Pre-balanced parallel excitation method and device

Abstract

The invention provides a pre-balanced parallel excitation method and device, and belongs to the technical field of lithium ion batteries, and the method comprises the steps: starting equipment, switching a relay to a current sharing gear, and carrying out the current sharing of different parallel battery monomers until the equipment detects that the current sharing is completed; switching the relay to an excitation gear, and carrying out an impedance test; and collecting excitation current and response voltage flowing through each parallel single body, switching the relay to a current sharing gear after the test is completed, and ending the test. The battery pack does not need to be disassembled to damage the integrity of the battery pack. Impedance data of all the batteries under the same SOC can be collected at a time, and compared with traditional single-channel equipment, the detection time can be saved by more than 99%.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a pre-equalization parallel excitation method and apparatus. Background Technology

[0002] Governments worldwide are increasingly concerned about environmental pollution, and traditional transportation powered by fossil fuels faces problems such as high pollution and fuel shortages. Therefore, more environmentally friendly and energy-efficient new energy vehicles are gradually replacing gasoline-powered vehicles. Lithium-ion batteries, with their high energy density, long lifespan, and environmental friendliness, are widely used in energy storage and power systems for new energy vehicles. However, with continuous use, the performance of lithium-ion batteries gradually declines, manifested as a decrease in usable capacity and an increase in internal resistance. Therefore, the actual capacity and internal resistance of the battery are generally used as evaluation criteria for the battery's state of health (SOH) and lifespan. With the continuous increase in the number of electric vehicles, the rapid and accurate estimation of battery health is of great significance. Therefore, efficient estimation of the health status of electric vehicle power batteries has become an important research direction.

[0003] Electrochemical impedance spectroscopy (EIS) is an important method for characterizing battery kinetics. Because EIS can reflect the impedance characteristics of a battery over a wide frequency range and has advantages such as high precision, wide bandwidth, and non-destructive nature, it is widely used in battery electrochemical kinetic reaction mechanism analysis, battery aging mode analysis, battery health state estimation, and lifetime prediction. However, traditional EIS methods can only test single cells, with an average testing time of up to 100 seconds per cell. In common scenarios such as production lines and energy storage power stations, it is often necessary to test hundreds of the same type of battery at once. Therefore, traditional single-cell testing becomes a major bottleneck for the application of EIS technology in these scenarios.

[0004] To address this issue, simultaneous series and parallel testing of batteries is a feasible approach. However, the series method requires high voltage withstand capability from the equipment, and operation without battery protection (such as when batteries are not grouped together) can easily lead to safety risks such as electric shock and short circuits, making it unsuitable for the one-time testing of large quantities of loose batteries on a production line. Therefore, this invention proposes a pre-equalized parallel excitation method that can directly apply excitation to a large number of identical batteries on the production line at once, obtaining data for all batteries within the same timeframe. Theoretically, this can save up to 99% of the testing time, significantly improving testing efficiency in production line and similar scenarios. Summary of the Invention

[0005] This invention provides a pre-equalized parallel excitation method and apparatus to solve the aforementioned technical problems.

[0006] This invention provides a pre-equalized parallel excitation method, comprising: S1: Start the equipment, switch the relay to the current sharing position, and perform current sharing on the different parallel battery cells until the equipment detects that the current sharing is complete; S2: Switch the relay to the excitation position to perform impedance testing; S3: Collect the excitation current and response voltage flowing through each parallel cell. After the test is completed, switch the relay to the current sharing position and end the test.

[0007] Preferably, the impedance-excited relay is initially in the current-sharing position. At this time, a loop is formed between the different individual cells connected in parallel, and the loop passes through the current-limiting resistor.

[0008] Preferably, the balancing termination condition is that the terminal voltage of all battery cells is less than a cutoff voltage. At this time, the battery is in a balanced state, the theoretical value of the current flowing through each battery is 0, and the process proceeds to S2.

[0009] Preferably, if the current of all battery cells does not exceed the threshold, the battery is determined to be in a balanced state. At this time, impedance excitation is performed, wherein the threshold is determined based on the rated voltage of the battery cells and the resistance value of the current-limiting resistor in the independent branch of each parallel battery cell.

