On The On-line Decision Arithmetic For The Transient Stability Of Power Systems

Along with the inter-connection and market formation of the state power systems, the decision table mode for the emergency control based on the off-line is less adapted to the new trends. Aiming at the second and the third defence-line for the transient stability of the power systems, the thesis studied the decision arithmetic safeguarding the transient stability. They are mainly constituted of:The iterative tangent plane (ITP) method for assessing the transient stability is presented which calculates critical cutting time (CCT) by the iterative arithmetic near the controlling unstable equilibrium point (UEP) based on the tangent plane closing to the stable manifold. The method is more accurate than the tangent plane method, and largely reduces the over-optimism.The thesis analyzes and compares the transient stability direct method such as potential energy boundary surface (PEBS), the boundary of stability region based on controlling unstable equilibrium point method (BCU) and the ITP method, and calculates the CCT according the WSCC system in different operation modes. According the characters of the inter-compensating and common calculating steps, the paper presents the multi-units-direct-method to screen the contingencies.The P-Q symbol method for system separation criterion with the prediction function for the out-of-step is presented. According to analysis of the active and reactive powers on the tie-line of the unstable machines, and definition some different indexes, the method can clearly identify the position of the operation points and its future trends. Therefore, the P-Q symbol method cannot only judges the out-of-step between the power systems, but also as early as identify the accurate time.The thesis analyzed the compensating principle for system separation, pointing that the reason of its invalidation. Based on the above, the modified compensating principle is presented according the sign of the relative curvature of the compensating voltages. It can identify the synchronous oscillation and the asynchronous oscillation and overcome the setting difficulty when the oscillation center is near the compensating ranges, which is not affected by the operation mode, setting of compensating resistance and the position of the oscillation center.The rotor angle predicting method adopting the forgetting index of auto regression (AR) model arithmetic is presented. The method can predict the trends of the rotor angle ahead of 200ms. The simulation shows that the method is more accurate than the AR arithmetic.The thesis presents two criteria to identify the critical machines cluster, which are complex rotor angle criterion and wavelet decomposing- relativity criterion. By the identifying the generators after distributed, the criteria can divide the cluster in short time which prepare for the decision of the emergency control.A real-time transient stability emergency control scheme is presented which is based on the wide area measurement (WAM) and high-speed communication technology. Assuming the rotor angles, speeds and active powers of the generators can be acquired during and post-fault, and sent to the local area stability control center in real time. The rotor angles are predicted and the emergency EEAC that is used to predict, analyze and estimate the degree of stability. The control action is a closed-loop rolling process that is enlightened from the general predictive control (GPC) theory. This scheme is applicable to any complex fault scenarios and any detail element models of the power system. The simulation showed that it could restrain the unmatched for some unpredicted serious contingency in the present emergency control and avoid a chain of events leading to large-scale power outage.