A system and method for detecting internal short circuit current in a lithium battery

Abstract

The application discloses a kind of detection system and detection method of lithium battery internal short circuit current.The system is connected by voltage detection module (1), OCV maintaining module (2), current detection module (3), analog-digital conversion module (4), control module (5) and power supply module (6).Use method includes: (1) measure the OCV of battery to be measured and control adjustable voltage source output equal to the test voltage VT of battery OCV value;(2) the battery to be measured is connected in parallel with adjustable voltage source;(3) continuously measure loop current and output data, to the output current change curve when measurement stops.The system can accurately and effectively measure lithium battery internal short circuit current in a short time.

Description

Technical Field

[0001] This invention relates to lithium battery testing systems and methods, and particularly to lithium battery internal short circuit testing systems and methods. Background Technology

[0002] In the field of lithium battery internal short-circuit detection, methods have been developed to identify the internal short-circuit state of lithium batteries through measured data deviations, abnormal voltage signals, changes in battery consistency, special circuit design, or detection of battery self-discharge. However, considering factors such as cost-effectiveness and operational difficulty, measured deviations require the development of sufficiently accurate predictive models through numerous case studies; abnormal voltage surges only exist in certain battery types; and consistency detection and special circuit detection both require simultaneous testing of multiple batteries, making it impossible to detect individual cells. Therefore, detecting self-discharge to monitor the internal short-circuit state of the battery is a better choice after comprehensive consideration. For the testing of individual cells, the self-discharge state is mainly tested by leaving the battery open-circuit for an extended period. For example, the latest lithium battery testing standard GB-T 18287-2013 requires that the battery or battery pack be left open-circuit for 28 days after charging to test the battery's charge retention capacity. Currently, lithium battery manufacturers and sellers also have similar regulations regarding the leave time for battery self-discharge testing. This method has advantages such as ease of operation and low cost, but the required long leave time remains a serious drawback in terms of efficiency and safety.

[0003] Therefore, existing technologies require a method to detect the self-discharge of individual cells in a short time to address the problem of short-circuit detection within individual cells. To reduce the impact of the detection system on the battery under test and improve detection accuracy, this method requires the current detection device in the test system to have extremely low resistance, while also placing high demands on the accuracy of the constant voltage source, the ammeter, and its impedance. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a detection system and method that can accurately and effectively measure the short-circuit current inside a lithium battery in a short time.

[0005] Technical solution: To achieve the above objectives, this invention proposes a detection system and method for the internal short-circuit current of a lithium battery.

[0006] The first aspect of the present invention provides a system for detecting the internal short-circuit current of the lithium battery, comprising the following modules:

[0007] The voltage detection module is connected to the positive terminal of the battery under test. It measures the OCV of the battery under test with the help of voltage divider resistors and outputs the result in the form of an analog signal.

[0008] The OCV holding module is connected to the positive terminal of the battery under test and receives digital signals from the host computer to output a test voltage V equal to the battery's OCV value. T And during the test, the battery OCV = V was maintained. T The configuration remains unchanged, with the DAC input connected to the host computer, the DAC output connected to the non-inverting input of the operational amplifier, and the operational amplifier output connected to the inverting input. V... T This refers to the battery's OCV value throughout the entire testing process;

[0009] The current detection module, connected in series with the battery under test and the OCV holding module, measures the internal short-circuit current in the circuit and outputs the result to the analog-to-digital conversion module in the form of an analog signal. The inverting input terminal of the operational amplifier is connected to the battery, the non-inverting input terminal is grounded, and the output terminal is connected to the inverting input terminal via a resistor.

[0010] The analog-to-digital converter module receives analog signals from the voltage detection module and the current detection module, converts them into digital signals, and connects them to the control module. One end of the single-pole triple-throw switch is connected to the ADC input terminal, and the other end is connected to the voltage detection module, the current detection module, and the ground respectively. The ADC output terminal is connected to the host computer.

