FACTS Technology

Flexible AC Transmission FACTS-Technology and Novel
Control Strategies For Power System
Stability Enhancement

Mohamed Shawky ElMoursi

Supervisor

Prof. Dr. A. M. Sharaf, P.Eng.

Electrical and Computer Engineering Department
University of New Brunswick
October 20, 2004

CONTENT

Voltage stability

Harmonic/ SSR stability

Renewable Dispersed Energy Systems

FACTS

Flexible AC Transmission System (Facts) is a new integrated concept
based on power electronic switching converters and dynamic controllers to
enhance the system utilization and power transfer capacity as well as the
stability, security, reliability and power quality of AC system

interconnections.

OPPORTUNITIES

Control power so that it flows on the desired routes.

Increase loading capacity of transmission lines.

Prevent blackouts.

Improve generation productivity.

Effective use of upgrading/ uprating.

FACTS KEY DEVICES

Static Synchronous Compensator (STATCOM)

Static Synchronous Series Compensator (SSSC)

Unified Power Flow Controller (UPFC)

STATIC SYNCHRONOUS COMPENSATOR (STATCOM)

It is a static synchronous generator as shunt static var compensator whose
capacitive or inductive current can be controlled independent of the system
voltage.

The STATCOM scheme in parallel with AC power grid system and is
controlled by a dynamic controller as shown in Fig.1.

Fig.1 Sample three-Bus study test system with the STATCOM located
at bus B2 to stabilize the AC system

Novel Controller

The new control system is based on a
decoupled control strategy using both
direct and quadrature current
components of the STATCOM AC
current.

The operation of the STATCOM
scheme is Validated in both the
capacitive and inductive modes of
operation. Fig. 2 Proposed STATCOM Decoupled Control System

Preliminary Simulation Results
L in e V o lta g e A c tiv e & R e a c tiv e p o w e r o f S T A T C O M d ir e c t & q u a d r a tu r e o f S T A T C O M
1 .2 0 1 .2 0 2 .0 0
Q

V L in e

0 .8 0 1 .0 0

Id & Iq o f th e S T A T C O M
P & Q o f th e S T A T C O M
0 .8 0
P
VL

0 .4 0 0 .0 0

0 .4 0 Q

0 .0 0 P - 1 .0 0

0 .0 0 - 0 .4 0 - 2 .0 0
0 .0 0 0 .4 0 0 .8 0 1 .2 0 1 .6 0 2 .0 0 0 .0 0 0 .4 0 0 .8 0 1 .2 0 1 .6 0 2 .0 0 0 .0 0 0 .4 0 0 .8 0 1 .2 0 1 .6 0 2 .0 0
T im e (S e c ) T im e (S e c ) T im e (S e c )

T r a n s m is s io n L in e d -q c u r r e n ts (p u ) A c tiv e & R e a c tiv e P o w e r o f th e T r a n s m is s io n L in e C a p a c ito r d c V o lta g e (p u )
4 .0 0 3 .0 0 1 .2 0

P
Id 2 .0 0
2 .0 0 0 .8 0
I d & I q o f th e T r a n s m is s io n L in e

P & Q o f th e T r a n s m is s io n L in e

1 .0 0

V dc
0 .0 0 0 .4 0
Iq
0 .0 0
V dc
Q

- 2 .0 0 0 .0 0
- 1 .0 0

- 4 .0 0 - 2 .0 0 - 0 .4 0
0 .0 0 0 .4 0 0 .8 0 1 .2 0 1 .6 0 2 .0 0 0 .0 0 0 .4 0 0 .8 0 1 .2 0 1 .6 0 2 .0 0 0 .0 0 0 .4 0 0 .8 0 1 .2 0 1 .6 0 2 .0 0
T im e (S e c ) T im e (S e c ) T im e (S e c )

System is subjected to load switching at t=0.5 sec (inductive load added), t=1 sec (capacitive load added)
and t=1.5 (Both inductive and capacitive load removed)

STATIC SYNCHRONOUS SERIES COMPENSATOR

It is a static synchronous generator operated without an external energy
source as a series compensator.

The o/p voltage is in quadrature with and controllable independently of the
line current.

It is increase or decrease the overall reactive voltage drop across the line
and thereby controlling the transmitted electric power.

