Research On DC/DC Converter Of Electric Vehicle Charger And Its Control Strategy

In recent years,electric vehicle(EV)batteries have been widely used as storage devices for electric energy,and the requirements for battery capacity and charging rate are increasing,which requires battery chargers to have higher voltage levels and power levels.However,the high-voltage input and high-power charger has a problem that the switching tube voltage stress is too large.For this reason,an input-series output-parallel(ISOP)DC/DC converter solution is adopted to reduce the voltage stress of the MOSFET and improve power level.Research on the ISOP DC/DC converter and its control strategy of the charger,design the sub-module phase-shifted full-bridge(PSFB)DC/DC converter,solve the problem of input voltage sharing and output current sharing,realize the independent control and improve the comprehensive performance of the charger play a key role in improving the comprehensive performance index of the charger.Firstly,in order to improve the efficiency of sub-modules,an improved PSFB converter with clamp diode is selected as the main circuit of ISOP DC/DC converter,and its working principle is analyzed.A clamp diode is introduced on the primary side of the transformer to suppress the voltage oscillation of the rectifier side rectifier,and a synchronous rectification technique is introduced to reduce reduce transformer secondary side loss.Based on this,the component parameters were calculated and selected,and the loss calculation was performed.The simulation model was built to verify the rationality of theoretical analysis and design.Secondly,in order to realize the power sharing of sub-modules,the relationship between input voltage sharing and output current sharing of ISOP DC/DC converter is studied.The stability analysis of input voltage sharing and output current sharing control strategies is carried out.The small-signal model of the ISOP DC/DC converter is further derived by modeling the small-signal of the PSFB DC/DC converter.An output current compensation without interconnection control is proposed.Under the premise of sampling the output current of each sub-module,the input voltage sharing loop is added to realize the no interconnection control and improve the modularity.The compensation circuit of the main and auxiliary modules is designed,and the feasibility of the control strategy is verified by simulation.Finally,a 1.2kW two-module ISOP DC/DC converter prototype based on the hardware-in-the-loop simulation system RT-LAB was built.The control circuit,the drive circuit,the sampling circuit,and the protection circuit are designed.The working condition and voltage sharing effect of the sub-module were tested.The experimental results verify the rationality of the hardware parameter design and the effectiveness of the control strategy to meet the design requirements of EV chargers.