[0011] The control module is connected to the OCV holding module and the analog-to-digital converter module via digital signals. The analog signals output from the voltage detection module and the current detection module are converted into digital signals by the analog-to-digital converter module and input to the control module. Based on the measured voltage, the control module controls the OCV holding module to output the corresponding test voltage V via digital signals. T It starts measuring the internal short-circuit current in the circuit through the current detection module, receives digital signals from the analog-to-digital conversion module, and transmits the received signals to the display or host computer.

[0012] The power supply module converts 220V AC power into stable DC power to power the OCV holding module, current detection module, analog-to-digital conversion module, and control module, and provides a reference voltage.

[0013] Furthermore, the voltage detection module includes two series resistors that act as a voltage divider, or it consists of an operational amplifier and a feedback resistor, which outputs the measured battery voltage to the analog-to-digital converter module in the form of an analog signal.

[0014] Furthermore, the OCV holding module consists of a DAC and an operational amplifier. The DAC converts the digital signal from the control module into an analog signal, and the operational amplifier amplifies the analog signal as a loop voltage source.

[0015] Furthermore, the current detection module consists of an operational amplifier and a resistor, forming a transimpedance amplifier to amplify the current in the circuit. The transimpedance amplifier has an adjustable amplification factor to increase the measurement range, and outputs the measured current to the analog-to-digital conversion module in the form of an analog signal.

[0016] Furthermore, the control module is composed of an STM32 microcontroller.

[0017] A second aspect of the present invention provides a detection method for the aforementioned lithium battery internal short-circuit current detection system, comprising the following steps:

[0018] (1) Measure the OCV of the battery under test and control the adjustable voltage source to output a test voltage V equal to the OCV value of the battery. T ;

[0019] (2) Connect the battery under test in parallel with the adjustable voltage source;

[0020] (3) Continuously measure the loop current and output the data until the measurement stops, then output the current change curve.

[0021] Furthermore, in step (3), the current in the circuit is the short-circuit current inside the battery to be tested, and the short-circuit current is obtained by measuring the circuit current.

[0022] Furthermore, the battery under test is connected to the circuit, and the voltage detection module measures the battery's OCV at this time. Specifically, after the battery is connected to the circuit, the voltage detection module is activated, and the voltage measuring device in this module measures the battery's OCV, then feeds the measurement result back to the host computer.

[0023] Furthermore, the host computer controls the OCV holding module to output a test voltage V equal to the battery's OCV value. T Specifically, after the host computer obtains the battery OCV measured by the voltage detection module, it outputs a test voltage V equal to the battery OCV value. T During the subsequent measurement process, the OCV holding module kept the battery OCV constant at the test voltage V. T Due to the presence of an internal short circuit, after being connected in series, the adjustable voltage source serves as the actual power source for discharge in the circuit, and the current in the circuit is the internal short circuit current of the battery under test.

[0024] Furthermore, the current detection module continuously measures the current and outputs data, eventually outputting a current change curve when the measurement stops. Specifically, a transimpedance amplifier amplifies the current in the loop, and then the current signal is transmitted to the host computer via an analog-to-digital converter for real-time display. When the change in current per unit time is less than the change threshold, the current change is considered to have stabilized, and the measured value at this point can be regarded as the value of the internal short-circuit current, thus outputting the current change curve for the entire measurement process.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] This invention provides a lithium battery internal short-circuit current detection system and method. The system can effectively and accurately measure the internal short-circuit current of the lithium battery in a short time, providing a new approach for subsequent detection of internal short circuit conditions in lithium batteries. Attached Figure Description

[0027] Figure 1 Schematic diagram of a short-circuit current detection system for lithium batteries;

[0028] Figure 2 A schematic diagram of a lithium battery internal short-circuit current detection system using a controllable voltage detection module.

[0029] Figure 3 A schematic diagram of a short-circuit current detection system for lithium batteries that uses an operational amplifier for voltage detection.

[0030] Figure 4 Current variation curves over time for some faulty batteries;

[0031] Figure 5 Schematic diagram of a multi-range lithium battery internal short-circuit current detection system. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be further described below.

[0033] Example 1:

[0034] This embodiment is based on Figure 1 To elaborate.