Fig. 3 Single line diagram representing the series SSSC scheme interfaced
at sending end of the Transmission line (Bus B1)

Novel Controller

The main function of the SSSC is
to regulate the TL power flow PL.
This can be accomplished by
either direct control of the line ∆α
current or indirect control by
compensating for the TL
impedance, Xs via a
compensating injected voltage,
Fig. 4. Control Structure of the SSSC scheme.
Vs.
Xref = Negative Vs lags IL by 90° plus ∆α (Capacitive Compensation)

Xref = Positive Vs Leads IL by 90° plus ∆α (Inductive Compensation)

SUPPLEMENTARYT CONTROL LOOP DESIGN IN SSSC

To enhance the dynamic performance
of the SSSC device an supplementary
regulator loop is added using the dc
capacitor voltage.

The operation of the SSSC scheme is
validated in both the capacitive and
inductive modes of operation under Fig.5. Supplementary regulator for the SSSC
controller to reduce oscillatory
severe disturbance such as switching
loads and fault condition

Simulation Results For SSSC

Fig. 6. Simulation results of the SSSC in capacitive mode

Fig. 7. Simulation results of the SSSC in inductive mode

UNIFIED POWER FLOW CONTROLLER (UPFC)

The UPFC scheme consists of two
basic switching power converter
namely shunt and series converters
connected to each other through a dc
link capacitor.

The shunt converter operates exactly
as STATCOM for reactive
power compensation and voltage
stabilization.

Fig.8. FACTS UPFC controller scheme
The series converter operates as
SSSC to control the real power flow

PROPOSED NOVEL CONTROL STRATEGY

The developed novel control strategy
for the UPFC scheme is based on the
magnitude and angle of series
inserted voltage and shunt reactive
current.
Fig.9. Proposed STATCOM Decoupled Current Control
System for the shunt converter (1)
Novel Control in the STATCOM
shunt converter 1

SSSC-Converter (2) controller

The system is subjected to severe disturbance
single line to ground fault at load bus at time
0.3 sec for a duration of 80 ms.
Fig. 10. Control Block diagram of SSSC series
converter (2) scheme.

Simulation Results for (UPFC)

Alpha vs time Iqref,Iqm vs time Id, Iq of STATCOM vs time P & Q of STATCOM vs time

P, Q of SSSC vs time Vdc vs time Line Voltage vs time Line voltage and current vs time

Fig. 11. The UPFC digital Simulation Results Under
single phase Fault Condition at load bus

CAPABLITIES OF DIFFERENT FACTS CONTROLLERS

Damping Reactive
Controller Voltage Transient Power Power Power Flow SSR
Control stability Oscillations Compensation Control Mitigation

STATCOM X x x x

SSSC X x x x x x

UPFC X x x x x X

POWER QUALITY ENHANCEMENT

This chapter studies the power system power quality and harmonics and
SSR/ Tortional stability enhancement to reduce harmonics, improve the
power quality and enhance the system harmonic stability.

Three different cases were studied in order to improve power quality and
enhance system stability using a novel Active Power Filter (APF)
combining with and Tuned arm filter switched capacitive compensation.

A COMBINED CAPACITIVE COMPENSATION AND
ACTIVE POWER FILTER

The Power Filter Scheme

The power filter scheme consists
of both a passive filter and active
filter. The passive filter removes
any load harmonics just as a
conventional one does and the
added active filter plays a role in
improving the filtering action.
Fig. 12.a. Sample study of the unified power system

Novel Tri Loop Dynamic Controller Design

The proposed SSCC capacitor
switching controller is an error
driven, error-scaled self adjusting
nonlinear tri loop dynamic
controller used the load voltage,
instantaneous and RMS load
currents deviation signals as
shown in Fig 12 (a, b).

2 2 2
Re = e v + i + I
e e Fig. 12.a. Sample study of the unified power system

Developed By Dr. Sharaf
(Excursion- Level Magnitude)

Fig. 12.b. The SSCC series capacitor switching compensator scheme using two
stage compensation per phase dynamic capacitor switching

Simulation Results
Without SSCC & APF With SSCC & APF
Load Voltages Voltage at Load Bus
Phase Voltage Va
Voltage of phase a Va
+1.25
VLa
+1 +0.75
+0.25
-0.25
-0.75
-3 -1.25
1.04 1.13 1.22 1.31 1.4 1.49 1.03 1.128 1.226 1.324 1.422 1.52
Phase Voltage Vb
Voltage of phase b Vb
+1.25
VLb
+1.25 +0.75
+0.25
-0.25
-0.75
-1
1.04 1.13 1.22 1.31 1.4 1.49 -1.25
1.03 1.128 1.226 1.324 1.422 1.52
Voltage of phase c Phase Voltage Vc
Vc
VLc +1.25
+1.25 +0.75
+0.25
-0.25
-0.75
-1.25
1.04 1.13 1.22 1.31 1.4 1.49 -1.25
1.03 1.128 1.226 1.324 1.422 1.52
Time (sec) Time (sec)

