Study on radial lithium battery voltage and temperature measurement method

　　Author ：Iflowpower – Nhà cung cấp trạm điện di động

Abstract: Battery is the source of the energy of electric vehicles, its performance and service life are focus of users concerned, battery performance and battery voltage and temperature are closely related. This paper proposes a monomer battery voltage measurement method that controls the transmittance of the photoelectric relay by shift register array. Related to other measurement methods, have the advantages of simple structure and convenient installation.

Keywords: series battery; voltage; temperature; shift storage array Under the background, new energy research is becoming the focus of public concern, one of the hotspots of electric vehicles with electricity power. The battery is the source of the energy of the electric vehicle, ensuring that the battery pack is good and extended, and the battery pack is managed and controlled, the premise is that the battery existing capacity parameters must be accurate and reliable. The voltage and temperature of the battery are two parameters closely related to battery capacity, so precise collection of monomer battery voltage and temperature is important.

Second, common measurement method analysis 1 , Photoelectric relay method, etc. The mechanical relay method can directly measure the voltage of each monomer, but the service life of the mechanical relay is limited, the operating speed is slow, and it is not advisable to use during long-term fast inspection. The measurement error of the differential amplifier isolation method is basically determined by the error of the isolation amplifier, but since the measurement cost is relatively high, it is slightly insufficient economy.

The voltage divider method is fast, the measurement is low, but the disadvantage is that it is not very good to adjust the voltage ratio, and the measurement accuracy cannot be satisfactory. The optic relay isolation method is fast, the operating life is long, the measurement is relatively low, the switch has no contact, can function as a voltage isolation, if the selected photoelectric relay takes the photomos technology, can achieve higher measurement accuracy , The optical relay isolation method is a more ideal method of cell voltage measurement. The cell voltage measurement method of this paper is achieved based on photoelectric relay isolation.

Conveying control strategy of photoelectric relay is an important issue to be solved by photoelectric relay isolation method. The control method of common photoelectric relay is: I / O direct control, decoder control, analog switch control, etc. I / O direct control method is simple, easy to implement, but to occupy a lot of I / O resources.

The decoder control and the analog switch control are similar, that is, the number of I / O to control the number of photoelectric relays, which reduces the I / O port occupation. Using I / O direct control, decoder control and analog switch control must be designed to switch control circuits, A / D conversion circuits, and processor in the same module, namely, the sampling module, such words, two electrodes of single cell You need to lead to the sampling module, and the entire battery pack will have a large number of wires to connect to the sampling module, causing the cumbersome and complexity of the electrical line. For the measurement of the cell voltage, three problems should be focused on using the electrical isolation of field and measurement systems, reduce costs and simplify design methods, and improve system accuracy.

I / O direct control, decoder control, and analog switch control the three-screen control method of these three photoelectric relays appears in terms of design. This paper proposes a photoelectric relay isolation unit battery voltage measurement method for controlling photoelectric relay by shift register array. This method uses the photother relay-off control circuit to be directly designed to be installed on the battery, and the wire is connected in series, so that the design method has been greatly simplified, easy to install, and the electrical line is simple and clear.

2, single cell temperature measurement method Analysis of battery temperature has a greater impact on battery capacity, voltage, internal resistance, charge and discharge efficiency, service life, safety and battery consistency, etc., the battery must be carried out Temperature monitoring. At present, the measurement of the monomer battery temperature generally uses a thermistor as a temperature sensor, and the voltage divider method reads the end voltage of the thermistor by A / D sample, according to the resistance.

—The temperature relationship can calculate the temperature value. The thermistor is mounted on each battery, and the thermistor on different batteries is subjected to temperature sampling on the A / D sampling circuit, and the type of battery temperature is realized. It is used in the thermistor measurement temperature, and its measurement accuracy is±1.

0 ¡ã C, large error. At the same time, due to manufacturing process, the temperature characteristics of the thermistor individual are not very consistent, thereby causing temperature measurement calibration difficulties. When conducting a multi-point temperature inspection, it is also necessary to solve the problem of closing channel gathers, so it is also necessary to consider the design simpleness problem.

Based on the thoughts of shift register control channel, this paper proposes a multi-point temperature sampling method using digital temperature sensors while simultaneous start-up data. The method is high, the sampling accuracy is high, the sampling speed is fast, and the installation is simple and convenient. Third, measurement principle and circuit 1, the principle of single battery voltage measurement This article has designed a battery management system based on the photoelectric relay isolation method, and the measurement of the monomer battery voltage is a method of timing measurement.

Both ends of each battery in the series battery group are isolated by the photoelectric relay, and then unified to the detection bus. Controlling the control of the photoelectric relay in accordance with a certain time policy, controlling the unit cell to separate the voltage on the detection bus at different time segments, thereby realizing the timing detection of the cell voltage. The method has a short inspection cycle, high measurement accuracy.

However, the control of the translation of the photoelectric relay should take a lot of I / O resources, which limits the number of battery management systems to manage the battery. At the same time, during the actual installation of the battery management system, due to the lead to the acquisition module on both ends, there will be more traces, resulting in an inconvenient and complexity of electric vehicles installed in the battery management system. In order to improve the shortcomings of the above, this paper proposes a new photoelectric relay control strategy.

The connection method of the photoelectric relay and the series battery pack is shown in Figure 1.