Method for estimating soc of battery system and battery system

Abstract

The application provides a SOC estimation method and a battery system, and the SOC estimation method comprises the following steps: S1: identifying a voltage difference abnormality flag of the battery system, wherein the voltage difference abnormality flag represents whether a difference between a maximum voltage value and a minimum voltage value in a plurality of cell strings connected in series in the battery system is abnormal; if the voltage difference abnormality flag represents that the voltage difference is abnormal, the method proceeds to step S2; S2: determining whether the battery system is fully charged; if yes, the method proceeds to step S3; if no, the method continues with step S2; S3: determining whether the battery system is at the end of discharging and is stably placed; if yes, a compensating value Cap_V_n of the available capacity of the battery system is determined according to a current available capacity Cap_n of the battery system and a stored available capacity storage value Cap_O; if no, the compensating value Cap_V_n of the available capacity of the battery system is determined according to a SOC jump range when the battery system is fully charged; S4: obtaining a compensated available capacity according to the compensating value Cap_V_n of the available capacity and a nominal available capacity Cap of the battery system, and obtaining a display SOC value SOCN of the battery system according to the compensated available capacity.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and in particular to a method for estimating the SOC of a battery system and a battery system. Background Art

[0002] In the field of power electronics, battery systems are widely used as energy storage elements in various scenarios, such as electric vehicles and energy storage.

[0003] In practical applications, during the use of a battery system, it is very necessary to monitor the state of charge (SOC) of the battery system to display the (remaining) capacity of the battery system to the user.

[0004] Typically, a battery system consists of multiple strings of cells connected in series. In practice, when assembling new equipment or replacing cell strings, poor consistency is common, causing the battery system's actual available capacity to be less than its theoretical available capacity. This, in turn, leads to poor SOC estimation accuracy and SOC jumps.

[0005] For example, a battery system is composed of cell strings with 50% SOC and 60% SOC. The capacity difference between the cell strings is 10% SOC. If the SOC of the battery system is still estimated at 100% capacity, there will be a maximum SOC estimation error of about 10% and a 10% SOC jump problem, resulting in a poor user experience.

[0006] In the existing technology, one approach is to adjust the SOC correction coefficient when the battery system is nearly fully discharged or fully charged to avoid significant jumps in SOC. However, this approach suffers from the problem that the SOC estimation is only corrected at the end of the charge and discharge cycle, the SOC estimation error is still large, and it only alleviates the end jump, but does not solve the problem of the impact of the voltage difference on the overall SOC. Another approach uses a fixed available capacity for calculation, waiting for the balancing strategy to balance the voltages of inconsistent battery cell strings to a consistent state to improve the SOC estimation accuracy. However, this approach suffers from the problem of long voltage balancing time, large SOC estimation errors for a relatively long period of time, and SOC jumps. Summary of the Invention

[0007] According to one embodiment, the present application provides an SOC estimation method for a battery system, wherein the battery system includes multiple battery cell strings connected in series, including: S1: identifying a voltage difference abnormality flag of the battery system, wherein the voltage difference abnormality flag represents whether the difference between the highest voltage value and the lowest voltage value in the multiple battery cell strings connected in series in the battery system is abnormal. If the voltage difference abnormality flag indicates that there is a voltage difference abnormality, step S2 is entered; S2: judging whether the battery system is fully charged, if so, step S3 is entered, if not, step S2 is continued; S3: judging whether the battery system has entered the end of discharge and is stably shelved, if so, determining an available capacity compensation value Cap_V_n based on the current available capacity Cap_n of the battery system and the stored available capacity storage value Cap_O, if not, determining the available capacity compensation value Cap_V_n based on the SOC jump amplitude when the battery system is fully charged; S4: obtaining the compensated available capacity based on the available capacity compensation value Cap_V_n and the nominal available capacity Cap of the battery system, and obtaining the battery system displayed SOC value SOCN based on the compensated available capacity.

[0008] Furthermore, the determination of whether the battery system has entered the end of discharge and is stably stored in step S3 is: determining whether an SOC value corresponding to the battery system entering the end of discharge and is stably stored is stored.

[0009] Furthermore, the available capacity compensation value Cap_V_n is determined based on the current available capacity Cap_n of the battery system and the available capacity storage value Cap_O in step S3, including: S311: obtaining the current available capacity Cap_n of the battery system based on the difference between the SOC value of the battery system when it is fully charged and the SOC value corresponding to the state of the battery system entering the end of discharge and being stably shelved, and the ampere-hour integral corresponding to the state of the battery system from full charge to entering the end of discharge and being stably shelved; S312: calculating the available capacity difference ΔCap_n between the available capacity storage value Cap_O and the current available capacity Cap_n; S313: determining whether the available capacity difference ΔCap_n is greater than k1*Cap_O, and if so, updating the available capacity compensation value Cap_V_n; Compensation value Cap_V_n = ΔCap_n, if not, go to step S314, where k1 is a percentage; S314: determine whether the available capacity difference ΔCap_n is less than 0, if so, update the available capacity compensation value Cap_V_n = Cap_V_n-1-k2*Cap_x, where Cap_x is the nominal available capacity Cap of the battery system or the current available capacity Cap_n, if not, keep Cap_V_n = Cap_V_n-1, where Cap_V_n-1 is the available capacity compensation value obtained last time, k2 is a percentage, and n is a natural number greater than or equal to 1; S315: update the available capacity storage value Cap_O to the current available capacity Cap_n of the battery system.

