Multi-parameter Static Bifurcation Analysis Of Wind Power System Voltage Stability

Wind power generation grows so fast that grid-connect has become an inevitable trend. The main challenge of grid-connect is the voltage stability, and it will be a bright future to research on wind power system voltage stability based on bifurcation theory. Wind power system is a high-dimensional nonlinear system with a large number of parameters, of which multi-parameter bifurcation analysis on voltage stability is so significant. Research of voltage stability static bifurcation is the basis and prerequisite of the whole system voltage stability bifurcation analysis, as well as the focus of this paper. Main tasks are as follows:(1) So as to reflect the influence of the continuous changes of wind power system parameters on the voltage stability and reveal the mechanism of voltage stability in wind power system, multi-parameter static bifurcation analysis and studies were detailed based on wind power system static model, also make up the lack of current single-parameter bifurcation analysis. With the help of ideas and methods calculating the two-dimensional parameters bifurcation boundary in conventional electric power system, two-dimensional saddle-node bifurcation boundary of the bus voltage in wind power system was calculated by using wind farm active power injection (P_inject), SVC parameters B_max and K_r as bifurcation control parameters. And on the basis of deep analysis, the laws that parameters affecting the wind power system voltage stability were obtained.(2) In order to take into account the characteristics of the dynamic components better, multi-parameter static bifurcation analysis and studies were detailed based on wind power system dynamic model. Multi-dimensional bifurcation hypersurfaces tracking method of the wind power system voltage static bifurcation was proposed. Two-dimensional saddle-node bifurcation boundaries and bifurcation hypersurfaces were calculated with the help of static bifurcation analysis method by using active wind power injection P₁, SVC parameters and excite parameters of power system equivalent machine as bifurcation parameters. Through analysis, bifurcation mechanisms of various parameters affect wind power system voltage stability were analyzed.(3) In order to mathematically give an accurate analytical description of the bifurcation boundary in the wind power system parameters space. A method that quadratic polynomial was considered as approximate analytical expression of saddle node bifurcation boundaries in wind power system parameters space was proposed. The method also solves the problem of dimension constraints of bifurcation parameters space. On the basis of calculation of saddle-node bifurcation boundary in the parameters space, the coefficients of nonlinear analytical expression were obtained by using the fitting method. The precision and effectiveness of the method to approach the real boundary were tested and verified with a simulation example.