[0035] Step 1: Connect the battery to be tested to the testing system, start the voltage detection module 1, and measure the battery's OCV at this time.

[0036] First, the control module 5, composed of STM32 microcontrollers, controls the switch between the analog signal input terminal of the analog-to-digital converter module 4 and the AD7172-2 to ground the ADC input terminal, thus measuring the offset error. In subsequent current measurements, the host computer subtracts this error from the measured data to improve measurement accuracy. The positive terminal of the battery under test is input to the ADC via a voltage divider resistor and a switch to measure the battery's OCV and record the result.

[0037] Step 2: Control module 5 controls OCV holding module 2 to output a test voltage V equal to the battery's OCV value. T .

[0038] Control module 5 controls the digital-to-analog converter AD5791 in OCV holding module 2 to output a voltage equal to the measured voltage as the test voltage V based on the measured OCV. T An operational amplifier AD8675 is used as an output buffer at the output of the DAC to improve the load-driving capability of this adjustable voltage source.

[0039] Step 3: The current detection module 3 continuously measures the loop current and outputs data until the measurement stops, at which point it outputs the current change curve.

[0040] Control module 5 controls current detection module 3 to begin measuring the internal short-circuit current. An operational amplifier AD8605, along with resistors, forms a transimpedance amplifier to convert the measured loop current into a voltage analog signal. This signal is then input to analog-to-digital converter (ADC) module 4 via a voltage divider resistor to match the input range of ADC module 4. The transimpedance amplifier amplifies the internal short-circuit current while minimizing its impact on the loop. The analog signal output from current detection module 3 is input to ADC module 4. Using the ADC's built-in digital filter and calibration register, the processed digital signal is transmitted to control module 5 for display on an external screen or for visualization and analysis via a PC. When control module 5 detects that the ADC input signal is approaching its maximum input value, it will disconnect current detection module 3 to prevent damage to the equipment.

[0041] Example 2:

[0042] For the voltage detection module 1 implemented using voltage divider resistors in Example 1, during the current detection period when the OCV holding module 2 is at a constant voltage output, the voltage detection module 1, being grounded, has a potential difference with the OCV holding module 2, resulting in current flowing through the resistors and increasing the load on the OCV holding module 2. Therefore, this solution adds a switch controlled by the control module 5 within the voltage detection module 1, such as... Figure 2 As shown, it closes only during voltage detection, thereby reducing the load on OCV holding module 2 during current detection. This scheme increases the voltage detection error due to the series connection of the switches; therefore, a low-resistance switch paired with a high-resistance voltage divider resistor is required.

[0043] Example 3:

[0044] The voltage detection module 1 implemented using switches and voltage divider resistors in Embodiment 2 can also be replaced by an operational amplifier, such as... Figure 3 As shown. The operational amplifier resistor can be approximated as infinite, therefore, during current measurement, the operational amplifier prevents current from passing through its ground to create a virtual open circuit, reducing the load on the OCV holding module 2 and avoiding the use of a switch, thus reducing errors during voltage detection. However, this solution is costly, and the voltage detection module 1 requires power from the power supply module 6 when detecting voltage, which increases the requirements for the power supply module 6.

[0045] Example 4:

[0046] The above embodiments do not consider other situations that may cause the current to change from a non-zero value, such as special faulty batteries, for example, batteries that output a large current at the start of current detection. Figure 4 As shown. This embodiment is based on embodiment 3, and the current detection module 3 is improved to address this deficiency, as follows: Figure 5 As shown. The improved current detection module 3 consists of a transimpedance amplifier with adjustable amplification factor. This function is achieved through feedback resistors of different resistance values ​​and single-pole triple-throw switches, which are controlled by the control module 5. During measurement, measurements are taken sequentially from largest to smallest range. When the current module starts, the maximum range is used by default, i.e., switch S1 is set to the minimum amplification factor end, and switch S2 is closed. If the measured value is higher than the maximum value of the next range, the current range is used for measurement until the measured value is lower than the maximum value of the next range. If the measured value is lower than the maximum value of the next range, the control module 5 performs a range switch. During the switch, switch S2 is first opened, and after switch S1 is closed again, switch S2 is closed. This cycle continues until the minimum range is reached, and the current change curve of the entire process is obtained, and a judgment is made on whether an internal short circuit has occurred.

