Studies On External Equivalence Of Power System

Now the power system is interconnected. When analyzing the state of the internal system on-line and off-line, the information of the external system does not send to the dispatching center. But the operation of the external system has important effect on the analysis of the internal system, so it requires external system equivalence. The reasonable equivalent model affects to other software application of the energy management system.In this paper the equivalent model is a static equivalent model. It bases on the state estimate or power flow calculation. It includes buffer system and uses the extended Ward equivalent approach. Based on the sensitivity analysis and the principle of reciprocity, this paper presents the method of selecting the important branches and buses by changing the voltage of the boundary bus and then analyzing the response of reactive power in the external branches. The important branches and buses constitute the buffer system. The rest of external system reduced to an equivalence using the extended Ward equivalent approach. Use Gauss elimination method to calculate the equivalent parameter.With the developing of DC transmission technology, the algorithm of the AC/DC system is also improved. Now the improved algorithms include power flow calculation, state estimation and optimum power flow etc. But there are few relevant researches which describe how to deal with the DC branches in external equivalence. In this paper, based on the studies of the external equivalence, presents the idea which uses the AC branch to instead the DC branch, then reduce the external system, and from the aspect of theory illustrates the algorithm is correct.In this paper, using the extended Ward equivalent reduce the external system and form an external equivalent model including a buffer system. Write the program and use the actual network and data of the Liaoning power system to test the model and the program. Outage the branch near the boundary bus testes the accuracy of the external equivalent model including the buffer system.Reduce the AC/DC system which includes DC branch in external system,...