Aggregation Of Dynamic Equivalence For Power System

With the expending scale of local power system and the formation of nation wide inter-connected power sytem, the amount of generation units and other composing components incease acutely, such that the burden of simulation and analysis of electromechanical transient process of power system are increasingly onerous. To alleviate the simulation burden of electromechanical transient process such as power system transient stability and catch the predominate dynamic characters of the power system quickly, the method of dynamic equivalance of power system is still important, though the ability of computer has elevated much nowadays, especially in the online and real time dynamic security assessment and the decision-making of preventive control. In dynamic equivalence methond an entire power system is to be divided into a study system and sevral exterior systems. Its principle is to replace the influence of the exterior systems to the study system by the approximate influence of simplified exterior systems.Dynamic equivalence of power system is comprised of three parts: identification of coherent generator group, reduction of network and parameter aggregation of coherent generators. This paper firstly introduces the basic concept of dynamic equivalence and the status of both domestic and abroad development. It specially introduces parameter aggregation of dynamic models and mainly analyzes the frequency domain method, which is mostly adopted by engineering grade softwares. The problem, brought by the frequency domain method, is that the calculation time is too long for the extremely complicated aggregation models. So this paper presents a practical method of parameter aggregation of coherent generators' detailed models, which is based on the weighting method. Parameters of equivalent generator units and its voltage and power control system'detailed models can be obtained by using this method. This method does not only aggregate parameters successfully and guarantee the precision of simulation, but also reduce the time of calculation greatly.Secondly, the model of induction motor is most common of all dynamic load models, in electrical power system simulation. Moreover, the parameters of induction motor model, which adopted in our country, are always the"typical parameters". It is demonstrated by research that the"typical parameters"of induction motor model cannot suitablly describe the practical composite dynamic load. To improve the model of practical composite dynamic load, this paper presents a practical method of parameter aggregation to induction motor groups, which is based on the weighting method. It is proved that this method cannot only aggregate parameters successfully by the simulation of simple distribution system. It may act as a powerful technique in developing an effective way to obtain a more acceptable model of composite dynamic load.