Design Of Wide Outout LLC Resonant Converter Based On Hybrid Control Strategy

The transformation of energy from non-renewable to renewable energy makes the advantage of clean energy such as electric energy stand out.Problems such as environmental pollution and the high price and shortages of oil have caused the government and people to turn their attention to electric vehicles,making the development of the electric vehicle industry alive.As the basic supporting facilities of electric vehicles,the importance of completing the charging module for electric vehicle charging is more self-evident.The high power,high efficiency and small size of the charging module pose new challenges to the power supply.The soft switching technology that appeared in the 1970 s made the loss of the switching device during turn-on or turn-off significantly reduced and solved the problem of efficiency.The emergence of parallel technology solves the power expansion problem,but at the same time leads to the current sharing problem when multiple modules are connected in parallel.The three-phase star structure of the three-phase star LLC resonant converter solves the problem of the current sharing of the multi-phase LLC resonant converter in parallel.That is mean the problem of power expansion is also solved.The resonant circuit of the LLC resonant converter solves the problem of high loss and high power density at high frequency of the power supply.For this reason,the three-phase star LLC resonant converter is used as the main circuit of the charging module,and the operating characteristics and the methods of control of the three-phase star LLC resonant converter are analyzed.Completing the PFC correction in the front-end three-phase VINNA of the whole charging module,and converting the AC input to DC by boost,and mading the DC voltage adjustable in wide range through the series connection of two three-phase star LLC resonant converters in backward stage.This article mainly introduces the design of the part that completes the DC voltage regulator at the backward stage,mainly including the following aspects:(1)The analysis of principle and parameter of a three-phase LLC star resonant converter.Firstly,several classical resonant converter circuits are analyzed and several advantages and disadvantages are analyzed and compared.According to the shortcomings of these several resonant converters,the three-phase LLC resonant converter topology is adopted in this paper in combination with the design requirements for output power.According to the analysis of the operation of the LLC resonant converter,the working waveform of the three-phase star LLC resonant converter is deduced,and the relevant parameters are calculated.(2)The design of System power main circuit and controller.According to the principle of maximum efficiency under high-frequency operation,combined with the design requirements of the charging module,the device parameters of the main circuit are designed.The auxiliary power supply is designed to output 3.3V,5V,8V DC voltage levels to meet the reliable power supply of various IC devices in the system.Based on current transformers,comparators,and precision operational amplifiers,sampling conditioning circuits and protection circuits are designed to achieve accurate sampling of output current and output voltage,as well as overcurrent protection of the main circuit.The system control circuit was designed with TMS320F28032 as the main control chip,the CAN bus technology was used to realize the communication function with the host computer,and the CAN communication circuit was designed.The PFM control strategy for three-phase LLC star resonant converters has the disadvantage of low light load efficiency.A kind of mixed control strategy of PFM and Burst is used to improve the light load efficiency.Finally,the system software design was completed.(3)The simulation and experiment of system.The simulation platform of LLC resonant converter was built by MATLAB.The effectiveness of the design was verified by simulation analysis.The main circuit of the threephase LLC star resonant converter,the driving circuit,the circuit and other modules were fabricated,a prototype of the system experiment was established,and the system was connected to the pre-rectifier circuit.The experimental results show that the output voltage of the three-phase LLC star resonant converter designed in this paper has a capability of the wide adjustment and higher light load efficiency and verifying the effectiveness of the system design.