Battery impedance detection, battery status detection method and system

Abstract

The present invention provides a battery impedance detection method, which includes: acquiring offline data; detecting the terminal voltage and temperature of all batteries in a battery group to be tested; determining an equalization temperature according to the temperature of all batteries in the battery group to be tested and the temperature of multiple battery offline test points, and adjusting the temperature of all batteries in the battery group to be tested according to the equalization temperature; determining an equalization voltage according to the terminal voltage of all batteries in the battery group to be tested and the voltage of multiple battery offline test points, and adjusting the terminal voltage of all batteries in the battery group to be tested according to the equalization voltage; in response to the temperature of all batteries in the battery group to be tested being equal to the equalization temperature, and the terminal voltage of all batteries in the battery group to be tested being equal to the equalization voltage, impedance detection is performed on all batteries in the battery group to be tested, thereby realizing online detection of power battery impedance. In addition, the present invention also provides a battery impedance detection system, a battery state detection method and system.

Description

Technical Field

[0001] The present invention relates to the technical field of impedance detection, and in particular to a battery impedance detection and battery status detection method and system. Background Art

[0002] In the new energy industry, electrochemical batteries are widely used as energy storage devices to provide power supply. For example, batteries are needed as energy storage devices to support the power grid in new energy power generation systems; lithium-ion batteries are used as vehicle power sources in new energy electric vehicles; and various types of electrochemical batteries are widely used as basic power sources in energy storage products supporting new energy.

[0003] Since batteries have low single-cell voltage or low current, they often need to be used in series and parallel to form a series battery system when used in new energy scenarios. At the same time, due to the imbalance of single-cell batteries, individual batteries in the series system will accelerate aging and decay during use. Due to improper use or manufacturing defects, individual batteries may have internal problems, such as lithium dendrite growth causing internal short circuits. If they are not identified in time, it will easily cause a decrease in system efficiency. In severe cases, it may even cause system failures, thermal runaway, battery system burnout and other major losses. However, such problems are often difficult to identify from the external characteristics of the battery and can only be identified through the inherent electrochemical characteristics of the battery. Therefore, how to detect the inherent electrochemical characteristics of each battery in the series battery system becomes a prerequisite for avoiding such problems.

[0004] Electrochemical impedance spectroscopy is an effective method for detecting the internal condition of lithium batteries and is widely used in the field of battery testing and research and development. Currently, battery impedance testing is mostly based on electrochemical workstations, but the equipment is bulky and not suitable for vehicle-mounted battery impedance measurement. Summary of the invention

[0005] Based on this, the present invention provides a battery impedance detection and battery status detection method and system, which can realize online detection of automobile power battery impedance.

[0006] In one aspect, the present invention provides a battery impedance detection method, comprising:

[0007] Obtaining offline data; wherein the offline data includes the battery offline data test point impedance measured by disturbing the battery with a single-frequency square wave signal under multiple groups of different test conditions; the test conditions include the battery offline test point temperature and the battery offline test point voltage;

[0008] Detect the terminal voltage and temperature of all batteries in the battery pack to be tested;

[0009] Determine a balancing temperature according to the detected temperatures of all batteries in the battery group to be tested and the temperatures of a plurality of battery offline test points, and adjust the temperatures of all batteries in the battery group to be tested to the balancing temperature;

[0010] Determine a balancing voltage according to the detected terminal voltages of all batteries in the battery group to be tested and the voltages of a plurality of battery offline test points, and adjust the terminal voltages of all batteries in the battery group to be tested to the balancing voltage;

[0011] Impedance detection is performed on all batteries in the battery group to be tested.

[0012] Furthermore, the impedance detection of all batteries in the battery pack to be tested includes:

[0013] The battery pack to be tested is disturbed by a sinusoidal excitation signal of a preset frequency, and the terminal voltage and cell current of each battery in the battery pack to be tested are collected; the preset frequency is 1 or 3 times the frequency of the single-frequency square wave signal;

[0014] Substitute the collected terminal voltage and cell current corresponding to each battery in the battery pack to be tested into a preset battery impedance calculation formula to obtain the corresponding battery impedance.

[0015] Further, the perturbation of the battery pack to be tested by a sinusoidal excitation signal of a preset frequency includes:

[0016] Grouping the multiple batteries in the battery pack to be tested so that each group has two batteries, applying a sinusoidal excitation signal to the batteries in each group, and collecting the terminal voltage and cell current of the corresponding battery;

[0017] The phase difference between the sinusoidal excitation signals applied to two batteries in the same group is 180°.

[0018] Further, the multiple batteries in the battery group to be tested are grouped so that each group has two batteries, a sinusoidal excitation signal is applied to the batteries in each group, and the terminal voltage and cell current of the corresponding battery are collected, which specifically includes:

[0019] If the number of batteries in the battery group to be tested is an even number, the batteries are grouped in pairs;

[0020] If the number of batteries in the battery group to be tested is an odd number N, the N-1 batteries in the battery group to be tested are grouped in pairs to obtain (N-1) / 2 groups, a sinusoidal excitation signal is applied to the batteries in the (N-1) / 2 groups, and the terminal voltage and cell current of the corresponding battery are collected;

[0021] The remaining battery in the battery group to be tested and the battery adjacent to it are combined into a last group, a sinusoidal excitation signal is applied to the batteries in the last group, and the terminal voltage and cell current of the corresponding battery are collected.

