Research On Dynamic Equivalent Methods And Evaluation Indices For Power Systems

With the rapid development of power system in various fields,integrated transmission systems of AC and DC has been formed,modern power systems is gradually grown up towards interconnection of large-scale regional grid.As a result,the scale and complexity of the power system have risen rapidly.Thus,how to guarantee safe and stable operation of large-scale power system becomes a significant and urgent issue.Modeling for large-scale power system is complex and the simulation efficiency cannot meet the requirements of rapid analysis and calculation.Using dynamic equivalence to simplify the system is an effective measure to solve this problem.Dynamic equivalence keeps the study area unchanged,and simplifies the external area without changing its dynamic impact to the study area.Coherent equivalence method is used to aggregate the coherent generator and simplify the network based on the Gaussian elimination method,which is the most commonly used dynamic equivalent method for large-scale power system off-line transient stability analysis.At present,the theory and application research of coherent equivalence are mature,but there are some urgent problems to be improved when the large-scale power system is simplified.The evaluation of the equivalent results is the basis to further optimization of the equivalence model,and currently there is no effective quantitative evaluation method.In view of above problems,this paper makes an intensive study of dynamic equivalence improvement methods and the quantitative evaluation index,meanwhile,a new dynamic equivalence procedure is developed.The improvement methods for dynamic equivalence include the improvement of the generator polymerization method,the negative resistance phenomenon study and the simplification of zero sequence networks.An equivalent model selection and optimization of equivalent generators based on the artificial fish swarm algorithm are proposed.This paper analyzes the causes of the occurrence of negative resistance lines,discusses its influencing factors,then puts forward a reasonable and effective negative resistance elimination method.In order to ensure the consistency of short-circuit current and dynamic response under the unsymmetrical fault between original system and equivalent system,this paper puts forward the zero-sequence network simplified method in detail.For the quantitative evaluation index,Prony algorithm is used to extract the dynamic characteristics of the system before and after the equivalence,then the similarity theory is used to define the frequency and damping similarity of the dynamic equivalent.The proposed indices can accurately quantify the approximate degree of the dynamic characteristics between original system and equivalent system,and can guide the optimization of the equivalent parameters.The existing dynamic equivalence procedures cannot meet the requirements of data compatibility,computational efficiency and equivalence accuracy at the same time.Based on the research results of this paper,a new dynamic equivalent software DSP-DES is designed and developed,application in China Southern Power Grid dynamic equivalent certificats its superiority.