Simplified Time Domain Analysis And Parameters Design Of LLC Resonant Converter

With the development of UAV technology,the long endurance has become an important indicator for the design of UAV.In addition,in order to strengthen the mounting ability of UAV,the system also needs to meet the lightweight requirements in the research and development of power supply unit.LLC resonant converter is widely used in the design of UAV power supply due to its high efficiency and high power density characteristics.However,in the design process of LLC resonant converter,the gain analysis based on the fundamental harmonic approximation(FHA)method will produce a large error when the switching frequency is far from the resonant frequency.At the same time,because the LLC resonant converter is a multi-resonant element converter,the solution is more complicated in the time domain.In view of the above UAV power supply design requirements and LLC resonant converter parameter design problems,this paper intends to study the gain analysis,parameters design and magnetic integration technology of the LLC resonant converter.Firstly,the working states of the full-bridge LLC resonant converter at different switching frequencies are divided,and the time-domain equations of each resonant mode are solved.A simplified time-domain(STD)analysis theory is proposed according to the operation law of the converter,and the resonant mode of the converter is simplified.The different resonant modes are connected through the boundary conditions between the modes,and the gain characteristics of the LLC resonant converter within the full operating frequency range are solved.Combined with the STD modal equation,the expressions of the effective value of the resonant current,the effective value of the switching tube current and the peak voltage of the resonant capacitor in the LLC resonant converter is are derived.Secondly,the parameters design of the main circuit of the converter is completed based on the LLC resonant converter gain model obtained from the STD analysis.In order to clarify the advantages of the STD analysis in parameters design,the parameters of the LLC resonant converter based on the FHA method are also completed.The design results show that the STD analysis method can design larger excitation inductors when the gain of the converter is satisfied compared with the FHA method.Then,according to the design parameters of the converter,combined with the theoretical expression of electrical parameters obtained from STD analysis,the selection of power devices and the design of magnetic integrated transformer are completed.According to the requirements of the control system,the principle analysis and hardware design of each part of the control circuit are completed.The corresponding theoretical loss analysis is completed based on the operation condition and hardware circuit of the converter.Finally,a PSIM simulation circuit and a 2000 W laboratory prototype with an input of 65～100V and an output of 48 V are built.The simulation and experimental results show that the gain analysis method based on the STD is much more accurate than the traditional FHA.The simulation and prototype test data of two sets of LLC resonant converters designed based on the STD analysis and the FHA method under the same power condition are compared and analyzed.The results show that the parameters of the LLC resonant converter based on the STD analysis has smaller effective value of the resonant current,the efficiency of the converter is optimized,and the peak efficiency reaches 96.67%.