Research And Design Of Li-ion Battery Charger For Hybrid EMU

With the development of China railway construction, the related technologies for emus have been deeply studied. In order to solve the difficulty of emu running on unelectrified cross electrification lines, and to solve the pollution problem of the DMUs running in the city, the environmentally-friendly hybrid emu arises at the historic moment. This project named "Hybrid emu key technology research and prototype development" is conducted by Beijing Jiaotong University and Changchun Railway Vehicles Co., Ltd. Hybrid emu is a kind of emu which has two kinds of energy sources at least.This battery charger is mainly done for hybrid emu emergency battery charging and for the emu’s all low-voltage dc load. Based on the theoretical and engineering foundation, the analysis of battery charging mode and design of the main circuit and design of the control system model simulation and experimental validation have been completed in this thesis.First of all, the emu battery characteristics were analyzed in the thesis. And Lithium titanate type battery was selected for hybrid emu emergency battery according to the characteristics of the new type of lithium battery. After the comparison of different charging ways, the stage of constant-current to constant voltage charging mode was selected.Secondly, the design of charger main circuit and the selection of main device were completed, and the overall efficiency of charger was estimated according to detailed calculations of the different device loss.Then the hardware of the charger’s control system was designed, and the sample link and modulus conversion link belonging to control system were completed. In this thesis, the suitable control mode was selected, and the pulse generating principle was analyzed. Some design programming work for key links such as the voltage current controlling, protections and restart was also completed.Again, the small signal model of the charger was established, and the transfer function of the control system was derived. After that, the PI controller has been designed in a suitable way, and the stability of the system was analyzed. Then the digital form of PI controller was derived, and PI controller programming in DSP was completed.Finally, the system simulation model was established using computer simulation software, then the feasibility of the design was verified. And the prototype was tested for the basic function and performance. In the end, loading test in hybrid emu was completed. The final test data showed that the charger prototype has reached the expected design requirements about the output voltage controlling, charging current controlling, protection and restart function. And this charger prototype has operated in hybrid the emu prototype reliably.