An optimal control strategy to alleviate sub-synchronous resonance in VSC-HVDC systems

The VSC-HVDC can enhance the performance of power systems and plays a major role in the dynamic stability of power systems. In addition VSC-HVDC controller can be utilized to mitigate torsional torque and prevent sub-synchronous resonance (SSR) effectively. In this paper a controller has been designed for VSC-HVDC to suppress sub-synchronous oscillations. The Control methodology that is employed as sub-synchronous damping controller is based on implemented direct power control (DPC). Reducing SSR and increasing dynamic stability of power system including VSC-HVDC are discussed through simulations. Digital simulation has been carried out via MATLAB software to analyze torsional torque of turbine generator shaft and rotor speed in the case system which consists of VSC-HVDC and series compensated line.