Research On Wide Gain LLC Resonant Converter

LLC resonant converter has excellent soft switching characteristics.In the frequency conversion control mode,it can achieve zero-voltage turn-on of the primary-side switch and zerocurrent turn-off of the secondary-side rectifier diode.Therefore,in the fields of new energy,electric vehicle charging,special power,etc.,LLC resonant converters have been increasingly used.However,the shortcomings of its output gain range is narrower within the rated operating frequency range,and it cannot be well adapted to the increasing working requirements now.In view of this problem,this paper analyzes and improves the existing wide output gain LLC resonant converter scheme,and also proposes a new wide output gain LLC resonant converter scheme.This paper first analyzes the operating characteristics of the full-bridge boost LLC resonant converter with variable-mode control and its improvement scheme,and the proportion of each loss in the circuit.The conclusion is that the magnetic loss and current sharing resistance loss in the circuit account for a relatively large amount.In response to this problem,this paper proposes an LLC resonant converter with parallel-series transformer connection and voltage doubler rectifier(PSVD LLC).Through the common boosting characteristics of the parallel-series transformers connection and the voltage doubler rectifier circuit,the turns ratio of the primary and secondary sides of the transformer is greatly reduced,thereby reducing the volume of the transformer and the overall magnetic loss.At the same time,the self-balancing characteristic of the voltage doubler rectifier circuit in the LLC resonant converter is also used to eliminate the voltage balancing resistor,thereby eliminating the losses on it.The experimental results verify the effectiveness of the improved scheme for improving the overall efficiency of the circuit.This paper analyzes the shortcomings of using the variable mode control LLC resonant converter to achieve low and medium voltage output through phase shift control.Aiming at this shortcoming,a new wide output gain LLC resonant converter topology scheme—multi-resonance cavity LLC resonant converter.This solution adds two additional resonant cavities on the primary side of the circuit and a rectifier circuit on the secondary side of the circuit,so that the circuit can switch between the actual working resonant cavity during operation,in three working modes: high voltage,medium voltage,and low voltage,so that can achieve wide output gain.At the same time,in each working mode,the circuit can also ensure that only the frequency conversion mode is used for control,thereby avoiding the shortcomings in phase shift control and improving the circuit's working efficiency.A design scheme of the resonant cavity parameters for this new topology is proposed to facilitate the design of this new topology.Finally,the experimental platforms of 1kW variable mode control LLC resonant converter,PSVD LLC resonant converter,and multi-cavity LLC resonant converter are designed and constructed respectively,and relevant verification experiments are performed to verify the above schemes.