Researches Of Performance Optimization Technology In DAB Converter Based On The EPS Control Strategy

With the global energy crisis and environmental pollution,distributed new energy is rapidly developing,and this has greatly promoted the formation and development of DC distribution networks.As a key element in the technology,Dual Active Bridge due to fast dynamic responses and good power transmission capacities,has been avtively developed to achieve Buck or Boost voltage conversion and to control bidirectional power flow.Indeed DAB has gradually become the core circuit of DC solid-state transformers and is the key unit of DC load controlled in DC distribution networks.The DAB determines the overall performance of the DC distribution network.DAB performance optimizations have become a focus of the R&D community,and have extensive economic and practical significances.This thesis would start from two aspects of the reflux power and ZVS soft switching characteristics.Based on the analysis of the performance optimization of the DAB converter,this paper presentes a comprehensive optimal control strategy,and verifies the proposed optimal control strategy using the simulation and experimental prototype.The main contents of this thesis are as follows:Based on controlling the voltage of the DAB converter using the extended phase shifted control algorithm,models regarding the power transmission and reflux power are established.This thesis demonstrates the advantages of EPS(extended-phase-shift)control compared to other control algoithms.The thesis describes the working principle of the EPS control algorithms,analyzes the working process of DAB converter employing the EPS control,and establishes the model of transmission power and reflux power in each feasible control domain of the DAB converter,with comparisons to the reflux power characteristics of SPS(single-phase-shift)control.The above aspects have been verified by simulation.For the DAB converter in different operating modes,the optimal reflux power control strategy was proposed in the whole power transmission regions.According to the cause of reflux power,this study has indentified the zero return power control area in the feasible control region of the DAB converter,and solved for the zero return power region through mapping the zero return power control area to the power transmission characteristics of the DAB converter.Due to the difference of the return power characteristics in different operating modes,this study has analyzed the characteristics of reflux power in each mode,based in which an optimal power control strategy has been proposed.The thesis further presents the study on the ZVS soft switching characteristic of the DAB converter under the EPS control,establishes the ZVS soft switching control region of the DAB converter,leading to a comprehensive optimal control strategy by mapping the characteristics of ZVS with the reflux power characteristics.The thesis introduces the realization principle of ZVS soft switching technique,obtaines the realization condition of ZVS conductions of each switch according to the working process of the DAB converter,solves the ZVS control region of each switches in the feasible control region,and summarizes the ZVS control area of the whole DAB converter.Recognizing the difference of the soft switching characteristics in different operating modes,the thesis presentes a comprehensive optimal control strategy by combining the switching characteristics of ZVS with the reflux power characteristics.The above contents have been verified by simulations.Based on the principle of the DAB converter,this study has built a prototype DAB platform to verify the effectiveness of the proposed optimal control strategy by comparing of reflux power and soft switching characteristics of other control points and drawing the corresponding efficiency curve and the integrated optimal control at the same output power.