Energy storage system and state of charge calibration method

Abstract

The embodiment of the invention provides an energy storage system and a state of charge calibration method. The energy storage system comprises a controller and a battery pack. Wherein the battery pack comprises a plurality of batteries. A plurality of batteries can be connected in a series-parallel combined manner, and the parallel battery pack is connected in series with other batteries which are not connected in parallel in the plurality of batteries. And a controller in the energy storage system is used for calibrating the SOC of the series batteries in the series battery pack based on the SOC variation generated by the parallel batteries in the parallel battery pack due to charging and discharging. Wherein the SOC of the batteries in the series batteries before calibration is obtained by using a traditional SOC detection method. The calibration operation in the embodiment of the invention can reduce the error caused by the traditional SOC detection method.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to energy storage systems and methods for calibrating the state of charge. Background Technology

[0002] Batteries are one of the core components of energy storage systems. Energy storage systems store and release energy through the charging and discharging of batteries, thereby balancing energy supply and demand. For example, energy storage systems can store electrical energy by charging batteries during periods of low grid load and release electrical energy during periods of high grid load, ensuring grid stability.

[0003] The state of charge (SOC) of a battery plays a crucial role in the performance of an energy storage system. SOC indicates the percentage of the battery's total capacity remaining. Energy storage systems need to monitor the battery's SOC in real time and adjust their charging and discharging strategies accordingly to ensure efficient operation and safe use. For example, when the battery's SOC is high, the system can stop charging to prevent overcharging. Overcharging can lead to increased internal voltage and even thermal runaway, causing battery damage or even safety incidents.

[0004] Therefore, determining the state of charge (SOC) of a battery is a topic worthy of discussion. Summary of the Invention

[0005] This application provides an energy storage system and a state of charge calibration method for more accurate calculation of the SOC of batteries in the energy storage system.

[0006] In a first aspect, embodiments of this application provide an energy storage system, characterized in that the energy storage system includes a controller and a battery pack, the battery pack including multiple batteries, a first battery and a second battery among the multiple batteries being connected in parallel, and then connected in series with other batteries among the multiple batteries excluding the first and second batteries, the other batteries including a third battery, wherein the controller is used to control the charging and discharging of the multiple batteries through the DC bus to which they are connected, and to determine the change in state of charge (SOC) of the first battery caused by charging and discharging; the controller is also used to calibrate the SOC of the third battery based on the change in SOC of the first battery.

[0007] The third battery can be a series battery (e.g., battery 1) as described in the embodiment. The first battery can be a parallel battery (e.g., battery 2) as described in the embodiment, and the second battery can be any other battery in the parallel battery pack besides the first battery (e.g., battery 3).

[0008] In the above embodiments, a parallel battery pack is introduced into the original series-connected batteries. The SOC change of the first battery in the parallel battery pack is used to calibrate the SOC of the third battery in the series-connected battery pack. Calibrating the SOC of the third battery indicates that its SOC can be obtained through calibration, thus reducing errors introduced by traditional SOC detection methods. During calibration, the object being calibrated can be either the detected SOC value of the series-connected batteries or the detected SOC change caused by charging and discharging. If the object being calibrated is the detected SOC value of the third battery, the calibrated SOC of the third battery is obtained based on the calibrated SOC value. If the object being calibrated is the SOC change of the third battery, the calibrated SOC of the third battery is obtained based on the calibrated SOC change. A more accurate battery SOC allows the energy storage system to better manage the charging and discharging of the battery pack.

[0009] In conjunction with the first aspect, in some embodiments, before calibrating the SOC of the third battery, the controller is further configured to determine that the SOC of the third battery changes due to charge-discharge variation to a first SOC; the controller is configured to calibrate the SOC of the third battery, including: the controller is configured to calibrate the SOC of the third battery from the first SOC to a second SOC based on the amount of SOC change of the first battery.

[0010] In the above embodiments, the first SOC is the measured SOC value of the third battery. During calibration, the object being calibrated is the measured SOC value of the third battery. The measured SOC value of the third battery is directly calibrated to obtain the calibrated SOC of the third battery. This method has broad applicability; regardless of the SOC detection method used to obtain the SOC value of the third battery, it can be calibrated to obtain the calibrated SOC of the third battery. However, when the object being calibrated is the change in SOC of the third battery, it is only applicable to SOC detection methods that can obtain the change in SOC, such as the ampere-hour integration method.

