Development Of Charging And Discharging Platform For Rechargeable Battery Of Maglev Train Based On SiC

The rechargeable battery of high-speed maglev train will charge from power grid when the speed is higher than 150km/h and supplies power for systems of suspension,control,ventilation and others when the speed is lower than 150km/h,so its reliability and capacity will directly influence the safe operation of trains.In order to ensure the performance of rechargeable batteries,the simulated operation of the selected battery should be evaluated according to the actual working conditions while choosing battery types.In conjunction with the project “Charging and discharging platform for high-speed maglev trains” commissioned by National center for maglev engineering of Tongji University,an efficient,energy-saving charging and discharging device is developed for evaluating rechargeable batteries of highspeed maglev trains in the thesis.With the technical requirements,the paper will mainly focus on the following work:The main circuit of the charging and discharging platform has been designed.The “Bidirectional AC/DC + isolated bi-directional DC/DC + non-isolated bi-directional DC/DC”structure and SiC devices are used for system solution,achieving the high charging and discharging performance.For “Bi-directional AC/DC”,the SiC-based two-level topology is more advantageous than Si-type IGBT-based three-level topology after comparing their complexity,efficiency and costs.The circuits like bi-directional CLLLC,bi-directional LLC and double active full bridge are all relatively suitable for isolated DC/DC converters.However,due to its soft switching characteristic and bi-directional symmetry,bi-directional CLLLC topology is applied.In order to reduce current and voltage ripple,the interleaving Buck/Boost topology is chosen for “non-isolated DC/DC”.The control methods for charging and discharging platform have been designed.The double closed-loop control structure with outer loop voltage and inner loop current,which applies the DQ axis decoupling control,is adopted for AC/DC.Moreover,the SPWM injected zero-order components,equivalent to SVPWM,has applied and simplified the complicate computation.Voltage regulation is not necessary for the CLLLC part,which is open-loop controlled by the certain frequency,equal to the resonant frequency.In this way,the highest efficiency of the converter is guaranteed.The control of DC/DC charging is double closedloop in series of output voltage and current.The current is limited to realize constant-current and limited-voltage charging and discharging.Besides,the discharging part adopts current closed-loop control.The experiment of charging and discharging platform has been verified.Combining with the enterprise project,the experience platform with the rated power of 2kw and ARM +FPGA(EP4)as control core is established in the paper.In the experiment,not only the control of active & reactive currents and stable DC voltage by bidirectional AC/DC,but also the constant frequency control by bidirectional CLLLC have been respectively verified,followed by verifying the voltage & current control by interleaving Buck/Boost.The theoretical correctness of the topology,the correctness of the algorithm,and the feasibility of charging and discharging are mainly verified.After all,the charging and discharging control of the system has been verified,as well.It’s concluded as the experiment result,that the designed system has the abilities of charging rechargeable batteries,energy feedback,achieving high power factor and low ripper,as well as has high efficiency in charging and discharging.