[0010] Further, the step S3 of determining the available capacity compensation value Cap_V_n according to the SOC jump range when the battery system is fully charged comprises: S321: calculating the difference between the SOC value when the battery system is fully charged and the SOC value SOC_p at the previous time before full charging, to obtain the SOC jump value SOC_J when the battery system is fully charged; S322: judging whether the SOC jump value SOC_J is greater than k3, if yes, updating the available capacity compensation value Cap_V_n=Cap_V_n-1+SOC_J*Cap, if not, entering step S323, wherein k3 is a percentage; S323: judging whether the SOC jump value SOC_J is less than 0, if yes, updating the available capacity compensation value Cap_V_n=Cap_V_n-1-k4*Cap, if not, keeping Cap_V_n=Cap_V_n-1, wherein Cap_V_n-1 is the available capacity compensation value obtained last time, Cap is the nominal available capacity of the battery system, k4 is a percentage, and n is a natural number greater than or equal to 1.

[0011] Further, before the step S1, there is further a step S0 of calibrating the pressure difference abnormality flag of the battery system.

[0012] Further, the step S0 of calibrating the pressure difference abnormality flag of the battery system comprises: S01: judging whether the battery system enters the end of discharge and stably rests, if yes, entering step S02, if not, continuing step S01; S02: when the battery system stably rests at the end of discharge, obtaining the cell string with the highest voltage and the cell string with the lowest voltage in the cell string, and querying the SOC-OCV parameter table of the cell string with the highest voltage and the cell string with the lowest voltage to obtain the SOC value SOC_h of the cell string with the highest voltage and the SOC value SOC_l of the cell string with the lowest voltage, and calculating whether the difference between SOC_h and SOC_l exceeds a set value, if yes, marking the pressure difference abnormality flag as indicating that there is a pressure difference abnormality, if not, marking the pressure difference abnormality flag as indicating that there is no pressure difference abnormality.

[0013] Further, before the battery system supplies power to the load, the battery system is fully charged, and then discharged to the end of discharge and stably rests, so as to calibrate the pressure difference abnormality flag of the battery system.

[0014] Further, when the battery system supplies power to the load, the pressure difference abnormality flag of the battery system is calibrated when the battery system enters the end of discharge and stably rests.

[0015] According to one embodiment, the present application also provides a battery system, comprising: a plurality of battery cell strings, the plurality of battery cell strings being connected in series, each battery cell string comprising a BMU; a BCU for interactive communication with the BMU, the BCU executing: S1: identifying the abnormal voltage difference flag of the battery system, the abnormal voltage difference flag representing whether the difference between the highest voltage value and the lowest voltage value in the plurality of battery cell strings connected in series in the battery system is abnormal, if the abnormal voltage difference flag indicates the presence of abnormal voltage difference, then proceeding to step S2; S2: determining whether the battery system is fully charged, if so, proceeding to step S 3. If not, continue with step S2; S3: determine whether the battery system has entered the end of discharge and is stably shelved. If so, determine the available capacity compensation value Cap_V_n based on the current available capacity Cap_n of the battery system and the stored available capacity storage value Cap_O. If not, determine the available capacity compensation value Cap_V_n based on the SOC jump amplitude when the battery system is fully charged; S4: obtain the compensated available capacity based on the available capacity compensation value Cap_V_n and the nominal available capacity Cap of the battery system, and obtain the battery system displayed SOC value SOCN based on the compensated available capacity.

[0016] Furthermore, the available capacity compensation value Cap_V_n is determined based on the current available capacity Cap_n of the battery system and the available capacity storage value Cap_O in step S3, including: S311: obtaining the current available capacity Cap_n of the battery system based on the difference between the SOC value of the battery system when it is fully charged and the SOC value corresponding to the state of the battery system entering the end of discharge and being stably shelved, and the ampere-hour integral corresponding to the state of the battery system from full charge to entering the end of discharge and being stably shelved; S312: calculating the available capacity difference ΔCap_n between the available capacity storage value Cap_O and the current available capacity Cap_n; S313: determining whether the available capacity difference ΔCap_n is greater than k1*Cap_O, and if so, updating the available capacity compensation value Cap_V_n; Compensation value Cap_V_n = ΔCap_n, if not, go to step S314, where k1 is a percentage; S314: determine whether the available capacity difference ΔCap_n is less than 0, if so, update the available capacity compensation value Cap_V_n = Cap_V_n-1-k2*Cap_x, where Cap_x is the nominal available capacity Cap of the battery system or the current available capacity Cap_n, if not, keep Cap_V_n = Cap_V_n-1, where Cap_V_n-1 is the available capacity compensation value obtained last time, k2 is a percentage, and n is a natural number greater than or equal to 1; S315: update the available capacity storage value Cap_O to the current available capacity Cap_n of the battery system.

[0017] Furthermore, step S3 determines the available capacity compensation value Cap_V_n according to the SOC jump amplitude when the battery system is fully charged, including: S321: calculating the difference between the SOC value when the battery system is fully charged and the SOC value SOC_p at the moment before full charging, to obtain the SOC jump value SOC_J when the battery system is fully charged; S322: judging whether the SOC jump value SOC_J is greater than k3, and if so, updating the available capacity compensation value Cap_V_n=Cap_V_n-1+SOC_J *Cap, if not, go to step S323, where k3 is a percentage; S323: determine whether the SOC jump value SOC_J is less than 0, if so, update the available capacity compensation value Cap_V_n = Cap_V_n-1-k4*Cap, if not, keep Cap_V_n = Cap_V_n-1, where Cap_V_n-1 is the available capacity compensation value obtained last time, Cap is the nominal available capacity of the battery system, k4 is a percentage, and n is a natural number greater than or equal to 1.

