Fast charging, also known as emergency charging, provides short-term charging services for electric cars within 20 minutes to 2 hours of parking with a large current for a short period of time. The general charging current is 150-400A. Fast charging is different from conventional charging. constant current and constant voltage charging methods. This charging method uses a high current of 150 ~ 400A to charge the battery with constant current, and strives to charge a large amount of electricity in a short period of time. The charging time should be close to the refueling time of a fuel car, so fast charging can also be called rapid charging. , mainly used in large charging stations.
The main object of the fast charging method is electric cars that drive long distances or need to quickly replenish electric energy. The charging time is generally 10 to 30 minutes, and the charging capacity can reach 80% of the battery capacity. The power of the charger is very large, generally 50- 100kw, using three-phase four-wire 380V power supply. The fast charging method adopts a large charging current of 1-3C. Due to the large current, the requirements for technology and safety are also high.
The fast charging method is mainly carried out in the charging station. Due to the high power and current ratings, this charging method has high requirements on the power grid. Generally, it should be close to the 10kV substation or the charging station self-built 10kV substation. Compared with the slow charging method, the installation cost of the fast charging method is relatively high, and it is only suitable for large charging stations. This charging method has a certain impact on the life of the battery, and receiving a large amount of electricity in a short period of time will cause the battery to overheat.
At present, there are no national standards or international standards for the pin definition, voltage, current value, control protocol, etc. of the charging socket of the fast charging method. Countries around the world are actively competing for the right to formulate standards, and major electric car manufacturers have also preemptively launched products, seized the market, and increased their market share, trying to make most charging stations have to use their charging equipment, thus becoming the de facto standard.
The fast charging method is realized by using the characteristics of the electric car battery that can accept a large charging current in the early and middle stages of charging, combined with the depolarization technology of charging stop and pulse discharge. If the charging current adopts the No. 1 curve as shown in Figure 3-1, then the battery charging time should be the shortest theoretically. However, in actual operation, it is impossible to charge according to the charging current of the No. 1 curve due to the difference in the age of the battery pack, the ambient temperature and the capacity of the battery. In order to ensure the safe use and service life of the battery, the No. 2 curve is often used according to experience during charging, and a certain margin is left in the continuous decreasing current, so that the charging current is slightly less than the maximum acceptable current. The No. 2 curve in Figure 3-1 can generally be obtained from multiple battery tests, but it is difficult to set the curve characteristic parameters in the actual operation of the user, so this charging method is rarely used.
The main advantage of the fast charging method is that the charging time is short, and the storage capacity of the battery can reach 80%-90% in a short time (10-15 minutes), which is similar to the refueling time. field.
Compared with the conventional charging mode, fast charging also has certain disadvantages. The charging efficiency of the charger is low, and the corresponding work and installation costs are relatively high; the fast charging is used, and the charging current is large, which brings forward the safety of charging technology and charging. Higher requirements, and the design of metering charges also needs special consideration.
Fast charging is suitable for electric cars with moderate driving mileage (the average daily mileage is greater than the battery’s driving mileage, i.e. 200km), that is, the battery is quickly replenished during car operation to meet operational needs, such as buses, taxis and other cars. The average mileage is about 300km, and there is still about 100km of electricity that needs to be replenished by fast charging. Fast charging methods can have detrimental effects on the utility grid and are therefore only suitable for dedicated charging stations.