| Against the background of energy crisis and environmental pollution,it is becoming more and more urgent to promote the development of new energy sources characterized by renewable and pollution-free.Bidirectional DC/DC converter has advantages of bidirectional power flow,high power density and high efficiency.And it is widely used in the field with bidirectional energy flow,including distributed energy generation system,energy router,electric vehicle,uninterruptible power supply,etc.Dual Active bridge(DAB)circuit is a typical isolated bidirectional DC/DC converter topology.With the characteristics of simple circuit structure,easy control,bidirectional power flow capability and easy to realize soft switching,it has become one of the hot research topics.In this paper,this kind of converter is studied in depth from optimizing the modulation strategy to improve conversion efficiency,broadening the topological gain characteristics and multi-port input characteristics.By analyzing the equivalent circuit of DAB,the circuit units that produce square-wave voltage source and the modulation method,operating modes and steady-state characteristics of the phase-shifting circuit are analyzed and summarized in detail.For phase-shifting circuit of the square-wave voltage sources with dual-active full-bridge unit,the mathematical model of the absolute average current with extended phase-shift modulation is derived.And an optimal modulation method of rectified mean current is proposed.According to the different voltage gain and output power,the inner phase-shifting angle of full bridge is selected for segmental modulation to improve system conversion efficiency.The prototype of 1.5 kW is established for verification.In order to adapt the center-tap dual active bridge circuit to step up and down voltage conversion with characteristic of soft switching in full power range,an improved dual active bridge bidirectional DC/DC converter with four-winding transformer is proposed.This converter is based on the traditional DAB by drawing out the center taps in the primary and secondary windings of the transformer.And the center taps are connected to the midpoint of the two voltage divider capacitors,respectively.Adopting triple phase shift control,the improved converter preserves the advantages of the traditional DAB.And the center taps from both sides can provide an inverted zero-voltage turn-on current for the power switches with the worst soft-switching conditions at low power levels.Firstly,the topological evolution process and the basic circuit structure of the improved DAB converter are introduced,and its angular equivalent circuit model is derived in this paper.Secondly,the operating modes,the steady-state operation process,the characteristics of soft switching and power transmission are analyzed in detail.Finally,the experimental prototype of 1 kW is established to verify the correctness of the theoretical analysis.In order to meet the needs of the integrated transformation of the photovoltaic storage system,a semi-isolated dual Buck/Boost and DAB integrated three-port bidirectional DC/DC converter is researched in this paper.On the basis of DAB circuit,two interleaved bidirectional Buck/Boost circuits are integrated by multiplexing active full-bridge unit at the primary side.The converter can be applied in the field of photovoltaic and battery combined power supply system.The modulation method,steady-state operation modes,power transmission and soft-switching characteristics of the three-port converter are analyzed.Finally,the feasibility of the topology is verified by experiments. |
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