[0018] Furthermore, before step S1, it also includes: S01: BCU determines whether the battery system has entered the end of discharge and is stably parked. If so, it enters step S02, if not, it continues with step S01; S02: When the battery system is stably parked at the end of discharge, the BMU obtains the voltage value of its own battery string and transmits the voltage value of its own battery string to the BCU; S03: The BCU obtains the battery string with the highest voltage and the battery string with the lowest voltage among the battery strings; S04: The BMU in the battery string with the highest voltage and the BMU in the battery string with the lowest voltage query their own SOC-OCV parameter tables, obtain the SOC value SOC_h of the battery string with the highest voltage and the SOC value SOC_l of the battery string with the lowest voltage and transmit them to the BCU; S05: The BCU calculates whether the difference between SOC_h and SOC_l exceeds the set value. If so, the voltage difference abnormal flag is marked as indicating that there is a pressure difference abnormality. If not, the pressure difference abnormal flag is marked as indicating that there is no pressure difference abnormality.

[0019] The features and technical advantages of the present disclosure have been summarized quite broadly above so that the detailed description disclosed below may be better understood. Additional features and advantages of the present disclosure will be described below, which form the subject matter of the claims of the present disclosure. It will be understood by those skilled in the art that the concepts and specific embodiments disclosed herein may be readily used as a basis for modifying or designing other structures or processes for achieving the same purposes of the present disclosure. It will also be appreciated by those skilled in the art that such equivalent structures do not depart from the spirit and scope of the present disclosure as set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description in conjunction with the accompanying drawings, in which:

[0021] Figure 1 shows a typical battery system schematic;

[0022] Figure 2 A flow chart of a method for estimating the SOC of a battery system according to an embodiment of the present application is shown;

[0023] Figure 3 It shows the use of an embodiment of the present application Figure 2 Schematic diagram of experimental waveform of SOC estimation method shown;

[0024] Figure 4 A schematic diagram of a method for estimating the SOC of a battery system according to another embodiment of the present application is shown;

[0025] Figure 5 A schematic diagram of a process for calibrating a voltage difference abnormality flag of a battery system according to an embodiment of the present application is shown.

[0026] Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. These figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale. DETAILED DESCRIPTION

[0027] The following is a clear and complete description of the technical solutions in this application in conjunction with the accompanying drawings. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0028] See also Figure 1 As shown in the typical battery system diagram, the battery system 10 includes multiple battery cell strings (labeled 111 to 11n), each battery cell string includes a BMU (Battery Management Unit) and a BCU120 (Battery Control Unit). The multiple battery cell strings are connected in series, and each battery cell string also includes multiple battery cells connected in series. Figure 1 As shown, each battery string includes a BMU, which is the core component of the battery management system. It is used to monitor the basic parameters of the battery string such as voltage, current, temperature, etc. in real time, and to estimate the state of charge (SOC) and health state (SOH) of the battery string. Figure 1 As shown, the BCU 120 is used to interact and communicate with the BMU and is responsible for the management and control of the battery system, such as estimating the state of charge (SOC) and state of health (SOH) of the battery system.

[0029] for Figure 1The battery system shown in this application proposes a method for estimating the SOC of a battery system, see Figure 2 The flowchart of the SOC estimation method of the battery system according to one embodiment of the present application is shown. The SOC estimation method of the battery system proposed in the present application includes:

[0030] S1: Identifying an abnormal voltage difference flag of the battery system, wherein the abnormal voltage difference flag indicates whether the difference between the highest voltage value and the lowest voltage value of a plurality of battery cell strings connected in series in the battery system is abnormal. If the abnormal voltage difference flag indicates that an abnormal voltage difference exists, proceeding to step S2;

[0031] S2: Determine whether the battery system is fully charged. If so, proceed to step S3. If not, proceed to step S2.

[0032] S3: Determine whether the battery system has entered the end of discharge and is stable. If so, determine the available capacity compensation value Cap_V_n based on the current available capacity Cap_n of the battery system and the stored available capacity storage value Cap_O. If not, determine the available capacity compensation value Cap_V_n based on the SOC jump amplitude when the battery system is fully charged.

[0033] S4: Obtain the compensated available capacity according to the available capacity compensation value Cap_V_n and the nominal available capacity Cap of the battery system, and obtain the battery system displayed SOC value SOCN according to the compensated available capacity.

[0034] In this way, a dynamic compensation mechanism for the pressure difference and the available capacity of the battery system is established. When the pressure difference in the battery system is abnormal, the available capacity parameters of the battery system and the SOC calculation logic are automatically adjusted, effectively solving the problem of inaccurate SOC estimation caused by the balancing strategy's inability to quickly balance the battery voltage to a consistent state. Moreover, during the entire use of the battery system, the battery system SOC can be quickly restored to normal and change smoothly in a short time, thereby improving the user experience.

[0035] In actual applications, when a battery string leaves the factory, it is provided with a calibrated SOC-OCV parameter table at room temperature. For an example of a partial SOC-OCV parameter table of a battery string, see Table 1.

[0036] Table 1

[0037]

[0038]

[0039] Where OCV represents the open circuit voltage of the battery string, and the SOC-OCV parameter table represents the corresponding relationship between OCV and SOC. In actual battery system applications, the open circuit voltage (OCV) of the battery string is usually monitored in real time. Therefore, the SOC of the battery string can be obtained based on OCV using the SOC-OCV parameter table.

[0040] Furthermore, as can be seen from the aforementioned SOC-OCV parameter table, at the end of discharge (e.g., within 30% SOC), the open-circuit voltage difference varies significantly compared to the range between 30% SOC and 98% SOC, with the same SOC change. This is typically referred to as the non-plateau region, while the range between 30% SOC and 98% SOC is referred to as the plateau region. Near full charge, such as between 98% SOC and 100% SOC, the open-circuit voltage difference also varies significantly, often referred to as the non-plateau region, but within a smaller range. To improve SOC estimation accuracy, it is best to select the end of discharge (i.e., the non-plateau region) and stabilize the parameters for estimation.

