Research On Efficiency Optimization And Power Balance Control Of Cascaded Double Active Full Bridge Converter

Considering the intermittent and fluctuating power generation of various distributed power sources in dc microgrid,the security problems such as stable operation and power supply quality are challenged.To solve this problem,experts and scholars proposed to add energy storage devices to the micro grid system to solve this problem.At present,the research of energy storage technology at home and abroad mainly focuses on how to obtain high performance bidirectional dc converter and energy storage medium.Therefore,this topic takes high-performance bidirectional dc converter as the research background,and considers the energy storage technology's own requirements on converter power density,transmission efficiency,bidirectional energy flow and so on.In this paper,the dual-active full-bridge(DAB)converter is selected as the research object.In order to meet the demand of DAB converter for dc power transmission and distribution capacity and voltage level improvement,a single DAB converter is required to be connected with input and output series and parallel combination.Therefore,this paper mainly focuses on the improvement of operation efficiency of DAB converter and the balanced power distribution of each module converter in the series and parallel combined system.Firstly,this paper introduces the basic working principle of DAB converter under phase shift control,and analyzes 6 working modes and power transmission characteristics of DAB converter under traditional single-phase shift(SPS)control.In order to solve the problem of large back-flow power and low efficiency of DAB converter under SPS control,an optimal back-flow power control strategy based on dual-phase shift(DPS)control was proposed.This method mainly establishes the mathematical model of back-flow power,voltage ratio and phase shift Angle between two operating modes under DPS control,and USES the derivative optimal solution idea to find the optimal combination of phase shift angles under different working conditions,and adopts piecewise optimization control to ensure the minimum loss of back-flow power and other indexes under full mode of DAB converter.At the same time,the simulation software Matlab is used to build the DAB converter model.The theoretical demonstration and simulation results show the feasibility of the back-flow power optimization strategy under piecewise control and the expected effect is achieved.Secondly,in order to meet the demand of DAB converter for high input voltage and high output current,this paper takes the input series multi-module converter system as an example to study the difficult problems such as power balance distribution control of each moduleconverter in the series and parallel combination system.Based on DPS control,an adaptive matching equilibrium control strategy with input voltage as control variable is proposed.In this method,the power model of the input series system is established,the disturbance shift Angle method is used to estimate the online equivalent system disturbance,and the goal of automatic equalization of the output power of each module converter is achieved.The theoretical analysis and simulation results show that when the parameters of each module of the system are not matched or the input voltage amplitude is not equal,the transmission power of each module of the system can be automatically balanced and the expected effect is achieved.Finally,in view of the module of power converter system more balanced control,established the mathematical model of the proposed control strategy and complete the relevant theoretical arguments,and use the simulation software Matlab to complete set ISOP system model,through theoretical and simulation results verified the ISOP system power equilibrium control strategy of advanced and scientific.