Research On MMC Circulating Current Suppressing Controller Based On Bridge Arm Common-Mode Voltage

The vast area and uneven distribution of natural resources are the characteristics of the distribution of natural resources in my country.Modular Multilevel Converter（MMC）is a representative solution to solve the problem of cross-regional electric energy deployment to alleviate the uneven distribution of natural resources.It has the advantages of low economic cost and high transmission efficiency in the long-distance transmission of high-voltage and high-power.,This article takes the MMC topology of the half-bridge sub-module as the research object,and conducts the following researches:（1）The topology and basic operating principles of MMC-HVDC are introduced.It focuses on the mathematical model of MMC-HVDC and the three-level control method.According to the basic assumptions of the MMC mathematical model,the average value model and the differential equation model based on the switching function are established for MMC.Finally,the three-level control strategy of MMC-HVDC is introduced,which lays the theoretical foundation for the subsequent research work.（2）Aiming at the problem of MMC circulating current suppression under the condition of balanced load in the power grid,a MMC circulating current suppression strategy based on the bridge arm common mode voltage（BACMV）is proposed.First,based on the average value model of the switching function,the mathematical relationship between the second harmonic component of the common-mode voltage of the bridge arm and the circulating current is deduced in d^-2q^-2rotating coordinate system,and it is proposed to establish the common-mode voltage of the bridge arm—the circulating current.Double closed-loop controller to suppress the MMC circulating current controller structure,in the MMC-HVDC model built by Simulink,through the analysis of the traditional PI and PR circulating current suppression effects,it verifies the effectiveness and feasibility of the BACMV circulating current suppression strategy proposed in this paper.Sex.（3）Aiming at the MMC control problem under complex AC grid conditions,the synchronization technology and control technology of MMC under the conditions of grid voltage imbalance and distortion,the control technology to ensure the stability of the bus voltage when power is supplied to the passive network,and the circulation suppression strategy are respectively studied.Using BACMV-based return suppression strategy,a dual-terminal MMC-HVDC simulation system was established in MATLAB/Simulink.Among them,the AC grid as the rectifier side of the sending end is the unbalance and distortion condition of the grid,and the inverter side as the receiving end is the point-to-point power supply to the passive network.The simulation results show that the MMC control strategy is practical under complex AC grid conditions,and the MMC circulation suppression strategy based on BACMV is equally effective under two complex AC grid conditions.This research was funded by Foundation of Liaoning Educational Committee,grant number LJ2019JL013 and project supported by discipline innovation team of Liaoning Technical University（LNTU20TD-29）.The paper has 29 figures,5 tables,and 58 references.