Research on Voltage Accuracy Detection of Lithium Battery Multi-circuit Series

Tandem battery packs are widely used in hand-held tools, notebook computers, communication radios, and portable electronic equipment, aerospace satellites, electric bicycles, electric vehicles, and energy storage equipment. In order to maximize the available capacity of the battery pack and improve the reliability of the battery pack, the functions of the single cells in the battery pack should be consistent, and then the single cells need to be monitored, that is, the voltage of the single cells needs to be measured.　There are many methods to measure the voltage of a series battery pack. Currently, the differential detection type [1] and the current source detection type [2] are more commonly used. The differential detection type requires strict matching of the resistance of the two resistor pairs, otherwise it will affect the detection accuracy of the battery pack voltage. In order to reduce the impact of the detection line leakage current on the battery pack consistency [3], the resistance of the resistor needs to be added. This will increase the difficulty of mass production and reduce the detection accuracy. However, the current detection type detection circuit only needs the resistance matching of one resistance pair. Literature [2] mentions that in order to improve the detection accuracy, a small resistance matching is required, but the leakage current of the detection line is increased. In the process of practical use, in order to reduce the impact of the leakage current of the detection line on the consistency of the battery pack and reduce the power consumption of the voltage detection circuit, it is necessary to add switch control equipment to the voltage detection circuit, and often choose an optocoupler or a photoelectric relay[4] . This article chooses the transistor Q1 to replace the MOSFET in the literature [2], firstly because the turn-on voltage of the MOSFET is generally above 2.5V, so when the single battery voltage is lower than 2.5V, the circuit in the literature [2] will not be able to Detection, and the battery voltage detection scale requires detection below 1V, and the improved circuit can meet this demand, as shown in Figure 1. In the figure, CELLn is the voltage of the n-th single cell. This circuit can measure the voltage of multiple strings of battery packs, and is not limited by the number of series connected nodes, and the first cell voltage in the series battery pack does not need to be selected. The circuit measurement can be directly measured or obtained through resistor divider. The operating principle of the circuit is as follows: When the circuit is operating normally, the op amp is in an enlarged state, and pins 1 and 3 of the op amp are in a virtual short and broken state, that is, the voltage of pin 3 is equal to the voltage at the CELLn+1 terminal, and because of the op amp’s The input impedance is very large, so the current on the resistor R3 can be neglected. The resistor R1 is the voltage of a single battery. The size of the current flowing through the resistor R1 is: 　 Together, the current from the emitter to the base of the transistor Q1 is relative to The current from the emitter to the collector can be neglected, so the voltage of the n+2 single cell is: 　Because the sampling circuit used in this experiment has a reference voltage of 2.5V, the battery voltage needs to be attenuated twice, so I chose R1u003d2R2, the capacitor C1 in the circuit is the decoupling capacitor, the resistor R5 is the current-limiting resistor, and the resistor R4 is used to ensure the reliable operation of the circuit. In order to reduce the leakage current of the voltage detection circuit, participate in AQW216 on the voltage detection line of each cell The photoelectric relay is used as a detection control switch. As shown in Figure 2, when the battery voltage needs to be detected, the photorelay is turned on through the control terminal and the photorelay is closed after the detection is completed, which can effectively reduce the leakage current during detection and the impact of the consistency of the battery pack. 3 Test table 1 Voltage measurement error table According to the analysis, the voltage detection error is mainly divided into the following parts: (1) The voltage drop on the photoelectric relay AQW216; (2) The voltage detection circuit error; (3) The sampling system Errors mainly include voltage errors and sampling errors of the reference source. Figure 3 The voltage drop of the optocoupler at different temperatures. Figure 4 The voltage detection circuit enlargement times and different temperatures. Figure 4 Test results and analysis. The above test results show that the photoelectric relay is the primary element that affects the battery voltage detection accuracy in normal temperature operation. The primary factor that affects the detection accuracy at different temperatures is the error of the photoelectric relay and the sampling system. It can be seen that the photoelectric relay is the primary element that affects the accuracy of the voltage detection, and this part is often ignored in practical use, and only focuses on the error of the voltage detection circuit, and then causes a large error in the measurement accuracy. Fig. 6 Principle of electronic switch Fig. 5 Conclusion u003cp font-size:18px;u003du003e　This article has made a useful improvement to the current source circuit in the voltage detection circuit of literature [2], and has been tested to analyze the voltage detection error Elements, the results show that photoelectric relay is a primary influencing element. Therefore, a simple and useful electronic switch is used to replace the photoelectric relay, and the error of the voltage detection circuit and the sampling system is reduced through the temperature segmentation calibration, and then the accuracy of the voltage detection is greatly improved. The detection circuit proposed in this article is simple, low cost, high measuring accuracy, and has very good useful value. Disclaimer: The articles published on this site are all from the Internet and do not represent the views of this site. If there is any infringement, please contact to delete WeChat: Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact delete A: Intelligent power supply monitoring system based on CAN bus