| Development of electric vehicles is an important way of Energy Conservation and Emission Reduction, as well as the climate improvement. The development of electric vehicle charger is the basis for the popularization of electric vehicles. The electric vehicle charger consists of a front stage rectifier and a post stage DC/DC converter. And the charging power control depends on the control of the DC/DC converter. The charging control method and the current-sharing strategy among the parallel modules of the transformer isolated DC/DC converter are studied for the application of electric vehicle charger.The main circuit topology of the isolated DC/DC converter used in electric vehicle charger is designed. The working principle of the DC/DC converter is analyzed. The linearized small-signal communication model of full-bridge two-level DC/DC converter is established. The main circuit parameters of the converter with power of 15kW are calculated and selected. And the control system structure of the converter is determined.In order to meet the control requirement of the constant-voltage current-limiting charging mode, a modulation-selection control structure is designed. When the DC charging voltage is limited, the constant voltage control is selected, and the constant current control is selected when the charging current is limited. The number of control-loops is reduced and the stability of control system is improved. The merits and drawbacks of the modulation-selection control and the traditional doub,le-closed-loop cascade control based on outer voltage-loop and inner current-loop are compared. The simulation model based on the PSIM platform is established,and the superiority of the constant-voltage current-limiting charging control strategy based on modulation-selection structure is verified by simulation.The electric vehicle charging pile is usually connected by a plurality of charger modules in parallel, which is convenient for expanding the charging power of the charging pile. The current-sharing control among the charger modules contributes to balance the service life of each module and improve the charging performance. The traditional analog control current-sharing method and the digital control current-sharing strategy based on double-closed-loop cascade structure are studied. A digital control current-sharing strategy of average current method based on modulation-selection structure is designed, and a system scheme of digital current-sharing control by using CAN communication to transfer information among the modules.The experimental prototype of electric vehicle charger with power of 15kW is established.The control system and its application program are designed. The feasibility of modulation-selection control is verified by testing the experimental prototype.The effect of the digital current-sharing control among the modules is verified by the load-switching experiments by using two parallel charger experimental prototype. |
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