Energy storage system and SOC correction method therefor

Abstract

Provided in the present application are an energy storage system and an SOC correction method therefor. The SOC correction method comprises: determining whether an energy storage system is in a double-voltage plateau interval of a lithium manganese iron phosphate battery cell; and when the energy storage system is in the double-voltage plateau interval, correcting an SOC of the lithium manganese iron phosphate battery cell according to the SOC of the lithium manganese iron phosphate battery cell. Therefore, by using the double-voltage plateau characteristic of a lithium manganese iron phosphate battery cell, each time the lithium manganese iron phosphate battery cell is charged and discharged, an SOC correction point located within a middle section of a plateau of the lithium manganese iron phosphate battery cell can be provided therefor, thereby avoiding a long-term accumulative deviation and improving the accuracy of SOC estimation. Moreover, by using the high-voltage plateau feature of lithium manganese iron phosphate, a PCS direct-current access voltage can be better adapted to, the voltage utilization rate is improved, and an energy storage system still maintains an active grid connection under high voltage ride through of a power grid. In addition, the wide-temperature operation performance of an energy storage battery system can also be improved by using the good low-temperature characteristic of lithium manganese iron phosphate.

Description

Energy storage system and SOC correction method thereof

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on October 19, 2022, with application number 202211291633.3 and invention name “A Energy Storage System and Its SOC Correction Method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of power electronics technology, and in particular to an energy storage system and a SOC correction method thereof. Background Art

[0003] Currently, lithium iron phosphate batteries are widely used in large-scale grid-connected energy storage. Due to the long plateau period of lithium iron phosphate's OCV (Open circuit voltage) and the limitations of existing software algorithms, its SOC (State of Charge, also known as remaining capacity) estimation is difficult and has long-term accumulated deviations. Calibration is required at the end of charging and discharging to eliminate factor errors.

[0004] Therefore, there is an urgent need for a solution to improve the SOC estimation accuracy of lithium iron phosphate batteries.

[0005] Summary of the Invention

[0006] The present application provides an energy storage system and an SOC correction method thereof to improve the SOC estimation accuracy of a lithium iron phosphate battery.

[0007] To achieve the above objectives, this application provides the following technical solutions:

[0008] In a first aspect, the present application provides a method for correcting the SOC of an energy storage system, wherein the energy storage system includes at least one lithium iron manganese phosphate battery cell and at least one lithium iron phosphate battery cell connected in series; the SOC correction method includes:

[0009] Determining whether the energy storage system is in a dual voltage platform interval of the lithium manganese iron phosphate battery unit;

[0010] If the energy storage system is in the dual voltage platform period, the SOC of the lithium iron phosphate battery cell is corrected according to the SOC of the lithium iron phosphate battery cell.

[0011] Optionally, correcting the SOC of the lithium iron phosphate battery cell according to the SOC of the lithium iron manganese phosphate battery cell includes:

[0012] The SOC of the lithium manganese iron phosphate battery cell is used as the SOC of the lithium iron phosphate battery cell.

[0013] Optionally, correcting the SOC of the lithium iron phosphate battery cell according to the SOC of the lithium iron manganese phosphate battery cell includes:

[0014] The SOC of the lithium iron phosphate battery cell is corrected using the curve segment parameters corresponding to the interval between the dual voltage platforms in the open circuit voltage (OCV) curve of the lithium iron phosphate battery cell and the voltage of the lithium iron phosphate battery cell.

[0015] Optionally, the curve segment parameters include: voltage and SOC;

[0016] Correcting the SOC of the lithium iron phosphate battery cell using a curve segment parameter corresponding to the interval between the dual voltage platforms in the open circuit voltage (OCV) curve of the lithium iron phosphate battery cell and the voltage of the lithium iron phosphate battery cell, including:

[0017] Determine the slope of the corresponding curve segment based on its voltage and SOC;

[0018] The SOC of the lithium iron phosphate battery cell is determined according to the slope and the voltage of the lithium iron phosphate battery cell.

