Study On Smooth Transition Control Of Charge/Discharge Of Bidirectional DC/DC Converter For Ship MG Energy Storage

In marine DC microgrid,energy storage bidirectional DC/DC converter maintains system power balance and DC bus voltage stability through charge discharge switching.In the process of charge discharge switching,the reversal of energy flow direction makes the converter prone to voltage and current disturbance,so the smooth charge discharge transition of bidirectional DC/DC converter has important academic significance and practical value.Aiming at the demand of smooth charge discharge transition of bidirectional DC/DC converter,this paper designs adaptive voltage outer loop control strategy,adaptive current inner loop control strategy and a set of bi-directional DC/DC converter experimental platform,which can be used to reduce unnecessary charge discharge switching of energy storage unit,improve dynamic performance of charge discharge and verify the feasibility of the proposed strategyFirstly,the background,significance,research status at home and abroad of marine DC microgrid and the control strategy of bi-directional DC/DC converter with energy storage are reviewed in detail.Aiming at the unnecessary charging and discharging switching problem of bi-directional DC/DC converter with energy storage in frequent charging and discharging switching state,a charging and discharging control strategy based on adaptive voltage outer loop is proposed,The voltage outer loop divides the energy storage unit into three working modes: charging,discharging and idle,and adaptively switches the working mode according to the bus voltage,thus reducing unnecessary charging and discharging switching on the premise of keeping the bus voltage stable.Secondly,in order to improve the dynamic performance of bidirectional DC/DC converter and solve the problem of insufficient dynamic performance of traditional linear controller in charge discharge switching,an adaptive current inner loop is introduced based on the voltage outer loop,which can adjust the feedback coefficient adaptively according to the feedback error,Thus,through the cooperation of the outer voltage loop and the inner current loop,the bus voltage stability can be maintained and the charge discharge smooth transition of the bi-directional DC/DC converter with energy storage can be realized.Then,the simulation verification of the proposed control strategy is carried out in the simulation environment,and a set of charging and discharging experimental platform for energy storage bidirectional DC/DC converter is built.The hardware part of the platform includes bidirectional DC/DC main topology circuit,IGBT driving circuit,sampling circuit,STM32 main control circuit and auxiliary power supply module,The software part of the platform includes voltage and current double closedloop control program,PWM output program,ADC+DMA sampling program,etc.To sum up,this paper studies the charging and discharging control strategy of bidirectional DC/DC converter from two aspects of voltage outer loop and current inner loop.Finally,detailed simulation and experimental verification are carried out based on the Simulink simulation model and bidirectional DC/DC converter charging and discharging experimental platform.Simulation and experimental results show that the proposed control strategy can effectively improve the dynamic performance of bidirectional DC/DC converter,shorten the charge discharge switching time,reduce the voltage and current overshoot,and improve the dynamic response speed.