Stability analysis of sub/super synchronous oscillation in direct-drive wind farm considering the energy interaction between PMSGs

A method to analyze the stability of sub/super synchronous oscillations in direct-drive wind farm considering the energy interaction between PMSGs is proposed. First, the dynamic energy model of direct-drive wind farm considering the energy interaction between PMSGs is built. Then, the farm-grid interaction energy is divided into three components: the disturbance energy, the self-coupling energy and the interaction energy between PMSGs, which characterize the initial disturbance effect of PMSG, the self-induction effect and the interaction between generators, respectively. On this basis, the variation characteristics of disturbance energy, coupling energy and the interaction energy are analyzed using Lyapunov's second stability theorem. It is revealed that, the interaction energy is the key factor that determines whether the oscillation will diverge or converge. In addition, the influences of PMSG integration distance, wind speed and control parameters on the stability are studied. Finally, the model of direct-drive wind farm is built in RT-LAB for hardware-in-the-loop tests. Simulation results show that, the longer the PMSG integration distance is or the higher the wind speed where the PMSG is located is, the stronger the interaction between PMSGs is, and the better it is for the sub-synchronous oscillation to converge. The larger the PMSG current loop parameters, voltage loop parameters and PLL parameters are, the stronger the dissipation effect of the interaction energy between PMSGs is, and the better it is for the super-synchronous stability control.