[0022] Further, determining the equalization voltage according to the detected terminal voltages of all batteries in the battery group to be tested and the voltages of the plurality of battery offline test points, and adjusting the terminal voltages of all batteries in the battery group to be tested to the equalization voltage, comprises:

[0023] Calculating the average value of the terminal voltages of all batteries in the battery group to be tested;

[0024] Determine whether there is a battery offline test point whose voltage is equal to the average value;

[0025] In response to determining that there is a battery offline test point whose voltage is equal to the average value, taking the average value as a first balancing voltage, and adjusting the terminal voltages of all batteries in the battery group to be tested to the first balancing voltage;

[0026] In response to determining that there is no battery offline test point voltage equal to the average value, determining a difference between the average value and each of the battery offline test point voltages;

[0027] Taking the battery offline test point voltage corresponding to the smallest difference as the second balancing voltage, and adjusting the plurality of terminal voltages in the battery group to be tested to the second balancing voltage;

[0028] And / or, determining the equilibrium temperature according to the detected temperatures of all batteries in the battery group to be tested and the temperatures of the plurality of battery offline test points, and adjusting the temperatures of all batteries in the battery group to be tested to the equilibrium temperature, comprises:

[0029] Comparing the detected temperatures of all batteries in the battery pack to be tested to determine the highest temperature;

[0030] Determine whether there is a battery offline test point whose temperature is equal to the highest temperature;

[0031] In response to determining that there is a battery offline test point whose temperature is equal to the highest temperature, taking the highest temperature as a first balancing temperature, and adjusting the temperatures of all batteries in the battery group to be tested to the first balancing temperature;

[0032] In response to determining that there is no battery offline test point temperature equal to the highest temperature, comparing the relationship between the highest temperature and each of the battery offline test point temperatures, screening out the battery offline test point temperatures greater than the highest temperature, and recording them as candidate battery offline test point temperatures;

[0033] Determine the difference between the temperature of the offline test point of the selected battery and the highest temperature;

[0034] The battery offline test point temperature corresponding to the smallest difference is used as the second equilibrium temperature, and the multiple temperatures in the battery group to be tested are all adjusted to the second equilibrium temperature.

[0035] In addition, the present invention also provides a battery impedance detection system, including: a memory and a processor;

[0036] The memory is used to store computer programs;

[0037] The processor is used to implement the above-mentioned battery impedance detection method when executing the computer program.

[0038] On the other hand, the present invention also provides a battery status detection method, comprising:

[0039] Obtaining offline data; wherein the offline data includes the battery offline data test point impedance measured by disturbing the battery with a single-frequency square wave signal under multiple groups of different test conditions; the test conditions include the battery offline test point temperature and the battery offline test point voltage;

[0040] Detect the terminal voltage and temperature of all batteries in the battery pack to be tested;

[0041] Determine a balancing temperature according to the detected temperatures of all batteries in the battery group to be tested and the temperatures of a plurality of battery offline test points, and adjust the temperatures of all batteries in the battery group to be tested to the balancing temperature;

[0042] Determine a balancing voltage according to the detected terminal voltages of all batteries in the battery group to be tested and the voltages of a plurality of battery offline test points, and adjust the terminal voltages of all batteries in the battery group to be tested to the balancing voltage;

[0043] Performing impedance detection on all batteries in the battery pack to be tested to obtain measured impedance;

[0044] Mapping the equalization temperature to the battery offline test point temperature, mapping the equalization voltage to the battery offline test point voltage, and searching for the corresponding battery offline data test point impedance in the offline data according to the equalization temperature and the equalization voltage to obtain a reference impedance;

[0045] For each battery in the battery group to be tested, a battery state is determined according to the reference impedance and the corresponding measured impedance.

[0046] Furthermore, the offline data generation method includes:

[0047] The battery is disturbed by using the single-frequency square wave signal, and the terminal voltage and cell current of the battery are collected under multiple groups of different test conditions;

[0048] For each set of test conditions, the corresponding collected terminal voltage and cell current are substituted into the preset battery impedance calculation formula to obtain the corresponding battery impedance;

[0049] For each set of test conditions, the corresponding battery impedance is fast Fourier expanded, and the impedance at a preset frequency is selected from the expansion result as the corresponding battery offline data test point impedance; the preset frequency is 1 times or 3 times the frequency of the single-frequency square wave signal, or the preset frequency includes 1 times and 3 times the frequency of the single-frequency square wave signal.

[0050] Furthermore, the frequency of the single-frequency square wave signal is in the range of 1 Hz to 100 Hz.

[0051] On the other hand, the present invention also provides a battery status detection system, including a memory and a processor;

[0052] The memory is used to store computer programs;

[0053] The processor is used to implement the above-mentioned battery status detection method when executing the computer program.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] The present invention provides a battery impedance detection and battery status detection method and system, wherein the battery impedance detection method obtains offline battery impedance data by adopting a single-frequency square wave signal excitation, thereby shortening the offline data acquisition time; the terminal voltage and temperature are controlled to be maintained at the battery offline data test point, and a single-frequency sine wave signal disturbance is used to realize online battery impedance detection, reduce the influence of inconsistent temperature and terminal voltage on impedance detection, reduce the complexity of controller processing data, and help to determine whether the battery status is abnormal by comparing the reference impedance under the same test conditions, so as to assist battery health status detection and battery fault diagnosis, thereby improving driving safety.

[0056] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 A schematic diagram of a flow chart of a battery impedance detection method provided by an embodiment of the present invention;

[0058] Figure 2 is a schematic diagram of the equivalent circuit of a lithium-ion battery;

[0059] Figure 3 Nyquist curve diagram for lithium-ion batteries;

[0060] Figure 4 It is the curve diagram of battery impedance change at different temperatures;

[0061] Figure 5 It is the battery impedance variation curve under different terminal voltages;

[0062] Figure 6 It is a curve diagram showing the influence of different excitation waveforms on temperature;

[0063] Figure 7 It is a curve diagram showing the influence of different frequency signals on temperature;

[0064] Figure 8 is a schematic diagram of applying a sinusoidal excitation signal in another embodiment of the present invention;

[0065] Fig. 9 A schematic diagram of ripple cancellation effect in another embodiment of the present invention;

[0066] Fig.10 A schematic diagram of a flow chart of a battery status detection method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] Figure 1 A schematic flow chart of a battery impedance detection method provided in an embodiment of the present invention is shown, and the battery impedance detection method includes:

[0069] Step S100: Acquire offline data.