[0010] Preferably, when starting impedance excitation, the relay is switched to the excitation position. At this time, the independent branch corresponding to the parallel battery cell is not connected in series with a current-limiting resistor.

[0011] Preferably, when a sinusoidal current excitation is applied to both the positive and negative excitation terminals, the current flowing through each cell and the response voltage across each cell satisfy the sinusoidal characteristics.

[0012] Preferably, the response voltage across the corresponding battery is acquired separately for each parallel circuit, and the acquisition process is synchronized with the acquisition of the excitation current. When the excitation ends, the relay is switched to the current sharing position. At this time, a current-limiting resistor is connected in series in the circuit formed by the parallel battery cells.

[0013] The present invention provides a pre-equalized parallel excitation device for performing any of the pre-equalized parallel excitation methods described above.

[0014] Compared with the prior art, the beneficial effects of this application are as follows: 1. This invention can realize impedance testing of parallel battery packs. Compared with the original single battery testing, this invention does not require disassembling the battery pack and thus does not damage the integrity of the battery pack.

[0015] 2. This invention can be used for factory testing of large quantities of the same type of battery cells on a production line. For hundreds of battery cells shipped simultaneously, this invention can collect impedance data of all cells at the same SOC (State of Charge), saving more than 99% of the testing time compared to traditional single-channel equipment. Subsequent analysis functions such as consistency sorting based on impedance data can also eliminate coupling factors caused by SOC differences.

[0016] 3. The device of the present invention has a high degree of integration, is suitable for indoor use, and the relevant detection data can be stored in a cloud server for monitoring and reviewing the detection results.

[0017] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of a pre-equalized parallel excitation method in an embodiment of the present invention; Figure 2 This is a schematic diagram of the detection circuit in an embodiment of the present invention; Figure 3 This is a connection diagram of a pre-equalized parallel excitation device according to an embodiment of the present invention. Detailed Implementation

[0020] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0021] Reference Figure 1 This invention provides a pre-equalized parallel excitation method, comprising the following steps: S1: Start the equipment, switch the relay to the current sharing position, and perform current sharing on the different parallel battery cells until the equipment detects that the current sharing is complete; The impedance-excited relay is initially in the current-sharing position. At this time, a loop is formed between the different individual cells connected in parallel, and the loop passes through the current-limiting resistor.

[0022] In some embodiments, such as Figure 2As shown, the relay described in this invention is initially in the current-equalizing position (corresponding to the solid red line in the figure). At this time, the circuit passes through the current-limiting resistor R0. The function of this current-limiting resistor is to prevent the current from becoming too large during the battery equalization process, exceeding the device's capacity. The current-limiting resistor has a value of 3.3 ohms. At this time, for commonly used lithium batteries below 4.2V, the maximum current that can flow through each parallel branch after current limiting does not exceed 1.27A, which is within the allowable range of the device.

[0023] In some embodiments, if there is a difference in the voltage of the individual cells of the parallel batteries to be tested, for example, the voltages of the two parallel battery cells are 3210mV and 3250mV respectively, then the cell with a voltage of 3250mV will charge the cell with a voltage of 3210mV. Theoretically, when the terminal voltages of the two batteries are both adjusted to 3230mV, the batteries are considered to have completed equalization, and the current flowing through each battery is 0.

