Study on the subsynchronous resonance mechanism of DFIG based on the analysis of stator and rotor torques

Starting from the expression of electromagnetic torque of doubly fed induction generator (DFIG), this paper divides the electromagnetic torque variation at a certain rotor speed variation into two parts, i.e., the rotor torque variation and stator torque variation. After working out the relationship of stator and rotor torque variations with the rotor speed variation, a novel mechanism interpretation of subsynchronous resonance (SSR) is put forward by analyzing the amplitude and phase characteristics versus frequency. With this method, this paper investigates the impact of rotor speed and compensation level on SSR stability. Results show that rotor-side electromagnetic torque variation has a positive damping effect on SSR but the stator-side torque variation has a negative damping effect. The speed of rotor speed mainly affects rotor-side torque variation and the compensation level has significant impact on the stator-side torque variation. SSR risk will increase with lower rotor speed or higher compensation level.