Research On Efficient Electromagnetic Transient Modeling And Parallel Simulation Methods Of Power Electronic Transformer

Power electronic transformer(PET),which is also called solid-state transformer(SST),plays an important role in achieving of large-scale AC-DC hybrid power grid and new energy grid-connection because it has distinctive performance in aspects of power collection and comprehensive regulation of various energy forms.However,due to the characteristics of many nodes,high frequency and small simulation step,the detailed electromagenetic transient(EMT)simulation efficiency of PET based on PSCAD/EMTDC separation components is extremely low,which seriously affects the efficiency of scientific personnel.Therefore,the construction of an efficient PET electromagenetic transient equivalent model and efficient simulation method have important engineering ignificance.Regarding the issue above,the main works of this paper are as follows:Firstly,a high-speed equivalent modeling method using admittance unit prestorage was proposed focuse on cascaded H-bridge(CHB)PET,a classical topological of PET.Power module is divided into different admittance unit circuits according to whether admittance is fixed It is deduced that H bridge with time-varying admittance contains only two kinds of equivalent admittance from perspective of loaded two-port.The admittance parameters of each unit are prestored,and the short-circuit current of port is calculated by superposition theorem,then equivalent circuit parameters of power module can be obtained quickly,and equivalent model of PET can be formed.In PSCAD/EMTDC,simulation and comparison tests are carried out with detailed model built by discrete components to verify the accuracy and acceleration effect of proposed equivalent model.Secondly,in order to optimize simulation accuracy of model,error analysis of PET electromagnetic transient simulation and optimization selection of time step were carried out from perspective of time domain and frequency domain.It is verified by simulation that improper step size selection will lead to larger error,and the influence mechanism of simulation error is analyzed from the perspective of numerical integration.In time domain,the truncation error was used to characterize local error characteristics of the system.On this basis,the maximum simulation time step was obtained based on the relative root mean square error.Considering the particularity of resonant converter system,a simulation step selection method based on discrete admittance relative error in complex frequency domain is proposed.After considering the time domain,frequency domain simulation errors and constraints of control system,the optimal selection scheme of PET simulation time step is given.Finally,in order to further improve simulation efficiency and CPU utilization,a PET multithreading parallel simulation framework is proposed,and the idea is provided for applicability of proposed equivalent algorithm.The parallelism of PET algorithm with admittance unit prestored is analyzed,and OpenMP parallel computing interface is called to realize parallel operation of independent sub-functions of each module,and influencing factors of parallel effect are analyzed theoretically.The simulation results in PSCAD/EMTDC show that proposed parallel simulation method retains the accuracy of original equivalent algorithm completely,and can achieve two to three times speed of original equivalent model.