[0019] Optionally, determining whether the energy storage system is in a dual voltage platform interval of the lithium manganese iron phosphate battery unit includes:

[0020] Determining whether the voltage of the lithium manganese iron phosphate battery cell is between the minimum voltage of its first voltage plateau period and the maximum voltage of its second voltage plateau period; the minimum voltage of the first voltage plateau period is greater than the maximum voltage of the second voltage plateau period;

[0021] If so, it is determined that the energy storage system is in the dual voltage platform interval.

[0022] Optionally, each battery unit is a battery cell, or each battery unit is a battery pack.

[0023] Optionally, also include:

[0024] Determining whether the energy storage system is at the end of charging or discharging;

[0025] If the energy storage system is at the end of charging and discharging, a conventional SOC correction is performed on each battery cell thereof.

[0026] A second aspect of the present application provides an energy storage system, comprising: a BMS and at least one battery cluster controlled by the BMS; wherein,

[0027] The battery cluster comprises one or at least two battery packs connected in series;

[0028] The battery pack comprises one or at least two battery cells connected in series;

[0029] There is at least one battery pack, and at least one battery cell therein is a lithium iron phosphate battery cell; and

[0030] There is at least one battery pack, and at least one battery cell therein is a lithium manganese iron phosphate battery cell;

[0031] The BMS is used to execute the SOC correction method of the energy storage system as described in any one of the first aspects above.

[0032] Optionally, the battery cluster includes at least two battery packs connected in series;

[0033] In the two adjacent battery packs, the battery cells inside one of the battery packs are all lithium iron manganese phosphate battery cells, and the battery cells inside the other battery pack are all lithium iron phosphate battery cells.

[0034] Optionally, the battery cluster includes at least two battery packs connected in series;

[0035] There is at least one battery pack, and all of its internal cells are lithium manganese iron phosphate cells;

[0036] The internal cells of the remaining battery packs are all lithium iron phosphate cells.

[0037] Optionally, each of the battery packs includes at least two battery cells connected in series, and two adjacent battery cells are respectively: a lithium manganese iron phosphate battery cell and a lithium iron phosphate battery cell.

[0038] Optionally, each of the battery packs includes at least two battery cells connected in series; and

[0039] At least one battery cell is a lithium manganese iron phosphate battery cell;

[0040] The remaining battery cells are lithium iron phosphate battery cells.

[0041] Optionally, it also includes: energy storage converter PCS or DC / DC converter;

[0042] The battery cluster is connected to the DC side of the PCS or the battery side of the DC / DC converter;

[0043] The AC side of the PCS is used to connect to the power grid and / or load;

[0044] The bus side of the DC / DC converter is used to connect to the DC bus of the new energy grid-connected power generation system.

[0045] The SOC correction method for an energy storage system provided in the present application determines whether the energy storage system is in a dual voltage platform interval of the lithium iron manganese phosphate battery cell. When the energy storage system is in the dual voltage platform interval, the SOC of the lithium iron phosphate battery cell is corrected according to the SOC of the lithium iron phosphate battery cell. Furthermore, the dual voltage platform characteristics of the lithium iron phosphate battery cell can be utilized to provide the lithium iron phosphate battery cell with an SOC correction point located in the middle section of its platform period each time the lithium iron phosphate battery cell is charged and discharged, thereby avoiding long-term accumulated deviations and improving the accuracy of SOC estimation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings to be used in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0047] FIG1 is a flow chart of a method for correcting the SOC of an energy storage system according to an embodiment of the present application;

[0048] FIG2 is an OCV curve waveform diagram of a lithium iron phosphate battery cell and a lithium iron phosphate battery cell provided in an embodiment of the present application;

[0049] FIG3 is a schematic structural diagram of an energy storage system provided in an embodiment of the present application;

[0050] FIG4 is another schematic structural diagram of the energy storage system provided in an embodiment of the present application;

[0051] FIG5 is another schematic structural diagram of the energy storage system provided in an embodiment of the present application;

[0052] FIG6 is another schematic structural diagram of the energy storage system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0053] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only 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 making creative efforts are within the scope of protection of the present invention.

