Abstract: In order to monitor the heat distribution of new energy vehicle power battery in real time, a multi-directional detection method is proposed based on infrared thermal imaging measurement technology, and a power battery heat distribution monitoring system is designed. The calibration of the infrared detector and the battery charging experiment in different environments were carried out, and real-time monitoring experiments were carried out on the power battery. The results show that the monitoring system has good stability and applicability, can be well applied to the thermal distribution monitoring of power batteries, and finds the shortcomings in the design of power battery devices at any time, providing effective data for thermal efficiency management and heat dissipation design of power batteries. in accordance with.
Keywords: power battery; real-time monitoring; infrared thermal imaging
CLC number: Q436 Document code: A Article ID: 2095-8412 (2017) 01-022-04
In recent years, the research and development of electric vehicles has gradually deepened. With the application of electric vehicles, the thermal balance control of their power batteries in operation is receiving more and more attention, especially in high temperature environments [1-4].
In order to ensure safety, in order to meet the frequent high-current charging and discharging operation conditions of electric vehicles, to prevent thermal runaway of the battery, to ensure the safety of the vehicle power supply system and the service life of the electric vehicle, it is necessary to carry out thermal balance and heat of the vehicle power supply system. Evaluation technology research, in which a system is needed to develop a real-time monitoring of the heat distribution of a power battery from multiple angles.
This paper develops a power battery monitoring system based on infrared thermal imaging technology and discusses it in detail.
1 Infrared Thermal Imaging Technology R\u0026D
Infrared thermal imaging technology is a widely used high-tech technology. It combines photoelectric imaging technology, computer technology and image processing technology to receive infrared rays (wavelength 0.78~) 1 000 μm), its thermal image is displayed on the fluorescent screen to accurately determine the temperature distribution of the surface of the object, which has the advantages of accuracy, real-time and fast.
Any object that radiates infrared heat from the outside due to the movement of its own molecules, thus forming a certain temperature field on the surface of the object. Infrared thermal imaging technology detects the temperature distribution of the surface of the device by detecting the energy of the infrared radiation, and depicts the surface thermal image through the thermal imaging system to determine the heating condition of the device. Therefore, infrared heat imagers have inherent advantages for heat source detection applications.
Research at home and abroad has progressed rapidly. The National Renewable Energy Laboratory (NREL Labs) and the UK Thermal Hazard Technology (THT) combine infrared thermal imaging technology and real-time dynamic thermal imaging analysis systems, thermal and flow field analysis techniques, thermal conductivity analysis techniques, and fast and accurate quantities. Thermal testing techniques are used in battery thermal management and thermal safety performance evaluation . In the aspect of battery thermal balance of hybrid electric vehicles, the American Renewable Energy Research Institute records the surface temperature of the battery through an infrared camera, and conducts temperature field distribution characteristics by arranging thermocouple measurements inside the battery . Toyota Corporation of Japan conducted research and thermal evaluation of cooling airflow parameters and vectors in battery modules through thermal imaging technology, improved some important parameters in battery module design, and developed a thermal management scheme to effectively reduce different parts of the battery module. Temperature difference. Zhang Zhijie et al  numerically simulated the temperature rise characteristics of lithium-ion battery under different discharge rates.
2 Multi-channel infrared thermal imaging monitoring system software
The power battery device has different design and functional requirements, which makes the heat dissipation of each part unbalanced. It may cause accidents such as burning or even explosion due to overheating caused by partial accumulation of heat. Therefore, it is very necessary to monitor the heat distribution of the power battery from multiple angles in multiple directions. It is possible to develop a multi-channel monitoring system based on infrared thermal imaging, and add special protection devices for the thermal imager, and timely according to the state of the power battery. Adjustment.
On the Microsoft Visual Studio 2013 platform, using C# language and .NET framework to develop a set of temperature trend analysis, temperature distribution state analysis, threshold alarm or numerical analysis, highest or lowest thermal defect search A full-featured online multi-channel infrared thermal imaging monitoring system software.
The monitoring system software mainly has three functions: multi-channel online monitoring, online infrared thermal image real-time operation processing, and infrared thermal image post-analysis processing.
Multi-channel online monitoring function includes: 8 infrared cameras can be connected at the same time, and infrared images of each channel are displayed to realize multi-channel real-time acquisition.
