Research On DAB Dual Active Bridge Based On UFPS Modulation And COPS Optimal Control

As the core circuit of the next generation High-Frequency-Link Power-Conversion-System,Dual-Active-Bridge converter has been widely studied and applied for its advantages of symmetrical structure,bidirectional energy transmission,and easy of realizing soft switching.Aiming at the problems of high inductor current stress,small ZVS soft switching range and large reactive power return power in DAB converters under traditional control methods,this paper describes in detail the phase-shift modulation principle,transmission characteristics and soft switching characteristics analysis of DAB converters,and proposes Unified-Phase-Shifting modulation and current stress Comprehensive-Optimization-Phase-shift Control algorithm,specifically including the following research contents:In this paper,starting from the topology of DAB converter and SPS control method,the basic working principle,modal characteristics,transmission characteristics and ZVS soft switching characteristics of the converter under phase shift control are analyzed,and the main problems are pointed out,such as high reactive backflow power,high current stress and narrow ZVS realization range.In addition,the continuous-time domain full-order dynamic model of the DAB converter is established by combining the generalized average method,which establishes a theoretical basis for further research and analysis.Then,this paper proposes a UFPS unified phase-shifting modulation method.The mathematical model of the modulation method is established according to the switch state function and Fourier series,and DAB is introduced in detail from the operating mode and working mode respectively.The boundary constraints under different operating modes and the three-dimensional definition domain of corresponding operating points are derived,and finally the full working condition expressions of the inductor current and the transmission power function are obtained.For the ZVS characteristics,the necessary and sufficient conditions for ZVS realization are analyzed in combination with the inductor current flow path and the resonance energy,which are used to consider the soft switching characteristics in the full range.The proposed UFPS modulation method will greatly broaden the optimization range and control freedom of the DAB converter,and establish a foundation for global optimization design.Furthermore,this paper designs a COPS comprehensive optimization control algorithm for the inductor current stress,based on the inductor current and transmission characteristic equations in the full working range of the DAB converter,combinde with the mathematical characteristics of partial derivatives and total differentials,by setting up dimensionless parameters under the same transmission power,the influence of the disturbance of each operating point in the adjacent domain on the total increase of current stress is investigated.In addition,according to different operating modes,the global analytical solution of the optimization equation is solved,and the realization of the ZVS characteristics is verified by inversely substituting the coordinates of the operating point.In addition,through closed-loop control structure design,simulation results verify that the COPS optimal control algorithm can not only reduce the inductance current stress to the greatest extent,but also realize the ZVS soft switching characteristics of all switching devices in the full working range of DAB converter.At the end of this paper,an experimental platform for DAB converter is built and designed,and the theoretical analysis of the full text is verified by experiments,which confirms the feasibility and global optimization characteristics of the designed UFPS modulation and COPS optimization control algorithm.