Basic knowledge of car charging machines and charging stations

1.Car charging machine
The car charging machine is a device that is connected to the AC power grid to provide DC power for rechargeable energy storage systems such as power batteries. It is generally composed of control unit, metering unit, charging interface, power supply interface and human-computer interaction interface. It realizes charging metering and other functions, and has multiple functions such as reverse connection, overload, short circuit, overheating protection, and delay start, soft start, Functions such as automatic start memory when power off.

1). Type of car charging machine
Electric car chargers can be divided into multiple types according to different classification standards, as shown in Table 1.

Classification standardCharger typeCharger type
Installation locationCar chargerOff-board charger
Input powerSingle-phase chargerThree-phase charger
Connection methodConductive charger (contact type)Inductive charger (non-contact)
Table 1 Types of electric car chargers

(1) On-board charger
The on-board charger is installed on the electric car and is connected to the AC socket through a plug and cable. The advantage of the on-board charger is that whenever the battery needs to be charged, it can be charged as long as there is an available power outlet. The disadvantage is that it is limited by the installation space and quality on the car, the power is small, it can only provide low current and slow charging, and the charging time is longer. Figure 1 shows the appearance of a typical car charger (charger).

Basic knowledge of car charging machines and charging stations
Figure 1 Appearance of a typical car charger

(2) Off-board charger
Non-car chargers, also called ground chargers, are generally installed in a fixed location or movable, and are connected to an AC input power source, and the DC output terminal is connected to the charging interface of an electric car that needs to be charged. Off-board chargers can provide high-power current output without being restricted by car installation space, and can meet the requirements for high-power fast charging of electric cars. Figure 2 shows the off-board chargers.

Basic knowledge of car charging machines and charging stations
Figure 2 off-board chargers

(3) Conductive charger and induction charger
The power supply part of the conductive charger is mechanically connected to the power receiving part, that is, the output end of the charger is directly connected to the charging interface of the electric car through the power cable. As shown in Figure 3, the electric car is not equipped with a power electronic circuit. The structure of this kind of charger is relatively simple and easy to realize, but the operator will inevitably have to contact with strong electricity, so it is prone to danger.

Basic knowledge of car charging machines and charging stations
Figure 3 Principle of conductive charging

The induction charger uses the principle of electromagnetic energy transfer to transmit electric energy to the electric car by means of electromagnetic induction coupling. There is no direct mechanical connection between the power supply part and the inductive part. As shown in Figure 4, the energy transfer between the two is only dependent on electromagnetic Conversion of quantification. This kind of structural design is more complicated. The power receiving part is installed on the electric car, and the power is limited by the car installation space. However, since the charging personnel do not need to directly touch the high-voltage components, the safety is high.

Basic knowledge of car charging machines and charging stations
Figure 4 Principle of inductive charging

2). Performance requirements of the charger
In order to achieve safe, reliable and efficient power battery charging, the charger needs to meet the following basic performance requirements.
①Safety: to ensure the personal safety of the operator and the safety of the battery pack when charging the electric car.
②Easy to use: The charger must have high intelligence and does not require excessive intervention by the operator in the charging process.
③Economy: The cost reduction of chargers plays an important role in reducing the overall cost of electric cars, improving operating efficiency, and promoting the commercialization of electric cars.
④Efficient: Ensure that the charger is highly efficient in the full power range of charging, and can save a lot of electric energy in the long-term effect. Improving the energy conversion efficiency of chargers plays an important role in the economics of the entire life of electric cars.
⑥ Low pollution to the power grid: The charger is a highly non-linear device that will produce harmonic pollution harmful to the power grid and other electrical equipment during use. Corresponding filtering measures need to be adopted to reduce the pollution of the power grid during the charging process.

2.Car charging station
Charging station mainly refers to the service infrastructure that quickly, efficiently, economically and safely provides various electric cars with the electric energy needed in operation. In order to improve the utilization rate and ease of use of the car, in addition to the on-board charging of the power battery, the replacement of the power battery system of the electric car and the auxiliary battery can also be adopted to enable the electric car to obtain the necessary electric energy for driving.
The main function of the charging station determines its overall layout. Generally speaking, a fully functional charging station consists of five basic parts: power distribution area, charging area, battery replacement area, battery maintenance area, and monitoring area. According to the scale of charging stations and the difference in service functions, there are certain differences in the setting of functional areas. For example, a charging station that does not need to replace the battery will not need to set up a replacement area and a storage device equipped with battery replacement equipment and a large number of batteries.

Basic knowledge of car charging machines and charging stations
Figure 5 Overall structure of charging station

(1) Power distribution area
The power distribution area provides the required power supply for the charging station, not only to provide electrical energy to the charger, but also to meet the needs of lighting and control equipment. All equipment for power transformation and distribution and power distribution monitoring system are built inside, and related control and compensation equipment also need to be considered. The power distribution area is the basis for the normal operation of the entire charging station. According to the needs of power distribution, the charging load, monitoring and office load are generally used to supply power separately.
(2) Charging area
The function of the charging zone is to complete the supply of electric energy for the power battery pack. The charging area is the core part of the entire charging station. It is equipped with various types of chargers. The charging platform and the network interface of the charging station monitoring system are built to meet various charging needs and provide convenient, safe and fast all-round charging services.
(3) Replace the battery area
The battery replacement area is a place where cars can replace batteries and battery dispatch. Battery replacement equipment is required, and a battery storage area should be built to store backup power battery packs.
(4) Battery maintenance area
The function of the battery maintenance area is to manage the quantity, quality and status of all batteries in real time, to perform battery reconfiguration, battery pack balancing, battery pack actual capacity testing, emergency treatment of battery failures, and routine maintenance.
(5) Monitoring area
The monitoring area is used to monitor the operation of the entire charging station, including charging parameter monitoring, smoke monitoring, power distribution monitoring, etc., and can be extended with car operation parameter monitoring, field station patrol monitoring and other functions, and complete management report printing. Each monitoring subsystem can be connected to the central monitoring room and the higher-level monitoring center through the local area network and TCP/IP to realize the functions of data aggregation, statistics, display and monitoring. The charging station monitoring system architecture generally adopts a hierarchical parallel structure.

Basic knowledge of car charging machines and charging stations
Figure 6 Charging station monitoring system architecture

The power distribution monitoring system needs to realize the exchange and management of the power supply system information of the power distribution station through the field bus. In addition to the conventional secondary equipment relay protection, safety automatic devices, measuring instruments, operation control and other functions, the system needs and monitoring system Realize communication to ensure that when the charging system fails, the power distribution system can take appropriate measures to deal with it.
The smoke alarm monitoring system mainly monitors the battery status on the charging platform, and sends out an alarm when the battery smokes, burns, and other dangerous situations. This system is independent of the battery management system and is part of battery safety measures.
The charger monitoring system completes the charging process monitoring. The charger data and battery data are transmitted to the monitoring computer through communication, and the monitoring computer completes data analysis and report printing. The monitoring computer can also control the start and stop of the charger and the output current and voltage.
The video surveillance system monitors the operation of the main equipment and personnel of the entire charging station.