The Design Of Control Algorithm For 100W Digital Multi-mode Single-stage PFC Flyback Converter

Power Factor Correction has been widely used.Single-stage PFC converter has the advantages of simple structure and low cost,and is used in the field of lighting,low power switching power supply and off-line charger.But large output voltage ripple,poor dynamic performance and nonlinear influence have limited its development and practical application.Using digital technology can help optimize the system loop,enhance the sampling precision,improve the dynamic and static performance and avoid the sub harmonic phenomenon.Using digital technology to control single-stage PFC flyback converter is a research hotpot.A design of digital multi-mode single-stage flyback converter with high dynamic response is put forward in this thesis.The basic principles of active power factor correction technology,typical topology and the basic control strategy of single-stage PFC flyback converter are analyzed in this thesis.The advantages and disadvantages of different topologies and control modes are summarized.In order to realize the PFC function under different modes in a wide power range,a fixed conduction time control algorithm is designed and used in DCM,CRM and CCM mode,which can avoid the subharmonic oscillation in CCM mode.Due to the large twice the supply frequency output voltage ripple,the average sampling algorithm and its compensation technique in CCM mode are designed,which decreases the probability of the wrong adjustment and improves the load regulation rate.In addition,the average sampling algorithm does not need to sample the input voltage and primary current and remarkably reduces the cost.Concerning the poor dynamic performance of single-stage PFC flyback converter,a digital dynamic variable parameter PI algorithm and fast dynamic response algorithm are designed to improve the stability and dynamic performance of the loop.Based on this scheme,the whole control strategy of single-stage PFC flyback converter is realized by digital algorithm,and the code-level simulation of the algorithm is realized by Matlab and Modelsim.Finally,the performance of the single-stage PFC flyback converter control algorithm is verified by FPGA in a power supply system of 20V/5A.According to the simulation and test results,the proposed single-stage PFC flyback converter control algorithm achieves a maximum PF value of 0.998 and a PF value greater than 0.90 in whole load range and whole input voltage range.In addition,the average efficiency of the system in constant voltage model arrives to 86.13%.What's more,the output ripple is less than 3.6V,and the switching time of over 50%load change is less than 100ms and the start-up time is less than 80ms.The simulation and test results meet the requirements of the design index.