Research On Key Technology Of Electric Vehicle Charging

The increasingly severe environmental and energy problems have impelled the rapid development of electric vehicles,The characteristics of the electric vehicle's environmental protection and low travel cost decide that it will become one of the main transportation tools in the future.The charging technology of electric vehicles will affect the service lifetime of the battery,and is also the key technology that restricts the extensive popularization of the electric vehicle.Charging technology is more related to the impact of electric vehicle charging on the power grid.The most direct effect is that large-scale disordered charging will harm the load characteristics of the power grid and the power quality of the distribution network,and injecting harmonics into the power grid and reducing the power quality of the power grid.The large-scale distributed load and distributed power grid,the interface is mostly in power electronic devices,The traditional power electronic converter lacks the damping and inertia of the rotating power system,although its response speed is fast,it is difficult to actively participate in the adjustment of the power grid,it lacks a "synchronization" mechanism with the power grid.Firstly,the charging system is regarded as a load of the power grid,and the AC interface is analyzed and studied.After the common rectifier is classified,the three-phase PWM voltage rectifier is selected,the work modal analysis is carried out,and the periodic average model of the switch is established.On this basis,the traditional control strategies are analyzed and compared.Aiming at the characteristics of traditional rectification control strategy,such as fast response,almost no inertia,difficult to participate in power grid regulation,and unable to provide necessary voltage and frequency support for power grid,a virtual synchronous motor rectifier technology with low THD and high power factor is studied.The power grid is given a certain of frequency and voltage to be supported on the load side of the grid.Adding a passive damping LCL filter to the AC side of the rectifier reduces the cost and inhibits the resonant peak and effectively improves the power quality of the power grid.The rectifier based on the principle of virtual synchronous motor is simulated and analyzed,a passive damping of LCL filter is added to reduce the total harmonic distortion of the AC interface to 0.84%,the frequency of the virtual synchronous motor can be stabilized at 50 Hz,and the output voltage of the DC side is stable at 600 V.The technology makes the distributed load side more interactive with the power grid,and can provide a certain frequency and voltage support in the event of a power grid accident.The correctness and superiority of the theory are verified by Matlab/Simulink simulation.Secondly,the post stage DC interface is analyzed and studied.After analysis and comparison,the half bridge LLC resonant converter is selected.It is divided into several parts,including the switching network,the resonant network,the isolation transformer,and the uncontrolled bridge.The working principle of the resonant converter is analyzed in detail.On this basis,a small signal model is established,and the control loop is designed,and the Bode diagram is simulated.The simulation results of the closed loop system show that the system can realize the ZCS and ZVS of the switch tube,and the sudden change of load and DC bus voltage also verifies the correctness and feasibility of the control loop.Finally,the half bridge resonant LLC circuit with DC interface is designed and verified by low power test.The power switch device is analyzed,designed,selected and debugged.In the end,a test platform is built.The feasibility of half bridge resonant circuit is verified by experiments,and the ZVS and ZCS of switch tube are realized.