[0041] Therefore, in actual applications, when the battery system is fully charged, enters the end of discharge, and is stable, the calculation of the available capacity of the battery system can be triggered, which will greatly improve the accuracy of the SOC estimation. Specifically, when the battery system is fully charged, enters the end of discharge, and is stable, the available capacity compensation value Cap_V_n caused by the voltage difference abnormality is determined based on the current available capacity Cap_n of the battery system and the stored available capacity storage value Cap_O. Furthermore, the available capacity compensation value Cap_V_n is determined based on the current available capacity Cap_n of the battery system and the stored available capacity storage value Cap_O, including:

[0042] S311: Obtain the current available capacity Cap_n of the battery system based on the difference between the SOC value of the battery system when fully charged and the SOC value corresponding to the battery system entering the end of discharge and being stable and the ampere-hour integral corresponding to the battery system entering the end of discharge and being stable and being stable;

[0043] S312: Calculating the available capacity difference ΔCap_n between the available capacity storage value Cap_O and the current available capacity Cap_n;

[0044] S313: Determine whether the available capacity difference ΔCap_n is greater than k1*Cap_O. If so, update the available capacity compensation value Cap_V_n = ΔCap_n. If not, proceed to step S314, where k1 is a percentage.

[0045] S314: Determine whether the available capacity difference ΔCap_n is less than 0. If so, update the available capacity compensation value Cap_V_n = Cap_V_n-1-k2*Cap_x, where Cap_x is the nominal available capacity Cap of the battery system or the current available capacity Cap_n. If not, maintain Cap_V_n = Cap_V_n-1, where Cap_V_n-1 is the last available capacity compensation value obtained, k2 is a percentage, and n is a natural number greater than or equal to 1.

[0046] S315: Update the available capacity storage value Cap_O to the current available capacity Cap_n of the battery system.

[0047] Specifically, in step S311, the current available capacity of the battery system, Cap_n, is calculated according to the formula Cap_n = ΔAh / ΔSoc, where ΔSoc is the difference between the SOC value of the battery system when fully charged and the SOC value corresponding to the end of discharge and stable storage, and ΔAh is the ampere-hour integral from the time the battery system is fully charged to the time it enters the end of discharge and stable storage. The SOC at full charge is 100%, and as mentioned above, the SOC queried at the end of discharge and stable storage is more accurate, thereby improving the accuracy of SOC estimation.

[0048] Specifically, in step S312, the available capacity difference ΔCap_n is calculated according to the formula ΔCap_n=Cap_O-Cap_n, where Cap_O is the available capacity storage value. In actual applications, when the battery system is fully charged and then enters the end of discharge and is stably placed, the calculation of the current available capacity Cap_n of the battery system is triggered, and the current available capacity Cap_n of the battery system calculated each time is updated to the available capacity storage value Cap_O as described in step S315. When the battery system leaves the factory, it will have a calibrated available capacity Cap. When the calculation of the current available capacity Cap_n of the battery system is not triggered, the available capacity storage value Cap_O is the calibrated available capacity Cap.

[0049] Furthermore, if ΔCap_n>k1*Cap_O, where k1 is a percentage, such as k1=3%, that is, step S313, it means that the current available capacity compensation amount is insufficient. At this time, the available capacity compensation value Cap_V_n is updated to the available capacity difference ΔCap_n calculated this time, that is, the single larger available capacity reduction amount is used as the available capacity compensation value Cap_V_n to increase the available capacity compensation amplitude.

[0050] Furthermore, if ΔCap_n<0, that is, step S314, it means that the current available capacity compensation amount has exceeded the actual demand value, that is, the available capacity has increased, and the available capacity compensation value Cap_V_n needs to be dynamically reduced. Specifically, the available capacity compensation value Cap_V_n is updated to Cap_V_n-1-k2*Cap_x, where Cap_x is the nominal available capacity Cap of the battery system or the current available capacity Cap_n, Cap_V_n-1 is the available capacity compensation value obtained last time, k2 is a percentage, such as k2=3%, and n is a natural number greater than or equal to 1.

[0051] Furthermore, if k1*Cap_O>ΔCap_n>0, it means that the current available capacity compensation amount is appropriate, and the available capacity compensation value Cap_V_n-1 obtained last time is maintained as the current available capacity compensation value Cap_V_n.

[0052] In this way, when the calculation of the current available capacity Cap_n is triggered, the optimal available capacity compensation value Cap_V_n is found through a dynamic change process.

[0053] However, in actual applications, the battery system cannot always be triggered to enter the end of discharge and be stable. In other words, the battery system may be in a state of charge and discharge for a long time, but it may not be triggered to enter the end of discharge and be stable. In this case, in order to quickly compensate for the SOC abnormality caused by the voltage difference, when the battery system is only triggered to fully charge, the available capacity compensation value Cap_V_n caused by the voltage difference abnormality can be determined based on the SOC jump amplitude when the battery system is fully charged. Furthermore, the available capacity compensation value Cap_V_n is determined based on the SOC jump amplitude when the battery system is fully charged, including:

[0054] S321: Calculate the difference between the SOC value of the battery system when it is fully charged and the SOC value SOC_p immediately before it is fully charged, to obtain the SOC jump value SOC_J of the battery system when it is fully charged;

[0055] S322: Determine whether the SOC jump value SOC_J is greater than k3. If so, update the available capacity compensation value Cap_V_n = Cap_V_n-1 + SOC_J*Cap. If not, proceed to step S323, where k3 is a percentage.

