Research On Control Strategy Of SSSC For Damping Power Oscillation

With the development of economy and technology, the scale of the modernpower grid is becoming larger, and the requirement of its reliability andcontrollability is higher and higher. In order to improve the security level of powergrid and provide excellent power quality, not only rational planning of grid andreliable power equipments but also advanced control methods are necessary. In recentyears, The Flexible AC Transmission System (FACTS) offers a possibility to find asolution to the difficulties in operation and development of power grid. It makesuncontrollable grid to be controllable, and improves the flexibility and stability ofpower system.Static Synchronous Series Compensator (SSSC) is a type of series compensationof FACTS devices based on the voltage source inverter technology. It inserts avoltage of which the magnitude and phase angle can be controlled into thetransmission line to change the effective impedance in order to adjust the power flow,damp power oscillation and improve the stability of system.This dissertation represents the basic structure and the work principle of SSSC.The Phillips-Heffron model of single machine infinite bus system installed withSSSC is established. On the basis of this model, effects of SSSC on the stability ofpower system and mechanism of damping power oscillation by SSSC are analyzed.The symbol of partial derivative of electromagnetic power to amplitude modulationratio is discussed. It is obtained that SSSC can provide positive damping torque tosystem in capacitive mode and negative damping torque to system in perceptual mode,thereby suppressing the power oscillation.The design of control law can base on the available Phillips-Heffron model. Themathematical model of a single-machine infinite-bus power system with SSSC isestablished. The nonlinear optimal control law of SSSC is designed in accordance with the differential geometry theory of exact feedback linearization. Themathematical model can be linearized based on exact feedback linearization. Then thecontrol law of SSSC can be designed according to linear quadratic optimal controltheory. In order to gain the best control law, disturbance variable is introduced in themathematical model, and control law of SSSC is designed based on feedbacklinearization H∞control of nonlinear robust control theory. The theoretical analysisand simulation results prove the good performance of control law of SSSC based onfeedback linearization H∞theory. It can better increase damping of power system,damp power oscillation and improve the stability of system.