Study On Two Stage Wide-range Input DC/DC Converter

In real life,input voltage changes of equipments would practically exceed its normal range in certain circumstances. The normal range of input voltage changes of equipments would be practically exceeded in certain circumstances. Instability of the control system may be caused by wide range input voltage, making the stress of electronic devices go beyond of its voltage and current pressure level therefore leading to overheating or damage. Special military vehicles are often faced with the problem of wide range input problem because of its unique application environment. While high stability of input voltage of DC 28V is perfectly required by the internal electronic equipments, sound dynamic performance, small size and high stability are also required by the power modules in special military vehicles. In this paper, a two-stage DC/DC converter solution, cascaded by a dual switch BuckBoost converter and forward converter, is proposed for the wide range input voltage problem in special military vehicles. The input voltage range in 85V~450V permits the steady performance of the cascade system while providing stable and low ripple 28V output voltage.In single voltage control system, the input voltage change bring about changes of other electrical system variables change. Only when the output voltage changes are caused by these variables would the voltage control loop play a regulatory role. Average current control system can response to the input voltage change and adjust system faster through constructing the inductor current feedback loop. In this paper, the average current control system is constructed as the control system of the former dual switch BuckBoost converter, and the applicability of this system in 85V~450V input voltage range is verified. Work principle of the dual switch BuckBoost circuit is introduced, and the small-signal models for the two working modes of the converter are established. The parameters of the main circuit are detailed designed and the selections of its components are discussed.The dual switch forward converter, the later stage of the cascade system, plays a role of step-downing voltage, electrical isolation and also has to maintain the output voltage be stable when the load changes. The single voltage loop control system is selected. The small-signal model of the converter is established. The parameters of the main and the single voltage loop control system are detailed designed.To ensure the stability of the proposed two-stage cascade converter, the relationship of the open-loop and closed-loop output impedance of the former converter and the closed-loop input impedance of the later converter is analyzed. Results show that the stability criteria for cascade system is accorded with the relationship.To prove fesibility of the proposed two stage converter and the correctness of theoretical analysis, a simulation model is established based on PSIM software platform. Simulation results show that the system can work stably with sound dynamic and static characteristics. The output voltage disturbances caused by the input voltage change and load change are little, so the output voltage can be considered as a constant.Finally, a prototype of the two-stage converter is fabricated and experiments is carried out. Experiments waveforms are listed and analyzed, verifying the feasibility and correctness of proposed two stage converter.