Modeling And Simulation Of Medium Voltage DC Power System Based On MMC

Ship integrated power system combines power system with propulsion system,which improves system efficiency and saves fuel remarkably.It is a new direction of ship power development.Aiming at the lack of System-Level Modeling and control in medium-voltage DC power system,this thesis builds a simulation model of medium-voltage DC(MVDC)power system based on modular multilevel converter(MMC)by using MATLAB/Simulink software,which lays a foundation for the construction of experimental platform of medium-voltage DC power system.Firstly,this thesis describes three kinds of structures existing in ship medium voltage DC power system,and analyses their working principles,illustrates the advantages and disadvantages of various structures and the applicable scenarios,and further compares the current rectifiers used on ships.By comparing and analyzing the advantages of full bridge modular multi-level converter rectifier applied in ship MVDC power system.Secondly,the detailed modeling and analysis of each part of MVDC power system are carried out,including speed regulation system model,excitation system model,synchronous generator model and MMC rectifier model.The structure and control principle of each part are analyzed,and its mathematical model is summarized and simplified accordingly.The double closed-loop control strategy of ship MVDC system is further proposed.In the outer loop,because of the power distribution problem of multi-machine,the control strategy combining DC voltage sag method with reactive power control is used;in the inner loop,the current inner loop decoupling control is used.The simulation models of each part and the double closed-loop control strategy are built in MATLAB/Simulink to form a complete simulation experiment model of ship medium voltage DC power system based on MMC.Finally,the simulation experiments of stability,sudden load,short circuit fault on DC side and parallel connection of two generators are carried out on the built simulation model.The results show that the control strategy adopted is correct,the model has good steady-state characteristics and dynamic performance,meets the design requirements of MVDC power system of ships,and can provide stable power support for ships’ navigation.At the same time,the test results show that the built model has good steady-state characteristics and dynamic performance.The model can accurately reflect the actual operation of MVDC power system,and avoid the high risk and high cost of the actual ship experiment.