Control Researches Of The Rectifier For Ship Electric Propulsion System

Due to its special function,electric propulsion ship have been irreplaceable role in the development of modern ships.The power factor of the existing electric propulsion ships rectifier is low,the existing rectifier allows a large number of harmonics injected into the ship’s power grid,seriously affect the normal operation of ships.In order to replacethe traditional phase-controlled and non-controlled rectifier,diode-clamped three-level rectifier is applied to eliminate the main source of harmonics in ship grid.Ship three-level rectifier simulation model is built,and several key issues about three-level rectifier were studied and improved.Firstly,this thesis selected the diode-clamped three-level topology as rectifier’s main circuit structure.The working principle is introduced,it’s mathematical model is deduced in the synchronous rotating coordinate.Next,the principle and realization method of three level SVPWM are illustrated.Instead of traditionalregiondetermination method,a new regiondetermination method base on 12 boundary linerelative position encodingis applied in this thesis.The three-level SVPWM generator simulation model is built,the resultsverified the correctness of the new regiondetermination method.Third,the structure of double closed-loop direct current control system which based on current feed-forward decoupling linkis deduced.The tuning process of PI parameters is introduced.The model of ship electric propulsion system using three level rectifier is built in MATLAB/SIMULINK,and the actual operation performance of three level rectifier in the ship electric propulsion system is analyzed.In order to improve the poor voltage tracking ability of the traditional PI regulator,the traditional PI regulator is improved by using an advanced anti-windup control structure and this new structure is verified in rectifier simulation model.Finally,we mainly focus on the research of neutral point voltage offset problem in diode-clamped topology.The cause and harm of neutral point voltage shift are introduced,and the neutral point current generated by each basic voltage vector is summed up.This thesis proposed a new neutral point voltage control method based on voltage balance factor method and virtual voltage vector method.The new method proposed in this thesis is applied to the model of three level rectifier,and the simulation results are analyzed.After the research,Diode clamped three-level PWM rectifier can control the harmonicwithin the minimum range,and can keep the DC side voltage stability.The control strategy proposed in this thesis completes the rectification task well.The new neutral-point voltage control method proposed in this thesis can also maintain the balance of the neutral-point voltage.