Research And Design On Series Parallel(LLC) Resonant Converter

The Rapid development and constant change of power electronics and computer technology require the power supplies for communication equipment,servers,desktops,laptops and LED lighting to provide more power delivery with smaller spaces.The series parallel(LLC)resonant converter is widely used in those fields above because of its soft-switching operation in high frequency,high power transmission density,low EMI and easy to magnetic integrate.However,different from the traditional PWM converter,the parameters design of LLC resonant converter is complicated,and the design process is cumbersome and not intuitive which are still deficiencies due to the high order resonant circuit.Moreover,it is difficult to control the current oscillation in resonant tank and the voltage stress during dynamic process such as the start-up,load transient,overload protection and so on.In view of the above problems,this paper mainly studies the key parameters design of LLC converter and the control strategy of the converter in the start-up process.Firstly,from the point of circuit topology,the advantages and disadvantages of each classified topology are analyzed and then the optimal topology of DC-DC resonant converter is explained.Then the working principle of LLC converter is analyzed,the converter is modeled and the working characteristics are given.The design of the key parameters is completed.The model of LLC converter is built and simulated by using software Matlab/Simulink,which verifies the correctness of the parameters.Finally,the control strategy during start-up process is studied and optimized,and the hybrid control strategy is proposed.The feasibility is verified by the simulation,and the start-up performance of the converter is improved greatly.A prototype of LLC resonant converter is built in this paper.By using L6599 as the main control chip of the trigger circuit,the steady state operation of LLC converter and the realization of soft-switching are verified in kind.The experimental results show that the LLC resonant converter has good operating characteristics and is suitable for high frequency,high power density and low profile.At the same time,the effect of variable frequency control on start-up process of is also verified.