[0070] Figure 2is the equivalent circuit of a lithium-ion battery; the equivalent circuit consists of the following components: 1. OCV (Open Circuit Voltage), in volts V, is the terminal voltage of the battery in the open circuit state; 2. Resistance R s , in ohm, is the ohmic resistance of the battery, mainly involving the electrolyte, collector, active mass resistance, and the resistance generated by the conversion between active mass and collector; 3. Inductance L, in Henry H, represents the state of the battery at high frequency. The inductance is determined by the geometry of the battery and the inductance of the wiring; 4. Capacitance C ct , in farads F, is the capacitance of the charge transfer region; 5. Resistance R ct , in ohms, is the resistance of the charge transfer region; 6. Impedance Z w , in ohms, is the Warburg impedance associated with diffusion phenomena. Taking a sinusoidal AC excitation signal as an example, a small amplitude AC sinusoidal potential wave with different frequencies is applied to the battery. The frequency of the applied disturbance is usually changed in the range of mHz to kHz. The relative amplitude of the response and the time shift (or phase shift) between the input signal and the output signal vary with the applied frequency, and finally a Figure 3 The Nyquist curve in .

[0071] like Figure 3 As shown in the figure, when the excitation signal frequency is lower than 1Hz, the Warburg impedance can be measured, and when the excitation signal frequency is between 1Hz and 1kHz, the charge transfer impedance (R ct / / C ct ), the excitation signal frequency is higher than 1kHz, and the ohmic impedance and the inductive reactance at high frequency can be measured. The impedance detected in this embodiment is the charge transfer impedance. In the actual measurement process, the impedance measured at different temperatures and different terminal voltages is different. Figure 4 The curve diagram of the battery impedance change at different temperatures in the embodiment of the present invention is shown. When the battery is in different temperature environments, the temperature will change the lithium ion transfer speed inside the battery, resulting in the charge transfer impedance (R ct / / C ct ) The impedance of some parts is quite different. The higher the temperature, the faster the lithium ion transfer speed and the smaller the impedance. Figure 5 The curve diagram of the battery impedance change under different terminal voltages in the embodiment of the present invention is shown. When the ambient temperature is the same, the distribution of lithium ions in the electrode and the electrolyte is different under different terminal voltages, which affects the charge migration of lithium ions and leads to the charge transfer impedance (R ct / / C ct) The impedance of some parts is quite different, where the higher the voltage, the smaller the impedance. There are many cells in the power battery pack of electric vehicles. Due to different cell batches and complex and changeable actual application conditions, the temperature and terminal voltage of the single cell vary greatly. If the impedance test is performed on the battery cells of the whole vehicle at this time, the impedance difference generated is large, and more complex algorithms are required to process the cell impedance in various states, which increases the difficulty of realizing vehicle-mounted applications.

[0072] The offline data acquired in this embodiment includes the battery offline data test point impedance measured by disturbing the battery with a single frequency square wave signal under multiple groups of different test conditions. The test conditions include the battery offline test point temperature and the battery offline test point voltage.

[0073] Specifically, the frequency F of the single-frequency square wave signal is in the range of 1 Hz to 100 Hz.

[0074] Optional methods for generating offline data include:

[0075] The battery is disturbed using a single-frequency square wave signal, and the battery terminal voltage and cell current are collected under multiple groups of different test conditions;

[0076] For each set of test conditions, the corresponding collected terminal voltage and cell current are substituted into the preset battery impedance calculation formula to obtain the corresponding battery impedance;

[0077] For each set of test conditions, the corresponding battery impedance is subjected to fast Fourier expansion, and the impedance at a preset frequency is selected from the expansion result as the corresponding battery offline data test point impedance.

[0078] Optionally, the preset frequency is 1 times or 3 times the frequency F of the single-frequency square wave signal; or the preset frequency includes 1 times and 3 times the frequency of the single-frequency square wave signal.

[0079] Specifically, the expansion result is an imaginary impedance spectrum of the battery or a real impedance spectrum of the battery at a preset frequency.

[0080] In the offline state, by measuring multiple sets of terminal voltages and battery currents corresponding to multiple different battery offline test point temperatures and different battery offline test point voltages of a new lithium-ion battery, the impedance of the battery under the corresponding test conditions can be obtained. Among them, if the battery state is characterized by SOH (state of health), then a new lithium-ion battery can be a lithium-ion battery with SOH = 100%.

[0081] Step S200: Detecting the terminal voltage and temperature of all batteries in the battery pack to be tested. When the battery pack is in operation, different batteries in the battery pack have their own temperature and voltage.

[0082] Step S300: determining a balancing temperature according to the detected temperatures of all batteries in the battery group to be tested and the temperatures of a plurality of battery offline test points, and adjusting the temperatures of all batteries in the battery group to be tested to the balancing temperature.

[0083] Step S400: determining a balancing voltage according to the detected terminal voltages of all batteries in the battery group to be tested and a plurality of battery offline test point voltages, and adjusting the terminal voltages of all batteries in the battery group to be tested to the balancing voltage.

[0084] Step S500: performing impedance detection on all batteries in the battery pack to be tested.

[0085] Optionally, step S500 includes:

[0086] The battery pack to be tested is disturbed by a sinusoidal excitation signal of a preset frequency, and the terminal voltage and cell current of each battery in the battery pack to be tested are collected.

[0087] Under the same state, the temperature rise rate of the battery cell using square wave excitation is faster than that of sine wave excitation (such as Figure 6 As shown), therefore, when the battery pack temperature is balanced, using sinusoidal wave excitation can reduce temperature fluctuations and improve detection accuracy.

[0088] Specifically, the preset frequency of the sinusoidal excitation signal in step S500 is 3 times the frequency F of the single-frequency square wave signal, that is, 3F; selecting a higher frequency point can shorten the detection time. In addition, when other conditions of the excitation signal are the same, the lower the frequency, the faster the temperature rise of the battery cell (such as Figure 7 Therefore, choosing a higher frequency point can slow down the temperature rise.