[0047] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the protection scope of the present invention.

Claims

1. A system for detecting short-circuit current in a lithium battery, characterized in that, Includes the following modules: The voltage detection module (1) is connected to the positive terminal of the battery under test. It measures the OCV of the battery under test with the help of a voltage divider resistor and outputs the result in the form of an analog signal. The OCV holding module (2) is connected to the positive terminal of the battery under test, receives digital signals from the host computer, and outputs a test voltage V equal to the battery's OCV value. T And during the test, the battery OCV = V was maintained. T The configuration remains unchanged, with the DAC input connected to the host computer, the DAC output connected to the non-inverting input of the operational amplifier, and the operational amplifier output connected to the inverting input. V... T This refers to the battery's OCV value throughout the entire testing process; The current detection module (3) is connected in series with the battery under test and the OCV holding module (2) to measure the internal short-circuit current in the circuit and output the result to the analog-to-digital conversion module (4) in the form of an analog signal. The inverting input terminal of the operational amplifier is connected to the battery, the non-inverting input terminal is grounded, and the output terminal is connected to the inverting input terminal via a resistor. The analog-to-digital conversion module (4) receives analog signals from the voltage detection module (1) and the current detection module (3), converts them into digital signals, and connects them to the control module (5). One end of the single-pole triple-throw switch is connected to the ADC input terminal, and the other end is connected to the voltage detection module (1), the current detection module (3), and the ground respectively. The ADC output terminal is connected to the host computer. The control module (5) is connected to the OCV holding module (2) and the analog-to-digital converter module (4) via digital signals. The analog signals output by the voltage detection module (1) and the current detection module (3) are converted into digital signals by the analog-to-digital converter module (4) and input to the control module (5). The control module (5) controls the OCV holding module (2) to output the corresponding test voltage V based on the measured voltage. T And through the current detection module (3), the internal short-circuit current in the circuit is measured, the digital signal from the analog-to-digital conversion module (4) is received, and the received signal is transmitted to the display or host computer; The power supply module (6) converts 220V AC power into stable DC power to serve as the power source for the OCV holding module (2), current detection module (3), analog-to-digital conversion module (4), and control module (5), and provides a reference voltage.

2. The lithium battery internal short-circuit current detection system according to claim 1, characterized in that, The voltage detection module (1) includes two series resistors that act as voltage dividers, or it consists of an operational amplifier and a feedback resistor, and outputs the measured battery voltage to the analog-to-digital converter module (4) in the form of an analog signal.

3. The lithium battery internal short-circuit current detection system according to claim 1, characterized in that, The OCV holding module (2) consists of a DAC and an operational amplifier. The DAC converts the digital signal from the control module (5) into an analog signal, and the operational amplifier amplifies the analog signal as a loop voltage source.

4. The lithium battery internal short-circuit current detection system according to claim 1, characterized in that, The current detection module (3) consists of an operational amplifier and a resistor, forming a transimpedance amplifier to amplify the current in the circuit and output the measured current to the analog-to-digital converter module (4) in the form of an analog signal.

5. The lithium battery internal short-circuit current detection system according to claim 1, characterized in that, The control module (5) is composed of an STM32 microcontroller.

6. The detection method of the lithium battery internal short-circuit current detection system according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Measure the OCV of the battery under test and control the adjustable voltage source to output a test voltage V equal to the OCV value of the battery. T ; (2) Connect the battery under test in parallel with the adjustable voltage source; (3) Continuously measure the loop current and output the data until the measurement stops, then output the current change curve.

7. The detection method of the lithium battery internal short-circuit current detection system according to claim 6, characterized in that, In step (3), the current in the circuit is the short-circuit current inside the battery to be tested, and the short-circuit current is obtained by measuring the circuit current.

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