Study on voltage and temperature measurement method of series lithium ion batter
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2022/06/16 16:51:16
One, the introduction
Under the background of advocating energy conservation and emission reduction, new energy research is becoming the focus of public attention, and electric vehicles powered by electricity is one of the research hotspots. Battery is the energy source of electric vehicle. In order to ensure good performance of battery pack and prolong its service life, it is necessary to manage and control the battery pack. The premise is to accurately and reliably obtain the existing capacity parameters of battery pack. Battery voltage and temperature are two parameters closely related to battery capacity, so it is very important to accurately collect the voltage and temperature of a single battery.
2. Analysis of common measurement methods
There are many measuring methods to analyze the voltage of single battery in series. The most common ones are mechanical relay method, differential amplifier method, electric voltage divider method, photoelectric relay method and so on. Mechanical relay method can directly measure the voltage of each monomer, but mechanical relay has limited service life and slow speed, so it is not suitable for long-term rapid inspection process. The measurement error of differential amplifier isolation method is basically determined by the error of isolation amplifier, but because of the high measurement cost of each way, it is a little less economical. Electric pressure partial pressure method has fast response speed and low cost of measurement, but its disadvantage is that it can not well adjust the proportion of partial pressure, and the measurement accuracy is not satisfactory. Photoelectric relay isolation method of fast response speed, long working life, the measurement cost is relatively low, contactless switch, can rise the voltage isolation purpose, if choose photoelectric relay using photoMOS technologies, can achieve high accuracy of measurement, so the photoelectric relay isolation method is ideal monomer battery voltage measurement method. The single cell voltage measurement method in this paper is based on the photoelectric relay isolation method.
The on-off control strategy of photoelectric relay is an important problem to be solved by the isolation method of photoelectric relay. The commonly used on/off control methods of photoelectric relay include I/O direct control, decoder control, analog switch control and so on. The DIRECT I/O control method is simple and easy to implement, but it consumes a lot of I/O resources. The idea of decoder control is similar to that of analog switch control, that is to use a small amount of I/O to control a large number of photoelectric relays. These two methods reduce the occupation of I/O ports. In the case of direct I/O control, decoder control and analog switch control, on-off control circuit, A/D conversion circuit and processor should be designed on the same module, that is, the sampling module. In this case, two electrodes of A single battery need to be led to the sampling module, and A large number of wires will be connected to the sampling module in terms of the whole battery pack. The installation is complicated and the electrical wiring is complicated. To measure the voltage of single battery, three problems should be solved: using the electric isolation between the field and the measurement system, reducing the cost and simplifying the design method, and improving the accuracy of the system. On/off control methods of I/O direct control, decoder control and analog switch control are insufficient in the simplicity of design.
This paper presents a voltage measurement method of isolated cell of photoelectric relay controlled by shift register array. In this method, the on-off control circuit of photoelectric relay is directly designed and installed on the battery, and the wiring between them can be connected in series with row wires, so that the design method is greatly simplified, the installation is convenient, and the electrical wiring is simple and clear.
2. Analysis of temperature measurement method of single battery
Battery temperature has great influence on battery capacity, voltage, internal resistance, charge and discharge efficiency, service life, safety and battery consistency, so the battery must be monitored in use.
At present, the temperature measurement of single battery generally adopts thermistor as temperature sensor, and the partial voltage method is adopted to read the end voltage of thermistor by A/D sampling, according to the resistance — The temperature relation can be used to calculate the temperature value. Install thermistors on each battery and connect thermistors on different batteries to an A/D sampling circuit for temperature sampling. In this way, the temperature of individual batteries can be inspected. Using thermistor to measure temperature, its measurement accuracy is &plusMn; 1.0℃, large error. At the same time, sometimes due to manufacturing process reasons, thermistor individual temperature characteristics are not very consistent, resulting in temperature measurement calibration difficulties. When conducting multi-point temperature inspection, it is also necessary to solve the time-sharing channel gating problem, so it is also necessary to consider the design simplicity.
Based on the idea of shifting register array control channel gating, a multi-point temperature sampling method using digital temperature sensor to simultaneously start time-sharing data reading is proposed in this paper. This method has high sampling precision, fast sampling speed, simple and convenient installation.
This article is posted on Battery Community by Lankway Electronics Technology
Address: https://dianchishequ.com/20224532
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