[0056] S323: Determine whether the SOC jump value SOC_J is less than 0. If so, update the available capacity compensation value Cap_V_n = Cap_V_n-1-k4*Cap. If not, maintain Cap_V_n = Cap_V_n-1, where Cap_V_n-1 is the available capacity compensation value obtained last time, Cap is the nominal available capacity of the battery system, k4 is a percentage, and n is a natural number greater than or equal to 1.

[0057] Specifically, in step S321, the SOC jump value SOC J at full charging of the battery system is calculated according to the formula SOC J = 100%-SOC p, wherein SOC p is the SOC value at the previous time before full charging of the battery system, and 100% is the SOC at full charging of the battery system. In actual application, the SOC of the battery system is calculated at intervals of a certain interval time, such as 100 ms or 1 s, and thus the SOC value at the previous time before full charging of the battery system is the SOC value calculated once before the SOC of 100% is reached, which can be referred to Table 1, i.e., 98% SOC.

[0058] Further, if SOC J > k3, wherein k3 is a percentage, such as k3 = 3%, i.e., step S322, it indicates that the current available capacity compensation is insufficient, and thus the available capacity compensation value Cap V n is updated as Cap V n-1 + SOC J * Cap, wherein Cap V n-1 is the available capacity compensation value obtained last time, and Cap is the nominal available capacity of the battery system, i.e., a single larger SOC jump amplitude is taken as the available capacity compensation value Cap V n to increase the available capacity compensation amplitude.

[0059] Further, if SOC J < 0, i.e., step S323, it indicates that the SOC of the battery system reaches 100% in advance, i.e., the current available capacity compensation exceeds the actual demand value, and thus the available capacity compensation value Cap V n needs to be dynamically reduced, and specifically, the available capacity compensation value Cap V n is updated as Cap V n-1 - k4 * Cap, wherein Cap is the nominal available capacity of the battery system, Cap V n-1 is the available capacity compensation value obtained last time, k4 is a percentage, such as k4 = 3%, and n is a natural number greater than or equal to 1.

[0060] Further, if k3 > SOC J > 0, it indicates that the current available capacity compensation is moderate, and thus the available capacity compensation value Cap V n-1 obtained last time is continued to be taken as the current available capacity compensation value Cap V n.

[0061] In this way, without triggering the current available capacity Cap n calculation, an optimal available capacity compensation value Cap V n is found through a dynamic change process.

[0062] In practical applications, determining whether the battery system has entered the end of discharge and is stable in step S3 involves determining whether a corresponding SOC value is stored for the battery system entering the end of discharge and is stable. That is, when the battery system triggers a full charge, if a query finds that the battery system has stored a corresponding SOC value for the battery system entering the end of discharge and is stable, it indicates that the battery system entered the end of discharge and is stable before the full charge. Therefore, calculation of the current available capacity Cap_n is triggered. The specific calculation process can be found in step S311.

[0063] In this way, the available capacity compensation value Cap_V_n caused by the voltage difference is obtained. When calculating the SOC value of the battery system, the system available capacity parameter used is adjusted according to the available capacity compensation value Cap_V_n to obtain a more accurate SOC value.

[0064] In this way, the SOC estimation method of the battery system provided in the present application takes into account the available capacity compensation value Cap_V_n caused by the voltage difference abnormality between the battery strings, that is, a dynamic compensation mechanism for the voltage difference abnormality and the system available capacity is established. When the voltage difference abnormality exists between the battery strings of the battery system, the available capacity parameters and the SOC calculation logic are automatically adjusted. The SOC estimation method provided in the present application can realize the rapid return of the battery system SOC to normal and smooth changes in a short time, overcoming the shortcomings of the prior art of using a fixed available capacity value to calculate the SOC value of the battery system, and is fast, thereby improving the customer experience.

[0065] For details, please refer to Figure 3 The embodiment of the present application shown in FIG. Figure 2 The experimental waveform diagram of the SOC estimation method is shown in FIG. Figure 3 In (a), it can be seen that when a battery system is stable and static at the end of discharge, a large voltage difference exists between the highest voltage value Vmax and the lowest voltage value Vmin in the multiple battery strings connected in series in the battery system by looking up the table, that is, there is a voltage difference abnormality. This can be obtained by connecting battery strings with SOC differences of about 40% in series to form a battery system and then charging and discharging them. Based on this battery system, the SOC estimation method provided by this application is used to estimate the SOC value of the battery system, such as Figure 3 As shown in (b), the battery system is charged and discharged and then kept at a stable state, where the negative current represents charging of the battery system, the positive current represents discharging of the battery system, and 0 represents that the battery system is kept at a stable state, that is, the battery system is cycled through constant current charging, stable state, constant current discharging, and stable state. Figure 3 (c) is the available capacity compensation value Cap_V_n obtained according to the SOC estimation method provided in this application, Figure 3(d) is the SOC value obtained by the SOC estimation method provided by this application. It can be seen that at the beginning, due to the serious pressure difference, the SOC value will jump, resulting in poor customer experience. With the dynamic adjustment of the available capacity compensation value Cap_V_n ( Figure 3 (c) in Figure 2), after several charge and discharge cycles, although the voltage difference remains unchanged ( Figure 3 As shown in (a) in the figure), the SOC value SOCN displayed to the customer becomes smoother, which greatly improves the customer experience.

