1). Power battery charging function
Power battery charging should usually achieve the following three functions.
①Restore the battery to the rated capacity as soon as possible, that is, under the premise of restoring the battery capacity, the shorter the charging time, the better.
② Eliminate the adverse consequences caused by the battery in the process of discharging, repair the battery performance damage caused by deep discharge, polarization, etc.
③Supply charge the battery to overcome the adverse effects caused by battery self-discharge.
2). Power battery group charging method
According to different modes of operation, electric vehicle power battery pack charging can be divided into two ways: ground charging and on-board charging.
Ⅰ. Ground charging
Ground charging is when the vehicle is charging supplementally, the battery that needs to be charged is removed from the vehicle, and the fully charged battery is installed. The vehicle will leave and continue to run, and the disassembled battery will be supplemented by the ground charging system. Adopting ground charging method is conducive to battery maintenance, improves battery life and vehicle efficiency, but puts forward higher requirements on vehicles and battery replacement equipment. There are two methods for ground charging: sub-tank charging and whole group charging.
(1) Separate charging
When charging in separate boxes, each charger charges a box of batteries in the battery pack and communicates with the battery management unit of the box to complete the charging control. In this way, it is beneficial to improve the balance of the battery pack and prolong the service life of the battery pack. However, there are many chargers, the connection between the battery pack and the charger is many, the monitoring network is complicated, and the cost is high. Its structure is shown in Figure 1.
Among them, the charging platform includes a DC power supply consistent with the low-voltage power supply of the vehicle, a battery storage rack, a charger communication interface connector, a charger output connector, and a smoke sensor. When a single box battery is placed on the charging platform, the low-voltage power supply provides power to the battery management unit, and the charger connector is transmitted from the charger to the battery production site and communicates with the battery management unit to realize charging control, and the energy is output through the charger to the sensor , Temperature sensors, etc. to realize on-site monitoring during the charging process.
When split-box charging is used, the battery scheduling system is required to monitor and manage the quantity, quality and status of all batteries in real time, complete battery storage, replacement, reconfiguration and battery pack balancing, actual capacity testing and emergency handling of battery failures And other functions.
(2) The whole set of charging
When using the whole set of charging, the batteries removed from the electric vehicle are connected according to the application on the vehicle, and the whole set of batteries is charged through a charger, and all battery management units communicate with the charger through the battery management host , Complete charging control. In this way, the number of chargers is small and the monitoring network is simple, but compared to the sub-box charging method, the battery pack has poor balance and has a low service life. Its structure is shown in Figure 2.
The comparison of the advantages and disadvantages of the sub-box charging and the whole group charging method is shown in Table 1.
|Serial number||Whole set of charging||Sub-box charging|
|1||High charging voltage, poor safety||Low charging voltage, good safety|
|2||A single charging device has high power, immature technology, and high equipment cost||The single power of the charging equipment is small, the technology is mature, and the overall cost is low|
|3||Consistency differences increase fast||Slow down the increase in consistency differences|
|4||Relatively large harmonics||Relatively small harmonics|
|5||Not suitable for symmetrical arrangement of batteries in replacement mode||Suitable for symmetrical arrangement of batteries in replacement mode|
|6||Short battery life||Taking into account the consistency, effectively improve the battery life|
Ⅱ. Car charging
The on-board charging method is that when the vehicle is supplemented for charging, the charger and the charging vehicle are connected through the charging plug, and the battery can be directly charged without being removed from the vehicle. As shown in Figure 3. The advantage of this charging method is that the charging process is simple and does not involve operations such as battery storage or battery replacement, but the vehicle charging time takes up more running time, which is not conducive to maintaining the balance and reliability of the battery pack Life. Figure 4 shows a typical charging connector terminal layout. Figure 5 shows the connection of each terminal. The function of each terminal is shown in Table 2.
|DC+||750V 125A||DC power supply|
|DC-||750V 125A||DC power supply total negative|
|S＋||30V 2A||Charging communication CANH|
|S﹣||30V 2A||Charging communication CANL|
|CC1||30V 2A||Charging connection confirmation 1|
|CC2||30V 2A||Charging connection confirmation 2|
|A+||30V 20A||Low-voltage auxiliary power supply|
|A-||30V 20A||Low-voltage auxiliary power supply|
The system is connected to the internal CAN network of the electric vehicle through the CAN network connection line on the charging plug, communicates with the on-board battery management host, and completes the charging control.