[0054] In this application, the terms "comprises," "comprising," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not preclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0055] The present application provides a SOC correction method for an energy storage system to improve the SOC estimation accuracy of a lithium iron phosphate battery.

[0056] The energy storage system includes: at least one lithium iron manganese phosphate battery cell and at least one lithium iron phosphate battery cell connected in series; and in the corresponding series branches, the number and connection order of the two battery cells are not limited; in addition, in actual applications, each battery cell can refer to a battery cell, or it can also refer to a battery pack; it depends on its application environment and is within the scope of protection of this application.

[0057] Referring to FIG1 , the SOC correction method of the energy storage system includes:

[0058] S101. Determine whether the energy storage system is in a dual voltage platform interval of the lithium manganese iron phosphate battery unit.

[0059] Figure 2 shows the OCV curves of LMFP (LiFexMn1-xPO4, lithium manganese iron phosphate) cells and LFP (LiFePO4, lithium iron phosphate) cells. As shown in Figure 2, the OCV curve of the LMFP cell has two plateaus, namely: a first voltage plateau with a voltage of about 4V, and a second voltage plateau with a voltage of about 3.5V; the minimum voltage of the first voltage plateau is greater than the maximum voltage of the second voltage plateau; there is a certain interval between the two plateaus, which corresponds to the middle section of the OCV curve plateau of the LFP cell, that is, about 50% of its plateau.

[0060] Determining whether the current energy storage system is in the interval stage, that is, the dual voltage platform interval of the lithium manganese iron phosphate battery unit, can be specifically done by: determining whether the voltage of the lithium manganese iron phosphate battery unit is between the minimum voltage of its first voltage platform period and the maximum voltage of its second voltage platform period; if so, determining that the energy storage system is in the dual voltage platform interval, and executing step S102.

[0061] It should be noted that when each battery cell is a battery cell, the minimum voltage of the first voltage plateau period may be 4V as shown in FIG2 , and the maximum voltage of the second voltage plateau period may be 3.5V as shown in FIG2 ; when each battery cell is a battery pack, the minimum voltage of the first voltage plateau period may be 4nV, and the maximum voltage of the second voltage plateau period may be 3.5nV, where n is the number of battery cells in the battery pack; in actual applications, the specific judgment parameters of the two plateau periods may also depend on the specific specifications of the lithium iron manganese phosphate battery cell, and are not limited to the parameter examples shown in FIG2 .

[0062] S102 , correcting the SOC of the lithium iron phosphate battery cell according to the SOC of the lithium iron manganese phosphate battery cell.

[0063] In practical applications, the SOC of the lithium manganese iron phosphate battery cell can be directly used as the SOC of the lithium iron phosphate battery cell. See Figure 2, taking discharge as an example:

[0064] The SOC of the lithium iron phosphate cell is recorded as SOC1, and the SOC of the lithium iron phosphate cell is recorded as SOC2; when the BMS (Battery Management System) detects that the voltage v of the lithium iron phosphate cell changes from 4.1V to 4V, its SOC2=SOC21, such as 60%. At this time, the SOC1 of the lithium iron phosphate cell is forced to be corrected, that is, SOC1=60%; when the BMS detects that the voltage v of the lithium iron phosphate cell is V2, the SOC2 of the lithium iron phosphate cell is SOC22, such as 50%. At this time, the SOC1 of the lithium iron phosphate cell is forced to be corrected, that is, SOC1=50%; when the BMS detects that the voltage v of the lithium iron phosphate cell changes from V2 to 3.5V, the SOC2 of the lithium iron phosphate cell is SOC23, such as 40%. At this time, the SOC1 of the lithium iron phosphate cell is forced to be corrected, that is, SOC1=40%. V1 in FIG2 is the voltage of the lithium iron phosphate battery cell when the voltage v of the lithium iron phosphate battery cell is equal to V2.

