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PRESENTATION ON:UNIFIED POWER FLOW CONTROLLER

GROUP MEMBER:

CHANDNI SHARMADEEPANK GUPTA

DIKSHA TIWARI

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Introduction:

Upfc concept was proposed by Gyugyi in 1991

Upfc is a combination of static synchronous compensator (statcom) and a static

synchronous series compensator (sssc) which are coupled via a dc link,to allow

bidirectional flow of real power between the series output terminals of the sssc and

the shunt output terminals of the statconm,and are controlled to provid concurrent

real and reactive power series line compensation without an external electric energy

source

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Basic Operating Principle:

UPFC is generalized synchronous voltage source(SVS),represented at the

fundamental frequency by voltage phasor Vpq with controllable magnitude

Vpq(0VpqVpqmax) and angle (02) in series with the transmission line

In functionally unrestricted operation which clearly includes voltage and angle

regulation , the SVS generally exchanges both reactive and real power with the

transmission system

SVS is able to generate only reactive power exchanged , the real power must be

supplied to it , or absorb from it by a suitable power supply or sink

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In UPFC arrangement the real power exchanged is provided by one of the end buses

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Vseff=Vpq+Vs

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The UPFC consists of two voltage sourced converters . These back to back

convertors labelled convertor 1 and convertor 2 are operated from a common dc link

provided by a dc storage capacitor

This arrangement functions as an ideal ac to ac power convertor in which the real

power can freely flow in either direction between the ac terminals of the two

convertors and each convertor can independently generate reactive power at its own

ac output terminals

Convertor 2 provides the main function of the UPFC by injectin g a voltage Vpq

with controllable magnitude Vpq and phase angle in series with the line via an

insertion transformer

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The basic function of convertor 1 is to supply or absorb the real power demanded

by converter 2 at the common dc link to support the real power exchange resulting

from the series voltage injection.

Basic power flow control function of UPFC are:

Voltage regulation

Series reactive compensation or line impedance compensation

Phase angle regulatormultifunction power flow control

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a)Voltage regulation:

Voltage regulation with continuously variable in

phase/antiphase voltage injection for voltage in elements

Vpq=V

Voltage can be increased or decreased at a particular point

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(b) Series reactive compensation or line

impedance compensation:

In this Vpq=Vq is injected in quadrature with the line current I

We can change the value of the reactance of the line so that we

can change the reactive power flow in the line we make

Vpq=Vq=90 to the line current that will be same as if we are

increasing or decreasing the reactance of the line ie we can add a

voltage either at +90or -90to the line current we can vary the

Vq also

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(c) Phase angle regulator:

In this Vpq=Vis injected with an angular relationship

with respect to Vs that achieves the desired phase shift

without any change in the magnitude

By changing the phase angle of the voltages magnitude of

the voltage remains constant

By changing the phase angle we can control the real

power flow of the line more effectively

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(d) Multifunction power flow control:

It can be achieved by combining all the three

characteristics.Multifunction power flow control executed by

simultaneous terminal voltage regulation,series capacitive line

compensation and phase shifting where Vpq=V+Vq+V

This functional capabiltity is unique to the UPFC. No single

conventional equipment has similar multifunctional capability

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Control structure of UPFC

The control of the UPFC is based upon the vector control approach

The UPFC control system is divided functionally into

Internal Control

Functional Operation Control

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BASIC UPFC CONTROL SCHEME

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The internal controls operates the two converters so as to produce the comanded

series injected voltage and simultaneously draw the desired shunt reactive current

The internal controls provide gating signals to the convertor values so that theconverter output voltages will properly respond to the internal reference variables

iqnet

,ipnet,Vpnet

The series compensator responds directly and independently to the demand for

series voltage vector injection

In contrast the shunt converter operates under closed loop current control structure

whereby the shunt real and reactive power components are independently controlled

The shunt reactive power responds directly to an input demand

The closed loop for the shunt real power ensures the required real power balance

between the two converters

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OVERAL UPFC CONTROL STRUCTURE

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The control and functional operation control defines the functional operating mode

of the UPFC and is responsible for generating the internal reference Vpq and iqreffor

the series and shunt compensation to meet the prevailing demands of the transmission

system

The functional operating modes and compensation demands reprsented by external

reference inputs can be set manually by the operator or dictated by an automatic

system

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Applications:

UPFC may be required whenever the problems of voltage and power flow are

present. The planning studies are required to determine the need of UPFC [1]

Increase transient stability of the system. The UPFC allows a secondary but important

function such as stability control to suppress power system oscillations improving the

transient stability of power system.[2]

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Reference:

1) 1-FACTS controllers in power transmission and distribution by K. R. Padiyar2) Application of UPFC to Increase Transient Stability of Inter-Area Power System