Design of Additional Damping Controller for VSC-HVDC Transmission System Based on Variable Structure Control

The HVDC based on voltage source converter (VSC) and pulse width modulation (PWM) is a new transmission technology which can improve power system stability due to its fast and flexibly capability to control the active and reactive power.A nonlinear auxiliary controller for VSC-HVDC in AC/DC power system is developed to damp inter-area oscillation.The method treats the dynamics of DC power regulation as a first-order inertia-block and simplifies the AC/DC multi-machine system into a two-machine power system.Based on the third-order model obtained,the state-feedback linearization and the variable structure control theory are applied to design the nonlinear auxiliary controller.Numeral simulation results validate that the controller can-effectively damp inter-area oscillation and quickly restore the power system stability.