Research On Multi-Rate Simulation Of Large Scale Renewable Energy Connected System Based On Time-Frequency Transformation And Identification Aggregation Theory

In recent years,with the rapid growth of wind power,photovoltaic and other renewable energy power generations,as well as the wide applications of HVDC converter equipment and flexible AC power transmission and distribution equipments,the power system has gradually become a complex large system with complex control system,large time scale span and high proportion of electrical and electronic equipment.The access of a large number of converters has greatly changed the basic structure and dynamic behavior of the power grid.For a long time,accurate time-domain transient simulation,as the basis of the whole system security and stability analysis and the basis of control and protection design,has always been the main means of system analysis.It is of great theoretical significance and application value to study the theory and technology of time-domain transient simulation,which can accurately consider the switching action of power electronic equipment and the dynamic process of control system.At present,the commonly used electromechanical transient,electromagnetic transient and electromechanical/electromagnetic hybrid simulation software are generally difficult to meet the requirements of the accuracy and rapidity of power electronic system transient simulation.The main reasons are as follows:(1)the transient stability analysis model is based on many assumptions,such as fundamental frequency,three-phase symmetry and lumped parameters,which is essentially only suitable for studying the electromechanical transient process of large power grid,not It can meet the accuracy requirements of detailed dynamic process analysis of AC/DC system including power electronic equipment;(2)the electromagnetic transient analysis model has a high degree of simulation for the actual physical system,and the calculation results are accurate,but it needs to adopt the minimum step size simulation(2-50 ?s).The same step length makes the calculation time-consuming;(3)the common electromechanical/electromagnetic transient simulation software uses equivalent circuit to simplify the AC system in different degrees according to the needs of the research object and the use scenario,which generally can not simulate the nonlinear dynamic response process caused by the generator and the transmission line,and the system interface has information loss.These problems need to be solved when studying the broadband dynamic process of large-scale renewable energy grid connected system.In order to solve the above problems,this paper studies the multi-rate simulation of large-scale renewable energy connected system,including the following contents:1)The time-domain transformation theory based on rotation coordinate transformation is used to model the components in large-scale AC/DC system.With this method,the instantaneous value waveform of the required research variable and the phasor value waveform under wide frequency can be obtained simultaneously,and the phasor value waveform is the envelope of the instantaneous value waveform.In the actual large-scale AC/DC system case test,by comparing with the traditional electromechanical transient model and electromagnetic transient model,the advantages of the modeling method in simulation accuracy,simulation efficiency and flexibility are verified.2)The modeling theory and identification aggregation model algorithm of wind power and photovoltaic converter are studied.Based on the topological structure of wind power converter and photovoltaic inverter,the corresponding mathematical model is constructed,and the operation strategy of controlling the inverter voltage is designed;based on differential evolution algorithm,the identification aggregation model and algorithm of wind power photovoltaic converter suitable for practical engineering application are proposed,and the model and algorithm are verified by comparing with the measured data of converters.3)In this paper,an interface model between frequency shifting quantum system and electromagnetic transient subsystem is proposed.The transmission line is modeled in detail by multi rate multimode model and multi frequency correlation multimode model,which is especially suitable for large-scale system simulation considering the detailed dynamic process of power electronics.In particular,the multi-frequency correlation multi-modal model can capture the high-frequency effects in the interface,and the two transmission line models can get instantaneous and phase domain models simultaneously.Based on these two transmission line models,the operation results of power electronic equipment in wide frequency can be obtained accurately.At the same time,a multirate joint simulation structure based on frequency shift model,network partition and multi rate multimode transmission line model is proposed,and the efficiency of the method is fully verified in the real case of large-scale AC power grid including wind farms.4)This paper presents a multi-modal hybrid simulation method based on timefrequency transformation for large-scale AC/DC power grid simulation including largescale photovoltaic station access.In this method,the system is divided into two parts:frequency-shift AC network subsystem based on time-frequency transformation and photovoltaic power plant subsystem based on identification aggregation.In the study,the photovoltaic station composed of multiple groups of converters is represented by a lumped identification model,and the dynamic response of the model is consistent with the overall measurement results of the photovoltaic station.The identification model of Photovoltaic Station is connected with the quantum system based on frequency shift phase by multimode transmission line model,which can ensure the accuracy of the simulation results of the whole system in wide frequency band.With this method,the PV Plant model can be updated by the identification based measurement method.In addition,the integrated model of photovoltaic power plant can be directly applied to multimodal simulation without building detailed component model,so it is especially suitable for practical engineering application.