BMS is BATTERY MANAGEMENT SYSTEM, called the predicate battery management system.
A. BMS Functions
BMS roughly contains three large functional modules.
First, the measurement function mainly includes voltage sampling and temperature sampling of the module, total voltage sampling and total current sampling of the Pack, high-voltage interlock detection, and insulation detection.
The measurement function monitors the basic state of the battery in real-time, which is the basis of all the functions of the BMS. Without these measurements, all the core algorithms and application functions of the BMS are difficult to execute.
Second, the core algorithms mainly include SOC (battery state of charge) algorithm, SOH (state of life) algorithm, SOP (state of power) algorithm, and battery balancing algorithm.
Among them, the SOC algorithm, typical solutions in the industry include ampere-hour integration, open-circuit voltage, artificial neural network, and Kalman filter. There are shortcomings in a single solution. The current mainstream solution uses ampere-hour integration and Kalman filter. the way.
SOH algorithm, currently commonly used algorithms include Coulomb calculation plus open-circuit voltage, Kalman filtering, and other algorithms.
SOP algorithm, the current reliable method is still relying on test data, using the look-up table method to achieve.
The principle of the equalization function can be associated with the barrel principle, and there are two methods of active equalization and passive equalization. Active balance means that the long planks are cut and then fill up the short planks so that all planks are averaged; passive balance means that the long planks are cut to keep all the long planks as long as the shortest plank.
Third, the application functions mainly include high-voltage power-up and power-off, low-voltage power-on and power-off, AC charging and DC charging, battery system thermal management, and battery system fault diagnosis.
Among them, high-voltage power-on and low-voltage power-on and power-off require other controllers, such as the cooperation of VCU and BMS. After the BMS completes high-voltage power-on, it can supply power or charge to the high-voltage load of the vehicle (there are also manufacturers with high integration, BMS can handle the power-on and power-off process by itself).
AC charging is to charge the power battery through an AC charging pile and on-board charger; DC charging is to charge the power battery through a DC charging pile.
The charging function has relevant national standards.
Battery thermal management is mainly to ensure that the battery is in a reasonable temperature range and that the charge and discharge functions are in the best state.
The fault diagnosis section contains a lot of content, and the safety of the battery depends on this section, including over-voltage and under-voltage protection, over-current protection, relay stickiness detection, battery pressure difference protection, and other functions.
Highfive BMS implements the following functions:
(1) Measurement of battery terminal voltage
(2) Energy balance between the cells of a single battery:
It is the equilibrium charging for the single battery, which makes every battery in the pack can reach the equilibrium state.
The balancing technology is the key technology of a battery energy management system, that is being studied and developed in the world.
(3) Measuring the total voltage of the battery pack
(4) Measurement of the total current in the battery pack
(5) SOC calculation
Accurately estimate the State of Charge (SOC) of the power battery pack, that is the remaining capacity of the battery, ensure that SOC is to be kept within a reasonable range, and prevent battery damage due to overcharge or over-discharge.
(6) Dynamic monitoring of the working state of the power cell group:
During battery charging and discharging, the terminal voltage and temperature, charge and discharge current, and battery total voltage of each battery in real-time, and prevent the battery from overcharging or over-discharging.
(7) Real-time data display
(8) Data recording and analysis
At the same time, an abnormal battery must be selected out and replace to maintain the reliability and efficiency of the whole battery pack operation.
(9) Function of communication networking.
B. BMS Hardware
1. The mainboard, as the brain of the BMS, collects sampling information from each slave board (usually called LCU), communicates with the entire device through a low-voltage electrical interface, controls the action of the relay in the BDU (high-voltage disconnect box), and implements battery monitoring Various states to ensure the safe use of the battery during charging and discharging;
2.The slave board (LCU), as the sentinel of the BMS, monitors the cell voltage, cell temperature, and other information of the module, and transmits the information to the mainboard. It has the function of battery balancing. The communication method between the slave board and the mainboard is usually CAN Communication or daisy chain communication;
3. BDU is the gate for battery pack power to enter and exit. It is connected to the overall equipment high-voltage load and fast-charging harness through the high-voltage electrical interface, including pre-charging circuit, total positive relay, total negative relay, fast charging relay, etc., controlled by the mainboard;
4. The high-voltage control board, the door guard for the battery pack’s power in and out, can be integrated on the mainboard or independently. It monitors the voltage and current of the battery pack in real-time. It also includes pre-charge detection and insulation detection functions.
C. BMS Software
- Service Layer, the service layer, located at the top layer of the BSW, seals up various basic software functions in the form of services and calls the application layer, including RTOS, communication and network management, memory management, diagnostic services, status management, program monitoring, etc. service.
- ECU Abstraction Layer, the electronic control unit abstraction layer, seals the microcontroller layer and the drivers of peripheral drive devices, unifies the access to the peripherals in the microcontroller and separates the upper software application from the ECU hardware.
- Microcontroller Abstraction Layer, the microcontroller abstraction layer, is located at the bottom of the BSW, contains the drive to access the microcontroller, and separates the upper layer software from the microcontroller, facilitating the transplantation of applications.
- Complex Drivers Layer, complex driver layer, in order to meet real-time requirements, you can use complex drivers to allow the application layer to directly access the hardware through RTE or use complex drivers to seal existing non-layered software to achieve the AUTOSAR software architecture Implement gradually.