

whereas the swing curves of system with an IPFC can return to

stable equilibrium point

[47]

Interline power flow controller (IPFC) for power flow stability

In general whether the IPFC or the other fact devices, last goal

should balance the quality and stability of power flow. The IPFC

provide together with independently controllable reactive series

compensation of each individual line, a ability to directly

transfer active power between the compensated lines[14]. This

capability makes it possible to equalize both real and reactive

power flow between the lines; transfer power demand from

overloaded to under loaded lines; compensate against resistive

line voltage drops and the corresponding reactive power demand;

increase the effectiveness of the overall compensating system for

dynamic disturbances. The power flow and power quality

improvrment come reactive compansion, voltage stability control

and control of transient stability. Because without controlling


Power stability

Large disturbance stability

Frequency stability

Large disturbance stability

Rotor angle stability

Voltage stability

Small signal stability

Transient stability

Small disturbance stability


these parametters control and maintain power flow quality is

unthink able [28].


Short term stability

Large term stability Short term stability Long term stability JIT department of electrical and computer engineering Nov 2014 /15

Fig.4 block diagram of powerstability [47]

As seen from the above power diagram controlling the stability ofparameters such as voltage, frequency, rotor angle are leads tothe quality of power flow.

1.4. Advantages of interline power controller over the otherfact devices

Both the IPFC and UPFC are based on the self-commutated, voltage

sourced switching converters (VSCs) coupled through a common DC

voltage link. Unlike the UPFC, the IPFC employs at least two VSCs

respectively connected in series with different lines, due to

this it can address the problem of compensating multiple

transmission lines at a substation [2]. Comparing Converter

basedFACTS devices controllersto conventional switched capacitor

or reactor and thyristorbased FACTS controllers such as Static



VarCompensator (SVC) and Thyristorcontrolled Series Capacitor

(TCSC), have the advantage of producing or absorbing reactive

power without theuse of ac capacitors and reactors. However,

IPFCs provide independent control of reactive power of each

individual line, while active power could be transferred via the

dc-link between the compensatedlines. An IPFC can also be

usedtransfer power from higher loaded lines to fewer loaded one

and to balance real and reactive power between transmission

lines, and

Interline Power Flow Controller (IPFC) isan extension of the

UPFC, which can be efficientlyused to control the transmission

line parameters in case of interconnected systems. However, UPFC

aims to compensate a single transmission line, whereas the IPFC

is suitable controller forpower flow management of multi-line

transmission system and for the compensation of reactive power.

Interline power flow controller (IPFC) is a new and more

technological FACT devices controllers. [20]

Generally when we compare interline power flow controller with

the other

IPFC controller active and reactive power simultaneously.

It can equalize both active and reactive

It suitable for multiline transmission



Conclusion

IPFC is used in steady state to increase the capacity of lines

power transfer, regulate and manage the power flow, reactive

power compensation, avoid the loop current and prevent the

overloading the system. In addition to thecapabilities of

improvement voltage stability, dynamic disturbance andtransient

stability correction it also has application ofpower filtering in

distribution system have all made this tool into multifunction

device. The interline power flow controller is the latest FACT

devices controller. Therefore it can control and manage multi

lines simultaneously.Lastly IPFC is more technological and need a

great research.



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Interline Power Flow Controller (IPFC) NegussieNegash Power Engineering Msc Student at

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