Research On Computer Aided Design Of Hybrid Controller For LLC Converter

Charging facilities are an essential infrastructure for electric vehicles.The voltage range of electric vehicle power batteries is rather wide,with a typical voltage range of 200 V ~ 450 V.The wide voltage range output has a significant impact on the conversion efficiency of the charger,which brings great challenges to the charging circuit topology selection and control design.LLC converters are widely used in electric vehicle charging circuits due to their excellent characteristics such as high efficiency.However,it is difficult for LLC converter to apply in applications with a wide voltage range due to its gain characteristics.In order to improve the charging efficiency to reduce the charging cost,the charger should achieve high conversion efficiency within a wide output voltage range.For the hybrid control method combining resonance and frequency modulation control,in order to find the best design scheme,a computer aided automatic optimization algorithm is designed.The scheme with the best global weighting efficiency is produced according to the losses of different design schemes under different working conditions and the weighted efficiency evaluation algorithm.In order to improve the accuracy of the algorithm's loss analysis,the paper analyzes the loss distribution characteristics of the LLC circuit under the three different operating modes of below resonant frequency,resonant frequency and above resonant frequency,and improves the formula for calculating the turn off loss at above resonant frequency.A double pulse test data is used for optimization calculations.Experimental results show that the automatic optimization algorithm effectively optimizes the design process of LLC converters.Aiming at the problem of high frequency and low efficiency of LLC in the above resonant frequency,this paper improves the design using variable frequency and phase shift hybrid control in the low-voltage section based on the hybrid control method combining resonance and frequency modulation control.The theoretical analysis of the hybrid strategy is conducted,the characteristics of continuous and discontinuous operation modes are compared,the time domain expressions of capacitor voltage and resonance current are derived,the ZVS turn-on region is analyzed,and the path optimization method with the lowest loss is analyzed.The variable frequency and phase shift hybrid control method achieves the efficiency improvement goal of the low output voltage section and further optimizes the global efficiency of the optimal scheme.Based on the research content of this paper,the theoretical analysis and simulation analysis were experimentally verified on a 7.5kW prototype.