Analysis And Control Of Chaotic Oscillations In Power Systems With Periodic Power Disturbances

In recent years,with the development of society and the increasing demand for electricity,the power system has become increasingly large and its structure has become more complex than past decades.With the operating parameters changing or external disturbances occurring,chaotic motions seeming to be similar to random phenomenon often appear in the power system that can easily cause voltage instability and angle divergence,which threaten the security and stability of power grid.Therefore,detailed research on chaotic oscillations in the power system and designing control method that is easy to be implemented to suppress the chaos phenomenon and improve the stability of the power system are necessary.In this dissertation,the transient behaviors of the fourth-order model and the seventh-order model of the power system are studied through theoretical analysis and numerical simulation respectively.The different controllers are designed to suppress the chaotic oscillations in the power system.The main research contents are given as follows:Firstly,the dynamic properties of the fourth-order power system model including synchronous generator exciter are investigated through bifurcation diagrams,Lyapunov exponent spectrums and Poincare maps.The parameter ranges of the chaotic motions are obtained through the calculation method.At the same time,the bifurcation diagrams of power system model are complemented by adopting different integral initial values,so that the coexistence of attractors is observed and quantitatively analyzed.Besides,the state synchronization controller is designed based on the nonlinear feedback control method,and both theoretical proof and numerical simulation results verify its effectiveness.Secondly,due to the power disturbances in the actual power system,the fourth-order power system model is built with periodic electromagnetic power disturbance term and periodic load power disturbance term.When only one of the power disturbance items is included in the system,the bifurcation and chaotic phenomena of the power system model with only one kind of disturbance items is analyzed through changing parameters such as mechanical input power,damping coefficient,excitation gain,amplitude and frequency of the disturbance term.Compared with previous content,the addition of disturbance items and their changes bring the power system model with new nonlinear dynamic behaviors.Then,two kinds of disturbances existing in the system model at the same time is considered,and the above parameters are varied to observe the evolutionary process of bifurcation and chaos in the system under various parameter settings.In addition,the obvious distinction of the bifurcation processes of the power system with different frequency ratios between the two power disturbance items is analyzed.Moreover,based on the dynamic surface sliding mode control method,the controller is designed for the fourth-order power system model with power disturbances to suppress the chaotic oscillations in power system quickly and smoothly.Finally,the seventh-order mathematical model of the three-node power system is derived,and the periodic power disturbance terms are added to the model as well.The phenomena of chaos oscillations in the high-order model with the change of parameters such as mechanical input power,damping coefficient,amplitudes and frequencies of disturbances are investigated through numerical simulation method.The change process of the system attractor is observed with phase portraits and Poincare maps.