[0066] In practical applications, when there is no pressure difference abnormality, that is, when the pressure difference abnormality flag indicates that there is no pressure difference abnormality, the conventional existing SOC estimation method can be used to estimate the SOC value. Figure 4 The diagram shows a method for estimating the SOC of a battery system according to another embodiment of the present invention. Specifically, the SOC estimation method provided by the present invention is invoked when a voltage differential abnormality is triggered, and a conventional SOC estimation method is used when a voltage differential abnormality is not triggered. Thus, a relatively accurate SOC value can be obtained during the use of the battery system.

[0067] Furthermore, in practical applications, step S0 is further included before step S1: calibrating the battery system's voltage difference abnormality flag. This allows the battery system SOC estimation method described above to determine whether the battery system has a voltage difference abnormality. Specifically, the voltage difference abnormality flag indicates whether the difference between the highest voltage and the lowest voltage of multiple battery cell strings connected in series within the battery system is abnormal.

[0068] In one embodiment, see Figure 5 The flowchart of calibrating the abnormal voltage difference flag of the battery system according to one embodiment of the present application is shown as follows: Step S0: calibrating the abnormal voltage difference flag of the battery system includes:

[0069] S01: Determine whether the battery system has reached the end of discharge and is stable. If so, proceed to step S02; if not, continue to step S01;

[0070] S02: When the battery system is at a stable standstill at the end of discharge, the cell string with the highest voltage and the cell string with the lowest voltage in the cell string are obtained, and the SOC-OCV parameter table of the cell string with the highest voltage and the cell string with the lowest voltage is queried (as shown in Table 1), and the SOC value SOC_h of the cell string with the highest voltage and the SOC value SOC_l of the cell string with the lowest voltage are obtained. It is calculated whether the difference between SOC_h and SOC_l exceeds the set value. If so, the voltage difference abnormal flag is marked as indicating that there is a voltage difference abnormality. If not, the voltage difference abnormal flag is marked as indicating that there is no pressure difference abnormality.

[0071] In actual applications, once the battery system is triggered to enter the end of discharge and is stable, the above-mentioned method of calibrating the abnormal voltage difference flag of the battery system can be used to update the abnormal voltage difference flag, and the abnormal voltage difference flag can be maintained until the abnormal voltage difference flag of the battery system is triggered again (that is, triggered to enter the end of discharge and be stable). Furthermore, before the battery system supplies power to the load (that is, before the battery system leaves the factory), the battery system is fully charged, and then enters the end of discharge and is stable to calibrate the abnormal voltage difference flag of the battery system. That is, when the battery system is put into use, there will be a calibrated abnormal voltage difference flag. Furthermore, during the process of the battery system supplying power to the load (that is, during the use of the battery system), once it is triggered to enter the end of discharge and be stable, the above-mentioned method of calibrating the abnormal voltage difference flag of the battery system is used to update the abnormal voltage difference flag. And because the abnormal voltage difference flag is calibrated when the battery system is stable and static at the end of discharge, the calibration result is more accurate.

[0072] Furthermore, the present application also provides a battery system, which can be found in Figure 1 , and see Figures 2 to 5 , the battery system of the present application comprises:

[0073] Multiple cell strings, multiple cell strings are connected in series, and each cell string includes a BMU;

[0074] The BCU is used to communicate with the BMU. The BCU performs:

[0075] S1: Identifying an abnormal voltage difference flag of the battery system, wherein the abnormal voltage difference flag indicates whether the difference between the highest voltage value and the lowest voltage value of a plurality of battery cell strings connected in series in the battery system is abnormal. If the abnormal voltage difference flag indicates that an abnormal voltage difference exists, proceeding to step S2;

[0076] S2: Determine whether the battery system is fully charged. If so, proceed to step S3; if not, continue to step S2;

[0077] S3: Determine whether the battery system has entered the end of discharge and is stable. If so, determine the available capacity compensation value Cap_V_n based on the current available capacity Cap_n of the battery system and the stored available capacity storage value Cap_O. If not, determine the available capacity compensation value Cap_V_n based on the SOC jump amplitude when the battery system is fully charged.

[0078] S4: Obtain the compensated available capacity according to the available capacity compensation value Cap_V_n and the nominal available capacity Cap of the battery system, and obtain the battery system displayed SOC value SOCN according to the compensated available capacity.

[0079] Furthermore, the step S3 of determining the available capacity compensation value Cap_V_n according to the current available capacity Cap_n of the battery system and the available capacity storage value Cap_O includes:

[0080] S311: Obtain the current available capacity Cap_n of the battery system based on the difference between the SOC value of the battery system when fully charged and the SOC value corresponding to the battery system entering the end of discharge and being stable and the ampere-hour integral corresponding to the battery system entering the end of discharge and being stable and being stable;

[0081] S312: Calculating the available capacity difference ΔCap_n between the available capacity storage value Cap_O and the current available capacity Cap_n;

[0082] S313: Determine whether the available capacity difference ΔCap_n is greater than k1*Cap_O. If so, update the available capacity compensation value Cap_V_n = ΔCap_n. If not, proceed to step S314, where k1 is a percentage.

[0083] S314: Determine whether the available capacity difference ΔCap_n is less than 0. If so, update the available capacity compensation value Cap_V_n = Cap_V_n-1-k2*Cap_x, where Cap_x is the nominal available capacity Cap of the battery system or the current available capacity Cap_n. If not, maintain Cap_V_n = Cap_V_n-1, where Cap_V_n-1 is the last available capacity compensation value obtained, k2 is a percentage, and n is a natural number greater than or equal to 1.

[0084] S315: Update the available capacity storage value Cap_O to the current available capacity Cap_n of the battery system.

