| Facing of environmental pollution, energy shortage and the demand of low-carbon, newenergy vehicles with electric vehicles(EV) represented ushere in a period of rapiddevelopment.Energy supply facilities for electric vehicles are essential. Battery charging stations andbattery replacement stations with charging-discharging machines as the core equipment are thefoundation of industrilization of EV.Compared to battery chargers in conventional stations, Thecharging-discharging machines can not only charge the electric vehicles,but also connect thebatteries used as energy storage units with the grid, which can “cut peak and fill valley” on the gridwith its characteristics of bi-direction energy flowing and improve power qualities and its operationalstability.Charging-discharging machines generally use the cascade structure of bi-directional AC-DC andbi-directional DC-DC. The multi-phase bi-directional Buck/Boost converter used in high powercharging-discharging machines is researched. First of all, comparing the advantages anddisadvantages of several conventional bi-directional DC-DC converters, the topology of multi-phaseBuck/Boost converters is selected. A reasonable countermeasure is given by the consideration ofsoft-switch of the high power converter and voltage spikes in hard-switch. The control method of thebi-directional Buck/Boost converter is established by analyzing the characteristics of the li-on battery.In order to improve the efficiency, the converter is optimized and a method to choose the inductance ispresented based on the analysis of the losses and its volume. By adopting this program of theinterleaved DC-DC converters, it can improve the efficiency, reduce output voltage ripple of theconverter and lower the filter component sizes. It can also improve light-load efficiency to broadenhigh-efficiency operation range with dropping-phase control which changes the number of parallelphases running simultaneously under different output power.Finally, a prototype of18kW Buck/Boost converter is built based on the demand ofcharging-discharging machines and the detailed design process is presented. Regarding of thesimulation and experimental results, it verifies the abrove analysis and related theories. |
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