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
CONTENTVoltage stabilityHarmonic/ SSR stabilityRenewable Dispersed Energy Systems
FACTS Flexible AC Transmission System (Facts) is a new integrated conceptbased on power electronic switching converters and dynamic controllers toenhance the system utilization and power transfer capacity as well as thestability, security, reliability and power quality of AC systeminterconnections.
OPPORTUNITIESControl 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 DEVICESStatic 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 whosecapacitive or inductive current can be controlled independent of the systemvoltage.The STATCOM scheme in parallel with AC power grid system and iscontrolled 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 ControllerThe new control system is based on adecoupled 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 0I 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 COMPENSATORIt is a static synchronous generator operated without an external energysource as a series compensator.The o/p voltage is in quadrature with and controllable independently of theline current.It is increase or decrease the overall reactive voltage drop across the lineand 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 isto 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 SSSCTo enhance the dynamic performanceof 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 oscillatorysevere disturbance such as switching loads and fault condition
Simulation Results For SSSCFig. 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 twobasic switching power converternamely shunt and series convertersconnected to each other through a dclink capacitor.The shunt converter operates exactlyas STATCOM for reactivepower compensation and voltagestabilization. Fig.8. FACTS UPFC controller schemeThe series converter operates asSSSC 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) controllerThe system is subjected to severe disturbancesingle line to ground fault at load bus at time0.3 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 timeP, 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 ReactiveController Voltage Transient Power Power Power Flow SSR Control stability Oscillations Compensation Control MitigationSTATCOM X x x x SSSC X x x x x x UPFC X x x x x X
POWER QUALITY ENHANCEMENTThis 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 FILTERThe Power Filter SchemeThe power filter scheme consistsof both a passive filter and activefilter. The passive filter removesany load harmonics just as aconventional one does and theadded active filter plays a role inimproving the filtering action. Fig. 12.a. Sample study of the unified power system
Novel Tri Loop Dynamic Controller DesignThe proposed SSCC capacitorswitching controller is an errordriven, error-scaled self adjustingnonlinear tri loop dynamiccontroller used the load voltage,instantaneous and RMS loadcurrents deviation signals asshown in Fig 12 (a, b). 2 2 2Re = 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 nonlinearcoordinated dynamic error driven scaled error-controller for both the static series capacitorswitching 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 novelline power transfer and the power coordinated CC/TAF filter quality.
SSCC switched/modulated Tuned Arm Filter ControllerThe proposed self adjusting Tri-loop error scaled controller is based onthe load voltage, RMS source current and the dynamic current rippledeviation 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 & TAFFig 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 EnergyThe research will investigate the use of renewable dispersed energy system(wind-small hydro, hybrid scheme) and resulting grid interface problemsand need for effective mitigative FACTS-based solution. Both stand-aloneand grid connect wind energy conversion will be studied
CONCLUSIONThe research investigates FACTS topologies & novel control strategies forvoltage stability enhancement, T.L power flow control and harmonic/ SSRmode stabilization of an interconnected AC system.The use of FACTS devices in renewable energy utilization is also studiedfor small Hydro/ Wind hybrid renewable energy scheme.
FUTURE WORKValidation of (UPC) Universal Power Compensator controllable schemeusing the dynamic error driven controllers (P, Q) in SSR-stabilityenhancement.Application of the (UPC) Universal Power Compensator using dual Triloop 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 CombinedCapacitive 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 PAPERSA.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.