Research On Bidirectional CLLC Resonant Converters

Isolated bidirectional DC-DC converter is widely used in new power generation system,microgride,electric vehicles,spacecraft power system and hybrid energy storage.How to implement wide range of voltage regulation and high efficiency in the whole range of load makes great challenge to the design of bidirectional DC-DC converter.Moreover,the capability of switching naturally and smoothly between the forward and backward power transmission modes is also significant to the bidirectional DC-DC converter in these applications.Firstly,this paper studies the common modulation strategies of CLLC bidirectional resonant converter and analyzes the disadvantages of these strategies.In view of these deficiencies,a new modulation strategy with same phase of voltage waves in original and secondary side is studied.This paper analyzes the working principle and characteristics with the presented modulation strategy.Furthermore,two kinds of concrete implementation of the strategy are induced.PWM and dual phase-shift strategies are used in CLLC converter which have the following advantages: 1)The voltage gain characteristics has nothing to do with the transferred power which can simplify the design,control and realization of the converter.2)With the help of an auxiliary inductor,zero voltage switching can be achieved for all the active switches on both primary and secondary sides within the entire operation range,and the efficiency can be increased at the same time.3)Natural and smooth transmission mode switching can be achieved.A 1kW prototype is built to verify the feasibility of the presented strategies in CLLC converter.In addition,by coupling transformer windings,the bidirectional CLLC converter can be extended to a three-port resonant converter.The presented modulation strategies can also be applied in the three-port resonant converter and realize the power transmission between each port.In particular,this kind of modulation method can help to achieve natural control decoupling and avoid complex control loop design.The feasibility and effectiveness of the presented converter and modulation strate is fully verified by the experimental results from a 1kW prototype.