Introduction to the Principle of Electric Vehicle Fast Charging Technology

As an energy supply device for electric vehicles, the charging performance of the charger is related to the service life and charging time of the battery pack. The basic principle of electric vehicle charger design is to achieve fast, efficient, safe and reasonable power supply to the power battery. In addition, the applicability of the charger to various power batteries must also be considered.

FIG1 shows the composition of the control system of the fast charger. Different from the continuous current charging and pulse current charging methods used by traditional chargers, the system adopts an intelligent variable pulse charging method, that is, a charging current pulse as shown in FIG2, including a charging pulse T1, an intermittent pulse T2, and a discharge pulse T3.

The fast charger implements segmented adjustment of the charging current pulse width T1, the intermittent time T2, and the discharge current pulse T3 according to the terminal voltage, charging current, temperature, dynamic internal resistance and other information of the battery pack detected in real time and in accordance with the Mars charging law by adopting an intelligent control algorithm to eliminate the polarization phenomenon of the charged battery pack, so that the battery pack is always in a better current acceptance state, and the charging speed and charging efficiency are improved. The specific adjustment process is that firstly, a wider charging pulse is used for charging, and the terminal voltage of the battery rises. When the charging time T1 is reached, the charger suspends charging, and when the charging intermittent time reaches T2, the charger continues to charge, and so on and so forth; when the voltage rises to the set voltage value V1, according to the setting of the program, the charging pulse duty cycle is reduced, and the battery is charged. When the battery terminal voltage reaches the set value V2, the charger suspends charging intermittently; the duty cycle of the output pulse is automatically adjusted according to the feedback voltage, and after a short period of charging is stopped, the polarization voltage of the battery drops rapidly, and so on and so forth are repeated until the charging termination voltage V3 of the battery pack is reached. This fast charger realizes for the first time the intelligent real-time adjustment of the pulse charger charging pulse according to the actual charging state of the charged battery (current, voltage, temperature, dynamic internal resistance, etc.), comprehensively considers the charger and the charged battery as a system problem, and introduces an intelligent adjustment algorithm to make the charger more widely applicable.

Figure 3 shows a typical charger scheme in a ground charging station. The charger consists of a rectifier that can convert the input AC power into DC power and a power converter that can adjust the DC power. By inserting the plug with a wire into the matching socket on the electric vehicle, the DC power is input into the battery to charge it. The charger is equipped with a locking lever to facilitate the insertion and removal of the plug. At the same time, the lever can also provide a signal to confirm that it has been locked to ensure safety. According to the communication between the charger and the battery management system on the vehicle, the power converter can adjust the DC charging power online, and the charger can display the charging voltage, charging current, charging amount and charging cost, etc.