[0024] In some embodiments, it is necessary to monitor the voltage flowing through each battery cell in real time. If the voltage difference between any two battery cells does not exceed the cutoff voltage of 10mV, the batteries are considered to have reached an equilibrium state, and the impedance excitation step can be performed. Specifically, if the current of all battery cells does not exceed a threshold value, the batteries are considered to have reached an equilibrium state. In this case, the threshold value is calculated as (rated voltage of the battery cell / resistance of the current-limiting resistor) × k1, where k1 is an adaptation coefficient ranging from 0.0025 to 0.0035, calibrated using experimental data. When k1 = 0.003, it ensures that the current is ≤3mA when the voltage difference is ≤10mV. The voltage difference-current relationship was recorded through equilibrium experiments with 10 different types of batteries (5 groups of lithium iron phosphate and 5 groups of ternary lithium), as shown in Table 1. Table 1. Pressure Difference-Current Correspondence Table Battery Type Pressure difference (mV) Branch current (mA) k1 value Lithium iron phosphate 5 1.49 0.003 Lithium iron phosphate 10 2.95 0.0029 Lithium ternary lithium 5 1.50 0.0028 Lithium ternary lithium 10 2.97 0.0029 In some embodiments, if it is necessary to simultaneously perform parallel balancing on N batteries, then Figure 2 Each independent branch containing at least N-1 batteries needs a current-limiting resistor R0 and a relay device to ensure that when the relay is in the current-sharing mode, the current will not exceed the limit if there is a voltage difference between any two batteries forming a circuit.

[0025] S2: Switch the relay to the excitation position to perform impedance testing; In some embodiments, starting impedance excitation requires the relay described in this invention (corresponding to the appendix) to be activated. Figure 2 (The red dashed line in the image) Switch to the excitation mode. At this time, the independent branch corresponding to the parallel battery cell does not have a series current-limiting resistor R0. For each battery cell, from the excitation positive terminal to the excitation negative terminal, there are only the battery itself and the shunt element for collecting current. Here, the shunt element is equivalent to a 5 milliohm standard resistor. The current magnitude of the parallel branch is obtained by measuring the voltage change across the element.

[0026] In some embodiments, with Figure 2 Taking the circuit diagram in the image as an example, assume the total loop current is... The total voltage is The currents flowing through the two parallel branches are respectively and The voltages collected at both ends of the battery are respectively and The resistance values ​​of shunt are respectively and Then the following relationship exists: ; ; Solving for: ; ; Therefore, by applying a sinusoidal current excitation to both the positive and negative excitation terminals, the current flowing through each battery cell will ideally also satisfy a sinusoidal wave. Frequency domain information can be extracted from the current and voltage flowing through the battery to obtain the impedance calculation results.

[0027] S3: Collect the excitation current and response voltage flowing through each parallel cell. After the test is completed, switch the relay to the current sharing range and end the test. In some embodiments, the current in each parallel circuit differs due to the impedance differences of each parallel battery cell. Furthermore, because of the presence of a series shunt, the voltage across each battery cell is not exactly equal to the voltages across the excitation positive and negative terminals. Therefore, each parallel circuit requires separate sampling of the voltage across the battery cells; the voltages at the excitation terminals cannot be simply substituted.

[0028] In some embodiments, after the excitation ends, the relay described in this invention is switched to the current sharing mode, such as... Figure 2 As shown by the red solid line, a current-limiting resistor R0 is connected in series in the circuit formed by the parallel battery cells to protect the equipment from overcurrent.

[0029] This invention provides a pre-equalized parallel excitation method, further comprising: Collect battery terminal voltage characteristics to identify battery type; Collect the equalization back-end voltage of the battery Real-time internal resistance Battery type and battery temperature ; based on , Battery type and battery temperature The dynamic parameters are calculated using the following formula: Dynamic current fluctuation threshold : Where k is the safety factor, and The value ranges from 0.03 to 0.05; Preset temperature; This is a temperature correction factor, ranging from 0.01 to 0.03, determined by fitting experimental data. MOS transistor gate voltage change rate : ,in, This refers to the resistance value of the current-limiting resistor in balanced mode. Adjust the time based on the baseline, and ; This is the gate-source voltage when the MOSFET is fully turned on. This is the gate-source voltage when the MOSFET is turned off; This refers to the resistance value of the current-limiting resistor in balanced mode; In this embodiment, ,and In engineering, The default value is 2Ω, while the battery's real-time internal resistance... The resistance is typically between 50mΩ and 500mΩ, which is normal for aging batteries.