[0089] It should be noted that the preset frequency of the sinusoidal excitation signal in step S500 is equal to the preset frequency used when selecting impedance from the expansion result in step S100, or the preset frequency used when selecting impedance from the expansion result in step S100 at least includes the preset frequency of the sinusoidal excitation signal in step S500.

[0090] In this embodiment, the preset frequency used when selecting impedance from the expansion result in step S100 is 3F, or includes F and 3F.

[0091] In other embodiments, if the preset frequency of the sinusoidal excitation signal in step S500 is the frequency F of the single-frequency square wave signal, the preset frequency used when selecting the impedance from the expansion result in step S100 is F, or includes F and 3F.

[0092] Substitute the collected terminal voltage and cell current corresponding to each battery in the battery pack to be tested into a preset battery impedance calculation formula to obtain the corresponding battery impedance.

[0093] The battery impedance is measured by perturbing the battery with a small current of sweep frequency f and measuring the associated voltage response. The battery impedance is calculated as follows:

[0094]

[0095] Where Z(f) is the battery impedance, Vbat(f) is the cell terminal voltage, Ibat(f) is the cell current, and θ is the phase between the cell terminal voltage and the cell current.

[0096] The battery impedance detection method provided in this embodiment shortens the offline data acquisition time by using a single-frequency square wave signal to excite and obtain offline battery impedance data; by controlling the terminal voltage and temperature to keep them at the battery offline data test point, and using a single-frequency sine wave signal disturbance, the battery impedance is detected online. When the temperature of all batteries in the battery pack to be tested is adjusted to a balanced temperature, and the terminal voltage is adjusted to a balanced voltage, the impact of voltage imbalance and temperature imbalance on impedance detection can be reduced, the algorithm difficulty can be reduced, and the detection efficiency can be increased. It is convenient to compare the measured impedance with the reference impedance under the same test conditions to obtain the gap between the current battery and the new lithium-ion battery (SOH=100%), so as to determine whether the battery state of the current battery is abnormal, which is helpful to assist battery health status detection and battery fault detection, and improve driving safety.

[0097] It should be noted that Figure 1 The flowchart shown is only for expressing the process steps of an embodiment of the present invention, but the process steps of the present invention are not limited to be strictly executed in the order of S100 to S500. In an optional implementation, the execution order of S300 and S400 can be interchanged.

[0098] Optionally, step S300 includes:

[0099] Calculating the average value of the terminal voltages of all batteries in the battery group to be tested;

[0100] Determine whether there is a battery offline test point whose voltage is equal to the average value;

[0101] In response to determining that there is a battery offline test point voltage that is equal to the average value, the average value is used as the first balancing voltage, and the terminal voltages of all batteries in the battery group to be tested are adjusted to the first balancing voltage. Usually, a battery management system includes a balancing control circuit. Balancing refers to the process of keeping the terminal voltage balanced through balancing control when the terminal voltage of each battery cell is unbalanced.

[0102] In response to determining that there is no battery offline test point voltage equal to the average value, determining a difference between the average value and each of the battery offline test point voltages;

[0103] The battery offline test point voltage corresponding to the smallest difference is used as the second balancing voltage, and the plurality of terminal voltages in the battery group to be tested are all adjusted to the second balancing voltage.

[0104] That is, by determining the balancing voltage using the method provided in this embodiment, multiple batteries can be brought into a balanced state as quickly as possible.

[0105] Optionally, step S400 includes:

[0106] Comparing the detected temperatures of all batteries in the battery pack to be tested to determine the highest temperature;

[0107] Determine whether there is a battery offline test point whose temperature is equal to the highest temperature;

[0108] In response to determining that there is a battery offline test point whose temperature is equal to the highest temperature, the highest temperature is used as a first balancing temperature, and the temperatures of all batteries in the battery group to be tested are adjusted to the first balancing temperature.

[0109] In response to determining that there is no battery offline test point temperature equal to the highest temperature, comparing the relationship between the highest temperature and each of the battery offline test point temperatures, screening out the battery offline test point temperatures greater than the highest temperature, and recording them as candidate battery offline test point temperatures;

[0110] Determine the difference between the temperature of the offline test point of the selected battery and the highest temperature;

[0111] The battery offline test point temperature corresponding to the smallest difference is used as the second equilibrium temperature, and the multiple temperatures in the battery group to be tested are all adjusted to the second equilibrium temperature.

[0112] The equilibrium temperature determined in this embodiment is a value greater than the current maximum temperature of the battery cell. Compared with cooling, heating the temperature can shorten the test time and improve the test efficiency. It should be noted that in other embodiments, a temperature value not greater than the maximum temperature of the battery cell can also be selected as the equilibrium temperature. For example, a portion of the batteries are heated and another portion of the batteries are cooled. However, this method requires the deployment of two sets of heating devices and cooling devices around the battery pack, and each battery in each battery pack needs to be equipped with a heating device and a cooling device, respectively, in order to achieve the fixed-point heating or cooling operation.

[0113] Exemplarily, to facilitate understanding of the above steps, when generating offline data, a square wave with a measurement frequency of 1 Hz is measured. It is assumed that the battery offline test point temperature takes values ​​of 10°C, 15°C, 20°C, 25°C, and 30°C, and the battery offline test point voltage takes values ​​of 2.8V, 3.0V, 3.2V, 3.4V, and 3.6V. The battery impedance is obtained according to the battery impedance calculation formula, and the battery impedance is decomposed by fast Fourier transform to obtain the impedance values ​​at 1 Hz and 3 Hz, so that the battery offline test point temperature, battery offline test point voltage value, and battery offline data test point impedance corresponding to each other at 1 Hz and 3 Hz can be obtained.

