Research On Control Strategies Of Phase-Shifted Full Bridge ZVZCS Converter

As as an important research direction of power electronics technology in power transformation, DC/DC converter has been paid more and more attention by many countries. The phase-shifted full bridge(PS-FB) ZVZCS converter can achieve zero-voltage-switching for the leading leg and zero-current-switching for the lagging leg, and reduce power consumption,so it has become the mainstream in the larger power DC applications. To meet higher performance requirements of the system,it is necessary to adopt advanced control strategies.Therefore,the research on control strategies of the PS-FB-ZVZCS converter is tremendously significant.Firstly,the principles and circuit characteristics of the PS-FB-ZVZCS converter are analyzed, and on the basis of which, the paper designs the key parameters of the main circuit, and then the main circuit is simulated. The simulation results show that the design of main circuit can well realize zero-voltage-switching for the leading leg and zero-current-switching for the lagging leg under a given drive signal, which has confirmed the rationality of the parameters of main circuit. Meanwhile, according to the small signal modeling method of Buck converter, the small signal model of the PS-FB-ZVZCS converter is built,and the transfer functions in continuous conductive mode are deduced.In order to put the advanced control strategies into PID control, conventional PID control strategy is studied. The main research contents include:the conventional PID control theory and the basic principle of voltage mode control system and average current mode control system.Furthermore, the closed-loop simulation analysis of voltage mode single closed-loop control system and average current mode dual closed-loop control system are conducted with the Saber software under conventional PID control strategy. The simulation results show that the design of voltage mode single closed-loop control system and average current mode dual closed-loop control system can achieve the stable output of the PS-FB-ZVZCS converter, which proves that the design is reasonable.In order to improve the control performance, the paper studies two kinds of intelligent control strategies including fuzzy control and BP neural network control,and designs fuzzy adaptive PID controller and BP neural network PID controller respectively.Then the paper achieves closed-loop simulation under tne fuzzy adaptive PID control with the Saber software and Simulink co-simulation,and compiles the simulation program under the BP neural network PID control with Matlab M-file, comparing with conventional PID control respectively. The simulation results show that, using the designs of the fuzzy adaptive PID controller and the BP neural network PID controller, the system has smaller overshoot, faster response and shorter settling time,superior to the conventional PID controller. Meanwhile, the advantages and disadvantages of the two intelligent control strategies are discussed.Finally, in order to achieve digital control, the paper introduces the software structure design of the digital controller under the three control strategies.Then the produce scheme of phase-shift PWM control signal and the software process of digital control system are given based on the TMS320F2812DSP.