Control Scheme of Three-phase H-bridge Cascaded STATCOM

Since mathematic model of STATCOM is coupling and nonlinear,it is difficult to decouple active and reactive power.Another difficult point is voltage balancing control of dc side capacitors caused by H-bridge cascaded topology.Consequently,the exact feedback linearization control law is derived to accomplish the linearization of STATCOM model and to realize decoupled control of active and reactive power,and the model can be changed into two independent first-order linear system.Sliding mode control method is used to design the controller,which can solve the difficulties in adjusting parameters of traditional PI controller and to improve the robustness of the controller.The voltage balance of capacitors is realized based on the analysis of the single H bridge module and nearest level modulation A STATCOM model is established in the Matlab/Simulink.The results of numerical simulation show that the established model and designed controller are effective.The active and reactive power can be adjusted independently.The voltages of capacitors can be balanced well,and the system has good dynamic response which is better than the traditional PI controller,and also has robustness.