Stability analysis of sub-synchronous oscillation in power system connected with virtual synchronous DFIGs

Concerning sub-synchronous oscillation in power system connected with virtual synchronous DFIGs, an oscillatory stability analysis method based on the dissipation rate of dynamic energy is proposed. First, the dynamic energy function that reflects the sub-synchronous oscillation characteristics of virtual synchronous DFIG is built, and the expression of dynamic energy considering virtual synchronous control parameters is analysed. Then, according to Lyapunov's stability law, the variation rate of dynamic energy function is defined as the energy dissipation rate. The energy dissipation rate reflects the variation trend of system dynamic energy during oscillation, thus it is used as the stability criterion of sub-synchronous oscillation. On this basis, the effects of different virtual synchronous control parameters on sub-synchronous oscillation are analysed for a comprehensive consideration of system stability. Finally, simulation tests are conducted on RT-LAB platform. The results verify that, when the energy dissipation rate is positive, system oscillation diverges; when the energy dissipation rate is negative, system oscillation converges. Meanwhile, the larger the virtual resistance is, the worse the stability of system is; the larger PI control parameters of reactive power control loop are, the worse the stability of system is.