| Bidirectional DC-DC converters have been widely used in fileds such as energy storage system,solid state transformer,motor drive,and so on.Generally,bidirectional DC-DC converters are required to operate within wide voltage range,to achieve soft switching and to have low current ripple.For voltage-fed dual active bridge converters,issues including high peak current,high non-active power and losing soft switching will emerge when the input voltage and output voltage are mismatched.In traditional current-fed dual active bridge topology,even though two-phase interleaved parallel connected Buck/Boost circuits are used to solve the voltage mismatching issue,the current ripple at low voltage side is still rather large.A novel current-fed hybrid dual active bridge bidirectional DC-DC converter,along with the corresponding control strategy,is proposed in this thesis.The low voltage side circuit consists of two-phase interleaved parallel connected Buck/Boost circuits,and the switches at this side are modulated with duty cycle fixed at 50%.On basis of the full bridge,two reversed series connected switches are added at the high voltage side,and four-level modulation is employed for the high frequency ac voltage between the bridge center points.The transferred power of the converter can be adjusted by the phase shift angle between the two sides.Besides,all the power switches can achieve zero-voltage-switching within wide voltage range and wide load range when using the proposed control strategy.In this thesis,the operation principle and detailed working modes of the proposed converter are analyzed,and then the converter performances,including the power charactersistic,soft switching range,current ripple reduction and current stress,are derived and discussed.After that,key parameters of the main circuit for a 1k W prototype are designed.Finally,a 1k W experimental prototype is set up to verify the effectiveness of the proposed converter topology and the control strategy. |
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