Research On Wide Input Range Series-half-bridge LLC Resonant Converter

With the increasingly serious energy crisis and environmental pollution,the development and utilization of new energy have been very important.DC/DC converters are an integral part of the renewable energy generation systems in many applications,which is usually required the characteristics of a wide input range and high conversion efficiency.The series-half-bridge LLC resonant converter is taken as the research object.The key research is focused on how to widen the gain range and balance DC side series capacitors’ voltage,making it more suitable for the field of new energy power generation.Aiming at the problem of the narrow gain range of series-half-bridge LLC resonant converter,the topology of the secondary-side rectifier network is improved and a fourstage variable mode control method is proposed in this paper.Three-level variable duty cycle(TL-PWM),three-level phase shift(TL-PSM),frequency-doubling variable duty cycle(DF-PWM),and frequency-doubling variable frequency(DF-PFM)four modes are combined in this control method,the gain range of the converter is widened,and the switches have good soft-switching characteristics in all modes.The working principle of each mode is analyzed in detail,and a more accurate gain expression is obtained through simplified time-domain analysis.Furthermore,the combination and switching process of the four modes are discussed,and the theoretical analysis is verified by simulation software.Aiming at the problem of unbalanced capacitor voltage in TL-PWM and TL-PSM mode,a capacitor voltage control strategy based on redundant operating mode switching is proposed.The control method has two operating modes,which have opposite effects on the capacitor voltage.The two different working modes are obtained in this control method,which have opposite effects on the capacitor voltage.According to the offset state of the capacitor voltage,an appropriate working mode is selected,so as to realize the balance control of the capacitor voltage.The reasons for the offset of the capacitor voltage are analyzed in detail,and the working principles and switching methods of the two modes are studied in this paper.In addition,according to the relationship between mid-point current and capacitor voltage,the mechanism of automatic balancing of DFPWM and DF-PFM mode capacitor voltages is expounded.The main circuit parameter calculation,hardware design,and DSP software programming are completed,and an experimental prototype of an input voltage of110V～440V,the output voltage of 400 V,and the rated power of 1000 W are set.The experimental results show that the four-stage variable-mode control method has a wide gain range while ensuring efficiency;the capacitor-voltage control strategy based on redundant operating mode switching has a good voltage balance performance.