Research Of Wide Input DC Conversion Technology Based On Σ/Sigma Converter

As the energy problem becomes more and more serious,people pay more and more attention to energy conservation and emission reduction.In order to alleviate the energy loss in the lighting field,LED solid light sources have developed rapidly.LED drive power supplies usually use the electrolytic capacitors as bus capacitor.The use of electrolytic capacitor will greatly reduce the service life and power density of the LED drive power supply.A wide input converter can be used in the LED power supply to reduce requirement on the bus capacitance by sacrificing the voltage fluctuation value on the bus capacitor,thereby the electrolytic capacitor can be removed and the problem of short service time and low power density about LED drive power supply will be solved.Based on the traditional SIGMA structure can’t adapt to the wide input applications,this paper proposed an input-compensated SIGMA converter structure,and the resonance forward-flyback converter is also applied to the new Σ/SIGMA converter structure.By compensating the variation of input voltage,the structure forms a stable equivalent input,and the converts can change the working state from a wide input to a single-point working state,so that the converter can meet the requirements of wide input and still maintain a highly compact system structure and high efficiency.This paper first analyzes the basic operate principles and implementation methods of the SIGMA converter.By analyzing the limitations of the SIGMA converter under wide input,a new input compensation SIGMA structure is proposed,and the resonant forward-flyback converter is also proposed according to the optimized SIGMA structure.Second,the operating principle of the forward-flyback converter is expounded,and the two working states of CCM and DCM of the converter are also discussed in detail.The influence of duty cycle,turns ratio and switching frequency on the operating mode and output gain are studied.Then,the feedforward compensation control strategy of envelope tracking is designed according to the working characteristics of the converter.According to the the control strategy,the small-signal model of the flyback part of the converter and the compensation circuit are carried out.The feasibility of the feedforward compensation control strategy is also verified by simulation.Finally,the design process of the converter is introduced in detail.The transformer,main switch transistor,secondary side power device and its drive and control circuit are designed and optimized under the target parameters of the converter,and the experimental prototype is also designed and tested with the input voltage changes from 250 V to 400 V.The experiment verifies the adaptability of the resonant forward-flyback converter with wide input.