| With the gradual replacement of traditional energy by renewable energy sources,the DC microgrid which can effectively utilize renewable energy has started to rise.The bidirectiona l DC-DC converter can play an important role in balancing the DC bus voltage in the DC microgrid due to the bidirectional energy flow.A series of bidirectional DC-DC converters can be constructed by using basic switching units.However,due to the limitation of the structure,it can only perform relatively simple single-phase-shift modulation,which will cause problems such as excessive backflow power.At the same time,the increase of the converter capacity needs to increase the number of energy storage units connected in series at the input end,which makes the voltage stress of the converter switch continuously increase.For a DC microgrid system with a large number of energy storage units,this paper proposes a construction method of a doubleinput bidirectional DC-DC converter.The constructed double-input converter is more flexib le and can realize dual-phase-shift modulation,which reduces the backflow power and current stress of the converter,and reduces the voltage stress of the switch under the same maximum transmission power.It has more advantages than the single-input converter and is worthy of research.Firstly this paper introduces the research status of bidirectional DC-DC converters,the basic switching units for constructing isolated bidirectional converters and the common construction methods of multi-input converters.By analyzing the working principle of basic switching units,the paper points out the method of constructing bidirectional DC-DC converter with different switching units.The construction method of the double-input bidirectional DCDC converter is obtained by extending the single-input switching unit to the double-input switching unit,and the different control methods are introduced.Secondly,the single-input and double-input bidirectional DC-DC converters are constructed by taking the primary-side Buck/Boost switching unit and the secondary-side fullbridge switching unit as examples,and the working principle,switching mode,energy flow characteristics and soft switching process and conditions of the two converters are described in detail.Then,the steady-state models of the two converters are established,and their steady-state characteristics such as transmission power,backflow power,current stress,and soft switching range are compared and analyzed.It is pointed out that the double-input converter has better steady-state performance than the single-input converter.At the same time,due to its greater control freedom,there is a certain space for optimization in converter characteristics such as backflow power.Therefore,this paper takes the backflow power as the optimization objective,derive the method of calculating the ratio of internal and external phase shift in detail which can minimize the backflow power,and makes a comparative analysis of the optimization effect.Next,the hardware design of the proposed double-input bidirectional DC-DC converter is carried out,including the design of the main power circuit and various auxiliary and control circuits,and the experimental prototype is developed.At the same time,the corresponding software process is designed according to the optimized control strategy.Finally,the converter model is built in Matlab / Simulink,and the working principle and optimized control strategy of the converter are simulated and analyzed.At the same time,an experimental platform is built to further verify the corresponding simulation results.Both simulation and experimental results show that the double-input converter can effectively reduce the backflow power and current stress and improve the steady-state performance compared to the single-input converter.At the same time,the optimized control strategy can further improve the steady-state performances of the converter,which proves the rationality of the proposed topology and the effectiveness of the control strategy. |
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