| With the development of power electronics technology,the DC/DC power supply has being more and more widely used in various fields,such as aerospace,communications power,new energy and other applications.However,the demand of higher efficiency,higher power density and higher temperature endurance are more and more eager.To solve these problems,soft switching technology is proposed,by realizing the zero-voltage switch(ZVS)or the zero current switch(ZCS)during the turn-on and turn-off period,the system can significantly reduce its switching losses,the volume of heat sink and its electromagnetic interference.Meanwhile,the usage of soft switches in the application can also do a favor to increase switching frequency,thus the volume and mass of magnetic components can be decreased,then the power density can be further increased.However,there are many different kinds of DC/DC topologies and control strategies.It seems easy for the parameter design but it is really hard for the real debug.What is more,the switches are easily damaged by the high di/dt induced by the line stray inductance.So,it has a great influence on the system efficiency and reliability about choosing the proper main circuit topologies according to the electrical parameters,choosing the control circuit and control parameters according to the control demand and introducing the snubber circuit for protection of the switches.In this paper,the start DC/DC source for a certain type of helicopter,whose power was medium,input voltage was high while output current were high and output voltage was low,was developed to have high efficiency and high reliability.Firstly,the isolated circuit was chosen.By comparison of the different topologies of isolated transformer's primary side,the full bridge zero voltage switch topology was chosen owing to the high input voltage.For the secondary side,the full wave circuit and douber-current circuit were compared detailed and the full wave circuit was used.Then,the rectifier switches were contrasted between diodes and synchronous rectifier MOSFETs by the aspect of power loss and circuit structure and the diodes were used finally.Subsequently,the working process and principle were analyzed detailed.The phenomenon of duty cycle loss,the voltage spike across the primary side switches caused by resonance between the switch junction capacitance and parasitic inductance of primary side input port,the voltage spike and oscillation on secondary side switches caused by the resonance between their junction capacitance and the leakage inductance of the high frequency transformer or the extra resonance inductance were analyzed.To solve this problem,the RCD clamping snubber circuit at the primary side and the RC snubber at the second side were introduced to inhibit the voltage spike and voltage oscillation,the structures of them were simple and the hardware cost was low.According to the system indexes,the main circuits parameters of the chosen main circuit were calculate.The model in s domain of the shifted-phase full-bridge ZVS converter was analyzed detailed and its transfer function was deduced based on the small signal model.By the Bode diagram,the frequency domain characteristics were analyzed and single voltage loop PI controller was introduced to regulate the system frequency domain characteristic.Based on PSIM software,the main circuit and control circuit were built to verify the effectiveness of the design.Then the prototype with DSP TMS320F28377 control circuit was built and experiment was carried out.According to the experiment,the source realized the high input voltage,low output voltage and high output current,its dynamic and steady characteristics were satisfied and the voltage spike and oscillation were suppressed greatly. |
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