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

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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

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CONTENT

• Voltage stability
• Harmonic/ SSR stability
• Renewable Dispersed Energy Systems

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• 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.

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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.

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FACTS KEY DEVICES

• Static Synchronous Compensator (STATCOM)
• Static Synchronous Series Compensator (SSSC)
• Unified Power Flow Controller (UPFC)

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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.

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Fig.1 Sample three-Bus study test system with the
STATCOM located at bus B2 to stabilize the AC
system
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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
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Preliminary Simulation Results
System is subjected to load switching at t0.5
sec (inductive load added), t1 sec (capacitive
load added) and t1.5 (Both inductive and
capacitive load removed)
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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.

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Fig. 3 Single line diagram representing the
series SSSC scheme interfaced at sending end of
the Transmission line (Bus B1)
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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 current or
  indirect control by compensating for the TL
  impedance, Xs via a compensating injected
  voltage, Vs.

Fig. 4. Control Structure of the SSSC scheme.
Xref Negative Vs lags IL by 90 plus
(Capacitive Compensation) Xref
Positive Vs Leads IL by 90 plus
(Inductive Compensation)
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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 severe disturbance such as
  switching loads and fault condition

Fig.5. Supplementary regulator for the SSSC
controller to reduce oscillatory
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Simulation Results For SSSC
Fig. 6. Simulation results of the SSSC in
capacitive mode
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Fig. 7. Simulation results of the SSSC in
inductive mode
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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.
• The series converter operates as SSSC to control
  the real power flow

Fig.8. FACTS UPFC controller scheme
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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.
• Novel Control in the STATCOM shunt converter 1
• SSSC-Converter (2) controller

Fig.9. Proposed STATCOM Decoupled Current
Control System for the shunt converter (1)
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.
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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
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CAPABLITIES OF DIFFERENT FACTS CONTROLLERS
Controller Voltage Control Transient stability Damping Power Oscillations Reactive Power Compensation Power Flow Control SSR Mitigation
STATCOM X x x x
SSSC X x x x x x
UPFC X x x x x X
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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.

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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
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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).

Fig. 12.a. Sample study of the unified power
system Developed By Dr. Sharaf
(Excursion- Level Magnitude)
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Fig. 12.b. The SSCC series capacitor switching
compensator scheme using two stage compensation
per phase dynamic capacitor switching
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Simulation Results
Without SSCC APF
With SSCC APF
Fig. 13. The simulation results when the system
subjected to 3- phase fault disturbance
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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 line power transfer
  and the power quality.

Fig. 13. Single line diagram sample study of the
unified power system with one novel
coordinated CC/TAF filter
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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
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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
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Fig 15. The Power Transfer levels P Q without
and with SSCCTAF
Fig 16. Comparison of the load voltage, load
current and THD voltage and current without and
with (SSCC TAF)
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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

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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.

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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.

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ACCEPTED PUBLICATION

• A.M. Sharaf and M. S. El-Moursi, " A Novel
  Dynamic Controller For Stability Enhancement
  Using Capacitive Series Compensators" 2004 IEEE
  International Symposium on Industrial
  Electronics, May 4-7 , 2004, Palais des CongrÃs
  Expositions, Ajaccio, France.
• A.M. Sharaf and M. S. El-Moursi" Stability And
  Power Quality Enhancement Using A Coordinated
  Capacitive Compensation And Tuned Arm Filter" ,
  the 29th Annual Conference of the IEEE
  Electronics Society Sunday, November 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.
• 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.

SUBITTED JOURNAL PAPERS
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Thanks