Distributed Coherent Dynamic Equivalent For Multi-area Interconnected Power Systems

The modern power system is being developed in the market-based reform andmulti-area interconnection gradually, which requires transient stability analysis tomeet distributed computation under power market and multi-area interconnectionenvironment. Coherent dynamic equivalence is a valid approach to improvedynamical analysis speed of complicated power system. Under power marketenvironment, the operation of subsystems is comparatively independent and theparameters of a subsystem are relatively nontransparent to another subsystem. Tocomplete suitable dynamic equivalence between member companies, in this paper, thedynamic equivalent problem for multi-area interconnected power systems is analyzedto deal with such as data needs to be exchanged, the frequency of commutation, thequality request of exchanged data, how to get the correct data freely, and so on.In this paper, two distributed algorithms for coherent dynamic equivalence arepresented. Based on the time domain simulation algorithm, the system is splitted intosome sub-systems by bus cutting. System equations are realigned to get thedistributed computation form. While calculating in coordination, the data of voltageangle that connect to the cutting buses is exchanged at each time step. Then coherentgenerators are identified by coherent criterion. Based on the weak-coupling algorithm,the system is splitted into some sub-systems by branch cutting. Only a small amountof data between different subsystems needs to be exchanged to form sub-system statematrix, and then coherent generators are identified by weak-coupling algorithm. Onthe result of coherent generators identification, coherent generators are aggregated byinertial aggregation algorithm that is used at machine internal nodes, and network isreduced by current sink reduction method.The computer program based on the two distributed dynamic equivalencemethods is developed,and the examples on the 10-machine, 39-bus New EnglandSystem and the 50-machine, 145-bus System are given to validate the two methods.Through equivalence system and original system comparison of dynamic behavior, itis proved that the two methods presented by this paper are valid.