Interaction Analysis of Multi-terminal Direct Current Transmission Systems Connected to Wind Farm: Determining the Optimal Range of Controller Coefficients

The increasing demand for electrical energy, the limitation of fossil fuel resources, and the aggravation of environmental pollution have made it inevitable to use clean energy sources, such as wind energy. In the meantime, the doubly fed induction generators are commonly used due to their capability of controlling the reactive power with no need for capacitor banks. Furthermore, increasing the capacity of wind farms has made the high-voltage direct current (HVDC) transmission network in the form of multiple terminals a preferred option for transferring the power of these sources over long distances. In this situation, the interaction of transmission system controllers with other controllers and devices has become a primary concern of the network. Research has shown that power systems that undergo stress exhibit complex dynamic behaviors that increase the possibility of interaction between system components and can endanger the stability of the power system. The present study attempted to investigate the problem of interaction in multi-terminal HVDC transmission systems, and the problem of torsional interaction in wind farms connected to these transmission systems. The linear modal analysis was used to investigate the interaction, and the analytical results were validated using MATLAB/Simulink time-domain simulation. In addition, due to the change of system parameters over time, this paper comprehensively investigated the system damping over different system parameters, and a structured scheme was employed to obtain an optimal range of control coefficients, ensuring the stable operation of the system.