| The zero voltage switching(ZVS) phase-shifted full-bridge(PSFB) converter is the most popular topology in high power applications, due to its attractive features include ZVS of the primary switches. As a key parameter in PSFB converter, dead time has significant influence on the ZVS operation and the system performance, especially when the converter has wide load range. While dead time is related to the load condition, the switches in PSFB converter can not achieve ZVS over the full load range if we set fixed dead time. As a result, the efficiency on light load decreases and the system has poor stability. Therefore, it is of great value to study variable dead time method in the PSFB converter.In this thesis, a method and circuit of regulating dead time on different load conditions are proposed with the PSFB converter for On-board charger. The thesis is mainly organized as follows. Firstly, the influence of dead time on the ZVS of the PSFB converter is analyzed and analytical model of dead time is built. Secondly, the effects of three nonideal factors, including the nonlinear output filter inductance, varied miller plateau length and the blocking capacitance, are researched and an adaptive dead time control scheme and circuit based on STM32F051 is proposed for the application of On-board charger. Then the efficiency on light load is improved. Finally, the scheme is implemented by a 1.5KW PSFB converter prototype.According to the experiment results, analytical model of dead time built in this thesis is verified and the optimal dead time can be set based on these equations over wide load range. Due to the regulation technology of dead time, the PSFB converter can achieve ZVS in the process of battery charging. The maximum efficiency of the system is up to 94.1% and the efficiency at 20% load condition increases from 86.7% to 89.1%. So the target in the thesis is reached. |
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