The Design Of 120W Cascaded BUCK-BOOST Power Factor Correction Converter Based On Digital Control

Power Factor Correction(PFC)is an effective method to suppress harmonic pollution of power electronic equipment and improve energy conversion efficiency of power grid.The traditional Boost type PFC has an output voltage of nearly 400 V,which is not the best output voltage for the post stage converter with the requeiremnt of medium and low input voltage.The Buck type PFC can only output a low voltage below 90 V and this topology has a drawback of current dead-zone,which results in low PF value.Therefore,based on the research of cascaded Buck-Boost PFC topology,a power supply with media and low output voltage is realized,which provides convenience for the design of the post stage power supply.At the same time,high performance of power factor correction is obtained.This paper focuses on the working principle of cascaded Buck-Boost PFC converter and proposes an optimized control scheme of PFC performance under light load.Firstly,based on the state-space average method,the mathematical modeling of the topology is completed and the power level transfer function is obtained.Secondly,the parameter tuning of the digital compensation module is completed by using the derived power level transfer function.Thirdly,Matlab is used to build the whole system,which completes the simulation and verification of basic functions.Fourthly,the cause for the decrease of the power factor when the input voltage is high and output power is in light load is analyzed by using the simulation waveform and the strategy of line cycle skip control is used to optimize the performance of power factor correction in light load.Finally,the test prototype is built and the control algorithms are verifed.The test results show that the system can work normally within the full input range(90Vac~264Vac)and full load range(5W~120W).The value of PF is no less than 0.99 and the peak value of PF is 0.9993 when the system works in full load(120W).The value of PF is 0.9433 when the system works in light load(take 5W for example).The measured peak efficiency is 93.20% and the efficiency of light load is no less than 85.06%(take 5W for example).The test results above all meet the requirements of the design index.