[0114] Assuming that the detected battery pack terminal voltages are: V1 = 3.15V, V2 = 3.2V, V3 = 3.25V, the voltage average value is 3.2V, that is, the voltage average value is determined to be equal to 3.2V of the battery offline test point voltage, then the balancing voltage is 3.2V, and balancing is turned on so that V1 = V2 = V3 = 3.2V;

[0115] Assuming that the detected battery pack terminal voltages are: V1 = 3.45V, V2 = 3.45V, V3 = 3.45V, the voltage average value is 3.45V, that is, the difference between the voltage average value and the 3.4V of the battery offline test point voltage is the smallest, the balancing voltage is set to 3.4V, and balancing is turned on so that V1 = V2 = V3 = 3.4V;

[0116] After the battery pack terminal voltage is adjusted and balanced, temperature balance adjustment is performed;

[0117] Assuming that the detected temperatures are T1=27°C, T2=28°C, and T3=30°C, that is, the highest temperature is 30°C, and it is determined that the highest temperature is equal to 30°C in the battery offline test point temperature, then the equilibrium temperature is 30°C, and the heating mode is turned on to heat cell 1 and cell 2 to make the temperature of cell 1 and cell 2 reach 30°C;

[0118] Assuming that the detected temperatures are T1=21°C, T2=23°C, and T3=24°C, i.e., the highest temperature is 24°C, it is determined that the highest temperature is not equal to the battery offline test point temperature, and the minimum value 25°C is selected from the battery offline test point temperatures (25°C, 30°C) that are greater than the highest temperature 24°C, then the equilibrium temperature is 25°C, and the battery cells 1, 2, and 3 are heated to 25°C;

[0119] After the detection temperature reaches equilibrium, the battery is subjected to online impedance detection. A single-frequency 3Hz sinusoidal signal can be used to perturb the battery cell, and the terminal voltage and current can be measured. The calculated impedance can be compared and analyzed with the reference impedance under the same test conditions in the offline data, so as to determine whether the current working condition of the battery is abnormal through comparative analysis. Another embodiment of the present invention provides a battery impedance detection method, which includes steps S100 to S500 in the previous embodiment.

[0120] In step S500 of this embodiment, the battery pack to be tested is disturbed by a sinusoidal excitation signal of a preset frequency, including:

[0121] The multiple batteries in the battery group to be tested are grouped so that there are two batteries in each group, a sinusoidal excitation signal is applied to the batteries in each group, and the terminal voltage and cell current of the corresponding battery are collected; the phase difference between the sinusoidal excitation signals applied to the two batteries in the same group is 180°.

[0122] When the battery pack is subjected to impedance testing, voltage and current fluctuations will occur, which will eventually cause large ripples in the battery pack voltage, affecting the sampling accuracy. In order to solve the problem of additional inductive disturbance ripples caused by the sinusoidal excitation signal, combined with Figure 8 As shown, this embodiment sets the same group of batteries (for example, Fig. 9 The sinusoidal excitation signals corresponding to Bat1 and Bat2 in the figure differ by 180° relative to each other. When EIS measurement is performed on each battery in the same group, the disturbance ripple of the total output voltage Vbat is eliminated due to the superposition and cancellation of the sinusoidal excitation signals that are 180° apart from each other.

[0123] Specifically, the step of grouping the multiple batteries in the battery pack to be tested so that each group has two batteries includes:

[0124] If the number of batteries in the battery group to be tested is an even number, the batteries are grouped in pairs;

[0125] If the number of batteries in the battery group to be tested is an odd number N, the N-1 batteries in the battery group to be tested are grouped in pairs to obtain (N-1) / 2 groups, a sinusoidal excitation signal is applied to the batteries in the (N-1) / 2 groups, and the terminal voltage and cell current of the corresponding battery are collected;

[0126] The remaining battery in the battery group to be tested and the battery adjacent to it are combined into a last group, a sinusoidal excitation signal is applied to the batteries in the last group, and the terminal voltage and cell current of the corresponding battery are collected.

[0127] If the number of batteries in the battery group to be tested is an odd number N, when a sinusoidal excitation signal is applied to the batteries in the (N-1) / 2 groups, the sinusoidal excitation signal is not applied to the remaining battery; when a sinusoidal excitation signal is applied to the last group consisting of the remaining battery and its adjacent battery, the sinusoidal excitation signal is not applied to the batteries in the (N-1) / 2 groups, so that the ripple of the total output voltage Vbat can be offset in both cases. The ripple offset effect is as follows: Fig. 9 It should be noted that the method provided in any of the above embodiments can be used not only for battery impedance detection of a battery pack, but also for battery impedance detection of a battery pack. Exemplarily, in an embodiment applied to a battery pack, the battery pack includes a plurality of battery packs, and the battery impedance detection method includes:

[0128] Detect the temperature and terminal voltage of all battery groups in the battery pack (i.e., the voltage across the battery group);

[0129] Determine a balancing temperature according to the temperatures of all battery groups in the battery pack and the temperatures of multiple battery group offline data test points acquired in advance, and adjust the temperatures of all battery groups in the battery pack to the balancing temperature;

[0130] Determine a balancing voltage according to the group terminal voltages of all battery groups in the battery pack and the voltages of multiple battery group offline data test points acquired in advance, and adjust the group terminal voltages of all battery groups in the battery pack to the balancing voltage;

[0131] Impedance detection is performed on all battery groups in the battery pack.

[0132] in addition, Fig.10 A schematic flow chart of a battery status detection method in an embodiment of the present invention is shown. The battery status detection method includes steps S101 to S701, wherein:

[0133] Step S101: Acquire offline data.

[0134] The offline data includes the battery offline data test point impedance measured by disturbing the battery with a single-frequency square wave signal under multiple groups of different test conditions; the test conditions include the battery offline test point temperature and the battery offline test point voltage.

