Research On High Performance Power Supply And Its PFC Technology Based On GaN Power Devices

The function of the PFC module in the switching power supply is designed to reduce the harmonic pollution in the power grid.The input current waveform is controlled to follow the shape and phase of the input voltage to make the output load to be resistive.However,the traditional Boost PFC topology performance is difficult to meet the quality requirements of modern high-power,high-performance,high-power density power products.In recent years,the emergence of the third generation semiconductor material GaN has made the totem pole bridgeless PFC technology become the current research hotspot.In this paper,an improved control strategy is proposed to meet the GaN power device characteristics and solve the zero-crossing current distortion problem inherent in the totem pole bridgeless PFC,which can further reduce harmonic distortion and improve system efficiency.Firstly,the topology and performance of various bridgeless PFC converters are analyzed in this paper.It points out that the Si MOSFET used in the traditional totem pole bridgeless PFC has parasitic body diode reverse recovery characteristic,which will cause switching loss and conduction loss.That is,the traditional totem pole PFC can only work in the discontinuous conduction mode or the critical conduction mode.In order to make the totem pole bridgeless PFC converter stable in continuous conduction mode,we uses GaN power switching device as the main switching transisitor in the high frequency leg of the converter to avoid reverse recovery problem;the low frequency bridge leg uses Si MOSFET for synchronous rectification.Then,in this paper,a new control scheme of dead zone control plus bipolar control is designed for the problem of the input current has pulse spike near the input AC voltage zero crossing point.Among them,the dead zone control combined with the soft start of the high-frequency leg switching transistor to avoid the low-frequency leg output capacitor can not finish reverse current recovery on time to eliminate the phenomenon of current pulse spike;the bipolar control can solve the duty cycle limitation caused by the zero-crossing bridge leg,which it makes the input current is not be controlled,and causing distortion problems.In this paper,Simulink circuit simulation is carried out for the improved scheme.Compared with the traditional control scheme,the improved scheme can effectively reduce current harmonic distortion and electromagnetic interference,and improve the efficiency and PF value of the system.Next,this paper analyzes the switching loss and parasitic parameters for the high-frequency interference problem unique to GaN devices,proposes a digital isolation driving scheme,and adds negative voltage bias and RC filtering to the input side of PWM signal to improve voltage transients immunity of the converter.Finally,the software and hardware design of the totem pole bridgeless PFC converter prototype is given in this paper.The key point device selection,chip selection and sampling circuit design are analyzed in detail,and the DSP software design and debugging process are described based on CCS3.3integrated development environment.The experimental results show that the 1k W totem pole bridgeless PFC converter designed in this paper can work stably in continuous conduction mode and the input current has no obvious pulse spike at the input voltage zero crossing.Under the full load condition,when the working frequency is 100 k Hz,the power factor can reach 0.99 when the output power is 1k W;the peak efficiency of the system can reach 97.3% under the input condition of 110V;the full load peak efficiency can be reached 98.2% under the input condition of 220 V.The measured results shows that the smallest total harmonic distortion is 2.91%,which is 21.35% lower than other control strategies of the same specification.