Research On Topology Of High Gain DC/DC Converter Based On Coupled Inductor

In DC microgrid system,the diversity and fluctuation of microgrid elements bring new challenges to the design of power electronic interface equipment and greatly promote the development of relevant technologies.For example,the unidirectional and bidirectional DC/DC converters,applied to power generation and energy storage systems,need to achieve high voltage gain,high transmission efficiency and low input current ripple.When the duty cycle of switch approaches to 1,the conventional buck/boost converter can achieve infinite voltage gain,theoretically.However,it’s not suitable for DC microgrid system in practice,as the output voltage is still limited with the influencing of parasitic resistance.The construction of high gain DC/DC converter with superior performance has become a hotspot of research,currently.Coupled-inductor is a magnetic device that combines an inductor and transformer,and it’s often used in the construction of high gain DC/DC converters due to the advantages of good voltage regulation ability and high power density.However,the inherent leakage inductor and current ripple will increase the difficulty of topology design for high gain DC/DC converter.On the basis of coupled-inductor structure,this paper explores the energy recovery and current ripple suppression techniques,and then proposes unidirectional and bidirectional converters with high voltage gain.The main contents of this thesis are organized as follows:(1)In view of the insufficient of the existing coupled-inductor based unidirectional converters,a high gain DC/DC converter with low current ripple is proposed in this paper.The topology is constructed by introducing coupled-inductor and switched-capacitor techniques into two-level cascade boost circuit.Finally,the feasibility of the structure is proved theoretically and experimentally.Furthermore,two topologies are derived on the basis of above research.One is ultrahigh gain DC/DC converter with ZVS,and the other one is ultrahigh gain DC/DC converter with cascade switched-capacitor.In the first structure,all switches can be turned on with ZVS,and the transmission efficiency is improved.In the second structure,the output voltage level can be adjusted flexibly,and the application domain is broadened.(2)In view of the characteristic of bidirectional power flow in energy storage system,a coupled-inductor based bidirectional converter with wide ZVS range is proposed.This topology can realize flexible regulation of LVS voltage by utilizing the magnetic inductor,and the voltage gain is improved by adjusting the turns ratio.The leakage inductor current is used adequately to achieve ZVS of switches;meanwhile,the backflow power is also suppressed.The operation principle and steady-state analysis are presented in detail.Finally,the experimental prototype is constructed to verify the feasibility of the proposed converter.(3)In view of the high current ripple and high current stress in LVS of above high gain bidirectional topology,an interleaved high gain bidirectional DC/DC converter with coupled-inductor is proposed.In LVS,the interleaved buck/boost circuit is applied to reduce the current stresses of switches.In HVS,the secondary winding of coupled-inductors are connected in series to improve the voltage gain and reduce the current ripple of LVS.Furthermore,a DPDPS control strategy is proposed to overcome the problem of soft-switching lose in HVS.Finally,the experimental prototype is constructed to verify the feasibility of the proposed converter.