Digital Control Of High Power Phase-shifted Full Bridge DC/DC Converter

With the development of digital control theory and semiconductor technology, the application of digital control has become one of the most important research directions in the power electronic technology. Therein, for the switch-mode power supply(SMPS), the requirement of high frequency and modularization is a new target in this area, and the digital control method becomes a good solution from control view and attracts more attention in this decade.In this study, a transformer lag type diode clamp phase-shifted full bridge(PSFB) DC/DC converter is chosen as the controlled plant to test the proposed digital control methods. By utilizing a digital power supply control chip UCD3138, some controllers, for example PID controller, are designed and tested for the power module, and the digital controller design, technical implementation and algorithm verification for power modules are discussed mainly in this thesis. Compared with the traditional analog control techniques for power modules, the use of digital control techniques can reduce the electromagnetic interference(EMI) and improve the system response effectively. At the same time, the module space can be saved obviously.Focusing on the digital control for high power PSFB DC/DC converter discussed in this study, the thesis includes the following aspects:1. The working principle of the transformer lag type diode clamp PSFB DC/DC converter is discussed firstly. Particularly, the conventional ZVS based on the phase shift PWM control strategy which may cause the duty ratio loss phenomenon are analyzed emphatically. Focusing on the controlled plant(transformer lag type diode clamp PSFB DC/DC converter), the specific design procedure for the main transformer, the output filter inductor, resonant inductor and DC pulse transformer are discussed briefly. This is the basic step for the controlled plant design and the results can be used directly for the digital controller design.2. In order to apply the digital control to the high power PSFB DC/DC module power supply, a control chip UCD3138 used in this study is discussed firstly. Addressed on the DPWM(digital PWM) working mode in this PSFB DC/DC module power supply, a phase-shift PWM digital control method is proposed, and the PWM signal can keep the same performance as the traditional analogical control blocks do for the converter. Besides, the proposed control method can achieve the adaptive synchronous rectification in light-load mode.Based on the results for the DCM mode, by using the characteristics of the full wave rectifier synchronous rectification.3. Using the small signal model of PSFB ZVS converter, the closed-loop compensation characteristics of the PSFB DC/DC module power supply with digital controller are analyzed theoretically. In order to implement constant power constant current function of high power PSFB DC/DC module power supply, a digital control implementation method based on PID control is discussed to smooth the overshoot which occurs during the switching time between the voltage loop and current loop, and the experiment results also show that the proposed digital control method can reduce the electromagnetic interference effectively.4. Finally, the digital controller experiment verification is conducted using the peak current mode for the high power PSFB DC/DC converter in this study. The experiment results show that the proposed method can ensure the synchronous rectification phase-shifted PWM control and MOSFET ZVS effectively, and the step response can be monotonic without any overshoot.