[0011] In conjunction with the first aspect, in some embodiments, the controller is further configured to determine that the SOC of the third battery changes to a first SOC due to charge-discharge, including: the controller determining that the SOC of the third battery changes from a third SOC to the first SOC due to charge-discharge; the controller is configured to calibrate the SOC of the third battery from the first SOC to a second SOC based on the amount of SOC change of the first battery, including: the controller determining a fourth SOC using the third SOC, the amount of SOC change of the first battery, and the SOC change factor N between the third battery and the first battery during charge-discharge; the controller determining the calibrated second SOC, wherein the second SOC is a value between the first SOC and the fourth SOC.

[0012] In the above embodiments, compared to the third battery, the first battery, due to its parallel connection with the second battery, has better anti-interference capabilities. For example, compared to the third battery, the SOC detection of the first battery is less affected by factors such as temperature and noise, thus making the SOC change of the first battery due to discharge reliable. Specifically, the less temperature-dependent SOC detection of the first battery compared to the third battery includes the fact that the first and second batteries form a uniform temperature field distribution, significantly reducing the interference of temperature rise on SOC detection. Furthermore, the less noise-dependent SOC detection of the first battery compared to the third battery includes the fact that the current flowing through the first battery is 1 / N of the current flowing through the third battery; when using the ampere-hour integration method to detect the battery's SOC, the noise in the current has a smaller impact on the SOC detection of the first battery than in a series structure. Therefore, the SOC change of the first battery due to discharge provides a reliable reference for calculating the estimated SOC value of the third battery. Using the estimated SOC value of the third battery to calibrate the detected SOC value of the third battery can improve the accuracy of the third battery's SOC.

[0013] In conjunction with the first aspect, in some embodiments, the fourth SOC and the third SOC satisfy: SOC4 = SOC3 + N × ΔSOC; where SOC4 is the fourth SOC, SOC3 is the third SOC, N is the total number of the first battery and the second battery, the second battery is at least one battery connected in parallel with the first battery, and ΔSOC is the change in SOC of the first battery.

[0014] The above formula is equivalent to formula (3) in the embodiment. Wherein, SOC4 is SOC′1# in formula (3). SOC3 is SOC1 in formula (3). ΔSOC is ΔSOC2 in formula (3).

[0015] In conjunction with the first aspect, in some embodiments, the controller is also configured to use the second SOC as the SOC of the battery pack.

[0016] In the above embodiments, the second SOC (the calibrated SOC of the series-connected batteries) is used as the SOC of the battery pack because the current flowing through the series-connected batteries can be shunt among the different batteries in the parallel battery pack. Therefore, the batteries in the parallel battery pack are less prone to overcharging or over-discharging compared to the batteries in the series-connected battery pack. This can also be understood as the charging and discharging of multiple batteries being constrained by the SOC of the batteries in the series-connected battery pack. Based on this, in the above embodiments, the controller can determine the SOC of the battery pack using the calibrated SOC of the series-connected batteries (the second SOC) and manage the charging and discharging of multiple batteries in the battery pack based on this SOC, ensuring that the batteries in the series-connected battery pack are not overcharged or over-discharged, and also ensuring that the batteries in the parallel battery pack are not overcharged or over-discharged. This is beneficial for maintaining the efficient operation and safe use of the energy storage system.

[0017] In conjunction with the first aspect, in some embodiments, before the first and second batteries of the plurality of batteries are connected in parallel, the controller is further configured to switch the first and second batteries of the plurality of batteries connected in series from series to parallel if it is determined that the plurality of batteries have stopped charging and discharging through the DC bus to which they are connected.

[0018] In the above embodiments, the first and second batteries can be switched from series connection to parallel connection, making the connection method more flexible and not fixed. This allows for switching the first and second batteries to parallel connection only when calibration is required. When calibration is not required, the first and second batteries can be switched to series connection, resulting in multiple batteries being connected in series. This allows for more efficient utilization of the power in the first and second batteries. Furthermore, the series-parallel connection switching of batteries in the parallel battery pack is limited to situations where multiple batteries have stopped charging and discharging through their connected DC bus. This avoids current interference when the isolating switch switches from open to closed, making the switching operation safer and more controllable.

[0019] In conjunction with the first aspect, in some embodiments, the controller is configured to switch the first battery and the second battery among the series-connected batteries from series connection to parallel connection when it is determined that the plurality of batteries have stopped charging and discharging through the DC bus to which they are connected, including: if a first condition is met, when it is determined that the plurality of batteries have stopped charging and discharging through the DC bus to which they are connected, the controller switches the first battery and the second battery among the series-connected batteries from series connection to parallel connection; the first condition includes at least one of the following: the SOC of the battery pack is less than a first threshold, and the plurality of batteries have been continuously charging and discharging through the DC bus to which they are connected for a first time.

