Research On Asymmetric Modulation And Control Technology For Dual Active Bridge Converters

In recent years,with the national goal of achieving the carbon peak in 2030,the promotion of new energy power generation and new energy vehicles is imperative.DualActive-Bridge（DAB）converter has the advantages of bi-directional energy flow,simple structure and easy to realize soft switching,etc.It has been widely used in medium and high power applications such as new energy storage system and electric vehicle charging system.However,the soft switching range of DAB converter becomes smaller when the input and output voltages are not matched,and the backflow power increases,leading to the problem of low light-load efficiency.The following research has been done to address these issues.1.An Asymmetric-modulation-Strategy for Compressed-Duty-cycle（ASCD）strategy that can improve the light-load efficiency is proposed for the problem of low light-load efficiency of DAB converters when the voltage is not matched.This strategy reduces the power transfer time by compressing the primary side voltage duty cycle of the DAB converter,reduces the forward and backflow power,and achieves soft switching and current reduction,thus reducing losses and improving the light-load efficiency.Compared with the conventional strategy,the backflow power,current stress,rms current,and soft switching are improved,and the conclusion that asymmetric duty cycle compression can indeed improve light-load efficiency is obtained at the theoretical level and verified by experiments.2.An Asymmetric-Phase-Shift（APS）modulation strategy that breaks through the existing symmetric modulation system of the DAB converter is proposed by expanding the modulation range based on ASCD.This strategy is a more generalized basic modulation strategy that includes eight secondary modulation strategies,including ASCD,and broadens the basic modulation scheme of DAB converters to an asymmetric range.A comprehensive analysis of the proposed APS strategy is carried out,including power characteristics,current stress distribution,soft switching range,backflow power distribution and root mean square current distribution.Many unique properties of the APS are obtained and the properties of the APS strategy are verified with hardware experiments.3.An APS-based optimal RMS current traj ectory hybrid modulation strategy is proposed.It is able to realize the full power range to achieve soft switching while significantly reducing light-load losses and improving light-load efficiency.For the proposed hybrid strategy,the optimal RMS target is established after loss analysis starting from determining the principle.The optimal RMS current trajectory was solved by the discrete fitting method,and the obtained traj ectory was modified by combining the soft-switching range to determine the final modulation strategy.It was also compared and analyzed with other strategies,and the conclusion that the light-load efficiency can be improved was theoretically determined,and finally the correctness of the theory was verified by experiments.4.A wide output range model predictive control technique based on the DAB bridge arm model is adopted for the problem that the traditional fixed frequency phase shift output range is not wide enough and the generality is poor.The forward power model and reverse power model are established based on the DAB bridge arm model,and the model is modified according to the problem.Finally,the steady-state and dynamic performance of the control algorithm is verified with simulation experiments.