Research And Design On Digital Full-Bridge LLC Resonant Converter

The full-Bridge LLC resonant converter is very suitable for working under the condition of high frequency and efficiency,because zero-voltage switching and zero-current switching for the rectifier in the full load and the range of the input voltage can be realized.Full-Bridge LLC resonant converter has been widely used in communication power supply,computer,automobile,more electric aircraft and new energy and other fields.The full-Bridge LLC resonant converter working in the variable frequency control and fixed frequency control are studied detailedly.According to application background and technical index,the main topology structure and the overall framework of the system are given.The main topology structure is the Buck cascade LLC resonant converter,and in order to improve the efficiency,syschronous rectifier method is adopted.The system is achieved by the combination of software and hardware design.On the one hand,the hardware includes sampling circuit,drive circuit,auxiliary power supply circuit,synchronous rectifier circuit,and so on.On the other hand,the software includes the design of the parameters of the e PWM module,PI algorithm design and implementation,closed loop control strategy,the design of the main program and interrupt service subroutine,and so on.The specific circuit design of auxiliary power supply including 5V,1.8V and 1.8V is given.The synchronous rectifier circuit adopts the method of multiple MOSFET parallel,the detailed design method of the main transformer and the resonant inductor is given.The parameter design of e PWM module includes the design of counting mode,the parameters design of register module and parameter design of the dead module.The PI algorithm subroutine is written,and the double closed loop control strategy which inductance current as the inner ring and the output voltage as the outer ring is put forword,and a driving method of synchronous rectifier is provided at the same time.The discrete double closed loop control module based on C MEX S-Function and the implementation methods of drive module of the full-bridge LLC resonant converter are given.The discrete closed-loop simulation model of the Buck cascade LLC resonant converter under the MATLAB simulation environment is built.Simulation results show that the system output voltage is 24 V,ripple voltage is 0.01 V,output current is 12.5A,ripple current is 0.05 A,and power is 300 W.When the load is mutational,the time of dynamic adjustment is about 1ms.Consequently,the dynamic performance is excellent,and indicators meet the design requirements.