Research On Control Technology Of Static Synchronous Compensator

As society is progressing, large-scale power grid and long-distance transmission not only meet people's needs for electrical power, but also cause power system reliability and voltage stability problems. Power system voltage stability is closely related with reactive power of electrical grid. As an important device of FACTS (Flexible AC Transmission System), STATCOM (Static Synchronous Compensator) can improve power system voltage stability by controlling reactive power of power system. Compared to the traditional reactive compensation devices, STATCOM is widely focused and studied by researchers in recent years because of its fast dynamic response to reactive power and low harmonic pollution to power system.The paper studies the control structure and strategy of STATCOM system. Based on Kirchhoff's law and Lagrange equation separately, the paper presents STATCOM differential equation model in abc coordinate. The differential equation model of STATCOM in dq coordinate is achieved by utilizing dq synchronous transformation.The paper analyzes the characteristics of STATCOM model in dq coordinate with the small-signal method, and certifies its non-minimum phase property, which the structure of inner current loops and outer voltage loop is designed based on. Passivity characteristics of STATCOM model is analyzed in order to further utilize passivity theory for its controller design.Based on non-minimum phase property and Passivity characteristics of STATCOM model, this paper designs two control schemes for STATCOM system. The first scheme is designed based on feedback linearization decoupled strategy in order to decouple the nonlinear system. The second scheme is designed based on Passivity-Based Control, combining with sliding mode control. The two proposed control schemes are validated by Matlab/Simpower platform. The simulation results show that the two proposed control schemes achieve control objective of STATCOM system.Finally, this paper establishes a STATCOM prototype in order to verify effect of control scheme designed for STATCOM system. The experimental results show that the controller based on feedback linearization decoupled theory achieve control objective on the prototype of STATCOM. The excellent character of STATCOM fast dynamic response to reactive power and low harmonic pollution to power system is verified by the experimental results.