[0030] RC low-pass filter cutoff frequency : ,in, , The soft-start process time refers to the total time for adjusting the circuit impedance through the MOSFET. Based on the calculation Adjusting the rate of change of the MOSFET gate voltage enables adaptive adjustment of the circuit impedance; Based on the calculation Adjust the cutoff frequency to filter high-frequency spike noise generated during mode switching; When switching from equalization mode to excitation mode, the backup relay K2 is closed. The impedance of the internal linear adjustment loop is adjusted until the loop current fluctuation is ≤ Then, close the main relay K1 and open the standby relay K2; When switching from excitation mode to equalization mode, the circuit impedance is adjusted in reverse. After the circuit current fluctuation stabilizes, the relay switching operation is performed.

[0031] In this embodiment, Battery impedance experiments were conducted within a temperature range of -10℃ to 60℃ to record the impedance data at different temperatures. The fit value was obtained by fitting. Relationship with temperature: when or hour, =0.03, if the temperature deviates significantly from r0, a stronger correction is needed; when hour, The value ranges from 0.01 to 0.02, and the temperature is close to r0, so the correction is weakened. In this embodiment, the battery terminal voltage characteristic refers to the nominal voltage attribute of the battery under stable conditions. For example, the nominal terminal voltage of a lithium iron phosphate battery is usually around 3.2V, and that of a ternary lithium battery is usually around 3.7V. The terminal voltage value of the battery after it has been left to stand is collected and compared with the preset voltage range of different battery types to identify the battery type.

[0032] In this embodiment, It is the stable terminal voltage of the battery after the equalization process. For example, after equalization, the voltage of each cell in a group of parallel lithium iron phosphate batteries is... After stabilizing at around 3.22V, wait 2 seconds after the equalization process is complete before collecting the voltage at each battery terminal again, and take the stable value as the final value. .

[0033] It is the internal equivalent resistance of the battery under its current operating state. For example, the real-time internal resistance of a ternary lithium battery at 25°C. The internal resistance is calculated by applying a small-amplitude AC signal to a value of 150mΩ and combining the collected current and voltage data. It refers to the current operating temperature of the battery, such as when the battery is running. The temperature is 30℃, collected directly by a temperature sensor.

[0034] It is the dynamic critical value for judging whether the loop current is stable, where the safety factor k is the adaptation coefficient to avoid overcurrent risk.

[0035] The preset temperature r0 is the reference temperature, which is fixed at 25℃.

[0036] These are parameters that control the turn-on / turn-off speed of the MOSFET. This refers to the resistance value of the current-limiting resistor in balanced mode, such as the current-limiting resistor. The value is 2Ω, which means that a fixed resistance value is pre-configured in the circuit or selected and entered into the system via a DIP switch.

[0037] In this embodiment, It is the gate-source voltage when the MOSFET is fully turned on. For example, 10V is commonly used for N-channel MOSFETs. This is the gate-source voltage when the MOSFET is turned off, typically taken as 0V. The parameters of the selected MOSFET are pre-entered into the system for calculation. linear adjustment logic control :Right now Press over time The rate increases linearly (excitation mode switching) or decreases linearly (equalization mode switching) to avoid current surges caused by voltage fluctuations.

[0038] In this embodiment, the filter parameters are adjusted according to the cutoff frequency, and the resistance value of the RC circuit is adjusted by a digital potentiometer, for example... The frequency must be 0.1Hz and the capacitance must be [value missing]. When the calculated resistance is 200kΩ, the digital potentiometer automatically adjusts to the corresponding resistance value.

[0039] In this embodiment, the process is as follows: Balancing → Excitation: Close the standby relay K2 → Delay for 0.1s (waiting for the relay contacts to stabilize) → Initiate soft start ( Internal impedance adjustment) → Real-time monitoring of current fluctuations → When fluctuation ≤ Continuous for 0.5s → close main relay K1 → delay for 0.1s → open K2; Excitation → Equalization: Initiating soft start (reverse impedance adjustment, (From 10V to 0V) → Real-time monitoring of current fluctuations → When the fluctuation is ≤50mA for 0.5s, K2 is closed → K1 is opened → Delay for 0.1s → K2 is opened (the current limiting resistor is connected in series to restore the equalization mode).

