Suppressing Subsynchronous Oscillation in Wind-Thermal-Bundled Power System via Flexible Excitation System

Wind-thermal-bundled power system is widely applied to solve the grid interconnection of wind farms, but it brings the high risk of subsynchronous oscillation (SSO) which is a threat to turbo generator and the stability of system. Conventional static excitation system uses Supplementary Excitation Damping Control (SEDC) to suppress SSO, but the response time is limited by the excitation winding time constant. Besides SEDC, flexible excitation system can provide an extra damping channel controlled by Subsynchronous Damping Controller (SSDC). This paper proposes a novel SSDC and its corresponding control method for flexible excitation system. Then the effect of SSDC is analyzed by complex torque coefficient method. Finally, the oscillation suppression effect of SEDC, SSDC and SEDC together with SSDC are compared by simulation with PSCAD/EMTDC.