Research On High Efficiency Multi-objective Optimized Control For Hybrid Three-level Dual Active Bridge DC/DC Converter

In energy storage system,electric vehicle,solid-state transformer and other applications,it is necessary to achieve electrical isolation and bi-directional power regulation through isolated bi-directional DC/DC converter.Dual active bridge converter(DAB)can meet the needs of the above applications.At the same time,due to the advantages of less passive components and flexible control,DAB is a prosperous candidate for these applications.The switching current of each device of the traditional two-level DAB converter is difficult to accurately control in the situation where the terminal voltage varies widely,and the soft switching range is limited,which is not conducive to further improving the power density and efficiency.The multi-level DAB converter increases the degree of control freedom by introducing the controllable middle level,so it can control the inductance current more flexibly,which provides an effective way to solve the above problems.Hybrid three-level DAB(H3L-DAB)converters use a three-level and two-level hybrid structure.Compared to the traditional two-level DAB converters,only two switches are added.The device has simple structure and controllable cost,and has good practical value.This thesis takes H3L-DAB converter as the research object.Firstly,this thesis evaluates the working principle of H3L-DAB converter under PWM+ phase shift control in detail,and the operating process is divided into different working modes.Meanwhile,several common working modes are selected to be investigated.The working principle and the soft switching characteristics of the converter are analyzed.Then,for the application of hybrid three-level dual-active bridge converter under the condition of high input voltage and high output current,a multi-objective optimization control strategy is proposed,in which multiple optimization objectives are considered and the modulation strategy is comprehensively optimizeed.The optimizing targets includes: ZVS is realized to reduce the on loss of high-voltage side devices;ZCS is realized to reduce the off loss of low-voltage and high current devices;the effective value of inductance current is decreased to reduce the on loss of switching devices and copper loss of magnetic components.Due to the significant reduction of switching loss,the multi-objective optimal modulation strategy can further improve the efficiency compared with the single objective optimal modulation strategy only considering the conduction loss,which is conducive to the improvement of switching frequency and power density of the converter.Finally,an experimental prototype based on GaN devices is built in the laboratory,and the optimal design method of H3L-DAB converter is given.The correctness of the converter principle and the effectiveness of the proposed control strategy are verified.