[0040] The beneficial effects of the above technical solution are: by dynamically adapting the parameter calculation of battery status, the soft-start logic of hierarchical control and the redundant relay switching mechanism, it can not only achieve accurate identification of battery type and strategy matching, but also smoothly adjust the circuit status and filter interference noise during mode switching, effectively improving the safety, stability and compatibility of parallel battery detection and multi-type battery compatibility, while reducing current surge and signal error during the switching process.

[0041] This invention provides a pre-equalized parallel excitation method, further comprising: The generated low-amplitude multi-frequency detection excitation signal is coupled and adapted to the excitation frequency range, wherein the capacitance value Satisfying the formula: ,in, f is the value of the isolation resistor; f is the operating frequency of the detection excitation; j is the imaginary number. These are the resistance values ​​of the first feedback resistor and the second feedback resistor, respectively. The reference matching impedance for the battery excitation input; This is a parallel operator; in, The first end is the excitation coupling end. The second end is connected to the output end of R0; The second end and The connection point at the first end is the voltage divider adapter terminal, which is connected to the excitation input terminal of the battery under test; The second terminal is the common ground adjustment terminal, which is grounded; Collect the response voltage of the battery under test at various frequency points; Perform feedback correction for the following equivalent internal resistance range estimation: Based on the partial pressure coefficient Adjust the sensitivity weights at each frequency point. ,in, Assign initial weights to battery types; Through formula Calculate the weighted equivalent internal resistance at each frequency point. ,in, Let be the sampled response voltage at the i-th frequency point. Let be the amplitude of the detection excitation current at the i-th frequency point; Let be the operating frequency at the i-th frequency point.

[0042] In this embodiment, "low amplitude" refers to a small current / voltage amplitude in the excitation signal to avoid affecting the battery state. "Multiple frequencies" refers to a signal covering multiple operating frequencies, such as generating a sine wave signal from 10Hz to 10kHz with the amplitude controlled within 5mA. A signal generator chip is used, and the frequency range and amplitude are set through programming, then adjusted to a low amplitude by an amplification circuit before output. Battery polarization experiments with different amplitude excitations were conducted, and the relationship between polarization voltage and excitation amplitude was recorded, as shown in Table 2. Table 2 Relationship between polarization voltage and excitation amplitude Excitation current amplitude (mA) Polarization voltage (mV) Error (%) in impedance detection 3 0.5 0.8 5 1.2 1.5 8 3.5 4.2 In this embodiment, the isolation coupling capacitor is the component that achieves this function. If the excitation frequency is detected... 1kHz, isolation resistor Take 200Ω, 100Ω 50Ω, reference matching impedance The resistance is 50Ω. Substituting this into the formula, we get... At least approximately 0.47 In practice, 0.5 can be selected. Ceramic capacitors are selected based on the excitation frequency range, and capacitors of corresponding capacitance are soldered to the corresponding positions in the circuit.

[0043] In this embodiment, a metal film resistor with an accuracy of 1% is selected, and according to... and The connection method involves soldering the components to the corresponding circuit nodes.

[0044] In this embodiment, the response voltage at each frequency point refers to the voltage signal across the battery under different frequency excitations. For example, when the excitation signal is 1kHz, the voltage value across the battery is collected. It uses an analog-to-digital converter chip and sets the sampling frequency to more than 5 times the highest excitation frequency to collect the voltage at both ends of the battery in real time and transmit it to the host computer.

[0045] In this embodiment, the battery type is associated with the initial weight. These are preset weights corresponding to different battery types. For example, wi is set to 1.2 for lithium iron phosphate batteries and wi is set to 1.0 for ternary lithium batteries. The corresponding preset value is called according to the battery type identification result, as shown in Table 3. Table 3 General Value Table Battery Type Temperature coefficient of impedance (% / ℃) wi value Lithium iron phosphate 0.3 1.2 Lithium ternary lithium 0.25 1.0 Lithium manganese battery 0.4 1.3 Lithium manganese iron phosphate 0.28 1.1 In this embodiment, the purpose of calculating the weighted equivalent internal resistance at each frequency point is that the excitation signal at different frequencies has different sensitivities to different internal characteristics of the battery (such as ohmic internal resistance and polarization internal resistance), and the voltage division will affect the actual amplitude of the signal. By correcting the sensitivity weight and calculating the weighted equivalent internal resistance, the detection information at each frequency can be more accurately integrated, the accuracy of battery internal resistance assessment can be improved, and the health status of the battery can be better reflected.

