[Dry Goods] Detailed Explanation of New Energy Vehicle Power Batteries

The power battery system refers to an energy storage device used to provide energy for the drive of electric vehicles. It consists of one or more battery packs and a battery management (control) system.

Power battery composition

The power battery system consists of four parts: power battery box, power battery pack, battery management system, and auxiliary components.

Power battery system structure diagram

Power battery box

The components that support, fix and surround the battery system mainly include the upper cover and the lower tray, as well as other auxiliary components such as transition pieces, guard plates, bolts, etc. The power battery box has the function of carrying and protecting the power battery pack and electrical components.

The main functions of the power battery box are (1) to help the battery ventilate and dissipate heat; (2) to insulate and waterproof the battery; and (3) to protect the battery from collision.

The battery box is installed under the vehicle floor. The lower shell is made of cast aluminum or steel plate, and the upper shell is made of fiberglass. There is sealant between the upper and lower shells. There are high-voltage connectors and low-voltage connectors on the rear side, and a maintenance switch on the top. The battery box has a sealing level of IP67 and above, "6" means protection against dust ingress, and "7" means protection against immersion in 1m deep water for 30 minutes.

Power battery pack

The function of the power battery is to receive and store high-voltage direct current from the charging device and provide high-voltage direct current to electric vehicles.

The main components of power batteries include cells, modules and battery packs. Cells are the basic units of batteries, modules are multiple cells assembled together in a certain way, and battery packs are complete battery systems that further integrate multiple modules and management systems. These components together form a complete power battery system that can meet the energy needs and performance requirements in different application scenarios.

Battery cell: The smallest single cell of a power battery. A power battery system is composed of many battery cells, each of which is usually composed of a positive electrode, a negative electrode, a separator and an electrolyte. The reaction between the positive and negative electrodes is achieved through ion transfer in the electrolyte, which provides the energy of the battery. A battery cell is a battery cell. According to the positive electrode material, it mainly includes lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate and nickel cobalt lithium manganese oxide ternary materials. According to the structural shape of the battery cell, it is mainly divided into three types: cylindrical battery cells, square battery cells and soft packs, and their respective advantages and disadvantages are also very obvious. To a certain extent, the performance of the battery cell determines the performance of the battery module and thus affects the performance of the entire power battery system.

Battery diagram

A power battery module is a combination of power battery cells that are connected in series and parallel and protected by circuit boards and casings, which can directly provide electrical energy. It is one of the secondary structures that make up the power battery system. A module is a combination of parallel battery cells, the rated voltage of which is equal to the rated voltage of the battery cells. It is the smallest grouping of battery cells connected in physical structure and circuit. Then, multiple identical battery modules are connected in series to form a battery module.

Module Icon

During the battery assembly process, the module can support, fix and protect the battery cell, so its design requirements need to meet the requirements of mechanical strength, electrical performance, heat dissipation performance, and fault handling capabilities. These are also the criteria for judging the quality of battery modules. Although the module plays a big role, it also occupies and consumes a certain amount of space. When assembling the module, it is necessary to add end plates, side plates, and fasteners such as screws for fixing the module; when assembling the battery pack, it is necessary to add battery management systems, high and low voltage wiring harnesses, insulation plates, boxes and other structural parts, which leads to an increase in the volume and mass of the battery, and a decrease in the energy density of the battery pack.

The following aspects need to be considered in battery module design:

1. The fixed connection method of the battery group should be carried out according to the overall requirements of the power battery system design for the selected battery cell structure shape.

2. The assembly of battery modules requires moderate tightness and each structural component has sufficient strength to prevent deformation or damage due to internal and external forces of the battery.

3. The battery cells and battery modules must have special fixing devices with compact structure and ventilation and heat dissipation channels should be set according to the heat dissipation conditions of the battery box.

4. The conductive connection distance between battery cells should be as short as possible, the connection should be reliable, and flexible connection is preferred. The conductivity of each conductive connection part should meet the maximum current capacity of the electrical equipment.

5. Fully consider the insulation protection issues between the high-voltage connections of battery series and parallel, such as insulation gaps.

Battery pack: A combination of multiple battery modules connected in series to form the power battery assembly of an electric vehicle. The battery pack is composed of multiple battery modules, usually including the electrical connection, cooling system, insulation protection, etc. of the battery modules. The battery pack is a key component of the entire power battery system.

Battery Pack Diagram

Power battery installation location: The power battery of an electric vehicle is generally located between the front and rear axles and the longitudinal beams on both sides of the vehicle.

The advantages of installing here are:

1. It can make it have higher collision safety 2. Lower the center of gravity of the vehicle to make the vehicle more maneuverable; 3. Facilitate disassembly and assembly operations to avoid scattered installation of power batteries; 4. Reduce the use of high-voltage connection harnesses between power batteries, avoid the problem of too many line connections, and save costs.

Battery Management System

Battery Management System (BMS): monitors the status of the battery (temperature, voltage, state of charge), can provide communication, safety, cell balancing and management control for the battery, and provide a system with a communication interface with the application equipment. Battery Management System Composition: includes hardware and software. The hardware consists of the master control box BMS, slave control box, high-voltage box, voltage acquisition line, current sensor, temperature sensor, battery internal CAN bus, etc. The software consists of programs such as monitoring voltage, monitoring current, monitoring temperature, monitoring insulation resistance, and SOC estimation. The role of the master control box: receive the real-time module voltage and module temperature sent by the slave control box, and calculate the maximum and minimum values; receive the total voltage and total current sent by the high-voltage box; communicate with VCU, charger, etc. through the new energy CAN, and communicate with DC charging piles and data acquisition terminals through the fast charging CAN; control the charging and discharging current (the executive components are the on-board charger, DC fast charging pile and motor controller); control the heating of the power battery. The role of the slave control box: real-time monitoring of each module voltage; real-time monitoring of each module temperature; monitoring SCO value; transmit the monitored data to the master control box. Functions of the high-voltage box: 1. Monitor the total voltage of the power battery, including the four monitoring points inside and outside the main relay (inside the main positive relay, outside the main positive relay, inside the main negative relay, outside the main negative relay); 2. Monitor the charge and discharge current; 3. Monitor the insulation of the high-voltage system; 4. Monitor the high-voltage connection; 5. Transmit the monitored data to the main control box. The battery management system is an important link between the power battery and the electric vehicle. Its main functions include: real-time monitoring of battery physical parameters, battery status estimation, online diagnosis and early warning, charge and discharge and pre-charge control balance management, thermal management, etc.

1. Data Collection

The terminal voltage, charge and discharge current, total voltage and temperature of each battery module in the power battery are collected in real time. This data information is the input of all BMS algorithms.

2. Battery status calculation

Battery status calculation mainly includes two aspects: the state of charge (SOc) of the battery pack and the state of health (SOH) of the battery pack. SOC is used to indicate the remaining power of the power battery pack and is the basis for calculating and estimating the driving range of electric vehicles. SOH is a parameter used to indicate the technical status of the battery and estimate the health status of the battery such as the available life. The capacity (SOC) prediction function calculates the capacity of each battery and the entire group in real time throughout the process, and finds the battery with lower capacity to issue a balancing command to the acquisition box, while accumulating the capacity of a single battery. The status information returned by the acquisition box is received during the balancing process. The remaining capacity of the entire battery system can be given at any time. (Meet the SOC requirements of hybrid buses) and control the display screen. Maximum capacity detection: >5000AH, accuracy not higher than 5%.