Power capacity Transfer Capacity of power transfer
P&Q
P Q
power transfer P&Q
+25
P Q
+70
+19
+54
+13
+38
+7 +22
+1 +6
-10
-5 0 0.6 1.2 1.8 2.4 3
0 0.6 1.2 1.8 2.4 3
Time (sec) Time (sec)

Fig. 13. The simulation results when the system subjected to 3- phase fault disturbance

A COORDINATED CAPACITIVE COMPENSATION AND
TUNED ARM FILTER

This chapter presents a nonlinear
coordinated dynamic error driven
scaled error-controller for both
the static series capacitor
switching compensator SSCC and
the added tuned arm filter TAF,
for the enhancement of voltage,
transient stability, capacity of tie Fig. 13. Single line diagram sample study of the
unified power system with one novel
line power transfer and the power coordinated CC/TAF filter

quality.

SSCC switched/modulated Tuned Arm Filter Controller

The proposed self adjusting Tri-loop error scaled controller is based on
the load voltage, RMS source current and the dynamic current ripple
deviation signals.

Fig 13. Proposed novel tri loop error-driven, error -scaled Tri-loop
dynamic feed back controller.
Developed By Dr. Sharaf

Simulation Results For SSCC/TAF Scheme

Without SSCC & TAF With SSCC & TAF

Fig 14. the p.u. load voltage at bus 4, terminal voltage at bus 2, total load current iL and the induction load current
when the system subjected to 3 phase fault at bus 2

Fig 15. The Power Transfer levels P& Q without and with SSCC&TAF

Fig 16. Comparison of the load voltage, load current and %THD voltage and
current without and with (SSCC & TAF)

Renewable Energy

The research will investigate the use of renewable dispersed energy system
(wind-small hydro, hybrid scheme) and resulting grid interface problems
and need for effective mitigative FACTS-based solution. Both stand-alone
and grid connect wind energy conversion will be studied

CONCLUSION

The research investigates FACTS topologies & novel control strategies for
voltage stability enhancement, T.L power flow control and harmonic/ SSR
mode stabilization of an interconnected AC system.

The use of FACTS devices in renewable energy utilization is also studied
for small Hydro/ Wind hybrid renewable energy scheme.

FUTURE WORK

Validation of (UPC) Universal Power Compensator controllable scheme
using the dynamic error driven controllers (P, Q) in SSR-stability
enhancement.

Application of the (UPC) Universal Power Compensator using dual Tri
loop stabilization control for wind & small hydro.

ACCEPTED PUBLICATION
A.M. Sharaf and M. S. El-Moursi, " A Novel Dynamic Controller For Stability Enhancement Using Capacitive Series
El-Moursi,
Compensators" 2004 IEEE International Symposium on Industrial Electronics, May 4-7 , 2004, Palais des CongrÃ¨s
Expositions, Ajaccio, France.
A.M. Sharaf and M. S. El-Moursi" Stability And Power Quality Enhancement Using A Coordinated Capacitive
El-Moursi"
Compensation And Tuned Arm Filter" , the 29th Annual Conference of the IEEE Electronics Society Sunday, November
Sunday,
2-Thursday, November 6, 2003 conference Center, Roanoke , Virginia, USA.
A.M. Sharaf and M. S. El-Moursi," Stability And Power Quality Enhancement Using A Combined
Capacitive Compensation And Active Power Filter" ICECS 2003, 10th IEEE International Conference
on Electronics, Circuits and Systems, 14.12.2003-17.12.2003, Sharjah, United Arab Emirates.

SUBITTED JOURNAL PAPERS

A.M. Sharaf and M. S. El-Moursi," Voltage Stabilization And Reactive Compensation Using A FACTS-
STATCOM Scheme" IEEE Power Delivery Trans. Proc. 2004.
A.M. Sharaf and M. S. El-Moursi," Transmission System Reactive Compensation And Stability
Enhancement Using A 48-Pulse Static Synchronous Series Compensator" IEEE Power Delivery Trans.
Proc. 2004.
A.M. Sharaf and M. S. El-Moursi," Power System Stabilization And reactive Compensation
Using FACTS-Unified Power Flow Controller" IEEE Power Delivery Trans. Proc. 2004.

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