[0046] The beneficial effects of the above technical solution are as follows: by generating a suitable detection excitation signal, achieving stable signal transmission and adaptation through hierarchical means, and combining precise acquisition with weight correction and weighted equivalent internal resistance calculation of multi-frequency data, the excitation signal can be used to avoid interference with the battery, and the battery internal resistance can be accurately evaluated by comprehensively considering multi-frequency information, thereby effectively improving the accuracy and adaptability of parallel battery excitation detection.

[0047] This invention provides a pre-equalized parallel excitation device, such as... Figure 3 As shown, this is a parallel excitation method for performing any of the pre-equalization methods described above. It includes a detection device 1 and a host computer 2.

[0048] The detection device 1 includes an equalization board 11, an excitation board 12, and a sampling board 13. The equalization board 11 is used to equalize all parallel battery cells, switching between equalization and excitation modes via an impedance-driven excitation relay. In the equalization mode, the relay is open and protected by a current-limiting resistor R0; in the excitation mode, the relay is closed and protected by the current-limiting resistor R0 to reduce excitation current attenuation. The excitation board 12 applies excitation to all parallel battery cells, resulting in a sinusoidal current signal passing through each cell, generating a corresponding response voltage signal. The sampling board 13 collects the state of all batteries, including the terminal voltage of each cell, the excitation current, and the response voltage, sampling these physical quantities. The sampling board also transmits data to the host computer described in this invention.

[0049] The host computer 2 is used to select operating conditions, configure parameters, start the excitation, and display the data collected by the sampling board on the screen.

[0050] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A pre-equalized parallel excitation method, characterized in that, include: S1: Start the equipment, switch the relay to the current sharing position, and perform current sharing on the different parallel battery cells until the equipment detects that the current sharing is complete; S2: Switch the relay to the excitation position to perform impedance testing; S3: Collect the excitation current and response voltage flowing through each parallel cell. After the test is completed, switch the relay to the current sharing position and end the test.

2. The pre-equalized parallel excitation method according to claim 1, characterized in that, The impedance-excited relay is initially in the current-sharing position. At this time, a loop is formed between the different individual cells connected in parallel, and the loop passes through the current-limiting resistor.

3. The pre-equalized parallel excitation method according to claim 1, characterized in that, The balancing termination condition is that the terminal voltage of all battery cells is less than a cutoff voltage. At this time, the battery is in a balanced state, the theoretical value of the current flowing through each battery is 0, and the process proceeds to S2.

4. The pre-equalized parallel excitation method according to claim 1, characterized in that, If the current of all battery cells does not exceed the threshold, the battery is determined to be in a balanced state. At this time, impedance excitation is performed, wherein the threshold is determined based on the rated voltage of the battery cells and the resistance value of the current-limiting resistor in the independent branch of each parallel battery cell.

5. The pre-equalized parallel excitation method according to claim 1, characterized in that, When starting impedance excitation, switch the relay to the excitation position. At this time, the independent branch corresponding to the parallel battery cell is not connected in series with a current-limiting resistor.

6. The pre-equalized parallel excitation method according to claim 1, characterized in that, When a sinusoidal current is applied to the positive and negative terminals of the excitation electrode, the current flowing through each cell and the response voltage across each cell satisfy the sinusoidal characteristics.

7. The pre-equalized parallel excitation method according to claim 1, characterized in that, Each parallel circuit individually acquires the response voltage across the corresponding battery terminals, and the acquisition process is synchronized with the acquisition of the excitation current. When the excitation ends, the relay is switched to the current sharing position. At this time, a current-limiting resistor is connected in series in the circuit formed by the parallel battery cells.

8. A pre-equalized parallel excitation device, characterized in that, Used to perform the pre-equalization parallel excitation method as described in any one of claims 1-8.

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