Since the first electric vehicle appeared in the 19th century, rechargeable batteries have been used as its power source. For an electric vehicle, the battery charging equipment is one of the indispensable subsystems. Its function is to convert the electric energy of the grid into the electric energy of the electric vehicle on-board battery. There are different ways to classify electric vehicle charging devices, which can be generally divided into on-board charging devices and off board charging devices.
On board charging device refers to the device installed on the electric vehicle that uses the ground AC power grid and the on-board power supply to charge the battery pack, including the on-board charger (Figure 1-13), the on-board charging generator set and the operating energy recovery charging device. A AC power cable with a plug is directly inserted into the charging socket of the electric vehicle to charge the battery. On board charging devices usually use contact chargers with simple structure and convenient control, or inductive chargers. It is designed completely according to the type of on-board battery, with strong pertinence. Off board charging device, i.e. ground charging device, mainly includes special charger, special charging station, general charger, charging station for public places (Figure 1-14), etc. It can meet various charging modes of various batteries. Generally, the power, volume and weight of off board charger are relatively large, so as to adapt to various charging methods.
In addition, according to the different ways of energy conversion when charging the electric vehicle battery, the charging device can be divided into contact type and inductive type. With the rapid development of power electronics technology and converter control technology, and the maturity and popularization of high-precision controllable converter technology, the staged constant current charging mode has been basically replaced by the constant voltage current limiting charging mode with continuous changes in charging current and charging voltage. The constant voltage current limiting charging mode dominates the charging process. The biggest problem of contact charging is its safety and universality. In order to make it meet the strict safety charging standard, many measures must be taken in the circuit to enable the charging equipment to charge safely in various environments. Constant voltage current limiting charging and staged constant current charging are contact charging technologies. The new induction charging technology for electric vehicles has developed rapidly. The induction charger is to use the transformer principle of high-frequency AC magnetic field to sense the electrical energy from the original side of the vehicle to the auxiliary side of the vehicle, so as to achieve the purpose of charging the battery. The biggest advantage of inductive charging is safety. This is because there is no direct point contact between the charger and the vehicle. Even if the vehicle is charged in bad weather, such as rain and snow, there is no danger of electric shock.
