Research On Transient Stability Of Direct Method Based On Two Time Scales

In recent years,increasing attention is taken to the multi-time scale characteristics of power system.In order to adapt to the increasingly complex power system,time scale feature is necessary to be considered in the traditional direct transient stability analysis.This paper studies the direct method based on two-time scales,which combines the time scale chracteristics of a class of power systems with the direct method,and studies the effectiveness of the method in the transient stability analysis of multi-machine systems.First,the research dynamics of the direct method is briefly introduced.The theoretical basis of the controlling unstable equilibrium point method(the CUEP method),which is commonly used in direct transisent stability analysis,is expounded.Based on the concept of stability region and the theory of energy function,the essence of the CUEP method is to approximate the stable boundary by the equal energy plane of the CUEP.The method to use the stable boundary tracking technique to find the CUEP is also proposed.Second,the basic theory of direct method based on two time scales is explained in detail,and how to use the CUEPs of the fast and slow subsystem to obtain the uniform CUEP of the original system is also introduced.On the basis of theory,the detailed steps of the two-time-scale direct transient stability analysis are proposed.Then,based on the two time scale propertity of third-order generator model,the energy function is constructed where the network uses the structure preserving model.The energy function corresponding to the fast and slow subsystem is also constructed respectively.Finally,the Kundur's four-machine system,the IEEE 14 node system and the New England 10-machine system are used as the example systems to set up the fault scene for simulation,and the simulation results are compared with the traditional CUEP method and the time domain simulation method.The calculation results show that,the two-time-scale direct method is feasible and effective for multi-machine system transient stability analysis.It is consistent with the theoretical analysis.The calculation accuracy is equivalent to the traditional CUEP method,but still be conservative compared with the time domain simulation method.