[0135] Specifically, the method for generating offline data includes:

[0136] The battery is disturbed using a single-frequency square wave signal, and the battery terminal voltage and cell current are collected under multiple groups of different test conditions;

[0137] For each set of test conditions, the corresponding collected terminal voltage and cell current are substituted into the preset battery impedance calculation formula to obtain the corresponding battery impedance;

[0138] For each set of test conditions, the corresponding battery impedance is subjected to fast Fourier expansion, and the impedance at a preset frequency is selected from the expansion result as the corresponding battery offline data test point impedance.

[0139] Step S201: Detect the terminal voltage and temperature of all batteries in the battery pack to be tested.

[0140] Step S301: determining a balancing temperature according to the detected temperatures of all batteries in the battery group to be tested and the temperatures of a plurality of battery offline test points, and adjusting the temperatures of all batteries in the battery group to be tested to the balancing temperature.

[0141] In the offline state, by measuring multiple sets of terminal voltages and battery currents corresponding to multiple different battery offline test point temperatures and different battery offline test point voltages of a new lithium-ion battery, the impedance of the battery under the corresponding test conditions can be obtained. Among them, if the battery state is characterized by SOH (state of health), then a new lithium-ion battery can be a lithium-ion battery with SOH = 100%.

[0142] Specifically, step S301 includes:

[0143] Comparing the detected temperatures of all batteries in the battery pack to be tested to determine the highest temperature;

[0144] Determine whether there is a battery offline test point whose temperature is equal to the highest temperature;

[0145] In response to determining that there is a battery offline test point whose temperature is equal to the highest temperature, taking the highest temperature as a first balancing temperature, and adjusting the temperatures of all batteries in the battery group to be tested to the first balancing temperature;

[0146] In response to determining that there is no battery offline test point temperature equal to the highest temperature, comparing the relationship between the highest temperature and each of the battery offline test point temperatures, screening out the battery offline test point temperatures greater than the highest temperature, and recording them as candidate battery offline test point temperatures;

[0147] Determine the difference between the temperature of the offline test point of the selected battery and the highest temperature;

[0148] The battery offline test point temperature corresponding to the smallest difference is used as the second equilibrium temperature, and the multiple temperatures in the battery group to be tested are all adjusted to the second equilibrium temperature.

[0149] Step S401: determining a balancing voltage according to the detected terminal voltages of all batteries in the battery group to be tested and a plurality of battery offline test point voltages, and adjusting the terminal voltages of all batteries in the battery group to be tested to the balancing voltage.

[0150] Specifically, step S401 includes:

[0151] Calculating the average value of the terminal voltages of all batteries in the battery group to be tested;

[0152] Determine whether there is a battery offline test point whose voltage is equal to the average value;

[0153] In response to determining that there is a battery offline test point whose voltage is equal to the average value, taking the average value as a first balancing voltage, and adjusting the terminal voltages of all batteries in the battery group to be tested to the first balancing voltage;

[0154] In response to determining that there is no battery offline test point voltage equal to the average value, determining a difference between the average value and each of the battery offline test point voltages;

[0155] The battery offline test point voltage corresponding to the smallest difference is used as the second balancing voltage, and the plurality of terminal voltages in the battery group to be tested are all adjusted to the second balancing voltage.

[0156] Step S501: performing impedance detection on all batteries in the battery pack to be tested to obtain measured impedance.

[0157] Specifically, step S501 includes: disturbing the battery pack to be tested by a sinusoidal excitation signal of a preset frequency, and collecting the terminal voltage and cell current of each battery in the battery pack to be tested; the preset frequency is 1 times or 3 times the frequency of the single-frequency square wave signal;

[0158] Substitute the collected terminal voltage and cell current corresponding to each battery in the battery pack to be tested into a preset battery impedance calculation formula to obtain the corresponding battery impedance.

[0159] Optionally, the perturbation of the battery pack to be tested by a sinusoidal excitation signal of a preset frequency includes:

[0160] The multiple batteries in the battery group to be tested are grouped so that there are two batteries in each group, a sinusoidal excitation signal is applied to the batteries in each group, and the terminal voltage and cell current of the corresponding battery are collected; the phase difference between the sinusoidal excitation signals applied to the two batteries in the same group is 180°.

[0161] Optionally, the step of grouping the multiple batteries in the battery pack to be tested so that each group has two batteries, applying a sinusoidal excitation signal to the batteries in each group, and collecting the terminal voltage and cell current of the corresponding battery specifically includes:

[0162] If the number of batteries in the battery group to be tested is an even number, the batteries are grouped in pairs;

[0163] If the number of batteries in the battery group to be tested is an odd number N, the N-1 batteries in the battery group to be tested are grouped in pairs to obtain (N-1) / 2 groups, a sinusoidal excitation signal is applied to the batteries in the (N-1) / 2 groups, and the terminal voltage and cell current of the corresponding battery are collected;

[0164] The remaining battery in the battery group to be tested and the battery adjacent to it are combined into a last group, a sinusoidal excitation signal is applied to the batteries in the last group, and the terminal voltage and cell current of the corresponding battery are collected.

[0165] If the number of batteries in the battery group to be tested is an odd number N, when a sinusoidal excitation signal is applied to the batteries in the (N-1) / 2 groups, the sinusoidal excitation signal is not applied to the remaining battery; when a sinusoidal excitation signal is applied to the last group consisting of the remaining battery and its adjacent battery, the sinusoidal excitation signal is not applied to the batteries in the (N-1) / 2 groups, so that the ripple of the total output voltage Vbat can be offset in both cases. The ripple offset effect is as follows: Fig. 9 shown.

[0166] It should be noted that the preset frequency of the sinusoidal excitation signal in step S501 is equal to the preset frequency used when selecting impedance from the expansion results in step S101, or the preset frequency used when selecting impedance from the expansion results in step S101 should at least include the preset frequency of the sinusoidal excitation signal in step S501.

