Full-bridge Three-level LLC Resonant Converter With Wide Output Range Based On Hybrid Modulation

With the increasingly serious energy crisis and environmental issues,electric vehicles have received strong support and development from the country as a new type of energy-saving and environmental protection vehicle.High-power DC/DC converter,as the important part of electric vehicle chargers,is one of the current research hotspots.Therefore,the development of highly efficient,low-cost and versatile chargers is of great significance to electric vehicle industry.This paper uses a full-bridge three-level LLC resonant converter as the main circuit.The three-level converter can make the voltage stress of the switch tube is half of the input voltage,which is conducive to choose the switch tube.The full-bridge topology is ideal for high-power applications.The introduction of the LLC resonant network allows the switch to achieve soft switching throughout the entire range and increase efficiency.Aiming at the problem that the output voltage range is very narrow under the traditional frequency conversion control,this paper proposes a hybrid control strategy with variable frequency and phase-shifting.In the mode of low-voltage and low-power output,the converter adopts phase-shift control strategy,and in the mode of high-voltage and high-power output,the converter adopts variable frequency control strategy,which effectively widens the output voltage range of the converter.First of all,this paper describes the requirements of DC/DC converters for electric vehicle chargers.Through analysis and comparison,FBTL-LLC is selected as the main circuit topology.Based on the advantages and disadvantages of the original control methods,a hybrid control of variable frequency and phase-shifting is proposed,and this paper makes a detailed analysis of its working principle.Secondly,through the modeling and analysis of the main circuit,the steady-state operation model of the LLC resonant converter and the gain model of the converter are established.Then the parameter design of the system is completed,and simulation verification is performed with PSIM software.Finally,using the TMS320F28035 as the main control chip,a prototype with 800 V input voltage and 200~750V/10 A output is built.The experimental results show that The voltage stress of all switch tube is reduced by half,and ZVS can be realized in the full range.