| Aeronautical Static Inverter (ASI) used in medium power is being researched in this thesis, after reviewing and analyzing the common DC/DC converters, the DC/DC stage of ASI employs half-bridge converter, which is simple and easy to control in this power range situation.The operation principles and characteristics of symmetry half-bridge converter which is controlled by pulse-width modulation mode and appending with passive and lossless snubber circuit were first presented. Then a 550W DC/DC converter of 270V DC input and 360V DC output PWM symmetry half-bridge converter is designed and the converter designed above had effective impact on restraining the high voltage stress of rectifying diodes at the side of secondary coil. Nowadays, high performance,high efficiency and light weight are the most important performance figure of all kinds of DC/DC converter. Adding a inductance and capacitance into the PWM symmetry half-bridge converter above, the LLC series-parallel resonant converter was gained. Using variable frequency control mode with a refined small times together, achieves the effect of Zero Voltage Switching (ZVS) with the MOSFET and the effect of Zero Current Switching (ZCS) by the resonance of resonant inductor, resonant capacitance and the magnetic inductor of the transformer.The thesis discusses the operation principles within different frequency rang, especially focusing on DC gain characteristics,normalized input impedance and ZVS constraints. By concluding the influence brought on the converter by the main parameters, the method of designing parameters of converter is outspreaded. The LLC resonant converter is produced with the same converter specification. At last the loss of these two converters is discussed including MOSFET, rectifier diode, magnetic components and etc., by means of Mathcad, also the loss distribution and theoretical efficiency are obtained. All of these are helpful to optimize further.
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