[0020] In the above embodiments, the controller initiates the calibration operation only when the first condition is met. If the first condition is not met, it indicates that the error is small and negligible, and the controller may not initiate the calibration operation, switching each battery in the parallel battery pack to series connection, and then connecting it in series with the batteries in the series battery pack. In this way, all batteries in the battery pack are connected in series, which is beneficial for fully utilizing the power of each battery in the parallel battery pack, so as to perform balanced battery SOC calibration and utilize the power of each battery in the parallel battery pack.

[0021] In conjunction with the first aspect, in some embodiments, the first battery and the second battery are connected in parallel,

[0022] The controller is also used to switch the first battery and the second battery from parallel connection back to series connection if the multiple batteries stop charging and discharging through the DC bus to which they are connected again.

[0023] In the above embodiments, when the first and second batteries are switched to parallel connection, a calibration operation can be performed. After the calibration operation is performed, if the SOC of the battery obtained by the controller is accurate (accumulated errors have been eliminated) to a level sufficient to support the energy storage system in accurately managing battery charging and discharging, the controller then restores the batteries in the parallel battery pack to a series connection to fully utilize the power of each battery in the parallel battery pack.

[0024] In conjunction with the first aspect, in some embodiments, before switching the first battery and the second battery from parallel connection to series connection, the controller is further configured to determine that the calibrated SOC of the third battery is equal to the SOC of the first battery.

[0025] The above embodiments ensure that when the batteries in the battery pack are restored to a series connection, the State of Charge (SOC) of each battery in the battery pack is consistent. This ensures that the voltage of each battery in the battery pack remains consistent during subsequent charging and discharging processes, avoiding voltage imbalance problems caused by inconsistent SOC of the batteries after switching from parallel to series connection.

[0026] In conjunction with the first aspect, in some embodiments, before switching the first battery and the second battery from parallel connection to series connection,

[0027] The controller is also used to control the first battery and the second battery to discharge through a non-DC bus, or to control the third battery to discharge through a non-DC bus, such that the calibrated SOC of the third battery is equal to the SOC of the first battery.

[0028] When the SOC of the third battery after calibration is greater than that of the first battery, the controller controls the third battery to discharge through the non-DC bus. When the SOC of the third battery after calibration is less than that of the first battery, the controller controls each battery in the first battery pack to discharge through the non-DC bus. Discharging a battery on the non-DC bus includes discharging through a resistor it is connected to, consuming electrical energy through the resistor. The circuit between the battery and the resistor is normally open; however, when equalization is required, the controller can control the circuit between the battery and the resistor to open, with the opening time depending on the SOC difference between the series-connected and parallel-connected batteries.

[0029] Secondly, embodiments of this application provide a state of charge (SOC) calibration method, characterized in that it is applied to an energy storage system, the energy storage system including a battery pack, the battery pack including multiple batteries, a first battery and a second battery among the multiple batteries being connected in parallel, and then connected in series with other batteries among the multiple batteries excluding the first and second batteries, the other batteries including a third battery, the method including: controlling the multiple batteries to charge and discharge through a DC bus to which they are connected, and determining the change in SOC of the first battery due to charging and discharging; calibrating the SOC of the third battery based on the change in SOC of the first battery.

[0030] In conjunction with the second aspect, in some embodiments, before calibrating the SOC of the third battery, the method further includes: determining that the SOC of the third battery changes due to charge-discharge changes to a first SOC; calibrating the SOC of the third battery specifically includes: calibrating the SOC of the third battery from the first SOC to a second SOC based on the amount of SOC change of the first battery.

[0031] In conjunction with the second aspect, in some embodiments, determining the SOC of the third battery as a first SOC due to charge-discharge changes specifically includes: determining that the SOC of the third battery changes from a third SOC to the first SOC due to charge-discharge changes; calibrating the SOC of the third battery from the first SOC to a second SOC based on the amount of SOC change of the first battery, specifically including: determining the fourth SOC using the third SOC, the amount of SOC change of the first battery, and the SOC change factor N between the third battery and the first battery during charge-discharge; and determining the calibrated second SOC, wherein the second SOC is a value between the first SOC and the fourth SOC.