[0065] The SOC correction method for the energy storage system provided in this embodiment, through the above-mentioned principle, can utilize the dual voltage platform characteristics of the lithium iron phosphate battery cell to provide the lithium iron phosphate battery cell with an SOC correction point located in the middle of its platform period each time the lithium iron phosphate battery cell is charged and discharged, thereby avoiding long-term accumulated deviations and improving the accuracy of SOC estimation.

[0066] In practical applications, the SOC correction method can retain conventional SOC correction at the same time, that is, it can also include: determining whether the energy storage system is at the end of charging and discharging; if the energy storage system is at the end of charging and discharging, then performing conventional SOC correction on each of its battery cells. At this time, if each battery cell is a battery cell, then compared to a battery pack composed of a single lithium iron phosphate battery cell, which only has SOC correction at the end of charging and discharging, the present application, based on this, also utilizes the dual voltage platform of lithium manganese iron phosphate to provide a battery pack with mixed battery cells with an SOC correction point at a plateau period of about 50%; similarly, if each battery cell is a battery pack, then the present application can also provide an intermediate SOC correction point for the battery cluster of the mixed battery pack.

[0067] Based on the previous embodiment, preferably, the SOC correction method of the energy storage system, step S102, may specifically include:

[0068] The SOC of the lithium iron phosphate battery cell is corrected based on the curve segment parameters of the lithium iron phosphate battery cell corresponding to the interval between the dual voltage platforms in the OCV curve and the voltage of the lithium iron phosphate battery cell.

[0069] The curve segment parameters specifically include: voltage and SOC; the specific process of this step includes:

[0070] (1) Determine the slope of the corresponding curve segment based on its voltage and SOC.

[0071] (2) Determine the SOC of the lithium iron phosphate battery cell based on the slope and the voltage of the lithium iron phosphate battery cell.

[0072] Still taking the battery cell as an example, let the SOC of the lithium iron phosphate cell be recorded as SOC1, and the SOC of the lithium manganese iron phosphate cell be recorded as SOC2. For the OCV curves of the two types of cells shown in Figure 2, the functional relationship between their respective SOC and cell voltage can be established:

[0073] For lithium iron phosphate batteries, SOC1 = f1(v);

[0074] For lithium manganese iron phosphate batteries, SOC2=f2(v).

[0075] Through the calibration correspondence described in the previous embodiment, we have: between 3.5V and 4V, SOC2=f2(v)=k*v, k is the slope of this curve, k=(SOC21-SOC23) / (4-3.5)=2*(SOC21-SOC23), and SOC1=f1(v)=k*v=2*(SOC21-SOC23)*v in this section can be obtained.

[0076] Therefore, in practical applications, during the dual voltage platform period of the lithium iron phosphate battery cell, the corrected SOC can be calculated in real time based on the voltage of the lithium iron phosphate battery cell.

[0077] Another embodiment of the present application further provides an energy storage system, comprising: a BMS and at least one battery cluster controlled by the BMS; wherein:

[0078] A battery cluster includes one or at least two battery packs connected in series, and generally includes multiple battery packs connected in series.

[0079] A battery pack includes: one or at least two battery cells connected in series; in actual applications, a battery pack usually includes multiple battery modules connected in series, and each battery module includes multiple battery cells connected in series.

[0080] This energy storage system differs from existing energy storage systems in that it not only includes at least one battery pack, at least one of which contains a lithium iron phosphate cell, but also at least one battery pack, at least one of which contains a lithium iron manganese phosphate cell. Furthermore, the BMS is also used to execute the SOC correction method for the energy storage system described in any of the above embodiments. The process and principles of this SOC correction method can be found in the above embodiments and will not be detailed here.

[0081] In addition, the energy storage system may also include: a PCS (Power Conversion System) or a DC / DC converter; wherein: each battery cluster is connected in parallel to the DC side of the PCS or the battery side of the DC / DC converter, the AC side of the PCS is used to connect to the power grid and / or load, and the bus side of the DC / DC converter is used to connect to the DC bus of the new energy grid-connected power generation system.

