Modeling And Simulation Of Voltage Source Converter Based On Multi-Frequency Band Dynamic Phasor

With the development of China’s new energy and the continuous construction of high-voltage DC transmission projects,China has built the world’s highest voltage level and largest AC/DC hybrid power grid.With the large-scale application of VSC and other power electronic devices in the power grid,large-scale AC and DC power grids are facing problems such as complex equipment characteristics,multiple time scales,and large system orders.The latest simulation computing technology and hardware platform are needed to improve simulation.In order to ensure accuracy,traditional electromagnetic transient simulation adopts small step size,large calculation amount,and slow simulation speed,which is no longer suitable for the simulation of large-scale AC/DC hybrid power grids.It becomes especially important to establish a VSC simulation method with high accuracy and fast speed.This paper aims to establish an efficient and fast VSC simulation method,and the main research work is as follows:In this paper,the signal is Fourier decomposed,and the multi-band dynamic phasor method is obtained according to the ideas of signal decomposition and recombination,frequency offset and dynamic phasor method.This method determines the frequency band bandwidth according to the requirements of the simulation step size,and then divides the signal after Fourier decomposition into N sub-bands according to the divided frequency bands.And according to the idea of frequency shift,each frequency band is shifted separately to achieve the purpose of frequency reduction,so as to obtain the dynamic phasor model of each frequency band.Since each frequency band has been reduced in frequency,large-step simulation can be used to shorten the calculation time,and after decoupling between frequency bands,multi-core CPUs can also be used for parallel calculation to further improve calculation efficiency.Compared with traditional simulation methods,the multi-band dynamic phasor method can take into account simulation accuracy and simulation speed,and provides an accurate and efficient electromagnetic transient simulation method.In order to meet the requirements of multi-band dynamic phasor method for higher-order switching functions,this paper proposes a method for solving VSC higher-order switching functions.This method decomposes the PWM wave into pulse pairs,obtains the expression of each pulse pair,and then superimposes the considered pulse pairs to obtain the final switching function expression.The Newton-Raphson iterative method is used to solve the switching time of VSC,and the solution formula is simplified by combining PWM wave half-wave symmetry and three-phase symmetry.In order to improve the calculation efficiency of harmonics,this paper also combines the characteristic harmonic characteristics of VSC,and proposes a method of allocating frequency bands according to the harmonic characteristics of VSC,which can calculate more harmonics under the same conditions and improve the accuracy of the switching function.The higher order function formula herein substituting VSC switch state equation,the VSC form a switch function model,and then introduced into the switching function of multi-band dynamic model VSC phasors to establish the multi-band dynamic phasor model of VSC.In order to further improve the simulation efficiency,the VSC multi-band dynamic phasor model is decoupled,so that the various frequency bands are decoupled from each other,and the multi-core CPU parallel calculation can be used to further improve the calculation speed.