The online operation function includes: mainly realizes the connection of each instrument, and performs separate parameter setting for each channel instrument, necessary point, line, area drawing and related clearing functions to realize image and data display.
Analysis processing functions include: open file function to be processed, information area specification (draw observation point, line, area) and information acquisition (display) function, single frame interception function, processing screen color label card setting function, export data function , system setting function, play related (play, pause, single frame forward and backward) functions, chart drawing function, parameter setting function and continuous monitoring function.
3 Power battery heat distribution experiment
The heat distribution experiment of power battery is carried out by multi-channel infrared thermal imaging monitoring system, which is mainly composed of two parts: one is the infrared camera image measurement calibration; the other is different working conditions and Comparison of thermal distribution of power batteries in the environment.
3.1 Infrared Thermal Imager Blackbody Calibration
Currently widely used infrared focal plane detectors have certain errors in the absolute temperature value of the detection target and the detection temperature value due to the differences in materials, production processes and software processing algorithms. In order to verify the temperature accuracy of the thermal imager, a blackbody calibration experiment is performed on the thermal imager to determine the absolute error of the measuring instrument. In this paper, the domestic large-scale infrared thermal imager is used as the infrared thermal image probe, and the standard black body is used as the detection target. At the same time, the self-developed monitoring system software V1.1.0 is used to build the experimental system platform for infrared thermal imaging blackbody calibration experiment, as shown in Fig. 1. Shown.
Adjust the standard blackbody temperature value, collect data through the monitoring system experimental platform, and form a black body temperature and infrared acquisition comparison table, as shown in Table 1.
It can be seen that there is a certain error between the data collected by the infrared camera and the standard blackbody temperature value, and the average value and standard deviation are obtained through data processing. The standard deviation is low, generally between 0.20 and 0.30, and the maximum error ratio is 0.8%.
The linear equation of the temperature measurement curve of the infrared camera is:
The linear equation of the standard blackbody temperature curve is:
The correlation coefficient of the equation (1) and the equation (2) is R=0.999 3 , close to 1, indicating a good linear relationship, the monitoring system software calibration meets project monitoring requirements.
3.2 Infrared Monitoring System Simulation Test
In order to ensure the effectiveness of the monitoring system, four 3.2 V iron iron phosphate batteries are charged and discharged using a battery control device to simulate the charging and discharging of new energy vehicles during different operating conditions. The process and the surface temperature distribution of the lithium iron phosphate battery are detected and analyzed by the monitoring system during the charging and discharging process.
(1) Pre-treatment of the battery
Since the surface of the battery is silver reflective material, the surface emissivity is low and the reflectivity is high, so the environmental change has a great influence on the detection temperature value. In order to reduce the impact of the environment on the detection of the infrared probe, the surface of the battery needs to be treated. By applying gelatin to the surface of the battery, the left battery pack is untreated, and the right battery pack is processed, which not only functions as a fixed battery pack, but also rapidly increases the surface emissivity of the battery.
Then, the temperature measurement of the two sets of battery packs is performed by an infrared camera, and the emissivity values ??detected by the infrared camera are continuously adjusted. After adjusting the measurement several times, it is finally determined that 0.9 is the optimum emissivity value of the surface of the transparent plastic.
The infrared thermal image of the battery pack is shown in Figure 2. It can be seen that the treated battery surface temperature is more uniform and the reflection on the background is significantly reduced.
(2) Different ambient temperature comparison experiments
Normally, the change trend of battery unit temperature is generally consistent with the trend of atmospheric temperature change. When the equipment is abnormal, such as circuit failure or mechanical failure, the equipment temperature may be abnormal. Variety.
At different ambient temperatures, the battery is tested for charging temperature. The measured ambient temperature is 29.2 °C and 30.8 °C, respectively, and the point is taken every 5 minutes, and the temperature curve is plotted, as shown in Figure 3. Three conclusions can be inferred:
1 The ambient temperature will affect the initial temperature of the battery's temperature rise;
2 At different background temperatures, the battery temperature during charging is on the rise;
3 After rising to a certain value, the temperature value fluctuates within a certain range.
4 Infrared Monitoring System Actual Test
The infrared temperature distribution diagram of the power battery and battery controller is monitored on a new type of new energy vehicle test vehicle, as shown in Figure 4 and Figure 5.
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