Research On AC/DC Converter Based On Totem-pole Soft Switching PFC Circuit

With the rapid development of big data era,energy required by data center is increasing.As an important part of data center,the main goal of AC/DC converters is to improve the efficiency and power density.Among them,due to its advantages of precise control and simple design,a two-stage AC/DC converter has huge potential.This paper presents an AC/DC conversion system based on totem-pole soft switching PFC circuit,which has simple circuit structure and few devi ces.The switches in the circuit have soft switching characteristics,which is suitable for higher working frequency and can improve the system power density while ensuring the efficiency.In this paper,the working principle of the Ga N totem-pole soft switching bridgeless PFC circuit is analyzed,and the constraint conditions of guaranteeing the soft switching characteristics in the full input voltage range are obtained.With digital controlling,the circuit switches between CRM and QSW mode,which ensures that the converter can be switched on at zero voltage while having power factor correction function.At the same time,according to the working characteristics of the converter,the design method of the main component parameters is proposed.In order to obtain better dynamic response,this paper analyzes the limitations of the traditional voltage loop control,and proposes an optimization closed-loop system design.Considering the output ripple of PFC converters,a comb filter is designed to eliminate the influence of voltage ripple on control circuit.A time-varying nonlinear system model is established and a compensation network was designed using Nyquist plots.Based on the compensation function and the corresponding difference algorithm,the parameters of the compensation link of the digital system are designed.In this paper,a digital dual-loop control method for totem-pole soft switching PFC circuit is proposed,and Simulink platform is used for simulation verification.Based on current zero crossing detection,the current inner loop controls the opening and closing moments of the switches,and the adaptive ZVS is realized.Meanwhile,a fault-proof trigger link and a over-current suppression link are designed to improve the stability of the system.The output voltage is precisely adjusted by sampling bus voltage in the outer voltage loop.In order to further increase the switching frequency and reduce the system loss,Ga N device is implemented and an optimal drive circuit design method is proposed.Furthermore,the planar magnetic element is used as the inductor to improve the power density of the system,and a variable width winding design is adopted to reduce the loss of the magnetic element.Finally,a 400 W and 2.1W /cm3 prototype was designed for experimental verification.When the input voltage was 220 V ac,the output voltage of the front stage of the converter was stable at 400 V and the peak efficiency of the whole system was 93.4%,which verified the correctness of the theoretical analysis.