Simplified Input-output Linearization Control for Wind Farm Interconnection Based on Multi-terminal Vsc-hvdc

The paper aims to exploit multi-terminal VSC-HVDC for wind farm interconnection and seek a control strategy that can improve the operational characteristics of the interconnection system. Firstly, the paper introduces the basic structure of the wind farm interconnection system and details the wind farm control schemes, including pitch angle control and rotational speed control. Secondly, it explains the commonly used linear decoupling control strategy of the grid side converter for controlling DC voltage. Because the model of VSC is highly nonlinear and coupling, small signal analysis based linear control strategy is hard to meet the requirements. Then the paper presents a more advanced nonlinear control strategy that is based on single-input single-output feedback linearization, namely simplified input-output linearization (SIOL), to better the operational characteristics of wind farms, especially in terms of the immunity to interruptions. Simulation has been carried out using MATLAB/Simulink to compare the linear control and the nonlinear control strategies. The simulation results demonstrate that SIOL has better performance than its linear counterpart.