Research On Charge Equalization And Protection Of Power Lithium Iron Phosphate Battery Pack

Compared with Ni-MH batteries, Lead Acid batteries, Lithium Ion batteries has theobvious merits of size, weight, charging speed, anti-memory effect. However, due to thesingle lithium-ion battery inconsistencies in the manufacturing process, the performancedifference between the series-parallel group use battery pack gradually increases in thecharging and discharging cycles, resulting in the battery pack in excessive charging ordeep discharge. Then, it often appears monomer battery overcharge or over-dischargephenomenon.Directed towards pure electric vehicles using lithium iron phosphate battery aspower supply, a distributed active equalization charging system of lithium ironphosphate dynamic battery pack was in depth studied by analysis the circuit of batteryequalization charge which can not only achieves quick charge but also eliminates thebattery pack overcharge or over discharge that caused by the inconsistency between thesingle battery.This paper uses a distributed active charging equalization system, it consists ofsingle battery manage circuit and vehicle controller unit. According to specific functionsclassification, the single battery manage circuit mainly consists of battery detection unit,battery charging equalization unit, battery charging protection unit and battery managecircuit automatic power off unit. Controller area network(CAN) bus is applied to eachmodule. CAN-USB bus adapter is applied to the communication between the managesubsystem and the vehicle controller unit. The flyback converter is used to the singlebattery to realize supplement charge from battery pack to the single battery that is lowstate of charge. According to the studied fuzzy logic control strategy, the converterachieves the adjustment of the PWM duty cycle of its field effect transistor and theoutput current of each battery charging equalization unit. Different charging current forinconsistent monomers battery carried ensuring the balance of the state of charge ofeach cell. Compared with the average method equalizer control strategy, the strategy cansignificantly reduce the equalization time and improve the balancing efficiency.This paper designs two sides of single battery protection circuit. Simultaneously,the system on the one hand achieves the battery charge protection through parallel withZener diode across the single battery in the constant voltage charging process of thebattery. At the same time, it achieves the single battery management circuit automatic power off when the battery terminal voltage is lower than the set value, therebyavoiding excessive loss of battery energy by monomer battery management circuit.Based on establish the link between the single battery manage module and thecharger, which making the charger can grasp battery information in real time anddetermine the charging control process. During the charger enter into constant voltagecharging model, the charging current can flow through regulator by means of parallel1N5334b diode across the single battery. Furthermore, the battery terminal voltage canbe stabilized at3.7V, thus avoiding the single battery over charged.This paper select micro-power voltage detector chip MCP102, making the singlebattery manage circuit can be automatic powered off when the cell voltage is lower thanthe cut-off voltage of2.65V. The time that the cell voltage lower than the cut-off voltageusually happened in the stationary or the large current discharge process. Thus, itachieves the level of micro-power consumption of the battery while the battery voltageis lower than the cut-off voltage.