| High-Voltage DC(HVDC) power system, which has the advantages such as light weight and easiness to realizes uninterrupted power supply, has been attracted more and more attentions. This dissertation is devoted to theoretical study and engineering practice on DC/DC converter of secondary power supply in HVDC power system.Phase-shifted Zero-Voltage-Switching PWM full bridge converter can realize ZVS for the power switches with the use of the leakage inductance of the transformer and the intrinsic capacitors of the power switches, so it is used widely for medium and high power applications. In order to eliminate the voltage oscillation caused by the reverse recovery of the rectifier diodes, a resonant inductance and two clamping diodes can be introduced to the primary side. The converter can be improved just by exchanging the position of the resonant inductance and the transformer such that the transformer is connected with the lagging leg. The improved converter has several advantages over its counterpart, e.g., the clamping diodes conduct only once in a switching period, and the resonant inductance current is smaller in zero state, leading to a higher efficiency and reduced duty cycle loss. The operation principle of the improved converter and the comparison with the original converter are analyzed in this paper. The effect of the blocking capacitor in series with the transformer or resonant inductance is discussed, and a best scheme is determined.The improved converter is adopted to design the DC/DC converter of secondary power supply in HVDC power system. A 3kW prototype converter is built to verify the effectiveness of the improved converter and the best scheme for the blocking capacitor, and the experimental results are also included in this paper.
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