[0085] Furthermore, the step S3 of determining the available capacity compensation value Cap_V_n according to the SOC jump amplitude when the battery system is fully charged includes:

[0086] S321: Calculate the difference between the SOC value of the battery system when it is fully charged and the SOC value SOC_p immediately before it is fully charged, to obtain the SOC jump value SOC_J of the battery system when it is fully charged;

[0087] S322: Determine whether the SOC jump value SOC_J is greater than k3. If so, update the available capacity compensation value Cap_V_n = Cap_V_n-1 + SOC_J*Cap. If not, proceed to step S323, where k3 is a percentage.

[0088] S323: judging whether the SOC jump value SOC J is less than 0, if yes, updating the available capacity compensation value Cap V n = Cap V n-1-k4*Cap, if no, keeping Cap V n = Cap V n-1, wherein Cap V n-1 is the available capacity compensation value obtained last time, Cap is the nominal available capacity of the battery system, k4 is a percentage, and n is a natural number greater than or equal to 1.

[0089] Further, before step S1, the following steps are further included:

[0090] S01: the BCU judges whether the battery system enters the end of discharge and stably rests, if yes, entering step S02, if no, continuing step S01;

[0091] S02: when the battery system stably rests at the end of discharge, the BMU obtains the voltage value of the cell string of itself and transmits the voltage value of the cell string of itself to the BCU;

[0092] S03: the BCU obtains the cell string with the highest voltage and the cell string with the lowest voltage in the cell strings;

[0093] S04: the BMU in the cell string with the highest voltage and the BMU in the cell string with the lowest voltage query the SOC-OCV parameter table of itself, obtain the SOC value SOC h of the cell string with the highest voltage and the SOC value SOC l of the cell string with the lowest voltage and transmit them to the BCU;

[0094] S05: the BCU judges whether the difference between SOC h and SOC l exceeds a set value, if yes, marking the voltage difference abnormality flag bit as representing that there is voltage difference abnormality, if no, marking the voltage difference abnormality flag bit as representing that there is no voltage difference abnormality.

[0095] The principle and advantages are the same as those of the above-mentioned SOC estimation method of the battery system, and will not be described here.

[0096] As described above, the SOC estimation method of the battery system and the battery system provided by the present application realize real-time monitoring of the voltage difference between the battery strings and automatic adjustment of the available capacity parameter through the voltage difference between the battery strings-available capacity dynamic compensation mechanism, actively compensate the deviation of the available capacity caused by the voltage difference, and realize accurate correction of the SOC in the whole cycle. The problems of continuously existing SOC jump in the prior art, i.e., only adjusting the SOC correction coefficient at the end of charging and discharging or ignoring the influence of the voltage difference between the battery strings on the available capacity, are overcome.

[0097] Although the embodiments of the present disclosure and their advantages have been described in detail, it should be understood that various changes, replacements and modifications can be made herein without departing from the spirit and scope of the present disclosure defined by the appended claims.

[0098] Moreover, the scope of the present application is not intended to be limited to particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein can be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope all processes, machines, manufacture, compositions of matter, means, methods, or steps substantially as such.

Claims

1. A method for estimating the SOC of a battery system, wherein the battery system comprises a plurality of battery cell strings connected in series, characterized in that: include: S1: Identifying an abnormal voltage difference flag of the battery system, wherein the abnormal voltage difference flag indicates whether the difference between the highest voltage value and the lowest voltage value of a plurality of battery cell strings connected in series in the battery system is abnormal. If the abnormal voltage difference flag indicates that an abnormal voltage difference exists, proceeding to step S2; S2: Determine whether the battery system is fully charged. If so, proceed to step S3; if not, continue to step S2; S3: Determine whether the battery system has reached the end of discharge and is stable. If so, execute: S311: Based on the difference between the SOC value of the battery system when it is fully charged and the SOC value corresponding to the end of discharge and stable storage, and the ampere-hour integral of the battery system from full charge to the end of discharge and stable storage, the current available capacity Cap_n of the battery system is obtained; S312: Calculate the available capacity difference ΔCap_n between the available capacity storage value Cap_O and the current available capacity Cap_n; S313: Determine whether the available capacity difference ΔCap_n is greater than k1*Cap_O. If so, update the available capacity compensation value Cap_V_n = ΔCap_n. If not, proceed to step S314, where k1 is Percentage; S314: Determine whether the available capacity difference ΔCap_n is less than 0. If so, update the available capacity compensation value Cap_V_n = Cap_V_n-1-k2*Cap_x, where Cap_x is the nominal available capacity Cap of the battery system or the current available capacity Cap_n. If not, maintain Cap_V_n = Cap_V_n-1, where Cap_V_n-1 is the available capacity compensation value obtained last time, k2 is a percentage, and n is a natural number greater than or equal to 1; S315: Update the available capacity storage value Cap_O to the current available capacity Cap_n of the battery system; if not, execute: S321: Calculate the difference between the SOC value of the battery system when fully charged and the SOC value SOC_p at the moment before full charge to obtain the SOC jump value SOC_J of the battery system when fully charged; S322: Determine whether the SOC jump value SOC_J is greater than k3. If so, update the available capacity compensation value Cap_V_n=Cap_V_n-1+SOC_J*Cap. If not, proceed to step S323, where k3 is a percentage; S323: Determine whether the SOC jump value SOC_J is less than 0. If so, update the available capacity compensation value Cap_V_n=Cap_V_n-1-k4*Cap. If not, maintain Cap_V_n=Cap_V_n-1, where Cap_V_n-1 is the available capacity compensation value obtained last time, Cap is the nominal available capacity of the battery system, k4 is a percentage, and n is a natural number greater than or equal to 1; S4: Obtain the compensated available capacity according to the available capacity compensation value Cap_V_n and the nominal available capacity Cap of the battery system, and obtain the battery system displayed SOC value SOCN according to the compensated available capacity.

