Research Of Voltage Stability In Power System Based On Indirect Method And Direct Method

Recently, big blackouts appeared continually, these blackouts indicate that the root cause of almost all of these major power system disturbances is voltage collapse and voltage instability, a great attention is devoted to study of voltage stability problem which has been an urgent problem in power system. An important analysis tool in power system stability is bifurcation theory that is used to study whether nonlinear systems maintain its constant characteristics under changing parameters. Well known local bifurcations in power system include saddle node bifurcation(SNB), Hopf bifurcation, singularity induced bifurcation (SIB) and limit induced bifurcation(LIB), equilibrium of the power system lose structural stability as the parameters pass through some bifurcation points, These bifurcation points form feasible and security stability regions of the power system.Computation of bifurcation manifold in parameter-space is an important issue of power system stability analysis and useful for power system secure operation and control. Methods to Calculate bifurcation points include indirect method and direct method. Continuation power flow program using new parameterization strategy derived from line power loss is made by MATLAB language; The most appropriate line is selected as continuation parameter automatically by voltage stability index. Different behaviors of system maximum load level considering different load variation patterns is evaluated and discussed. Total system mathematics model is deduced using polar coordinate and rectangular coordinate simultaneously, which number of used variables is less, and the combination of direct method and continuation method to track double-parameter bifurcation boundary curve is developed, particularly thoroughly study methods of getting hopf bifurcation points, give a detailed comparison of advantages and disadvantages of various methods to obtain hopf bifurcation points, then a new approach to calculate hopf bifurcation points is presented, which is not expensive to solve the extended system. A method to calculate limit induced bifurcation is proposed, Basic algorithm to calculate bifurcation manifold of double-parameter and three parameters power system is presented in this paper.Based on the proposed mathematical model and algorithm, practical programs are made by MATLAB language, which is applied to analyze single parameter and multi-parameter of WSCC 9-bus system and NewEngland 39-bus system considering detailed generator formulations. Considering reference set point V_ref and excitation gain K_a and excitation time constant T_a as controllable parameters, bifurcation boundary of multi-parameter simultaneous variation considering static load model and dynamical load model is studied respectively, simulation results demonstrate that the model and algorithm is practical, reliable and effective, the proposed algorithm is stable and fast and suitable for dynamic voltage stability in bulk power system.