Research On Model Predictive Control And Hybrid Modulation Strategy Of Multiport Interline DC Power Flow Controller

In a DC power grid with N converter stations,if there are more than N-1 lines,the converter station will not be able to independently control the power flow in all lines.Therefore,in order to improve the flexibility of power flow control in DC power grids,an additional type of device composed of power electronic devices,namely,DC power flow controller(DCPFC),has been introduced into DC power grids.Based on the basic work of establishing discrete mathematical models and analyzing modulation strategies,this paper mainly studies model predictive control and hybrid equivalent modulation strategies for multiport inter line DC power flow controllers against the background of multiport interline DC power flow controllers:(1)Firstly,This paper examines the topology and operation principles of Modular Multilevel Converter(MMC)and obtains a general dynamic mathematical model of IDCPFC by comprehensively considering the actual operating conditions of its installation in MMC-MTDC.After analyzing the topology and working principle of interline DC power flow controller IDCPFC,it also comprehensively considers the actual operating conditions of its installation in MMC-MTDC.Secondly,the advantages and disadvantages of the control strategies currently used by IDCPFC are introduced,leading to the significance of applying model predictive control strategies in the field of DC power flow controllers.Finally,using Inductor Sharing Interline DC Power Flow Controller(ISI-DCPFC),a special IDCPFC topology,a three terminal DC power grid electromagnetic transient model containing ISI-DCPFC is established in the MATLAB/Simulink simulation platform for simulation analysis,thereby verifying the working principle of IDCPFC.(2)Secondly,this paper proposes a model predictive control strategy suitable for Multiport Interline Power Flow Controller(MI-PFC).This paper establishes a dynamic mathematical model for a four-terminal DC power grid with a three-port MI-PFC.The model is then discretized using the forward Euler method.The discretized model can accurately represent the relationship between each control variable and the controlled variable,thereby achieving predictive output of voltage and current instructions,establishing the foundation for the MI-PFC model predictive control strategy designed in this article.Moreover,the established mathematical model is simulated and verified using MATLAB program,and the simulation results show that the mathematical model established in this paper is correct and accurate.This paper establishes a value function that includes line current and bridge arm voltage as control objectives for MI-PFC.To solve the multi-objective control problem,a weighting factor is introduced for normalization.The proposed model predictive control strategy is then simulated and validated using the MATLAB/Simulink simulation platform.(3)Finally,this paper proposes a equivalent hybrid modulation(EHM)strategy suitable for MI-PFC.By analyzing the topology and working principle of MI-PFC,a hybrid equivalent modulation strategy EHM based on equivalent level output mode of full bridge submodules is designed.This strategy can increase the equivalent output level of the bridge arm of the MI-PFC and solve the problem of high harmonic distortion caused by the small number of sub modules in the MI-PFC.Finally,a four-terminal DC power grid electromagnetic transient model with a three-port MI-PFC is built using MATLAB/Simulink for simulation verification.