Analysis Of Power Systems Dynamic Equivalence With Consideration Of Dynamic Characteristics Of Loads

With the completion of several major interconnected power systems in China,which makes it become the world's most complicated and nonlinear dynamic system.In order to meet the fast and accurate analysis and calculation to the large scale power system,dynamic equivalence is able to simplify and reduce the power system and becomes an important method of online analysis of power system security and stability.Therefore,a highly accurate and a widely applicative dynamic equivalence,which can meet the modern power system's need,has is of great practical value.In view of the existing dynamic equivalence methods,coherent equivalence has clear physical meaning and mature theoretical study.It has become the uppermost dynamic equivalence methods.Given the increasing dynamic load in power load,the existing coherent equivalence doesn't fit the modern power system development requirements Based on above background,this paper puts forward a new approach to coherent equivalence in the respect of source-network-load.Firstly,the generator power and angle characteristics are discussed from the respect of coherent equivalence and traditional methods of coherent equivalence are described in this paper.General coherent equivalence processes include identification of coherent generators,simplification of coherent generators bus,simplification of system load and parameter aggregation of coherent generators.A new generator coherent equivalence through thevenin equivalence and electric distance between generators to evaluate the electric connection between generator and the remaining power system is put forward.Namely,the power system is simplified a 2 generator system by thevenin equivalence and its relationship can be described by electric distance.The above electric distance is regarded as the coherent indicator.Secondly,this paper describes the load recoverable and unstable characteristics from power system stability perspective and indicates that dynamic characteristics of load and system transient characteristics are closely related.The dynamic characteristics of load can be replaced by induction motors and the eigenvalue of linear state equation of induction motor can reflect the condition of induction motor.The eigenvalue can be used as a indicator for identifying coherent induction motor.In order to obtain a realistic coherent equivalence programme,cluster analysis is introduced into coherent equivalence progress.Induction motor and generator in power system are very closely linked elements and in order to avoid dividing the induction motor which is closely associated with the generator into other generator group,the subsystem of generator and induction motor can be decided by the initial system power flow.Based on this subsystem,the whole power system can be divided several coherent groups through clustering analysis.Finally,through a EPRI-36 bus system,this algorithm is verified in PSASP simulation platform.The simulation results show that the algorithm,relying solely on locally measured electrical information or small amounts of information,can take the dynamic characteristics of load into the progress of dynamic equivalence,which is very applicable and meet the requirements of analysis and calculation of modern interconnected power system.