Studies On Smart Gird Oriented Generalized Synthesis Load Modeling

Informatization, digitization, automation and interaction are the main features of smart grid and it’s the mainstream of the development of power grids all around the world. On the background of the construction of smart grid, opportunities and challenges are brought about in the research of power system load modeling which are deriving from the informatization and interaction of power systems. Reasonable power system synthesis load model provides reliable support for the operating, planning and designing of smart grid, this dissertation realizes the real time synthesis load modeling that is based on the real time datum of daily load profile of SCADA and load control system. Using Simulink as a platform for building the simulation system of squirrel cage induction generator(SCIG)and doubly fed induction generator(DFIG), then the electromechanical model of DFIG, the generalized synthesis load model that takes distributed DFIG into consideration and the generalized synthesis load model that takes distributed SCIG and DFIG into consideration simultaneously are constructed. Specific contents are as follows:(1) To copy with the random time variation and regional divergence of synthetic load model, a daily load curve-based online method to modify substation’s structural proportion of synthetic load for power consuming-industries is proposed. According to different load levels, each year is divided into five load level periods, i.e., peak-load period in summer, valley-load period in summer, peak-load period in winter, valley-load period in winter and common-load period; typical daily load curve for each period is chosen and in each period four characteristic parameters, i.e., the load rate, maximum load rate, peak-valley difference rate and the occurrence time of maximum load are defined; by use of fuzzy C means clustering algorithm, the substations are classified and characteristic vectors of various types are obtained. Utilizing pattern recognition, the typical membership relation between characteristic vectors of various types of substations and industrial characteristic matrix obtained by clustering typical daily load curve of load control center is built and the typical mapping relation between the membership relation and substation’s structural proportion of synthetic load for power consuming-industries obtained by statistical synthesis is constructed. Thus, through combining the membership relation obtained by measured daily load curve of substation with typical mapping, online real-time modification of substation’s intraday structural proportion of synthetic load for power consuming-industries can be realized.(2) For the purpose of improving the accuracy of the load model and aiming at the time-variation problem of the synthesis load characteristic of substation in a daily period, on the basis of the above analysis and research, this paper proposes an algorithm for the revising of the parameters of load model of substation in different periods during a day. Firstly the ability in extracting load characteristic of different kinds of feature parameters were analyzed through qualitative analysis and measured active power was chosen as the characteristic parameter when takes modifying model parameters in different daily periods into consideration. Secondly, on the basis of the clustering centers of substations and synthesis daily load profiles of typical industries, the weight of every parameter in different daily periods was calculated via super weighting method. Then the real time synthesis load proportion of classical industries was computed based on the single element judgement sets in different daily periods and the weight of the parameters which corresponds to the same period by means of fuzzy comprehensive judgement. At last, the load model parameters of substation in different daily periods was worked out through combining the real time proportions and typical industrial parameters which were derived by other methods. The algorithm proposed by this paper was compared with the method which was based on the whole daily load profile and with the traditional component-based approach method respectively, the results show that it is rational and effective.(3) A load modeling oriented electromechanical model of DFIG was proposed. Firstly, the operating mechanisms of DFIG was analyzed deeply and ideas for equivalencing and the electromechanical model structure of DFIG were presented. Secondly, the transient equivalent model of DFIG was constructed, the description of the control procedure of rotor voltage was focused on and the mechanism relation among stator voltage, model response and rotor voltage was established. The strategy and the flowchart of model identification were presented. Once more, a DFIG simulation system were built and the dynamic model of DFIG was validated in different operation conditions, the description ability and stability of model parameters was analyzed. Finally the conclusion was made and the future work was proposed.(4) The distribution network-side generalized synthesis load model(GSLM) is constructed. Firstly, the analysis are fixed on the model structure of DFIG and induction motor, the necessary conditions for using the electromechanical model of DFIG to describe the induction motor were proposed and feasibility of them was evaluated, then the unified induction motor(UIM) was built for describing the transient characteristic of DFIG and induction motor during the transient course. The validation of UIM model was also made. Secondly, the UIM model was combined with the traditional distribution network-side synthesis load model and then GSLM was proposed that is composed of distribution network equivalent model, model of UIM, static load model and the compensation model of reactive power. At last, the effectiveness of GSLM was validated under different operating conditions and wind speed levels.(5) For the analysis of the penetration of SCIG and DFIG’s influence on the operation of distribution network, the IEEE-14node typical distribution network simulation system was constructed. Under the condition of different grid capacity and grid position, the capacity of SCIG and DFIG was combined and the grid form such as centralized and decentralized were applied on the wind power generator. The simulation results show that the synthesis load characteristic of distribution network is affected dramatically with the increasement of the penetration capacity of wind power generator. For analyzing the change of the synthesis load characteristic of distribution network, following the thinking above, based on the model of unified induction motor(UIM), the transient equivalent model of synthesis power source(SPS) that contains SCIG and DFIG simultaneously was constructed and furthermore the effectiveness of the model was verified. Finally, the equivalent model of SPS was integrated with the traditional distribution network-side synthesis load model for deriving the distribution network-side generalized synthesis load model that contains SCIG and DFIG. Model identifications were applied and the fitting results show that this generalized synthesis load model can make a perfect description on the transient behavior of distribution network-side synthesis load characteristic.