Lithium battery protection board (BMS) selection principles
General continuous discharge current is less than 200A, the maximum voltage of the battery pack does not exceed 100V, and the customer does not have special requirements such as battery information and communication, then you can choose the ordinary protection board program. The performance requirements of the protection board are as follows:
1.1 Common equalization functions:
A, end equalization function; B, voltage difference real-time equalization function.
1.1.1 Lithium ternary batteries do not use A equalization function, can choose B equalization function.
1.1.2 Li-FePO4 battery adopts B equalization function as far as possible; A equalization function can be selected, and the fixed point voltage is 3.50?3.60V.
1.1.3 Equalizing current is 30-100mA, and the temperature rise of the equalizing circuit does not exceed 40 degrees.
1.2 Temperature detection and protection
1.2.1 Preferred charging normal temperature range 0~45, beyond the normal temperature range will stop charging, temperature detection accuracy is ±5. Optional charging high temperature 45±5 protection.
1.2.2 Preferred discharge normal temperature range?20~60, beyond the normal temperature range will stop discharging, temperature detection accuracy of ±5. Optional discharge high temperature 65±5 protection.
1.3 Charging overcharge protection
1.3.1 Lithium cobaltate, ternary material single cell battery overcharge protection voltage 4.20?4.25V, overcharge protection voltage precision 25mV.
1.3.2 Lithium iron phosphate single-cell battery overcharge protection voltage 3.70?3.90V, overcharge protection voltage precision 25mV.
1.3.3 Lithium titanate single-cell battery overcharge protection voltage 2.80V-2.90V, overcharge protection voltage precision 50mV.
1.4 Discharge over-discharge protection
1.4.1 The over-discharge protection of lithium iron phosphate material battery cell is 2.0?2.5V, and the accuracy of over-discharge protection voltage is 80mV.
1.4.2 The over-discharge protection of lithium cobaltate and ternary material cell is 2.5?3.0V, and the accuracy of the over-discharge protection voltage is 80mV. The over-discharge protection voltage is defined according to the specification of the cell.
1.4.3 The over-discharge protection of lithium titanate battery cell is 1.4-1.5V, and the accuracy of over-discharge protection voltage is 80mV. Adjust the over-discharge protection voltage according to the actual situation.
1.5 Overcurrent protection
1.5.1 Discharge overcurrent protection is available, overcurrent protection delay value is defined according to the specific project.
1.5.2 Charging overcurrent protection is available, overcurrent protection delay value is defined according to the specific project.
1.6 Short circuit protection
1.6.1 Output short-circuit protection is available, and the short-circuit protection delay value is defined according to the specific project.
1.7 Self-consumption design
1.7.1 Ordinary hardware protection board, self-consumption requirements <100uA.
1.7.2 Charge communication and other special features of the protection board, self-power requirements <200uA. self-power > 200uA special projects, the engineer adjusts the requirements according to the project.
1.8 Conductivity internal resistance
1.8.1 The protection board's on-resistance is defined according to the specific product, and the full-load temperature rise is less than 40 degrees.
1.9 Continuous current
1.9.1 Rated continuous discharge current, temperature rise of all components is less than 40 degrees.
1.9.2 Maximum continuous discharge current, working at maximum continuous discharge current for 20 seconds without protection, temperature rise of all components is less than 50 degrees.
1.9.3 Continuous charging current, temperature rise of all components is less than 25 degrees.
1.10 Temperature rise
1.10.1 Resistor, MOS and other heating components of the maximum temperature rise <50 ℃, to be able to continue to work with the maximum current discharge and charging.
1.11 Output anti-reverse function
1.11.1 Optional protection board output with anti-reverse function
1.12 Voltage resistance
1.12.1 When the charging voltage at the input is higher than 1.2 times the normal charging voltage, the protection board is required not to be damaged.
1.13 Fuse
1.13.1 The circuit has a FUSE fuse, FUSE fuse continuous operating current of 1.25?1.7 times the normal operating current, and the PCM overcurrent protection can not turn off the FUSE fuse.
1.14 Conductor load capacity, color marking and wire number marking
1.14.1 The wire load capacity is designed according to the long-term load current 4A of 1 square copper core wire.
1.14.2 Battery charge/discharge positive terminal is defined as red; battery charge/discharge negative terminal is defined as black;
1.14.3 Voltage detection line different potentials need to do color differentiation, 8 strings of the following (including 8 strings) battery color is not allowed to repeat; more than 8 strings of batteries according to the specific circumstances of the project to determine the type of color, for example, 10 strings of batteries can be used in 5 colors to mark; 5 voltage arrangement and then repeat the order; auxiliary line number marking to ensure that the wiring of the daze-proof and reliable.
1.14.4 Voltage detection line, different potential harnesses need to be described with a line number to distinguish, line number from the high potential to the low potential sequential number: 1, 2, 3, 4 ... ...; with a plug harness, the plug end can not add a line number, the terminal must be added to the line number labeling; without a plug harness, the connection between the two sides need to be added to the line number of the anti-dumbing Labeling.
Design of lithium battery management system
Battery management system is tightly integrated with the battery, detecting the voltage, current and temperature of the battery at all times, as well as leakage detection, thermal management, battery equalization management, alarm reminder, calculating the remaining capacity, discharging power, and reporting the SOC&SOH status, and also controlling the maximum output power with an algorithm based on the battery's voltage, current and temperature, as well as controlling the charging machine with an algorithm to carry out the optimal charging flow.
Real-time communication with total controller, energy control system, display system, etc. through communication bus interface.
Real-time communication with total controller, energy control system, display system, etc. through communication bus interface.
Functions of lithium battery BMS system
General BMS management system has the following functions, different projects depending on the circumstances of the flexible adjustment of parameters and functions;
(1) Thermal management (high and low temperature detection and protection); generally, low-temperature charging projects should avoid heating management as much as possible; the overall heat dissipation should try to use air-cooled or water-cooled cooling physical measures;
(2) Equalization management; divided into active equalization and passive equalization; products with larger capacity should prefer active equalization.
(3) Capacity calculation of SOC; combining the battery discharge curve and load voltage and current, the SOC is dynamically estimated by integrating the current; power batteries should be controlled within 10% error; energy storage batteries should be controlled within 5% error;
(4) Alarm reminder; all kinds of information of the battery pack (voltage, current, temperature, SOC, charging status, charging fault, etc.) are shown on the display, which can also be transmitted to the host computer through communication; when there is a malfunction, the buzzer sends out an alarm reminder to the user, and the specific type of malfunction is shown on the display at the same time; it can be adjusted according to the customer's requirements and the actual situation of the project.
(5) Power detection; generally upload the operating conditions to the host computer for analysis.
(6) Voltage detection; through the isolation and amplification of the voltage of the series-connected monomer, real-time detection of the voltage of each monomer can be realized; the voltage detection range is 0~5V, and the detection accuracy is ±5mV.
(7) SOC&SOH state detection; according to the performance indicators detected by the inspection, the health status of the battery can be analyzed.
8) Display system; able to display voltage, current, temperature, SOC, charging status, charging fault, etc.
9) Communication function; design the communication type and function according to the customer's requirement.
10) Leakage detection;
11) Optimal charging current control;
12) System self-test;