[0082] In practical applications, the battery cluster in this energy storage system has many specific implementation forms, such as:

[0083] (1) The battery cluster includes at least two battery packs connected in series; and, in two adjacent battery packs, the battery cells in one battery pack are all lithium manganese iron phosphate (hereinafter referred to as LMFP) battery cells, and the battery cells in the other battery pack are all lithium iron phosphate (hereinafter referred to as LFP) battery cells.

[0084] As shown in Figure 3, battery packs composed of LMFP cells (LMFP PACK) and battery packs composed of LFP cells (LFP PACK) are alternately connected in series to form a battery cluster (RACK). The SOC of the LFP battery pack can be corrected by referring to the SOC of the adjacent LMFP battery pack using the above-mentioned SOC correction method to increase the SOC correction point.

[0085] Furthermore, the use of half LFP cells in this battery cluster significantly reduces the operating voltage window. As shown in Figure 2, during the first voltage plateau of the LMFP cells, the median voltage is 0.6-0.7V higher than that of the LFP cells; during the second voltage plateau, the median voltage is 0.1-0.2V higher. For example, if the LMFP cell operating voltage range is 2.7-4.1V, a battery cluster with 384 cells in series has a voltage range of 1123.2-1574.4V, exceeding the 1500VDC DC link voltage limit of a conventional PCS. If half of the battery cluster uses LFP cells, the operating voltage range is 1123.2-1488V, fully utilizing the upper limit of the PCS DC link voltage. This increased platform voltage of the LMFP cells better meets the PCS's requirement for maintaining active power connection during high-voltage surges.

[0086] In practical applications, the steps for determining the number of LMFP battery cell strings in a battery cluster may be as follows: determining the DC voltage design upper limit U0, which is explained below by taking U0=1500V as an example; determining the port voltage upper limit U1 of the battery cluster, and the initial value is U1=U0; determining the LMFP battery cell single voltage upper limit U11, taking U11=4.1V as an example; determining the LMFP battery cell single voltage lower limit U12, taking U12=3.5V as an example; determining the LFP battery cell single voltage upper limit U21, taking U21=3.65V as an example; determining the LFP battery cell single voltage lower limit U 22, taking U22 = 2.7V as an example; determine the number of strings Y0 of pure LFP battery cells constituting the battery cluster, then Y0 = U1 / U21 = 410; calculate the number of LMFP battery cell strings X = INT((U1-U21*Y) / U11) = INT((1500-3.65*Y) / 4.1), where INT is an identifier used to define integer type variables, and the starting value of Y is Y0 and decreases successively. The value of X can be calculated accordingly, and the lower limit of the port voltage U2 of the corresponding battery cluster can be obtained as shown in Table 1. RACK in Table 1 represents the battery cluster.

[0087] Table 1 Example of setting the number of strings of LMFP cells and LFP cells in a battery cluster

[0088] Table 1 only shows some of the two cell string number configurations in a battery cluster. The calculations above and the examples in Table 1 show the lower port voltage limit U2 when both X and Y are maximized, i.e., X = 194, Y = 193, or X = 193, Y = 194. In this case, the lower port voltage limit U2 = 1200 V, and the upper port voltage limit U1 = X * U11 + Y * U21 = 1499 V. Compared to a battery cluster composed entirely of LFP cells, the lower port voltage limit U2 is increased by over 15%. The maximum lower port voltage limit U2 is most beneficial for maintaining active power output during high-voltage fault ride-through.

[0089] (2) The battery cluster includes at least two battery packs connected in series; and there is at least one battery pack whose internal cells are all lithium manganese iron phosphate cells; and the internal cells of the remaining battery packs are all lithium iron phosphate cells.

[0090] As shown in Figure 4, battery packs composed of lithium iron phosphate cells (such as the LFP PACK in the figure) are connected in series, and a battery pack composed of lithium manganese iron phosphate cells (such as the LMFP PACK in the figure) is connected in series at any position within the battery pack (the first end of the series connection is used as an example in Figure 4) to form a battery cluster (such as the RACK in the figure). Using the above-mentioned SOC correction method, the SOC of the lithium iron phosphate battery pack can be corrected by referring to the SOC of the lithium manganese iron phosphate battery packs within the cluster.