2. The SOC estimation method of the battery system according to claim 1, characterized in that: In step S3, it is determined whether the battery system has entered the end of discharge and is stable and stored. Determine whether the battery system has entered the end of discharge and stabilized the corresponding SOC value.

3. The SOC estimation method of the battery system according to claim 1, characterized in that: Before step S1 , the method further includes step S0 : calibrating the abnormal voltage difference flag of the battery system.

4. The SOC estimation method of the battery system according to claim 3, characterized in that: Step S0: calibrating the abnormal voltage difference flag of the battery system, including: S01: Determine whether the battery system has reached the end of discharge and is stable. If so, proceed to step S02; if not, continue to step S01; S02: When the battery system is at a stable standstill at the end of discharge, obtain the cell string with the highest voltage and the cell string with the lowest voltage in the cell string, and query the SOC-OCV parameter table of the cell string with the highest voltage and the cell string with the lowest voltage to obtain the SOC value SOC_h of the cell string with the highest voltage and the SOC value SOC_l of the cell string with the lowest voltage, calculate whether the difference between SOC_h and SOC_l exceeds the set value, if so, mark the voltage difference abnormal flag as indicating that there is a voltage difference abnormality, if not, mark the voltage difference abnormal flag as indicating that there is no pressure difference abnormality.

5. The SOC estimation method of the battery system according to claim 3 or 4, characterized in that: Before the battery system supplies power to the load, the battery system is fully charged, then discharged to the end of discharge and left to stand for stabilization to calibrate the abnormal voltage difference flag of the battery system.

6. The SOC estimation method of the battery system according to claim 3 or 4, characterized in that: When the battery system supplies power to a load, when the battery system enters the end of discharge and is stably stored, the abnormal voltage difference flag of the battery system is calibrated.

7. A battery system, characterized in that: include: A plurality of battery cell strings, wherein the plurality of battery cell strings are connected in series, and each battery cell string includes a BMU; The BCU is used to communicate with the BMU. The BCU performs: S1: Identifying an abnormal voltage difference flag of the battery system, wherein the abnormal voltage difference flag indicates whether the difference between the highest voltage value and the lowest voltage value of a plurality of battery cell strings connected in series in the battery system is abnormal. If the abnormal voltage difference flag indicates that an abnormal voltage difference exists, proceeding to step S2; S2: Determine whether the battery system is fully charged. If so, proceed to step S3; if not, continue to step S2; S3: Determine whether the battery system has reached the end of discharge and is stable. If so, execute: S311: Based on the difference between the SOC value of the battery system when it is fully charged and the SOC value corresponding to the end of discharge and stable storage, and the ampere-hour integral of the battery system from full charge to the end of discharge and stable storage, the current available capacity Cap_n of the battery system is obtained; S312: Calculate the available capacity difference ΔCap_n between the available capacity storage value Cap_O and the current available capacity Cap_n; S313: Determine whether the available capacity difference ΔCap_n is greater than k1*Cap_O. If so, update the available capacity compensation value Cap_V_n = ΔCap_n. If not, proceed to step S314, where k1 is a percentage; S314: Determine whether the available capacity difference ΔCap_n is less than 0. If so, update the available capacity compensation value Cap_V_n = Cap_V_n-1-k2*Cap_x, where Cap_x is the nominal available capacity Cap of the battery system or the current available capacity Cap_n. If not, maintain Cap_V_n = Cap_V_n-1, where Cap_V_n-1 is the available capacity compensation value obtained last time, k2 is a percentage, and n is a natural number greater than or equal to 1; S315: Update the available capacity storage value Cap_O to the current available capacity Cap_n of the battery system; If not, execute: S321: Calculate the difference between the SOC value of the battery system when fully charged and the SOC value SOC_p at the moment before full charge to obtain the SOC jump value SOC_J of the battery system when fully charged; S322: Determine whether the SOC jump value SOC_J is greater than k3. If so, update the available capacity compensation value Cap_V_n=Cap_V_n-1+SOC_J*Cap. If not, proceed to step S323, where k3 is a percentage; S323: Determine whether the SOC jump value SOC_J is less than 0. If so, update the available capacity compensation value Cap_V_n=Cap_V_n-1-k4*Cap. If not, maintain Cap_V_n=Cap_V_n-1, where Cap_V_n-1 is the available capacity compensation value obtained last time, Cap is the nominal available capacity of the battery system, k4 is a percentage, and n is a natural number greater than or equal to 1; S4: Obtain the compensated available capacity according to the available capacity compensation value Cap_V_n and the nominal available capacity Cap of the battery system, and obtain the battery system displayed SOC value SOCN according to the compensated available capacity.

8. The battery system according to claim 7, characterized in that: Before step S1, the method further includes: S01: The BCU determines whether the battery system has reached the end of discharge and is stable. If so, it proceeds to step S02; if not, it continues to step S01. S02: When the battery system is at a stable state at the end of discharge, the BMU obtains the voltage value of its own cell string and transmits the voltage value of its own cell string to the BCU; S03: The BCU obtains the cell string with the highest voltage and the cell string with the lowest voltage among the cell strings; S04: The BMU in the cell string with the highest voltage and the BMU in the cell string with the lowest voltage query their own SOC-OCV parameter tables, obtain the SOC value SOC_h of the cell string with the highest voltage and the SOC value SOC_l of the cell string with the lowest voltage, and transmit them to the BCU; S05: The BCU calculates whether the difference between SOC_h and SOC_1 exceeds a set value. If so, the pressure difference abnormal flag is marked as indicating that a pressure difference abnormality exists. If not, the pressure difference abnormal flag is marked as indicating that no pressure difference abnormality exists.

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