Research On Control Strategy Based On Five-level MMC Power Router

This paper studies an electric power router based on a five-level modular multilevel converter(Modular Multilevel Converter,MMC)power electronic transformer.Firstly,introduce the concept of Energy Internet,and summarize the research status of power router at home and abroad.And introduce the three-level architecture of power router based on power electronic transformer.Summarize the literature on MMC internal circulation suppression strategies in recent years.Secondly,analyze the working principle of the input,middle and output stages of the power router and establish its mathematical model to prepare for the design of subsequent control strategies.Then,when the MMC is running in a normal and steady state,a circulating current will be generated inside it,which will increase the loss of the MMC during operation and reduce the system reliability,in order to reduce the operation loss of the power router and improve the reliability.Therefore,the causes and components of the internal circulation of the MMC three-phase are analyzed,and the components of the internal circulation of the MMC and the laws of the harmonic generation of the circulation are obtained.According to the PI control-based circulating current double frequency suppression strategy proposed in the existing literature,a simulation model is built to verify its effectiveness.In order to further optimize the performance of circulating current suppression,this paper takes advantage of the strong robustness of sliding mode control,and proposes a sliding mode variable structure control strategy based on feedback linearized hyperbolic tangent function to suppress circulating current,by improving the switching function in sliding mode control and the law of reaching to weaken the chattering phenomenon.Using Matlab/Simulink software to establish a simulation platform,the proposed control strategy was simulated and verified,and its suppression effect was compared with the effect based on PI control and pure sliding mode control and the proposed control strategy.Finally,on the basis of suppressing the internal circulation of the MMC,the control strategies of the input,middle,and output stages of the power router are designed respectively,and the effectiveness of the control strategies of the input,intermediate and output stages of the power router is verified by simulation.Design the control strategy of photovoltaic and energy storage modules,add photovoltaic and energy storage modules to the power router simulation model,simulate and verify the dynamic performance of the power router control strategy at all stages when the photovoltaic output changes under the grid-connected and off-grid situations.