A Full-bridge Single-stage Power Factor Correction Converter Based On Digital Control

Capacitor filters are widely adopted in the front end of powerelectronic equipment, which will bring harmonic pollution to the power grid. Activepower factor correction (APFC) is a kind of effective method to improve the powerfactor of the electric equipment and suppress the harmonic pollution of powerelectronic equipment. The conventional power factor correction converter is realizedby analog controlling methods. Compared with analog controlling methods,digitalcontrolling methods has the advantages of small volume, low powerconsumption, large amount of data processing, high precision of processing, easy toexpand and upgrade. With the development of power electronic equipment to theminiaturization, intelligent direction, digital control has aroused people’s favor. Withthe introduction of the high speed, low cost digital signal processors, digital controlof PFC circuit will become an important research direction in the field of powerelectronics.Compared with conventional PFC converter, full-bridge single stage PFC hasobvious advantages: suitable for high power applications, the input andoutputelectrical isolation, the circuit does not exist through risk. However, due to theleakage inductance on the primary side of the transformer, great voltage peak onthe bus will be induced during the switching transient. In order tosuppress the voltage spike, this paper presents a passive snubber circuitcomposed ofinductors, capacitors and diodes. The buffer capacitor of the snubbercircuit can effectively absorb the transformer primary side voltage spikes, and byresonatingwith inductor, the energy on the capacitor can be transferred to theload. Therefore, the passive snubber can greatly reduce the voltage stress of theswitches and improve the reliability of the circuit. Detailedanalysisof the work process of the buffer circuit is given in this paper. By researching theinfluence law ofsnubber circuit parameters with the voltage stress, the design methodof each buffer circuit parameters is presented thoroughly. The experimental resultsshow that, the buffer circuit is presented in this paper has effectively suppressed thevoltage spike.In order to solve the shortcoming of the traditional PFC control algorithm, such as complex structure and huge large amount of computation, this paper studies a dutycycle predictive algorithm. This algorithm has the advantages of simpleprinciple, less computation, can give full play tothe advantages of digitalcontrol. Power factor correction can be realizedthrough the establishmentof relationship between the duty cycle and the input voltage, input current and outputvoltage. In this paper, the theoretical derivation and analysis of the algorithm aregiven in detail, software resource is allocated, the main program andinterruptprogramsare presented in flow charts, and suitable sampling method is selectedaccording to the characteristics of the input current. Finally, the feasibility of thealgorithm is verifiedby Matlab.By designing the main circuit, the sampling circuit and the drive circuitbased ontheoretical analysis and Matlab simulation, the hardware experiment platform hasbeen built. For the problem of electro-magnetic interference exists in high frequencyswitch power supply, hardware and software solutions are puttingforwardrespectivelyFinally, the experimental results show that, the converter canachieve good power factor correction effect.