FACTS devices

Electronically Controlled

Compensations and Network

Controllers

FACTS Devices

Dr. M. EL-Shimy 2014 EPM622_523 PS Control - ASU 1

References

Kundur, P. (1994). Power system stability and control. Tata McGraw-Hill

Education.

Miller, T. J. E., & Concordia, C. (1982). Reactive power control in electric

systems.

Ekanayake, J., Jenkins, N., Liyanage, K., Wu, J., & Yokoyama, A. (2012).

Smart grid: technology and applications. Wiley.

Milano, F. (2010). Power system modelling and scripting. Springer.

Acha, E., Agelidis, V., Anaya, O., & Miller, T. J. E. (2001). Power electronic

control in electrical systems. Newnes.

Mathur, R. M., Varma, R. K., & Varma, R. K. (2002). Thyristor-based FACTS controllers for electrical transmission systems (pp. 147-149).

IEEE.

Dr. M. EL-Shimy 2 2014 EPM622_523 PS Control - ASU

Power flow control by FACTS devices and FACTS

connections (Shunt, series, and hybrid)





Static VAR

Compensators (SVCs)


SVCs SVCs are static shunt compensators

Ideal SVC

From equivalent circuit point of view an SVC is

constructed of controllable shunt reactor (CSR) and

controllable shunt capacitor (CSC)


An ideal SVC can fix the AC voltage a specific

desired value given that the reactive power

capability limits of an ideal SVC are infinite and

the response time is zero


Realistic SVCs do not have infinite capacity and

their response time is limited


Simplified power system V-I characteristics



Composite SVC – power system characteristics

System

SVC


Effect of switching capacitor


Thyristor Controlled Reactors (TCRs)





Harmonics

TCRs injects only odd harmonics

For single phase TCR




Three phase TCRs

Delta connected all triple harmonics are

eliminated by the connection

In Y-connection the harmonics are of the same

orders as the single phase TCR



TCR-FC SVC



Examples










Report



SVC Voltage Regulator


The SVC voltage regulator processes the

measured system variables and generates an

output signal that is proportional to the desired

reactive-power compensation. Different control variables and transfer functions of the voltage

regulator are used, depending on the specific SVC application.

The measured control variables are compared with a reference signal,

usually Vref , and an error signal is input to the controller transfer

function.

The output of the controller is a per-unit susceptance signal Bref , which

is generated to reduce the error signal to zero in the steady state.

The susceptance signal is subsequently transmitted to the gate pulse–

generation circuit.


Implementations of current droop

(slope) in the voltage regulator The SVC current is

explicitly measured and

multiplied by afactor

KSL representing current

droop before feeding as

a signal VSL to the

summing junction.

RR = response rate


In certain cases, it may be difficult to faithfully

obtain the current signal.

This occurs when the SVC is operating close to its

floating state, that is, zero MVA reactive power.

The current signal then comprises a

predominant harmonic component and a

fundamental resistive component corresponding

to the real losses in SVC.


To overcome this problem, in certain SVC

controllers the reactive power is computed and

fed back instead of using the SVC current.

The reactive-power signal is calculated by

multiplying the phase currents in SVC by a

fundamental-frequency voltage lagging behind

the actual phase voltage by 90o.


The other easily

realizable option is the

susceptance-droop

feedback demonstrated

It is implicitly assumed

that the SVC bus voltage

remains close to 1 pu;

thus the SVC current

that is strictly equal to

Bref


The previous loop can be

simplified to the gain-

time constant form





SVC Applications


SVC Applicatio

ns

Increase in steady-state

power-transfer capacity

Enhancement of

transient stability

Augmentation of power-system

damping SVC mitigation

of subsynchro

nous resonance

(SSR)

Prevention of voltage instability

Improvement of

HVDC link performanc

e


Increase in steady-state power-transfer

capacity


Let the transmission line be compensated at its

midpoint by an ideal SVC.




Enhancement of transient stability


STATCOM (or SSC)


The STATCOM (or SSC) is a shunt-connected

reactive-power compensation device that is

capable of generating and / or absorbing

reactive power and in which the output can be

varied to control the specific parameters of an

electric power system.

A STATCOM connected to the distribution

circuits is normally called a D-STATCOM.


It is in general a solid-state switching converter

capable of generating or absorbing

independently controllable real and

reactive power at its output terminals

when it is fed from an energy source or energy-storage device at its input terminals.

REM: SVCs can not generate or absorb active power


STATCOM applications

Dynamic voltage control in transmission and

distribution systems;

Power-oscillation damping in power transmission

systems;

Transient stability enhancement;

Voltage flicker control; and

Control of not only reactive power but also (if

needed) active power in the connected line, requiring

a dc energy source.


STATCOM Operation



V-I Characteristics

Unlike the SVC,

the STATCOM can provide

full capacitive-reactive power

atany system voltage - even as

low as 0.15 pu.

It is also capable of yielding

the full output of capacitive

generation almost

independently of the system

voltage (constant-current

output at lower voltages).


D-STATCOM for load compensation




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