Stability Analysis And Controller Design Of Power Systems With Time-Delay Based On Wide Area Measurement System

The secure, stable, and economic operation of power system is the goal that engineers in electricity utilities and power system scholars have tried to obtain for many years. Despite a variety of methods and measures have been carried out, power system instability and blackout still take place occasionally. Low frequency oscillations, which are caused by weak damping, belong to a typical power system instability phenomenon in a large-scale interconnected power system. In order to damp low frequency oscillations, WAMS has been applied into the stabil-ity control of wide area power systems, which inevitably brings time-delay problem. The time-delay can degrade the system performance and even destroy the system stability. Compared to non-delay scenarios, controller design in delay scenarios is more complex and difficult.In this thesis, based on the characteristics of wide area power system, the time-delay is introduced into the modeling process of wide area pow-er system. Then the power system steady stability model and damping control model based on linear time-delay system theory are established, and the time-delay power system steady stability criterion and damping controller design method based on free weight matrix method are pro-posed. The research results mainly include the following aspects:(1) The power system steady stability model in consideration of time-delay is established.When the delay influence is taken into account, power system should be described by time-delay dynamic system instead of general dynamic system. Correspondingly, its mathematical model is retarted functional differential equation (RFDE) instead of differential equation. Therefore, in order to analyze the influence of delay on wide-area power system, power system model with time-delay should be constructed. Based on the proposed model, a power system steady stability criterion in the form of linear matrix inequality is derived by adopting free weight matrix method. Delay margin instead of eigenvalue is suggested to judge and analyze the stability performance of time-delay power system. Case studies on a single machine infinite bus power system have verified the effectiveness of the proposed power system steady stability model and its stability criterion.(2) The relationship among delay margin, SDC gain, and the damp-ing performance is analyzed. An optimization design method of UPFC damping controller is proposed with considering the effect of delay sta-bility margin and damping ratio.In order to solve insufficient damping ability of UPFC damping controller in delay scenarios, a UPFC damping control model with time-delay is constructed on the basis of conventional UPFC damping control model by considering the time-varying and stochastic features of signal transmission delay in WAMS. The interactive influence among controller parameters, delay margin and damping performance indexes is intensively investigated, and an optimal design method of UPFC damp-ing controllers with considering signal transmission delay is proposed. Simulation results show that the UPFC damping controller obtained by the proposed method can not only effectively damp interarea oscillations but also endure a certain communication delay, and overcomes the dis-advantage of conventional damping controllers which can not adapt to longer communication delay.(3) A phase angle based multi-objective particle swarm optimization algorithm (PAPSO) is proposed for solving the multi-objective optimiza-tion problem of wide-area damping controller for time-delay power sys-tem.Delay margin and damping performance should be simultaneously satisfied in the design of wide-area damping controller. It belongs to mul-ti-objective optimization problem, which can be solved by evolutionary algorithm since co-evolution mechanism in the algorithm ensures that multiple solutions can be obtained in a run. An improved multi-objective particle swarm optimization algorithm is proposed to solve optimal pa-rameters of wide-area damping controller. The proposed algorithm con-siders a potential solution in the optimization problem, or called a particle, as a phase angle vector with attributes of location and direction. The transition can ensure that each optimization sub-function has equal upper bound and lower bound, initial particles are distributed in solution space with evenly probability, and accelerate particle searching speed with more compact search process. Besides, sharing pool concept is intro-duced into particle flight information sharing mechanism, and sharing pool update strategy based on related predominance sorting and similari-ty degree sorting are presented to improve the diversity of Pareto solu-tions. Sigma leading strategy and chaos variation operation balance its ability of finding optimal solutions rapidly and extensively.(4) FACTS damping control model with time-delay is constructed, and a PSO based SDC multi-objective optimization design method is proposed with considering the objectives of maximizing damping ratio and delay margin simultaneously.In the environment of WAMS, damping controller to be designed not only damp out low frequency oscillations with larger damping ratio, but also maintain the system stability even if a certain signal transmission delay within delay margin exists. PAPSO is proposed to solve SDC mul-ti-objective optimization problem in wide-area damping control and ob-tain a set of Pareto solutions which satisfy SDC design objectives. The proposed method implements, the extension from conventional SDC de-sign method in non-delay scenarios to SDC design method in delay sce-narios, and gives a new thinking for FACTS damping controller design considering signal transmission delay in WAMS. Simulation case studies verify the feasibility and effectiveness of the proposed method.