Research On Electric Vehicle Charger Based On Three Phase LLC Resonant Converter

Single-phase LLC resonant converter has simple topology and can achieve zero voltage conduction(ZVS)in the whole load range.It has the characteristics of high power density,high efficiency and low EMI.It has been widely applied in electric vehicle charging pile,mobile power station and other fields.However,the output filter circuit of the single-phase LLC resonant converter has no filter inductance and only capacitance,which results in large output current ripple,large capacity need of filter capacitor.The volume of filter circuit cannot be easily reduced and the life of equipment is limited by the life of filter capacitor.In addition,the rectifier output current of single-phase LLC resonant converter is all passing through rectifier diodes.Under the condition of large current,the current stress of secondary side rectifier tube is very high,and the loss is proportional to the square of the current.The loss is large,which limits the improvement of power level.In this paper,the single-phase LLC and three-phase LLC’s topology and working principle are studied in detail.A three phase staggered parallel LLC resonant converter is proposed.The three-phase staggered parallel LLC resonant converter surpasses the single-phase LLC in performance.First,the neutral point N of the Y connection is no longer connected to the ground.When the resonant network is not matched,each phase voltage can be automatically adjusted by the Y connection and the current between the phases can be automatically balanced.Secondly,the three-phase bridge arm is delayed 120 degrees in sequence,and the rectifying output ripple is reduced by the superposition effect of the phase shift current.In order to cope with the different requirements of battery voltage,this paper adopts the dual three-phase LLC with input-parallel and output-series,which can realize wide range regulation of output voltage and achieve the effect of automatic voltage sharing,simplifying the control algorithm.On the basis of theoretical analysis,the calculation method of resonant parameters of three-phase LLC resonant converter is given in this paper,and the simulation model of asymmetrical half bridge LLC,three-phase LLC and DC charger system is built based on PSIM software.The correctness of the theoretical analysis is demonstrated by comparing the simulation waveforms at different working frequencies with the typical waveforms.Finally,an experimental prototype of 15 kW is built and the typical experimental waveforms in different working areas are given,which tests the intermittent control under the condition of no load and verifies the correctness of theoretical analysis and the feasibility of the scheme.