[0032] Thirdly, embodiments of this application provide an energy storage system, which includes a controller and a memory. The memory is coupled to the controller and is used to store computer program code, which includes computer instructions. The controller invokes the computer instructions to cause the energy storage system to perform the state of charge calibration method as described in any of the second aspects. Attached Figure Description

[0033] Figure 1 An exemplary energy storage system is shown when the batteries in the battery pack are connected in series;

[0034] Figure 2 An exemplary energy storage system is shown, in which the batteries in the battery pack are connected in series and parallel.

[0035] Figure 3 An exemplary process is shown when an energy storage system calibrates the state of charge (SOC) of a battery.

[0036] Figure 4 A schematic diagram is shown illustrating the process of calibrating the SOC of a battery in an energy storage system.

[0037] Figure 5 This illustrates another exemplary energy storage system in which the batteries in the battery pack are connected in series and parallel.

[0038] Figure 6 Another exemplary energy storage system is shown, in which the individual batteries in the battery pack are connected in series and parallel. Detailed Implementation

[0039] To facilitate understanding of the energy storage system and state of charge calibration method provided in the embodiments of this application, the traditional SOC detection method (hereinafter referred to as the SOC detection method) and its application in the charging and discharging process of the energy storage system are first introduced.

[0040] like Figure 1 As shown, an energy storage system using the SOC detection method may include a battery management system (BMS), a battery pack, a direct current to direct current (DC / DC) converter, and a power conversion system (PCS).

[0041] The battery management system of the energy storage system includes a controller for managing battery charging and discharging, including but not limited to at least one of the following: a main controller and a battery control unit (BCU). The battery pack of the energy storage system includes multiple batteries (e.g., batteries 0-5), which are connected in series.

[0042] Multiple batteries in the battery pack are charged and discharged through the DC bus (Bus) to which they are connected, in response to power dispatching by external devices. Charging and discharging here includes: multiple batteries charging through the DC bus they are connected to, and / or multiple batteries discharging through the DC bus they are connected to.

[0043] Multiple batteries discharge through their connected DC bus, including: a DC / DC converter receiving DC voltage from the multiple batteries through the DC bus; the DC / DC converter then boosting the DC voltage from the batteries and transmitting it to an energy storage converter; the energy storage converter converts the boosted DC voltage into AC voltage and transmits it to external devices, providing power to external devices (e.g., the power grid).

[0044] Multiple batteries are charged via their connected DC bus, including: a DC / DC converter stepping down the DC power from the energy storage converter and then supplying the stepped-down DC power to the multiple batteries via the DC bus. The DC power supplied by the energy storage converter to the DC / DC converter is obtained by converting AC power supplied by an external device.

[0045] Optionally, the charging and discharging process of multiple batteries in the battery pack via their connected DC bus is scheduled by the main controller, including: the main controller generating charging and discharging control commands based on the battery pack's SOC and power dispatch commands from external devices. Then, the main controller sends the charging and discharging control commands to the energy storage converter. These commands instruct the energy storage converter to adjust the voltage of its DC port to create a controllable voltage difference with the voltages of the multiple batteries, thereby driving the DC / DC converter to convert the current voltage according to this controllable voltage difference, causing the current to flow in the desired magnitude and direction, thus enabling the multiple batteries to charge and discharge in response to the power dispatch commands.

[0046] The State of Charge (SOC) of the battery pack can be determined by the main controller based on the SOC of the batteries transmitted from the battery controller. When multiple batteries in the battery pack are connected in series, the SOC of the batteries transmitted from the battery controller to the main controller can include the SOC of at least one battery in the battery pack. If the SOC of at least one battery contains only the SOC of a single battery, the main controller uses the SOC of that single battery as the SOC of the battery pack. If the SOC of at least one battery contains the SOCs of two or more batteries, the main controller can average the SOCs of the at least one battery to obtain the SOC of the battery pack.

[0047] When measuring the SOC of a battery, the battery controller may use methods such as ampere-hour integration or open-circuit voltage detection.

[0048] The ampere-hour integration method is used to detect the state of charge (SOC) of a battery (e.g., series or parallel batteries) in real time according to frequency, for example, detecting the battery's SOC once per second. The SOC detected in the i-th time is based on the SOC obtained in the (i-1)-th time detection, or the initial SOC plus the SOC increase during charging; or, the SOC detected in the i-th time is based on the SOC obtained in the (i-1)-th time detection, or the initial SOC minus the SOC decrease during discharging. The increase or decrease in SOC is obtained by integrating the current. i is an integer greater than or equal to 1. When i equals 1, the SOC at the time of the first detection is obtained by integrating the current based on the initial SOC. The initial SOC here includes, but is not limited to, the battery's rated capacity, or, after interrupting the ampere-hour integration, the SOC detected using the open-circuit voltage detection method.

