Equalization charging simulation model of lithium battery protection board

With the development of science and technology, the demand for lithium batteries is increasing. However, when charging a group of lithium batteries in series, it is necessary to ensure that each battery is charged in a balanced manner, otherwise the performance and life of the whole group of batteries will be affected during use. Therefore, the equalization technology for charging lithium batteries also needs to be improved. Commonly used equalization charging techniques include constant shunt resistance equalization charging, on-off shunt resistance equalization charging, average battery voltage equalization charging, switched capacitor equalization charging, step-down converter equalization charging, inductance equalization charging, etc., while the existing single-cell lithium The battery protection chip does not contain the equalizing charge control function; the equalizing charge control function of the multi-cell lithium battery protection chip requires an external CPU, which is realized through serial communication with the protection chip, thus increasing the complexity and design difficulty of the protection circuit, and reducing The efficiency and reliability of the system are improved, and the power consumption is increased. To balance the basic principle of the circuit work of the charging protection board, a system simulation model has been built in the Matlab/Simulink environment to simulate the work of the protection board during the charging and discharging process of the lithium battery pack and verify the feasibility of the design scheme. In order to let everyone understand, the company first gave a simulation model of a lithium battery pack consisting of only two lithium batteries in series, as shown in the figure.

Model A controlled voltage source is used instead of a single-cell lithium battery to simulate the charging and discharging of the battery. As shown in the figure, Rs is the total internal resistance of the battery in the series battery pack, RL is the load resistance, and Rd is the shunt discharge branch resistance. The adopted single-cell lithium battery protection chip S28241 is packaged as a subsystem, which makes the overall model expression more concise.

The protection chip subsystem model mainly uses logic operation module, symbolic function module, one-dimensional look-up table module, integral Modules, delay modules, switch modules, mathematical operation modules, etc. simulate the sequence and logic of protection actions. Due to the difference between the simulation environment and the real circuit, there is no need for filtering and strong and weak electrical isolation during simulation, and redundant modules can easily lead to a long simulation time. Therefore, in the actual simulation process, circuits such as filtering, optocoupler isolation, and level conditioning are removed, and the resistor network designed for large current shunts is changed to a single resistor, which reduces the complexity of the simulation system. When establishing a complete system simulation model, pay attention to the possible differences in the input and output data and signal types of different modules. The connection sequence of the modules must be correctly arranged, and the data type conversion is carried out if necessary. The voltage detection module is used in the model to achieve strong and weak signals. The conversion connection problem.　　

In the simulation model, the given signal of the controlled voltage source may have a slight difference under the premise that the waveform is roughly the same, to represent the difference of individual battery charging and discharging. Figure 6 shows the simulation results of the voltage detection of a single cell in the battery pack. It can be seen that the circuit can work normally by adopting the equal charge method of the overcurrent discharge branch.