In the early production of electric vehicles, because there is no unified standard, there are many forms of charging interfaces, as shown in Figure 6. my country issued a national standard for new energy vehicles in 2011, unifying the charging interface structure. In December 2015, the National Standardization Management Committee officially released five new national standards for electric vehicle charging interfaces and communication protocols, and officially began to implement them on January 1, 2016. After the new national standard basically unified the physical interface in the previous version, it focused on the unified communication protocol of the charging pile. This means that the charging interface is finally unified at the hardware and software levels. The newly constructed charging piles will be constructed in accordance with the unified new standards. After the transformation of the old public charging piles and the unification of service standards, the new charging piles will meet the charging requirements of various types of electric vehicles.
There are two forms of on-board batteries: one is a charger installed and carried with the car. Generally, the power is small. For electric vehicles, most of them are below 5KW and the charging current is small. Usually, the charging time is long on the 220V AC power grid (civil power grid). , So it is also called slow charging, suitable for charging at night and operating electric vehicles during the day. The second type is off-board chargers, which can generally be charged within 30 minutes to ensure that the vehicle can drive more than 50KM. The AC 380V industrial power grid is often used for charging, and the charging speed is faster, so it is also called fast charging.
Commercially produced electric vehicles, in order to meet the application of these two types of chargers, usually have an on-board charger and a fast charging interface on the vehicle at the same time. Figure 7 shows the charging interface of BYD e6 pure electric vehicle. The left interface in the appearance diagram is the fast charging interface, the right one is the slow charging interface, and Figure 8 is the terminal layout of the two interfaces.
3) Smart charging management
Intelligent charging management is a charging management mode that is carried out jointly by the charger charging management system and the on-board BMS without excessive manual intervention.
The realization of the charging strategy requires effective data transmission and real-time parameter judgment between the battery system and the charger. BMS completes the collection of parameters in the battery system. In the existing smart charging, by realizing the communication with the charger, the safety of charging is ensured, and the effective control of the charging process is realized.
The role of BMS is to realize online monitoring of battery status (battery temperature, single battery voltage, working battery, insulation between battery and battery box), SOC estimation, status analysis (whether SOC is too high, whether battery temperature is too high /Low, whether the voltage of the single battery is too high/low, whether the temperature rise of the battery is too fast, whether the insulation is faulty, whether it is overcurrent, the consistency analysis of the battery, whether the battery pack is faulty, whether there is a communication fault, etc.), Implement necessary thermal management. The main tasks of the charger are power conversion, closed-loop control of output voltage and current, necessary protection, and communication with BMS to achieve a comprehensive understanding of battery status and dynamic adjustment of output current. When the battery pack needs to be charged, in addition to the total positive power line and the total negative power line of the charger that need to be connected to the battery pack, a communication line for data sharing is added between the BMS and the charger.
The characteristics of the intelligent charging mode: Data sharing is realized by establishing a communication link between the BMS and the charger system, so that the battery voltage, temperature, insulation performance and other safety-related parameters can participate in the battery during the entire charging process The charging control and management of the battery enable the charger to fully understand the status and information of the battery and change the charging current accordingly. The safety of battery charging; in addition, this charging mode improves the management and control functions of the BMS, improves the safety and intelligence of charging, and simplifies the tedious work of the operator to set the charging parameters, making the charger better Adaptability. Through this mode, the charger does not need to distinguish the types of batteries, and only needs to obtain the current command provided by the BMS to achieve safe charging.