Research And Design Of PSFB DC/DC Converter Based On Digital Control

With the improving of the switch mode power supply(SMPS)attention to small volume and high efficiency, digitization and soft-switching technology have become the focus of the research content of SMPS. So less switching loss, high energy conversion efficiency and reducible output ripple current, especially suitable for high power occasion technology, namely the phase-shift bridge current doubler rectifying DC/DC converter gradually attract the researchers’ attention.The improved 24V/600 W digital control phase-shift bridge DC/DC converter was acomplished with the combination of digitization and soft-switching technology. The topology of the phase-shift bridge DC/DC converter and its control circuit was researched in detail. The main work and results are summarized as follows:(1) The basic working principle of the phase-shift bridge current doubler rectifying DC/DC converter was introduced and the key problem of phase-shift bridge current doubler rectifying DC/DC converter was researched. The topology of the secondary side of the phase-shift bridge converter was detailed researched. Several key points were analyzed,such as secondary duty cycle loss, the ZVS realization of lag bridge arm,secondary parasitic oscillation, transformer magnetic saturation. At last an improved the phase-shift bridge current doubler rectifying DC/DC converter was put forward, by using saturation inductor as resonant inductor to increase the range of ZVS and reduce the loss of duty cycle,adding clamp circuit to suppress secondary diode parasitic oscillation,and the block capacitor is added to avoid transformer magnetic saturation.(2) The main circuit of the phase-shift bridge DC/DC converter was achieved. According to the parameters of the converter, the main circuit parameters of the phase-shift bridge current doubler rectifying DC/DCconverter were designed, including power switch, clamp diode, rectifier diode, high frequency transformer, output filtering inductor and output filtering capacitor, resonant inductor, blocking capacitor, and so on, the calculation method of the parameters was presented in detail.(3) The control circuit of the phase-shift bridge current doubler rectifying DC/DC converter was designed based on DSP. The converter is controlled by TMS320F28335. The method of generating phase shift PWM drive signal based on TMS320F28335 was proposed. The detailed design of the drive circuit and sampling circuit were also completed. The small signal model of the phase-shift bridge current doubler rectifying DC/DC converter and peak current-controlled model were established and their transfer functions were derived.The MATLAB sisotool tool was employed to design the parameters of analog PID controller of peak current-controlled model according to dynamic response of system. The digital PID controller was completed though discretization.At last, the main program and subprogram was fulfilled.(4) The main circuit was simulated and the prototype was manufactured. Using Saber software simulates the main circuit, the results was analyzed in detail and show that the theoretical design is reasonable and the features are effective. A 24V/600 W prototype is tested,the performance of the converter is as follows: the converter reach soft-switching at 20% load, the ripple voltage is less than 0.5%, the efficiency up to 80% at 20% load, the efficiency up to 90% at 60% or more load.This result reaches designed requirements.An improved phase-shift bridge current doubler rectifying DC/DC converter is put forward,many shortcomings of the traditional phase-shift bridge converter were overcome.The converter has its own merit of high energy conversion efficiency and reducible output ripple voltage.There are good practical performance and application prospect.