| The main focus of this doctoral dissertation is the development of an improved isolated Zero-Voltage and Zero-Current Switching PulseWidth Modulation Full-Bridge (ZVZCS-PWM-FB) dc-dc converter with dual voltage outputs of 42 V and 5 V, and suited for automotive applications. The leading leg of the converter achieves zero-voltage and zero-current switching during turn-on, and the lagging leg achieves zero-current switching during turn-on and turn-off. A Phase-Shifted (PS) PWM technique is used to obtain ZVZCS and to equalize the small dead times. Also, this PS-PWM strategy in conjunction with a robust average current-mode control can regulate the output voltage to obtain the desired stability and reliability of the system.;Moreover, the dissertation analyzes two solutions for ringing voltage problems, which normally occur in the output voltage of a ZVZCS converter. An RCD snubber and the modified active snubber are designed to reduce the ringing voltages caused by the interaction among the transformer leakage inductance and the circuit parasitic capacitances. The typical active snubber circuit is replaced with a flyback converter operated in the ZCS discontinuous conduction mode to realize a modified active snubber. This configuration results in lower conduction losses in the primary side. The modified active snubber and RCD snubber have efficiencies of 92% and 91%, respectively, at 42 V and 1 kW operating conditions (i.e., the full load). The converter without any snubber has a lower efficiency of 88.7%. Experimental results are shown to verify simulation results and demonstrate the feasibility of the proposed ideas. |
