This paper designs a multi-channel lithium battery charge and discharge test system, with STM32F429 as the main control chip, with two-range current acquisition, charge and discharge control, dual detector temperature detection and voltage detection circuits, etc. Charge and discharge testing and protection of a series of power lithium battery packs. During the test, the charging and discharging test process of multiple lithium battery packs can be monitored by the host computer program, and the lithium battery charge and discharge test data can be displayed in real time.
1, the system hardware designThe system uses the high-performance, low-power, cost-effective STM32F429 produced by STMicroelectronics as the core controller of the whole system. It is connected to the current, temperature and voltage detection module via SPI (serialperipheralin-terface) bus and SMBus (systemmanagementbus) bus. Communication, control the opening and closing of the charge and discharge circuit through the ordinary IO pin, realize the corresponding protection function, and send the collected data to the host computer through the serial port to the USB module, real-time monitoring and data analysis of the collected data through the host computer And processing, system structure diagram shown in Figure 1. The system has 8 independent monitoring channels, each channel can monitor the charge and discharge status of 1 to 8 lithium batteries, and channels 1 and 2, channels 3 and 4, channels 5 and 6, and channels 7 and 8 can also be combined , to achieve monitoring of 9 to 16 series of lithium battery packs.
The hardware design of the system mainly includes lithium battery voltage detection module design, temperature detection module design, current detection module design and charge and discharge protection function module design.
1.1, current detection and charge and discharge control hardware designThe current is one of the important parameters of the charge and discharge state of the lithium battery pack. It is the basis for directly judging whether overcurrent occurs. It is also an important parameter for estimating the total charge and discharge by the integration method. Therefore, the accuracy of current detection directly affects the charge and discharge. Estimation and processing and analysis of charge and discharge data. Because of the differences in capacity, model, and performance of lithium battery packs used in portable power tools, the current sensing modules in the system must be versatile. The system uses double current sensing design range, it will ensure the detection accuracy at low current and high current situation, but also improve the ability of the system to detect current magnitude. Considering that the closed-loop Hall current sensor has the characteristics of wide measurement dynamic range, high measurement accuracy, fast response speed and isolation measurement, a closed-loop current Hall sensor MMI-200B is used in each channel of the system to realize the charging and discharging current collection. The charging and discharging current Ip of the lithium battery is the primary current input from the MMI-200B sensor through hole, and the relationship between the secondary side output current /out and the ID is:
n&TImes;Ia=K&TImes;/Ion. (1)
In the formula, K is the proportional coefficient, and its size is related to the Hall sensor model. K=1000 in MMI-200B; n is the number of turns of the primary coil, and the system is n=2.
The magnitude of the charge and discharge current Ip can be measured by measuring the voltage across the sampling resistor. In order to ensure the detection accuracy under the condition of large and small current, the system controls the on/off of the triode through the high and low levels of the IO pin of the main control chip STM32, thereby controlling the switching state of the relay G6K-2P to select the sampling resistance with different resistance values, and then The ADS1247, a high-precision, 24-bit ADC chip with two differential inputs, performs AD conversion. Finally, the main control chip reads the conversion value of the ADC chip of each current detection module through the SPI bus, and calculates the charge and discharge current of each channel.
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