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. 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 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 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)

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

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

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) Fig. 10. Control Block diagram of SSSC series converter (2) scheme. 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.

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

CAPABLITIES OF DIFFERENT FACTS CONTROLLERS Controller Voltage Control Transient stability Damping Power Oscillations Reactive Power Compensation Power Flow Control SSRMitigationSTATCOM Xxxx SSSC Xxxxxx UPFC XxxxxX

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). 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 Fig. 13. The simulation results when the system subjected to 3- phase fault disturbance Without SSCC & APF With SSCC & APF

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

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. 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 Compensators" 2004 IEEE International Symposium on Industrial Electronics, May 4-7, 2004, Palais des Congrès 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, , 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 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 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 SUBITTED JOURNAL PAPERS