Research On Bidirectional DC-DC Converter With Wide Conversion Gain And Its Soft-switching Technology

Energy storage technology is being applied in electric vehincle,hybrid energy generation system and micr-grid.The voltage ratings of each battery cells or super capacitors are comparatively low in storage side of these systems.In order to interface between the battery cells and the high voltage bus bidirectional dc-dc converter with high voltage gain ratio and high efficiency becomes more and more important.In this thesis,the topology construction and derivation method based on bidirecitional dc-dc converter with wide voltage are introduced and two novel bidirectional dc-dc converter with wide conversion gain and wide zero-voltage switching range are proposedFirstly,the operation principles and the static perfermoce of voltage-fed dual active bridge bidirectional dc-dc converter implemented with single-phase-shift modulation is studied.In the situation of voltage mismatching between ports,the converter will face problems such as the deacrease of soft-swtiching region,the circulationg power increasing.Current-fer dual active bridge bidirectional dc-dc converter is also studied.Implemented with PWM plus phase-shift modulation and the interleaved buck/boost circuit,the port voltage can be matched well.However interleaved buck/boost circuit results complex soft switching condition in low voltage side.Finally,simulation models of these converters are built to verify the validity of the analysis and their features are also summarized to provide construction direction for the bidirectional dc-dc converter with wide conversion gain.Secondly,a secondary side cascaded winding-coupled bidirectional converter is proposed for wide voltage gain application.The interleaved buck/boost circuit in the primary side is cascaded with the secondary side of full-bridge circuit through the winding coupled inductor to achieve high voltage gain and reduce the voltage stress on the switching elements.The differential voltage is designed to generate the bias current to realize soft switching of the eight power switches within wide range of load variation..The operation principle,steady-state analysis and comparison result are presented in detail.Finally,a 1k W experimental prototype is constructed to verify the feasibility and the correctness of the theoretical analyses is validated by experimental results.Finally,a multi-compound active bridge convter is proposed as the interface of different dc-sources with a load,and provide the load with the energy simultaneously or individually,which features wide voltage conversion gain,wide zero-voltage switching range and a reduced number of components and transformer windings.Based on voltage matching principle,voltage-second values between two sides of the transformer are set equally for optimized operation,which is utilized to realize soft switching of the six main power switches within full load range.Meanwhile,the other two switching elements can also operate in a wide region of soft switching.High frequency equivalent model is built up for parameter design,the experimental prototype is constructed to verify the feasibility,and the correctness of the theoretical analyses is validated by experimental results.