Research On Control Strategy Of Parallel Bidirectional DC/DC Converters

In recent years,a new round of energy reform begins with extensive development and utilization of new energy resources.We need large-capacity energy storage systems to better support renewable energy grid-connected.To meet the requirement of microgrid system capacity and the load power supply,this paper uses Vanadium redox battery(VRB)as energy storage unit,which is connected to DC bus by bidirectional DC/DC converter to form a parallel energy storage system.In parallel system,current sharing control and DC bus voltage control are very important.Therefore,the control technology of parallel bidirectional DC/DC converters is studied.The main research are as follows.Firstly,the mathematical models of VRB and bidirectional DC/DC converter are deduced and analyzed in detail,and then simulated in MATLAB/Simulink.Simultaneously,the effectiveness of models is verified.Secondly,VRB is used as energy storage unit and bidirectional DC/DC converter is used as interface to connect to DC bus,forming a single VRB energy storage system.When charging,charging control strategy of first using constant current then using constant voltage is adopted to obtain energy from DC bus.When discharging,discharging control strategy of double closed-loop control strategy is adopted to supply power to load with certain power and ensure the output voltage is consistent with bus voltage.Simulation results validate the effectiveness of the strategy,achieving the control of single VRB energy storage system.Thirdly,energy storage module composed of VRB and DC/DC is connected in parallel to build a parallel DC/DC converters energy storage system.Based on the average current scheme,a modified average scheme is proposed.This scheme uses three closed-loop structure,which includes a current-sharing loop,a voltage loop and a current loop.The given current is from the power required by load in DC microgrid.so as to improve the dynamic response and voltage stabilization performance of system.Then,the stability of the parallel system with modified average scheme is analyzed in detail by using Bode and Rootlocus analysis method.A model of parallel DC/DC converters energy storage system is built in MATLAB/Simulink to verify the feasibility and effectiveness of the proposed scheme.Results show that under the proposed scheme,the system has good current-sharing effect and fast dynamic response.And when considering output line resistance,the DC-bus-side voltage can still stabilize at the ideal value.Finally,semi-physical platform based on TMS320F28335 is built to further verify the feasibility and effectiveness of the proposed scheme.