Research On Fast Charger For Electric Vehicle

With the worsening of primary energy continuous consumption by the vehicle and pollution problems of automobile exhaust, more and more people have focused on the development of electric vehicle. EV is recognized as the most potential traffic tools in the future to replace fuel vehicle due to its energy conservation and environmental protection. So bidirectional DC fast charger for EV has been one of the most important research areas in power electronics for its great effects on increasing the cruising distance.The main points of this paper are analyzing the characters of fast charging methods and the design of the DC fast charging system for EV. Firstly,the paper compared the fast charging methods with the conventional charging technology to find the characters of the batteries charging in different methods. Then proposed a comparison method based on the same average current to analyze the advantages and disadvantages of constant current charging and pulse current charging. The results showed that the pulse current charging is faster but not suitable for EV charging. Applied the transformer with two switchable windings to output two AC voltage to achieve the wide output voltage range. Also, this paper analyzed the constant current and constant voltage charging control strategy and the feasibility of the discharging. After that, in order to decrease the impact of the unbalanced three-phase grid voltage, research on the two control targets under the unbalanced condition: to restrain the pulsation of the bus voltage and to restrain the grid current of negative order. According to the topology of the charger, this paper applied the feed-forward of the positive and negative order grid voltage to restrain the negative-order current.At last, built a 50 kW EV fast charger prototype and introduced the design of the hardware parameters and the control system of the charger. Based on the prototype some experiments had been done and the results showed that the charger can work on charging and discharging condition, it also had a good performance on unbalanced condition and could change the charging methods by the command of the EV. Experiment results verified the correctness and feasibility of the proposed design and the control system of DC fast charger.