DC Charging vs AC Charging
Charging pile can be divided into AC charging pile, DC charging pile and AC/DC integrated charging pile according to charging mode. AC charging has lower power, requires longer charging time, but has less loss to the battery. On the contrary, DC charging pile has higher charging power, faster charging, but has greater loss to the battery.
1. Charging Principle of Charging Pile
The charging pile is fixed on the ground, uses special charging interface and adopts conduction mode to provide AC electric energy for the electric vehicle with on-board charger, and has corresponding communication, billing and safety protection functions. Citizens simply need to buy an IC card and top it up to charge their cars with charging points.
After discharging the battery of an electric vehicle, the direct current is used to pass the battery in the opposite direction from the discharge current to restore its working capacity. This process is called battery charging. When the battery is charged, the positive pole of the battery is connected with the positive pole of the power supply, and the negative pole of the battery is connected with the negative pole of the power supply. The voltage of the charging power supply must be higher than the total electromotive force of the battery.
2. Charging Mode of Charging Pile
There are two charging modes: constant current charging and constant voltage charging.
(1) Constant Current Charging Method
Constant current charging method is to adjust the output voltage of the charging device or change the series resistance of the battery to keep the charging current intensity unchanged. The control method is simple, but because the acceptable current capacity of the battery is gradually decreased with the charging process, to the later stage of charging, charging current is used for electrolytic water, gas generation, so that the gas is too much, therefore, often choose stage charging method.
(2) Constant Voltage Charging Method
The voltage of the charging power supply remains constant throughout the charging time, and the current decreases gradually as the terminal voltage of the battery increases. Compared with constant current charging method, its charging process is closer to the optimal charging curve. Fast charging with constant voltage, due to the low electromotive force of the battery at the beginning of charging, charging current is very large, with the charging process, the current will gradually reduce.
3. Difference between DC Charging and AC Charging
(1) Charging Speed
Dc charging piles use direct current, while AC charging piles use alternating current, resulting in a difference in charging speed between the two types of charging piles.The charging speed of DC charging pile is faster, while that of AC charging pile is generally slower.Therefore, dc charging piles are generally used for quick charging piles.
Generally, DC piles are relatively large (because there are a certain number of AC-DC power modules inside, the higher the power, the more modules), while AC piles are relatively small. Secondly, the head is not the same, DC pile charging gun has 9 holes, in addition to PE grounding wire, there are positive and negative dc power supply, CC1, CC2 and so on. AC pile charging gun has 7 holes, generally including L, N AC power supply, PE grounding wire, CC charging connection confirmation and so on.
(3) Charging Principles
The DC charging pile directly charges the power battery of an electric vehicle. AC charging pile only provides power output and has no charging function. It needs to be connected to the on board charger to charge electric vehicles, which is equivalent to just playing a role of control power supply.
(4) Charging Power
The DC charging pile adopts three-phase four-wire power supply system, which can provide enough power and adjust the output voltage and current in a wide range to meet the requirements of fast charging. Power to 40kW, 60kW and higher.
AC charging pile is a power supply device that provides AC power for the on-board charger of electric vehicles (that is, the charger fixed on the electric vehicle). Power to 3.5kW and 7kW in the majority.
AC pile is cheaper and easier to be installed privately, and DC charging pile is generally installed by operating enterprises due to volume, price and other reasons.
(6) Influence to Battery
An AC charging pile equalizes the battery pack at the end of the charge phase, ensuring that each cell is as fully charged as possible.Slow charging is mild and helps extend battery life.
The DC charging pile has high requirements on the quality of the battery, and the reaction conditions of the battery under large current are too harsh and severe, deviating from the equilibrium state for a long time. Long-term fast charging will cause a certain loss of the battery life, and the safety factor will decline. Therefore, it is necessary to reasonably match the fast and slow charging. In addition, there will be some components of virtual electricity in fast charging, which cannot reach the nominal driving range of the vehicle.