Design Of 20kW Charging Pile Based On Composite LLC Resonant Converter

In order to meet the difference in voltage level of ev,ev charging piles must be output in a wide range.Therefore,this paper studies charging piles with a wide range of output voltage.According to the current research on charging piles,the two-stage topological structure of the former PFC plus the latter dc-dc is considered to have a good development prospect and is widely used by various manufacturers.In the two-stage topology of PFC plus back-stage dc-dc,the front-stage PFC circuit rectifies the input three-phase alternating current and outputs a large DC voltage to the back-stage dc-dc converter.Later dc-dc converters often use LLC resonant converter to convert the output voltage of PFC to meet the requirements of different electric vehicles.Due to the soft switching characteristics of the LLC resonant converter and its ability to operate at high operating frequencies,the loss of the whole converter is relatively low and the volume and weight of passive components are greatly reduced.Therefore,the whole machine can achieve high switching frequency,high efficiency and high power density,so it is widely used as the preferred topology of dc-dc converter.In this thesis for charging pile after level DC-DC converter to carry on the research and design,through the whole bridge of several common LLC resonant converter,three level clamping LLC resonant converter,staggered parallel LLC resonant converter and compound of LLC resonant converter is used in the comparison,compound of LLC resonant converter is chosen as the final topology design of this paper.The main advantage of the hybrid LLC resonant converter is that the wide output characteristic of the LLC resonant converter is realized by a set of resonators plus two sets of output transformers and a rectifier bridge.In this paper,the working mode of the hybrid LLC resonant converter is analyzed in detail,and the detailed process of circuit design is given.In the selection of power semiconductor devices for the whole bridge of the original transformer and the side rectifying bridge,Si C devices with better performance are selected to improve the working efficiency of the converter.At the same time,the temperature rise of power semiconductor devices,resonant inductors and transformers is verified,and their layout is improved.Finally,the hybrid LLC resonant converter designed by LTspice is verified by open-loop method.Then,small signal modeling and closed-loop compensator are designed for the hybrid LLC resonant converter to improve the performance of the whole unit.After that,simulink was used to conduct closed-loop simulation verification of the designed charging pile,and the efficiency of the whole machine under different output power was calculated.Through simulation and calculation results,the hybrid LLC resonant converter can achieve wide voltage output.At the same time,when the input voltage is 650 V,the efficiency of the whole machine will reach 98.4%.When the rated input voltage is 700 V,the working efficiency of the whole machine also exceeds 98%.