Small Signal Stability Control And Reliability Analysis Of Grid-connected Wind Power System Based On Sensitivity Model

Under the background of large-scale wind power integration,doubly-fed induction generator(DFIG)changes the damping characteristics and low-frequency oscillation degree of power system.Existing studies have established the sensitivity of grid oscillation mode to synchronous generator(SG)output,but there is no study on the influence of DFIG reactive power.The reactive power of DFIG indirectly affects the eigenvalue,it does not appear in the state matrix,so it is difficult to get the analytical expression of the sensitivity of the system oscillation mode to DFIG reactive power.In the existing research,the reliability calculation process of wind power system is complicated,which needs manual combination and search.It is inefficient to obtain the sensitivity of wind turbine fault repair rate by perturbation method.Therefore,it is very necessary to analyze the sensitivity of small signal stability and reliability of wind power grid-connected system.The innovations of this paper are as follows:(1)Based on detailed dynamic model of DFIG,the eigenvalue introduced by DFIG grid connection and its influence on the original eigenvalue of the system are analyzed.The formula is derived to analyze the mechanism of dynamic interaction between DFIG and SG affecting eigenvalues.(2)Analyze the elements in the state matrix affected by DFIG reactive power,and establish the relationship with node voltage by intermediate variables.The sensitivity of node voltage to DFIG reactive power is calculated based on power flow equation.An analytical expression of the sensitivity of weak damping mode to reactive power output of DFIG is proposed.It is found that the improvement effect of DFIG reactive power on weak damping mode is similar to SG active and reactive power.(3)Considering the variation of wind speed and the difference of reliability parameters of wind turbines,the microgrid state space is established based on hierarchical equivalence and combination.In order to avoid manual search and repeated calculation,the state number tracking algorithm is established,and the correlation matrix is obtained based on weighted clustering,thus forming the state correspondence of combination and equivalence,and the analytical expression of reliability and parameter sensitivity is put forward.