| The design of the AC/DC module as the PFC stage is the most important to achieve the high power quality,high efficiency and high reliability of the high-voltage DC uninterruptible power supply.Therefore,this thesis focuses on the PFC stage of a highvoltage DC uninterruptible power supply and designs an improved totem-pole bridgeless PFC converter.The main work of the thesis is as follows:(1)The characteristics of the three bridgeless PFC converters are compared and analyzed,and the totem-pole bridgeless PFC converter with the lowest conduction loss and lowest common mode interference is selected as the research object.The operating characteristics of Ga N-based totem-pole bridgeless PFC converter are analyzed in detail,and the Si C IGBTs with stable loss variation under temperature rise are selected as the highfrequency switches for passive conduction during renewal for its high-frequency switches with high loss during temperature rise and large inrush current during converter start-up;the Si C Schottky diodes are selected to build a conduction loop to reduce the inrush current at the moment of startup.The improved totem-pole bridgeless PFC converter is designed.The operating principle of the converter under CCM conditions is analyzed,and the main components in the converter are designed and selected.(2)The three common current control methods in the bridgeless PFC converter are compared and analyzed,and the average current control is selected as the basic control strategy.On this basis,the control strategy of adjusting the dead time of the line-frequency switching and delaying the conduction of the high-frequency switching is proposed to suppress the current spikes and their EMI interference and losses;the control strategy of indirect and direct voltage feed-forward is adopted to improve the phase following and reduce the impact of sudden changes in the input voltage.Finally,the control system of the improved totem-pole is designed.(3)For the control system designed in this thesis,the transfer function of the improved totem-pole is derived,the controller parameters in the double-loop of the control system are calculated by using MATLAB,and the loop stability is analyzed according to the obtained Bode diagram.Simulink is used to model the improved totem-pole bridgeless PFC converter and its control system,and simulation experiments are conducted under different conditions.The simulation results show that the input current waveform has no obvious abnormality at over-zero,the input current THD is less than 5%;the power factor is greater than 99.8%;and the system response time is reduced to 0.2 second.The comparative analysis of the simulation results shows that the improved totem-pole control system designed in this paper eliminates the over-zero current spikes and improves the dynamic response of the system.(4)The hardware circuit of the improved totem-pole is designed by using Jialichuang EDA,the digital control state machine is designed based on C2000 series MCU development board,and the experimental prototype is fabricated and tested in the built experimental platform.The test results show that the output voltage of the experimental prototype is constant at 400 VDC,the ripple is about 3.5%,and the full-load efficiency is 98.7%,which meets the expected design specifications.In summary,the improved totem-pole bridgeless PFC converter designed in this thesis can meet the application requirements of high-voltage DC uninterruptible power supply. |
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