| Switching converter is a power conversion device that works at high frequency.It is widely used because of its advantages of high efficiency and high power density.It has analog and digital control modes.But the digital control needs the cooperation of the peripheral auxiliary circuit,the noise interference in the auxiliary circuit can not be ignored,it will greatly affect the precision of the digital control.In this paper,digital control of switching converter and improvement of signal-to-noise ratio(SNR)research is carried out on digital control and signal conditioning technology with totem pole bridging PFC as the carrier.Based on the common mode interference of the typical traditional bridge-free PFC and the four bridge-free PFC,the bidirectional totem pole bridge-free PFC topology with obvious advantages was studied after the comparison and detailed analysis of the number of components,and the working mode of the topology was analyzed,paving the way for the digital control of the topology.CCM,CRM and DCM control modes are commonly used in the bidirectional totem bridgeless PFC topology,and the dynamic performance is good in the current critical mode.Valley bottom switching can be realized under certain conditions and the switching loss can be reduced.However,this control strategy can solve the problem of inductive current zero crossing,and three common current zero crossing detection modes are analyzed.A current zero-crossing signal detection and acquisition circuit is selected.The signal is also used as the initial trigger signal of the digital control PWM modulation wave to control the opening sequence of the high frequency tube.By analyzing the mode of totem pole bridge-free PFC circuit in critical conduction mode,the average current injection method was introduced to establish the small signal model in CRM mode,and MATLAB/Sisotool toolbox was used to design the voltage loop compensator to ensure the stability of the system.According to the digital control characteristics of DSP28035,the peripheral auxiliary circuit is designed,and the frequency conversion control,sampling frequency,sampling point and control sequence selection of high frequency tube are realized.Aiming at the noise of digital control peripheral auxiliary circuit,the dc error and AC noise value of current sampling circuit are calculated locally,and the correctness of noise calculation is verified by Pspice software simulation,and the compensation circuit is designed to suppress the noise,which achieves good noise suppression effect.Then the method of fitting system error curve is adopted to correct the whole error by software.Finally,the processing error of the digital chip is analyzed and the reference method to reduce the error is given to improve the SNR of the switching converter control signal.Finally,it is verified by experiment.A 300 W totem pole bridge-free PFC prototype was developed.Through testing the input and output characteristics,key working states and system efficiency points of the prototype,the waveform and experimental data obtained were all within the theoretical design range,which proved the correctness of the theoretical design. |
