LCC-HVDC Supplementary Controller Design Based on Global Fast Terminal Sliding Mode Control

Conventional LCC-HVDC is a non-linear, tightly coupled system. Since the performance of PI control varies from different operation conditions, the optimal of parameter tuning is only achieved under steady state. To improve dynamic performance and stability of system, A novel HVDC nonlinear supplementary controller based on Terminal sliding mode theorem has been proposed. First, the steady state mathematical model of the LCC-HVDC system is built, the approach of state feedback exact linearization is adopted to change the nonlinear model into a linear one, the decoupled relationship between the control variables are investigated; then based on sliding mode control method, the constant current and constant voltage control in rectifier and inverter has been achieved, respectively. The variables converge to equilibrium point fast and exactly. Finally, the strategy is demonstrated through Matlab/Simulink software, the simulation results show that the controller is capable of tracing the reference, and the robustness with respect to parameters' perturbations is satisfied. The controller contributes significantly toward improving transient performance comparing to conventional PI control and restraining commutation failure.