Research On Piecewise Hybrid Control For Half Bridge LLC Resonant Converter

The use of traditional fuel vehicles has exacerbated energy shortages and a series of environmental problems.The emergence of new energy electric vehicles has largely solved this problem.Therefore,the research on electric vehicles has received great attention,and the problem of electric vehicle charging is a current research hotspot.Due to the poor stability of using new energy sources(wind energy,solar energy)for electrical energy supply in actual power supply situations,the system output voltage fluctuates.In order to solve the problem of power supply stability of electric vehicles by new energy,the research on the control strategy based on converter-based system output voltage stability is of great significance for improving the efficiency and robustness of electric vehicle charging systems.The half-bridge LLC resonant converter uses PWM control voltage stabilization to improve the efficiency of the converter and the realization of soft switching has limitations.If the PFM control method is used for voltage stabilization,it is necessary to expand the operating frequency range at the expense.Therefore,this paper proposes a new segmented composite control method based on half-bridge LLC resonant converter.According to the input voltage change trend,three areas are divided for system control,which realizes stable control of system output voltage and improves charging efficiency.(1)Explain the working principle and traditional control method of resonant converter.Using the fundamental wave analysis method,the operating characteristics of the half-bridge LLC resonant converter are simply analyzed,and its equivalent circuit and transfer function are obtained.And the traditional methods(PFM control,PWM control)are studied and analyzed.(2)Establish a small signal model of the half-bridge LLC resonant converter.Using the extended description function method to derive the steady-state model and small signal modeling of the half-bridge LLC resonant converter for electric vehicles,calculate the transfer function and Bode diagram of the system,the controller can well offset the interference of high frequency,and the system has a high frequency Noise has a better suppression effect,while maintaining the stability of the entire system.(3)Propose a sectional compound control method for half-bridge LLC resonant converter.In view of the limitations of traditional control methods,a segmented composite control method suitable for the high-efficiency voltage stabilization requirements of the half-bridge LLC resonant converter for electric vehicle stabilization charging is proposed,and the specific implementation scheme is designed.When it is calculated that it can meet the ZVS condition,The relationship between duty cycle and frequency.According to the change of the converter,three control methods of PFM,PWM,PFM+PWM are used to switch,and the soft switching characteristics can be satisfied in the whole area,and related simulation experiments are carried out.The experimental results verify the proposed segmented composite control strategy.Feasibility and effectiveness.(4)Experimental prototype development and experimental verification.With DSP(TMS320F28062)as the core control chip,a low-power experimental prototype of a half-bridge LLC resonant converter was built,with an input voltage of280 V,a rated output voltage of 35 V,and a rated power of 245 W.Based on the proposed control method,hardware circuit experiments are carried out,and the results further verify the feasibility of the control method.