Research On Three-phase Grid-connected Converter With Un-damped LCL Filter

With the shortage of fossil fuels, human beings have to extenuate the dependence on fossil fuelsin the filed of transportation by starting to engaged in the research related to electric vehicles(EV).Among all the components of EV, the cost of the EV battery are the highest and therefore anappropriate control of charging and discharging is needed in order to extend its life and optimizecharging time. This paper is focused on the bidirectional three-phase AC/DC converter in the chargingand discharging system with its AC port connected to the grid and DC port cascaded with a DC/DCconverter which interact with the EV battery.Firstly, the current research status and trends of three-phase AC/DC converter are introduced,including a brief introduction of topology selections, output filter designing and control strategy. Afterchosen the three-phase half-bridge AC/DC converter with LCL filter as the final option, the basicmathmatic models and working principle of this topology are presented, the principles of SVPWMmodulation and its loss are derived and the inner current loop has also been designed.On this basis, a comprensive comparison between various types of AC side filters are introducedand the influence of a non-ideal magnetic core on an un-damped LCL filter and the current loop isanalysed followed with a stability analysis which derived the range of PI controller parameterscapable of maitaining system stability and also the parameters of the LCL filter has been designed.Owing to the relatively small range of PI controller parameters, this paper studied the dynamiccharacteristics and static characteristics of an three-phase AC/DC converter with un-damped LCLfilter, a novel soft starting method are proposed to reduce the stresses on the switch and improvereliability. The output current THD has also been caculated.Finally,18kVA three-phase AC/DC converter prototype based on DSP digital control is built andthe software and hardware design are introduced. The experimental results based on the prototypeshow the correctness the theoretical analysis and simulation results.