[0167] Step S601: Map the equalization temperature to the battery offline test point temperature, map the equalization voltage to the battery offline test point voltage, and search the corresponding battery offline data test point impedance in the offline data according to the equalization temperature and the equalization voltage to obtain a reference impedance.

[0168] Step S701: for each battery in the battery pack to be tested, determining a battery state according to the reference impedance and the corresponding measured impedance.

[0169] The battery status may include SOH (battery state of health) and battery fault status.

[0170] Specifically, step S701, determining the battery state of each battery in the battery pack according to the reference impedance and the corresponding measured impedance, includes:

[0171] For each battery in the battery pack, calculating the difference between the reference impedance and the corresponding measured impedance;

[0172] For each battery in the battery pack, a corresponding battery state is determined according to the corresponding difference value.

[0173] Further, for each battery in the battery pack, determining a corresponding battery state according to a corresponding difference value includes:

[0174] For each battery in the battery pack, determining whether the corresponding difference is less than a preset error value;

[0175] In response to determining that the corresponding difference is less than a preset error value, determining that the corresponding battery state is not abnormal;

[0176] In response to determining that the corresponding difference is greater than or equal to the preset error value, it is determined that the corresponding battery state is abnormal.

[0177] The preset error value may be an empirical value or a value determined according to a certain standard.

[0178] That is, by determining whether the difference between the reference impedance and the corresponding measured impedance is within the allowable error range, it is determined whether the battery state is abnormal, so as to perform battery health status detection and battery fault diagnosis in time.

[0179] The battery impedance detection method provided in this embodiment shortens the offline data acquisition time by using a single-frequency square wave signal to excite and obtain offline battery impedance data; by controlling the terminal voltage and temperature to keep them at the battery offline data test point, and using a single-frequency sine wave signal perturbation, the battery impedance is detected online. When the temperature of all batteries in the battery pack to be tested is adjusted to a balanced temperature, and the terminal voltage is adjusted to a balanced voltage, the influence of voltage imbalance and temperature imbalance on impedance detection can be reduced, the algorithm difficulty can be reduced, and the detection efficiency can be increased. By comparing the measured impedance with the reference impedance under the same test conditions, the gap between the current battery and the new lithium-ion battery (SOH=100%) can be obtained, thereby determining whether the battery state of the current battery is abnormal, which helps to assist battery fault detection and improve driving safety.

[0180] Optional methods for generating offline data include:

[0181] The battery is disturbed using the single-frequency square wave signal, and the terminal voltage and cell current are collected under multiple groups of different test conditions. The frequency F of the single-frequency square wave signal is in the range of 1Hz to 100Hz. A square wave is formed by the superposition of multiple harmonic sine waves and is easy to generate. Only a single-frequency square wave is needed to obtain a sine wave of the frequency required for the experiment through Fourier decomposition, which can shorten the experimental time.

[0182] For each set of test conditions, the corresponding collected terminal voltage and cell current are substituted into the preset battery impedance calculation formula to obtain the corresponding battery impedance; the battery being measured is a brand new lithium-ion battery.

[0183] For each set of test conditions, the corresponding battery impedance is subjected to fast Fourier expansion, and the impedance at a preset frequency is selected from the expansion result as the corresponding battery offline data test point impedance; the preset frequency is 1 or 3 times the frequency of the single-frequency square wave signal. The fast Fourier transform (fast Fourier transform) is a general term for an efficient and fast calculation method that uses a computer to calculate the discrete Fourier transform (DFT), referred to as FFT. The traditional full-frequency scanning impedance detection takes 9 to 30 minutes, while the above method can be detected by determining a single square wave frequency. After the fast Fourier transform, the real or imaginary part of the battery impedance at frequency F and frequency 3F can be obtained. At the same time, only one of the real or imaginary part of the impedance spectrum needs to be obtained, which can reduce the amount of offline data and greatly shorten the detection time.

[0184] That is, by obtaining the impedance of the battery offline test point under different test conditions, the corresponding relationship between the three is established. The corresponding relationship can be saved in the form of a data table, a coordinate distribution diagram, etc.

[0185] In order to support the above method to be implemented smoothly, accordingly, in one embodiment of the present invention, a battery impedance detection system is provided, and the battery impedance detection system includes: a memory and a processor;

[0186] The memory is used to store computer programs;

[0187] The processor is used to implement the above-mentioned battery impedance detection method when executing the computer program.

[0188] In addition, in another embodiment of the present invention, a battery status detection system is provided, and the battery status detection system includes a memory and a processor;

[0189] The memory is used to store computer programs;

[0190] The processor is used to implement the above-mentioned battery status detection method when executing the computer program.

[0191] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery impedance detection method, characterized in that: include: Obtaining offline data; wherein the offline data includes the battery offline data test point impedance measured by disturbing the battery with a single-frequency square wave signal under multiple groups of different test conditions; the test conditions include the battery offline test point temperature and the battery offline test point voltage; Detect the terminal voltage and temperature of all batteries in the battery pack to be tested; Determine a balancing temperature according to the detected temperatures of all batteries in the battery group to be tested and the temperatures of a plurality of battery offline test points, and adjust the temperatures of all batteries in the battery group to be tested to the balancing temperature; Determine a balancing voltage according to the detected terminal voltages of all batteries in the battery group to be tested and the voltages of a plurality of battery offline test points, and adjust the terminal voltages of all batteries in the battery group to be tested to the balancing voltage; Impedance detection is performed on all batteries in the battery group to be tested.

2. The battery impedance detection method according to claim 1, characterized in that: The performing impedance detection on all batteries in the battery pack to be tested comprises: The battery pack to be tested is disturbed by a sinusoidal excitation signal of a preset frequency, and the terminal voltage and cell current of each battery in the battery pack to be tested are collected; the preset frequency is 1 or 3 times the frequency of the single-frequency square wave signal; Substitute the collected terminal voltage and cell current corresponding to each battery in the battery pack to be tested into a preset battery impedance calculation formula to obtain the corresponding battery impedance.

