This paper introduces a planning method for a low-temperature intelligent lithium-ion battery processing system, which consists of 32 20Ah 4-series cells connected in parallel (8 cells in total). The method includes functions such as base protection, power metering, charge balancing, and defect recording. Experiments show that the system is fully functional and meets the planning requirements.
Current battery processing systems are mostly designed for applications involving large-capacity battery packs and short battery life. This processing system serves high-power devices with short battery cycles, and the system itself consumes a significant amount of power, making it unsuitable for low-power applications. On a remote gas monitoring surface, the current of the homogenizing system is only a few milliamps, requiring continuous operation at low temperatures for more than six months. To meet the application requirements of this project, this paper introduces a design method for a low-temperature intelligent lithium-ion battery processing system. This system includes functions such as base protection, charge measurement, charge balancing, and defect recording. Experiments show that the system is fully functional and meets the design requirements.
1. Overall System Structure
The low-temperature lithium-ion battery processing system mainly consists of a base protection circuit, a fuel gauge, a balancing circuit, and secondary protection, as shown in Figure 1.
Considering low power consumption, many low-power devices were selected in the design, such as the MSP430FG439 low-power microcontroller as the processor. The reference voltage is REF3325, with extremely low power consumption of only 3.9dB; the operational amplifier used is the LT1495, with an operating current of only 1.5A; the digital potentiometer is the AD5165, with a quiescent current as low as 50nA. A power processing circuit was added to the intermittent operation circuit, which has a large operating current, thus reducing energy consumption. The low-temperature battery pack has a rated voltage of 14.8V and consists of four batteries connected in series, each containing eight individual cells. The normal operating voltage is 2.5-4.2V.
Each acquisition cycle collects the voltage of each battery group. The processor sends instructions to the protection circuit based on this voltage and executes the corresponding protection action. The equalization circuit is implemented using a microcontroller and transistors instead of a dedicated equalization chip. The system records abnormal information such as maximum voltage, current, temperature, battery usage time, and remaining charge in the storage device. The processor provides a TTL communication interface, and the field computer reads the logs from the storage device through a TTLRS232 conversion module. To prevent abnormal situations such as microcontroller crashes during charging and subsequent protection failures, a secondary protection circuit has been added. If the voltage exceeds a preset value, the secondary protection circuit will be activated, blowing the three-terminal fuse to prevent a fault from occurring.
2 Hardware Planning
2.1 Protection Implementation Circuit
The protection execution circuit is the mechanism for performing protection actions. CH is the charging control switch and DISCH is the discharging control switch. The corresponding protection actions are performed by controlling CH and DISCH, as shown in the circuit diagram in Figure 2.
CH and DISCH are set to low level during normal operation when M1 and M2 are both turned on. In case of overcurrent or over-discharge, DISCH is set to high level, Q2 is disconnected, and Q3 initiates charge-sensitive discharge of the gate capacitor of M2, causing M2 to close momentarily and ending the protection. In case of overcurrent or overcharge, CH is set to high level and M1 is turned off. The MOSFET circuit uses the IRF4310 MOSFET, which has an on-resistance of only 7kΩ and a current rating of up to 140kΩ.
2.2 Balancing Circuit and Secondary Protection
Figure 3(a) shows the schematic diagram of a battery charging balancing circuit, which consists of four units connected in series. The voltage at the ADV terminal is acquired by the microcontroller to obtain the voltage of this group of batteries. During charging, if the charging voltage exceeds 4.2V, the BLA pin of the MCU control pin is set to a high level. At this time, this group of batteries is short-circuited, and the charging current flows through R4 to charge other groups of batteries, thus ensuring good consistency of the charge of each group of batteries after charging. The secondary protection is irreversible and can only be activated in the event of a major hazard.
