Research On Control Strategy Of Ship MVDC System Based On MMC

The traditional AC power system is no longer sufficient to meet the increasing power demand.Medium voltage DC(MVDC)is becoming the trend of choice for the design of allelectric ships.Modular multilevel converter(MMC),as a power conversion device with research potential in ship MVDC systems,is more suitable for DC transmission systems.However,the control and research of MMC in the ship MVDC system and the parallel operation strategy based on MMC rectifiers have not yet been fully understood,and there is a lack of system-level modeling and control.This thesis uses MATLAB/Simulink software to build the MMC-based simulation model of the ship MVDC power system,which lays the theoretical foundation for the construction of the medium-voltage DC power system experimental platform.This article first studies the structural components of the ship MVDC power system,further analyzes and compares the principles,advantages and disadvantages and application scenarios of several commonly used rectifiers,and finds that the MMC rectifier has scalability and fast restart capabilities in the ship MVDC power system.,More suitable for high-density power applications in DC power grids.Then this article carries out detailed modeling and analysis of various parts of the ship’s MVDC power system,including the modeling of generators and MMC rectifiers.The various structures and control principles of generators and MMC rectifiers are analyzed,and their mathematical models are summarized and summarized.Simplified processing accordingly.This thesis further proposes the dual closed-loop control strategy of the ship MVDC system,and proposes an outer-loop control strategy that combines the DC droop method and reactive power control to deal with the power distribution problem during multi-unit operation.At the same time,the current inner-loop solution is proposed.Coupling control strategy.Aiming at the voltage sequencing and circulating current suppression problems of MMC rectifiers,this thesis proposes a voltage sequencing strategy for optimized sequencing algorithm and a general suppression strategy for double-frequency circulating current.The simulation model of each part is built in MATLAB/Simulink to form a complete simulation experiment model of the ship’s medium voltage DC power system based on the MMC rectifier.Finally,simulation experiments such as stability,sudden load reduction,and two-machine parallel connection were carried out on the built simulation experimental model.The test results show that the control strategy proposed in this thesis is designed correctly,and the model built has good steady-state characteristics and dynamic performance.The control strategy designed by the MMC rectifier can effectively achieve the balance between the capacitor voltage and the effective suppression of the circulating current.A relatively stable DC side bus voltage is obtained,which can provide stable power support for ship navigation and meet the design requirements of the ship MVDC power system.At the same time,it shows that the built model can more accurately reflect the actual operation of the ship MVDC power system,avoiding the high risk and high cost investment in the actual ship experiment.