[0091] (3) Each battery pack includes at least two battery cells connected in series, and the two adjacent battery cells are: a lithium manganese iron phosphate battery cell and a lithium iron phosphate battery cell.

[0092] As shown in FIG5 , lithium manganese iron phosphate cells (LMFP cells shown in the figure) and lithium iron phosphate cells (LFP cells shown in the figure) are alternately connected in series to form a battery pack (PACK shown in the figure), and then multiple battery packs with such mixed cells are connected in series to form a battery cluster.

[0093] At this time, the SOC of the lithium iron phosphate battery cell can be corrected by referring to the SOC of the adjacent lithium manganese iron phosphate battery cell through the above-mentioned SOC correction method.

[0094] (4) Each battery pack includes at least two battery cells connected in series; and at least one battery cell is a lithium iron manganese phosphate battery cell; and the remaining battery cells are lithium iron phosphate batteries.

[0095] As shown in Figure 6, multiple lithium iron phosphate cells (such as the LFP cells shown in the figure) are connected in series, and a lithium manganese iron phosphate cell (such as the LMFP cell shown in the figure) is connected in series at any position (the first end of the series connection is shown in Figure 6 as an example) to form a battery pack (such as the PACK shown in the figure). Multiple battery packs containing mixed cells are connected in series to form a battery cluster. Using the above-mentioned SOC correction method, the SOC of the lithium iron phosphate cell can be corrected by referring to the SOC of the lithium manganese iron phosphate cell in the battery pack.

[0096] All of the aforementioned implementations can increase the SOC correction point. Furthermore, leveraging the high-voltage plateau of lithium manganese iron phosphate (LMP) allows for better adaptation to the PCS DC input voltage, improving voltage utilization and enabling the energy storage system to maintain active grid connection during high-voltage conditions. Furthermore, under the same conditions, LMP has a 10%-20% higher energy density than LFP, thus potentially increasing the energy density of mixed-cell battery systems.

[0097] It should be noted that the available charge and discharge capacity of lithium iron phosphate decreases rapidly at low temperatures, and lithium deposition is very likely to occur, which can lead to safety accidents. However, in the implementations shown in Figures 3 and 5, the excellent low-temperature properties of lithium iron phosphate can be utilized to accelerate the preheating of lithium iron phosphate battery cells, improving the wide-temperature operating performance of the energy storage battery system. For example, in the mixed-cell battery pack shown in Figure 5, the two types of cells are installed alternately, which can take advantage of the excellent low-temperature properties of lithium iron phosphate to heat the lithium iron phosphate cells, improving the overall performance of the battery pack.

[0098] In addition, due to the high cost of lithium iron manganese phosphate, the implementation forms shown in Figures 4 and 6 can reduce the cost investment of batteries by mixing a small amount of lithium iron manganese phosphate into the lithium iron phosphate battery cluster.

[0099] Figures 3 to 6 are only some optional examples. In actual applications, as long as the same battery cluster contains both lithium iron phosphate battery cells and lithium iron manganese phosphate battery cells, both can be battery cells or battery packs, and there is no limit on the number and series connection position, which can be determined according to the application environment.

[0100] The same or similar parts between the various embodiments in this specification can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Ordinary technicians in this field can understand and implement it without making any creative efforts.

[0101] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the above description has generally described the components and steps of each example according to their functions. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0102] With respect to the above description of the disclosed embodiments, the features described in the various embodiments in this specification may be interchanged or combined to enable those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A SOC correction method for an energy storage system, characterized in that: The energy storage system includes at least one lithium iron phosphate battery cell and at least one lithium iron phosphate battery cell connected in series; the SOC correction method includes: Determining whether the energy storage system is in a dual voltage platform interval of the lithium manganese iron phosphate battery unit; If the energy storage system is in the dual voltage platform interval, the SOC of the lithium iron phosphate battery cell is corrected according to the SOC of the lithium iron phosphate battery cell.

