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  1. 1. Power system stability improvement by FACTS devices: & a comparison between STATCOM, SSSC and UPFC
  2. 2. INTRODUCTION The rate of dissipation of transient energy is usually used as a tool to measure dynamic system damping.  This presentation applies and discusses the above control strategy for suppressing undesirable electromechanical oscillations in power system with a STATic synchronous COMpensator (STATCOM), static synchronous series compensator (SSSC) and unified power flow controller (UPFC). To transfer maximum power without loosing synchronism.
  3. 3. Definitions: Stability: Power system stability is the ability of an electric power system, for a given initial operating condition, to regain a state of operating equilibrium after being subjected to a physical disturbance, with most system variables bounded so that practically the entire system remains intact.
  4. 4. Facts: “AC transmission systems incorporating power electronic based and other static controllers to enhance availability and to increase power transfer capabilities” Facts controller: Power electronic based system or other equipment that provides control of one or more AC transmission system. They can be inserted in series or shunt and in some cases a combination of both.
  5. 5. POWER SYSTEM MODEL let us consider Single machine infinite bus diagram Single machine infinite equivalent circuit diagram. The output electrical power of the system without any FACTS devices is given by:
  6. 6. MODELLING OF POWER SYSTEM WITH STATCOM The STATCOM is a voltage-source converter (VSC) capable of generating or absorbing independently controllable reactive power at its terminal. It is represented by a shunt reactive current Is source as shown in figure. Circuit diagram of SMIB with STATCOM. Equivalent circuit diagram of SMIB with STATCOM.
  7. 7. MODELLING OF POWER SYSTEM WITH SSSC The SSSC is a solid-state voltage source inverter that generates a controllable AC voltage. Circuit diagram of SMIB with SSSC. Equivalent circuit diagram of SMIB with SSSC In case SMIB with SSSC, e P is rewritten as:
  8. 8. MODELLING OF POWER SYSTEM WITH UPFC  A unified power flow controller (UPFC) is the most promising device in the FACTS concept. Equivalent circuit diagram of SMIB with UPFCCircuit diagram of SMIB with UPFC  UPFC regroups features and properties of both SSSC and STATCOM.
  9. 9. RESULTS AND DISCUSSIONS  A three phase fault occurs at bus m at t=1s and is cleared by disconnecting line 2 at end. Rotor angle deviation response to this disturbance for different critical time is shown in figure. Relative angle position for different critical times
  10. 10.  For a critical clearing time tc= 0.088s, the same curves for the SMIB with and without FACTS devices are shown in figure. Relative angle position  Prefault and post fault values of the rotor angle position are not the same. These values are equal to 41.7714and 54.7260°, respectively. Figure shows that the uncompensated system is unstable, but when we added STATCOM and SSSC, the system remains stability, oscillations are damped out.
  11. 11.  Figure shows curves of machine rotor angle velocity plotted with and without FACTS devices. Relative angle velocity
  12. 12.  Figure shows curves of machine output electrical power for the two cases: with and without FACTS devices. The output electrical power in the prefault period is equal to it’s initial value 0.9 pu. Generator output power  At t=1s, output electrical oscillations are kept constant during faulted period and post faulted period for the uncompensated case.  For the case with FACTS devices, oscillations are rapidly damped out.
  13. 13. CONCLSIONS AND PROSPECTS FOR FUTUTRE WORK  The objective of this study was to reach an efficient control of an electrical power system plus FACTS devices under several perturbations. Facts is an application of power electronics in power transmission system. Facts has a important role in real and reactive power control. Facts makes a system stable.  All the above aspects show the effectiveness of these devices to suppress oscillations and stabilizing the power system.
  14. 14. [1] E.V. Larsen, D.A. Swann. Jones, “Applying power system stabilizers Parts I and II”,IEEE Trans.PAS, vol. 100, pp. 3017–3046. 1981. [2] M.Noroozian, L.Angquist, M. Ghandari, and G.Anderson, “Use of UPFC for optimal power flow control”, IEEE Trans. on Power Systems, vol. 12, no. 4, pp. 1629–1634. 1997. [3] Mehrdad AhmadiKamarposhti, MostafaAlinezhad, “Effects of STATCOM, TCSC, SSSC and UPFC on Static Voltage Stability”, International Review of Electrical Engineering, vol. 4, no. 6, pp. 1376–1382. 2009. [4] E. Z. Zhou,“Application of Static Var Compensators to increase Power System Damping”, IEEE Transactions on Power System, vol. 8, no. 2, pp. 655–661. 1993. [5] P. Kundur, Power System Stability and Control, Example13.1, page 863 McGraw- Hill, New York, 1994. REFERENCES