Design of a New Nonlinear Fuzzy State Feedback Controller for HVDC Systems

This paper deals with design and stability of a new nonlinear fuzzy state feedback controller for HVDC systems. A novel simplified nonlinear dynamic model is developed for HVDC system that can be used to design the controller. The proposed nonlinear dynamic model decomposes into several linear systems around its important equilibrium points. These local linear models describe the plant dynamical behavior at its different operating points. The proposed controller is used in the control loops of the HVDC system. The simulation is carried out based on the Cigre benchmark model. Simulation results show improvement of overall AC/DC/AC system performance when severe faults occur, compared to the conventional controller. Also, the stable behavior of a very weak AC/DC system (SCR<2) with proposed controller is very significant when a sudden change in current order and/or a switched reduction in ESCR is applied. The same situation with conventional control brings the system into unstable region