2. The SOC correction method of the energy storage system according to claim 1, characterized in that: Correcting the SOC of the lithium iron phosphate battery cell according to the SOC of the lithium iron phosphate battery cell includes: The SOC of the lithium iron phosphate battery cell is used as the SOC of the lithium iron phosphate battery cell.

3. The SOC correction method of the energy storage system according to claim 1, characterized in that: Correcting the SOC of the lithium iron phosphate battery cell according to the SOC of the lithium iron phosphate battery cell includes: The SOC of the lithium iron phosphate battery cell is corrected based on the curve segment parameters of the open circuit voltage OCV curve of the lithium iron phosphate battery cell corresponding to the interval between the dual voltage platforms and the voltage of the lithium iron phosphate battery cell.

4. The SOC correction method of the energy storage system according to claim 3, characterized in that: The curve segment parameters include: voltage and SOC; The SOC of the lithium iron phosphate battery cell is corrected based on the curve segment parameter corresponding to the interval between the dual voltage platforms in the open circuit voltage OCV curve of the lithium iron phosphate battery cell and the voltage of the lithium iron phosphate battery cell, including: According to the voltage and SOC of the corresponding curve segment, its slope is determined; The SOC of the lithium iron phosphate battery cell is determined according to the slope and the voltage of the lithium iron phosphate battery cell.

5. The SOC correction method of the energy storage system according to claim 1, characterized in that: Determining whether the energy storage system is in a dual voltage platform interval of the lithium manganese iron phosphate battery unit includes: Determine whether the voltage of the lithium manganese iron phosphate battery unit is between the minimum voltage of its first voltage plateau period and the maximum voltage of its second voltage plateau period; the minimum voltage of the first voltage plateau period is greater than the maximum voltage of the second voltage plateau period; If so, it is determined that the energy storage system is in the dual voltage platform interval.

6. The SOC correction method of the energy storage system according to any one of claims 1 to 5, characterized in that: Each battery unit is a battery cell, or a battery pack.

7. The SOC correction method of the energy storage system according to any one of claims 1 to 5, characterized in that: Also includes: Determining whether the energy storage system is at the end of charging and discharging; If the energy storage system is at the end of charging and discharging, a conventional SOC correction is performed on each battery cell.

8. An energy storage system, characterized in that: include: A battery management system BMS and at least one battery cluster controlled by the BMS; wherein, The battery cluster comprises one or at least two battery packs connected in series; The battery pack comprises one or at least two battery cells connected in series; There is at least one battery pack, and at least one battery cell therein is a lithium iron phosphate battery cell; and, There is at least one battery pack, and at least one battery cell therein is a lithium manganese iron phosphate battery cell; The BMS is used to execute the SOC correction method of the energy storage system according to any one of claims 1 to 7.

9. The energy storage system according to claim 8, characterized in that: The battery cluster includes at least two battery packs connected in series; In two adjacent battery packs, the battery cells inside one of the battery packs are all lithium iron manganese phosphate battery cells, and the battery cells inside the other battery pack are all lithium iron phosphate battery cells.

10. The energy storage system according to claim 8, characterized in that: The battery cluster includes at least two battery packs connected in series; There is at least one battery pack, and all of its internal cells are lithium manganese iron phosphate cells; The internal cells of the remaining battery packs are all lithium iron phosphate cells.

11. The energy storage system according to claim 8, characterized in that: Each of the battery packs comprises at least two battery cells connected in series, and two adjacent battery cells are respectively: a lithium iron manganese phosphate battery cell and a lithium iron phosphate battery cell.

12. The energy storage system according to claim 8, characterized in that: Each of the battery packs comprises at least two battery cells connected in series; and, At least one battery cell is a lithium iron manganese phosphate battery cell; The remaining cells are lithium iron phosphate cells.

13. The energy storage system according to any one of claims 8 to 12, characterized in that: Also includes: Energy storage converter PCS or DC / DC converter; The battery cluster is connected to the DC side of the PCS or the battery side of the DC / DC converter; The AC side of the PCS is used to connect to a power grid and / or a load; The bus side of the DC / DC converter is used to connect to the DC bus of the new energy grid-connected power generation system.

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