Charging piles can be divided into AC charging piles, DC charging piles, and AC/DC integrated charging piles according to the charging method. Among them, AC charging has low power and requires a long charging time, but the loss to the battery is small. On the contrary, DC charging piles have high charging power and fast charging, but the loss to the battery is also large.

1. Charging principle of charging piles

The charging pile is fixed on the ground, using a dedicated charging interface and a conduction method to provide AC power for electric vehicles with on-board chargers, with corresponding communication, billing and safety protection functions. Citizens only need to buy an IC card and recharge it, and they can use the charging pile to charge their cars.

After the battery of an electric vehicle is discharged, direct current is passed through the battery in the opposite direction of the discharge current to restore its working capacity. This process is called battery charging. When charging the battery, the positive electrode of the battery is connected to the positive electrode of the power supply, and the negative electrode of the battery is connected to the negative electrode of the power supply. The charging power supply voltage must be higher than the total electromotive force of the battery.

2. Charging method of charging piles

There are two charging methods: constant current charging and constant voltage charging.

(1) Constant current charging method

The constant current charging method is a charging method that adjusts the output voltage of the charging device or changes the resistance in series with the battery to keep the charging current intensity constant. The control method is simple, but since the battery's acceptable current capacity gradually decreases as the charging process proceeds, in the later stage of charging, the charging current is mostly used to electrolyze water to produce gas, causing excessive gas emission. Therefore, the stage charging method is often used.

(2) Constant voltage charging method

The voltage of the charging power supply remains constant throughout the charging time. As the battery terminal voltage gradually increases, the current gradually decreases. Compared with the constant current charging method, its charging process is closer to the optimal charging curve. When charging quickly with a constant voltage, since the battery electromotive force is low at the beginning of charging, the charging current is large. As charging proceeds, the current will gradually decrease. Therefore, only a simple control system is required.