3. The battery impedance detection method according to claim 2, characterized in that: The method of disturbing the battery pack to be tested by a sinusoidal excitation signal of a preset frequency includes: Grouping the multiple batteries in the battery pack to be tested so that each group has two batteries, applying a sinusoidal excitation signal to the batteries in each group, and collecting the terminal voltage and cell current of the corresponding battery; The phase difference between the sinusoidal excitation signals applied to two batteries in the same group is 180°.

4. The battery impedance detection method according to claim 3, characterized in that: The step of grouping the multiple batteries in the battery pack to be tested so that each group has two batteries, applying a sinusoidal excitation signal to the batteries in each group, and collecting the terminal voltage and cell current of the corresponding battery specifically includes: If the number of batteries in the battery group to be tested is an even number, the batteries are grouped in pairs; If the number of batteries in the battery group to be tested is an odd number N, the N-1 batteries in the battery group to be tested are grouped in pairs to obtain (N-1) / 2 groups, a sinusoidal excitation signal is applied to the batteries in the (N-1) / 2 groups, and the terminal voltage and cell current of the corresponding battery are collected; The remaining battery in the battery group to be tested and the battery adjacent to it are combined into a last group, a sinusoidal excitation signal is applied to the batteries in the last group, and the terminal voltage and cell current of the corresponding battery are collected.

5. The battery impedance detection method according to any one of claims 1 to 4, characterized in that: The step of determining a balancing voltage according to the detected terminal voltages of all batteries in the battery group to be tested and the voltages of a plurality of battery offline test points, and adjusting the terminal voltages of all batteries in the battery group to be tested to the balancing voltage comprises: Calculating the average value of the terminal voltages of all batteries in the battery group to be tested; Determine whether there is a battery offline test point whose voltage is equal to the average value; In response to determining that there is a battery offline test point whose voltage is equal to the average value, taking the average value as a first balancing voltage, and adjusting the terminal voltages of all batteries in the battery group to be tested to the first balancing voltage; In response to determining that there is no battery offline test point voltage equal to the average value, determining a difference between the average value and each of the battery offline test point voltages; Taking the battery offline test point voltage corresponding to the smallest difference as the second balancing voltage, and adjusting the plurality of terminal voltages in the battery group to be tested to the second balancing voltage; And / or, determining the equilibrium temperature according to the detected temperatures of all batteries in the battery group to be tested and the temperatures of the plurality of battery offline test points, and adjusting the temperatures of all batteries in the battery group to be tested to the equilibrium temperature, comprises: Comparing the detected temperatures of all batteries in the battery pack to be tested to determine the highest temperature; Determine whether there is a battery offline test point whose temperature is equal to the highest temperature; In response to determining that there is a battery offline test point whose temperature is equal to the highest temperature, taking the highest temperature as a first balancing temperature, and adjusting the temperatures of all batteries in the battery group to be tested to the first balancing temperature; In response to determining that there is no battery offline test point temperature equal to the highest temperature, comparing the relationship between the highest temperature and each of the battery offline test point temperatures, screening out the battery offline test point temperatures greater than the highest temperature, and recording them as the battery offline test point temperatures to be selected; Determine the difference between the temperature of the offline test point of the selected battery and the highest temperature; The battery offline test point temperature corresponding to the smallest difference is used as the second equilibrium temperature, and the multiple temperatures in the battery group to be tested are all adjusted to the second equilibrium temperature.

6. A battery impedance detection system, characterized in that: include: Memory and processor; The memory is used to store computer programs; The processor is used to implement the battery impedance detection method according to any one of claims 1 to 5 when executing the computer program.

7. A battery status detection method, characterized in that: include: Obtaining offline data; wherein the offline data includes the battery offline data test point impedance measured by disturbing the battery with a single-frequency square wave signal under multiple groups of different test conditions; the test conditions include the battery offline test point temperature and the battery offline test point voltage; Detect the terminal voltage and temperature of all batteries in the battery pack to be tested; Determine a balancing temperature according to the detected temperatures of all batteries in the battery group to be tested and the temperatures of a plurality of battery offline test points, and adjust the temperatures of all batteries in the battery group to be tested to the balancing temperature; Determine a balancing voltage according to the detected terminal voltages of all batteries in the battery group to be tested and the voltages of a plurality of battery offline test points, and adjust the terminal voltages of all batteries in the battery group to be tested to the balancing voltage; Performing impedance detection on all batteries in the battery pack to be tested to obtain measured impedance; Mapping the equalization temperature to the battery offline test point temperature, mapping the equalization voltage to the battery offline test point voltage, and searching for the corresponding battery offline data test point impedance in the offline data according to the equalization temperature and the equalization voltage to obtain a reference impedance; For each battery in the battery group to be tested, a battery state is determined according to the reference impedance and the corresponding measured impedance.

8. The battery status detection method according to claim 7, characterized in that: The method for generating offline data includes: The battery is disturbed by using the single-frequency square wave signal, and the terminal voltage and cell current of the battery are collected under multiple groups of different test conditions; For each set of test conditions, the corresponding collected terminal voltage and cell current are substituted into the preset battery impedance calculation formula to obtain the corresponding battery impedance; For each set of test conditions, the corresponding battery impedance is fast Fourier expanded, and the impedance at a preset frequency is selected from the expansion result as the corresponding battery offline data test point impedance; the preset frequency is 1 times or 3 times the frequency of the single-frequency square wave signal; or the preset frequency includes 1 times and 3 times the frequency of the single-frequency square wave signal.

9. The battery status detection method according to claim 7 or 8, characterized in that: The frequency of the single-frequency square wave signal is in the range of 1 Hz to 100 Hz.

10. A battery status detection system, characterized in that: Memory and processor; The memory is used to store computer programs; The processor is used to implement the battery status detection method according to any one of claims 7 to 9 when executing the computer program.

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