Research On Power System Transient Stability Prediction And Delay Stability Regions Based On Wide Area Measurement Signals

The Wide Area Measurement System (WAMS) is based on Synchronized Phasor Measurement (SPM) and the technology of modern communication. WAMS can provide synchronous signals of many nodes in a power system. These wide area signals are measured in real time with high precision and great reliability. The improvement of wide area signals in precision and speed brings about new progress in transient stability prediction. Several novel methods for transient stability prediction based on WAMS have been reported. Meanwhile, WAMS also provides new approches for wide area control. However, the effect of signal delays on power system small signal stability can not be neglected. The estimation of maximum allowed time delays that will not cause system instability is important in application of WAMS data and evaluation of control effects of wide area controllers.Transient stability prediction based on WAMS and evaluation of delay stability regions of power systems are studied in this research. The dissertation is organized as follows:The concept of WAMS and its applications in power systems are introduced. Traditional methods for transient stability prediction are summarized and new methods brought by WAMS are also reviewed. Time delay characteristics of WAMS and recent research on time delay phenomenon of wide area power systems are also introduced.A fast learning method to predict the transient stability of a power system is proposed. It adopts a widely used robotic ball-catching algorithm based on a continual stream of accurate generator rotor angle data from WAMS. The Particle Swarm Optimization (PSO) algorithm is used to perform multi-parameter optimization in this algorithm. This method can predict post-fault rotor angle of each generator. The rotor angle of a generator with respect to the inertial center of a power system can be used to judge whether this generator loses synchronism with the system. The prediction results can be used in on-line instability alarm and local control. Simulation results on two test systems demonstrate the effectiveness of the proposed method.The effects of time delays on small signal stability of power systems are studied. The model and stability concept of time-delayed systems are introduced. A power system with time delays is typically multi-delay dynamical and it can be modeled as differential-algebraic equations with delays. Small signal stability of power system with delays is analyzed. Time domain simulations on the New England Test System with a TCSC controller show that the dynamic performance of this TCSC controller deteriorates sharply with the feedback delay's increase.Delay stability margin of a power system with a single delay is computed with Clustering Treatment of Characteristic Roots (CTCR) method. Model of a power system with a single delay and definition of delay stability margin are introduced. A novel framework based on CTCR method is presented to determine the delay stability margin of a power system with a single delay. The characteristic equation of single delayed power system is converted into a polynomial equation through Rekasius substitution. The complete distribution of number of unstable characteristic roots on the complex plane is obtained with traditional Routh criterion and the delay stability margin is also determined. Delay stability margins of all kinds of single delayed systems can be obtaind through this method. The validity of this method is verified by the time domain simulation results.A noval method to determine the delay stability margin of power system with single control variable is proposed. The transcendental characteristic equation is converted into a polynomial equation at the imaginary axis without any substitutions. This method needs less computation than the CTCR method. The delay stability margins of two test systems at typical equilibrium point are obtained through this method. The effect of exciter parameters on delay stability margin is also discussed. Time domain simulation results and comparison with other methods show that this method is simple and effective.An improved CTCR method to determine delay stability regions of a power system with multiple delays is proposed. Firstly, the CTCR method to analyze the stability of power system with multiple delays is introduced. Then, the ' Building Block' concept is introduced as the preparatory steps of the CTCR method to simplify the computation of delay stability regions. Complete delay stability regions of test systems are obtained through the combination of CTCR and 'Building Block' concept. Time domain simulation results demonstrate the effectiveness and feasibility of this method.