Research On Optimized Modulation Strategy For Isolated Bidirectional DC-DC Converter

With the development of modern industry and society,the demand of energy is no longer limited to primary energy sources such as fossils,and green and clean energy has become necessary in the new era.Wind energy,photovoltaic and other new energy power generation have the characteristics of randomness,intermittency and uncontrollability,which have a certain impact on the stable operation of access to the grid.The hybrid AC / DC microgrid composed of power generation equipment,energy storage device and power grid can effectively solve the above problems.DAB converter is an important interface between new energy power and power grid.It can realize the bidirectional flow of energy,and has the advantages of simple and symmetrical structure,high power density,electrical fault isolation,and easy implementation of soft switching.In addition to the application in the field of microgrids,DAB converters also have important applications in new energy electric vehicles,DC solid state transformers,and electric traction.Therefore,isolated bidirectional full-bridge DC-DC converters have become a research hotspot.This thesis combines the development of modern power energy industry,briefly summarizes the application background and research status of isolated bidirectional fullbridge DC-DC converters,and clarifies the significance of its application in new energy.Focusing on studying the phase-shift modulation mode of DAB converter,this thesis introduces the principle of single-phase-shift modulation(SPS),extended phase-shift modulation(EPS),double-phase-shift modulation(DPS)and triple-phase-shift modulation(TPS),and proposes a unified phase-shift modulation model.Aiming at the above introduction of the principle of phase shift modulation,the mathematical models of converter transmission power,return power,current stress,etc.are established and their advantages and disadvantages are optimized.In order to improve the overall performance of the converter,the above-mentioned phase-shift modulations are comprehensively compared.Due to the simplicity of SPS modulation and the flexibility of TPS modulation,DPS modulation has become the most common modulation for DAB converter.In order to make full use of the advantages of twodegree modulation in dual-active-bridge converters,and reduce the peak current and the accompanying large backflow power of traditional DPS modulation under non-heavy load conditions,a novel dual-phase-shift(NDPS)modulation is proposed in this thesis.Compared with the traditional DPS modulation,the NDPS modulation has less reactive power and peak current under non-heavy load conditions,thereby improving the efficiency of the converter.Finally,an experimental prototype of the isolated bidirectional full-bridge dc-dc converter was built,and the design of experimental hardware and software was introduced.The experimental platform was used to realize the phase shift modulation,which verified the superiority and theoretical analysis of the performance of the novel dual phase shift in reactive power,current peak and efficiency under non-heavy load conditions.