Study On Preventive Control For Enhancement Of Transient Stability Based On Hybrid Method And Minimum Kinetic Energy

Modern power systems in operation have to possess the capability to withstand a set of possible single contingencies. By means of preventive control, the operators will shift the current working status from the alert region to the normal one where adequacy and security are thus ensured. Generation rescheduling, as a common measure of preventive control, has been extensively addressed for a long time.The early works of direct methods utilized the quasi-linearity of transient energy margin (TEM) to approximate the transient stability limits, which opened an era of this area. As far as the precision is concerned, the hybrid method is much more appealing to conduct transient stability-constrained preventive control. Moreover, compared with another kind of approaches, namely optimal power flow with transient stability constraints, the hybrid method adopted in this thesis is more appealing to practical application.This thesis briefly reviews the definition of transient energy function (TEF) in direct methods and the physical concepts in potential energy boundary surface (PEBS) approach, followed by a viable strategy for hybrid method analysis. Based on these grounds the characteristics of minimum kinetic energy (KE) are expounded. Such a minimum KE comes from an energy trajectory of the post-fault system, and is quasi-linear with the mechanical input power of the severely disturbed machine in two distinct slopes. The segment with a small slope corresponds to the configuration where the power system stays stable; such a minimum KE is called inactive KE. The points on the declining segment match the extra energy that the system fails to convert to potential energy (PE) at the PEBS, which is called active KE. The inflexion of the two segments indicates the generation limit.To make use of this property, a methodology is put up implementing the following functions: to recognize the severely disturbed generators; to calculate the sensitivity of minimum KE with respect to the mechanical input power of these generators; to evaluate the TEM by a hybrid method; and finally, to combine them together in an iterative analysis framework.A computer program is compiled to implement such an algorithm. Multiple operation modes and representative models are employed on the 10-machine 39-bus...