Research On Hybrid LLC High Power Charging Power Supply Based On An Operating Switching Mode

The rapid development of electric vehicles has put forward higher requirements and challenges for power conversion technology,among which high-power DC charging power supply has received widespread attention.LLC resonant converter has high conversion efficiency and is often used as circuit topology for high-power DC charging power supply,and its research has been intensified.To address the problems of high power high frequency transformer design and low light load efficiency of LLC resonant converter,this paper proposes a hybrid LLC resonant converter based on operating mode switching.Topologically,the primary side of the transformer is connected in series,the midpoint of the two transformers is connected to the negative side of the power supply,and the secondary side of the transformer is connected to the load in parallel via a rectifier circuit.The proposed hybrid LLC resonant converter is suitable for two-stage constant-current and constantvoltage charging process of power batteries by controlling the Pulse Width Modulation(PWM)to switch between full-bridge and half-bridge operation modes of the LLC resonant converter without adding additional switching devices.First,the circuit structure of the proposed hybrid LLC resonant converter is analyzed in detail.Based on this,the equivalent model of the circuit under the two operating modes is derived using Fundamental Harmonic Analysis(FHA),and the main operating modes and voltage gain characteristics under the two operating modes are further analyzed.The voltage gain curves under the two operating modes and the circuit structure are used to determine the magnitude of the power Ps at the operating mode switching point,which provides the basis for designing the control scheme.Then,the design specification of the hybrid LLC high-power charging power supply and the design steps of the main circuit parameters are given according to the power battery charging requirements,and the basis of the main device selection is given.In order to further verify that the switching of operating modes can improve the efficiency of the converter,the circuit losses at the switching point under two operating modes are analyzed.The operating mode switching principle is combined with the constant current and constant voltage charging curve to design a closed-loop control scheme for the charging power supply.Finally,to verify the correctness of the parameter design and closed-loop control scheme,the power supply is verified theoretically in PSIM software.Through a detailed analysis of the software and hardware design process of the charging power supply prototype,a high-power charging power supply prototype with a power level of 3.3k W was designed.According to the experimental results,the charging power supply prototype is able to meet the soft switching conditions in the full load range.The conversion efficiency of the prototype was also improved under light load,thus verifying the correctness and effectiveness of the designed topology and control system.