| Energy and environmental problems are becoming more and more serious,the global energy structure is rapidly adjusting,and the development of clean and low-carbon renewable energy is ushering in new opportunities.In response to the development trend of the power system with a high proportion of new energy access,the concept of electric energy router(EER)came into being.As the core equipment for realizing energy conversion in EER,power electronics transformer(PET)plays a key role in it.Hybrid three-level DAB(hybrid-three-level dual-active-bridge,HTL-DAB)converter has the advantages of high withstand voltage level of three-level topology and large current output of two-level full bridge,which is widely used in PET DC-DC converters.Popular in interface converter applications.However,the topology of the HTL-DAB converter is different from the classical two-level DAB,and there are still many deficiencies in the optimization of the system’s steady-state operating characteristics and dynamic response performance.This paper takes the HTL-DAB converter as the research object,analyzes its working principle and operating characteristics,establishes its mathematical model,optimizes the system control algorithm,and verifies its effectiveness through simulation and experiments.The specific work arrangement of this paper is as follows:Firstly,the topology of the HTL-DAB converter and the working principle of the PWMPS(Pulse Width Modulation Phase Shift,PWMPS)control strategy are introduced.Under the control of PWMPS,the Switching sequence working modes of the converter and its 12 types are analyzed according to the different switching states.The transmission power and current stress models in different modes are established.The KKT(karush-kuhn-tucker,KKT)conditions are used to optimize the system operating current stress,and then a steady-state optimization control strategy based on hybrid three-level DAB converter is proposed.The steady-state optimization control strategy is used to adjust different switching sequence combinations to make the converter meet the soft switching conditions while achieving the minimum current stress operation,thereby reducing the on-state and switching losses and improving the converter efficiency.Secondly,a state-space average model of all operating conditions suitable for 12 working modes of HTL-DAB converter is established,and the controller based on the state variable feedback exact linearization mode of HTL-DAB converteran is designed.An optimal control of transient current based on switching sequence reconstruction is proposed.The strategy reduces the DC bias current,reduces the transient current stress,and improves the dynamic response performance of the system by inserting the transition state of the half switching cycle when the switching sequence changes abruptly.Thirdly,in view of the inherent secondary voltage ripple problem of the DC bus in the power electronic transformer,the ripple suppression principle based on the secondary pulsating power transfer of the DAB converter is analyzed.For the Input-Independent OutputParallel(IIOP)structure of the converter,the secondary ripple voltage suppression strategy of the virtual power unit is used to suppress the voltage ripple of the high-voltage side DC bus.Based on the principle of symmetrical pulsating power superposition and cancellation,the lowvoltage side busbar voltage ripple is reduced,and the filter volume is effectively reduced.Finally,the experimental verification platform of HTL-DAB converter is built.Firstly,the hardware and software design of the experimental platform is introduced.The hardware design part mainly includes the selection of switching devices of the main circuit.The structural design of auxiliary circuits such as sampling,signal conditioning and control.The software part mainly includes the introduction of the control architecture and the control program;The effectiveness of the algorithm proposed in this paper is verified by experiments on the experimental platform. |
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