Digital Control Algorithm Design For 100W Synchronous Rectifier Primary Side Feedback Flyback Conveter

For the purpose of improving efficiency,reducing power loss and size,the switching power supply converters are developing towards miniaturization,high power and high efficiency.The flyback converter with synchronous rectification technology and digital control scheme is widely used in the applications of power supply which below 100 W.However,in high-voltage and high-power situations,due to the use of synchronous rectifier structure,the mature digital approximation double-line sampling method is not accurate any more.In addition,the efficiency of Continuous Conduction Mode(CCM)is lower than the efficiency of Discrete Conduction Mode(DCM).These two problems hinder the further use in the fields of power.In view of the above issues,it designs a digital control algorithm for 100 W synchronous rectifier Primary Side Regulated flyback converter.First of all,the main topology,digital sampling technology and efficiency optimization methods are put forth as the research points of this dissertation.Then,the basic theory of the converter is analyzed.Several works are proposed:(1)the control loop of synchronous rectifier is implemented with CCM and DCM.(2)A single DAC midpoint sampling algorithm is designed to replace the original approximation double line sampling method.No matter how the sampling waveform slope is and where the inflection point is,it can get higher sampling accuracy and better inflection point following effect.(3)A high precision sampling error compensation algorithm is proposed for CCM and DCM.By compensating the sampling voltage,the output voltage can be constant and precise.(4)Gained from the analysis and comparison of the loss model,an adaptive optimization scheme on dead time control in CCM is proposed,which improves the system efficiency under CCM and reduces the overall loss of the converter.Finally,based on the proposed algorithm,MATLAB Simulink is built to run algorithm level and behavior level simulation.MATLAB and Modelsim are also built to run RTL level simulation,so as to verify system loop function.PCB system board and power board are designed to test and verify the digital loop algorithm and performance of converter in the FPGA platform.Judging from the measured results,the single DAC midpoint sampling algorithm and the sampling error compensation algorithm can achieve a constant voltage and the precision is up to ±0.65% in the full load input voltage range.In addition,the average efficiency of the flyback converter in the full load range is 93.64%,of which the peak efficiency is as high as 96%.