Research On Key Technologies Of CLLC Bidirectional Resonant Converter For V2G Application

With the rapid development of renewable energy and electric vehicles(EVs),the vehicle-togrid(V2G)technology that realized the bidirectional interaction between EVs and the power grid has received extensive research and attention.The V2 G technology makes full use of the energy storage characteristics of the EV batteries.By charging and discharging a large number of EVs in order,it can achieve the functions of peak shaving and valley filling,smoothing the fluctuations of renewable energy,and optimizing the operation of power system.In the V2 G system,the bidirectional AC/DC converter that connects the EV and grid is the power interface and is an important part of the system.This paper takes the V2 G technology as the background and studies the back stage isolated bidirectional DC/DC converter in the two-stage V2 G on-board chargers.High efficiency CLLC bidirectional resonant topology is chosen as the research object of this paper.On the basis of the basic principles and design methods of CLLC converter,key issues such as synchronous rectification(SR)and inductor integration are studied.Corresponding methods are proposed and verified through both the simulation and experiments.Firstly,this paper proposed a SR method based on the resonant inductor voltage for CLLC converter.The resonant current is detected indirectly through the inductor voltage and the SR driving signal is determined by its polarity.Compared with the existing methods,the proposed method does not need additional current sensors,thus reducing the cost and size of the converter.Moreover,corresponding SR control strategy is proposed to handle the influence of parasitic oscillation in below resonance region.On this basis,the SR delay compensation and transient strategies are proposed to avoid the false turn-on problem caused by the delay and transient process.Secondly,a resonant tank structure with coupled resonant inductors is proposed to reduce the size of the converter.The two discrete resonant inductors on the primary and secondary side are replaced by a coupled inductor,which can reduce the number of magnetic components and optimize the size of the converter.In actual design,the turns ratio of coupled inductor might be different from the transformer and this situation is further analyzed.The specific design procedure in this case is given,and the insensitivity of the voltage gain to the turns ration deviation is proved.Finally,for the resonant tank with coupled inductors,the SR method proposed previously in this paper is modified accordingly.Both the simulation and experimental results proved the correctness of the SR method and inductor coupling scheme proposed in this paper.These two methods can reduce the secondary conduction loss and the volume of the magnetic components of the CLLC resonant converter,thereby further optimizing the efficiency and power density of the converter.