[0049] The open-circuit voltage detection method is used when the battery is at rest (e.g., when charging and discharging have stopped). It measures the battery's open-circuit voltage (OCV) and then maps this OCV to the battery's state of charge (SOC). There is a mapping relationship f between the battery's OCV and SOC, which can be understood as SOC = f(OCV). This mapping relationship can be represented by an OCV-SOC table. After detecting the battery's open-circuit voltage, the SOC can be determined by consulting the OCV-SOC table.

[0050] As can be seen from the foregoing description, the ampere-hour integration method is applicable during the battery charging and discharging process, while the open-circuit voltage detection method is applicable after the battery charging and discharging process is completed.

[0051] like Figure 1 As shown, when multiple batteries are connected in series in a battery pack, the current flowing through each battery is equal during charging and discharging. In this case, the battery controller can use the ampere-hour integration method to integrate the current flowing through a single battery (e.g., battery 1) to determine the state of charge (SOC) of that single battery, and transmit this SOC to the main controller. The main controller can then use the SOC of that single battery as the SOC of the battery pack.

[0052] However, the ampere-hour integration method is a cumulative form of SOC detection, and its cumulative error increases over time. Therefore, when the battery is at rest (e.g., when charging and discharging are stopped), the battery controller can use the open-circuit voltage detection method to measure the SOC of each battery in the battery pack and transmit the SOC of each battery to the main controller. This corrects the error in the SOC measured by the ampere-hour integration method. Generally speaking, if the difference in SOC between the batteries measured using the open-circuit voltage detection method is small, it indicates that the batteries in the battery pack perform consistently during charging and discharging. At this point, the main controller can determine the SOC of the battery pack based on the SOC of each battery, including but not limited to: the main controller using the largest SOC among the individual batteries as the SOC of the battery pack (e.g., if the battery's most recent charge / discharge state was charging before using the open-circuit voltage detection method to detect the SOC, the main controller can use the largest SOC among the individual batteries as the SOC of the battery pack), or using the smallest SOC among the individual batteries as the SOC of the battery pack (e.g., if the battery's most recent charge / discharge state was discharging before using the open-circuit voltage detection method to detect the SOC, the main controller can use the smallest SOC among the individual batteries as the SOC of the battery pack). If the SOC of each battery measured using the open-circuit voltage detection method differs significantly, it indicates that the batteries in the battery pack are performing inconsistently during charge and discharge. The main controller can perform a balancing operation to balance the SOC of each battery. The balanced SOC is then used as the SOC of the battery pack. This balancing operation includes, but is not limited to: controlling the battery with a non-minimum SOC in the battery pack to discharge on a non-DC bus, so that its SOC matches that of the battery with the smallest SOC. The battery discharges on the non-DC bus, including discharging through a resistor connected to it, consuming electrical energy through the resistor. The circuit between the battery and the resistor is usually open. When balancing is required, the main controller can control the circuit between the battery and the resistor to open; the opening time depends on the amount of electrical energy the battery needs to release.

[0053] However, when the battery's State of Charge (SOC) drops to a certain level, using the open-circuit voltage detection method to measure the SOC will result in significant errors. For example, after the battery's SOC drops below 90%, using the open-circuit voltage detection method to measure the SOC will enter a plateau region. At this point, the battery's open-circuit voltage changes very slowly or almost constantly with the battery's SOC. In other words, entering the plateau region means that as the battery's SOC continues to decrease, the change in the battery's open-circuit voltage is slow. If the accuracy of the measured open-circuit voltage is not high at this point, it will lead to a large error in the open-circuit voltage detection method. The aforementioned plateau region is even more pronounced in lithium iron phosphate (LiFePO4, LFP) batteries.

[0054] To more accurately measure the state of charge (SOC) of a battery, embodiments of this application provide an energy storage system including a controller and a battery pack. The battery pack includes multiple batteries. Figure 2 As shown, multiple batteries in a battery pack (e.g., batteries 0-5) can be connected in a series-parallel combination. The parallel battery pack is then connected in series with other batteries that are not connected in parallel. For example, batteries 2 and 3, after being connected in parallel, are connected in series with other batteries that are not connected in parallel (batteries 0, 1, 4, and 5). Here, the other batteries that are not connected in parallel can also be referred to as a series battery pack. Compared to the aforementioned... Figure 1 The battery pack shown is connected in series with multiple batteries. The connection method of multiple batteries in the battery pack involved in this application embodiment can be understood as: a parallel battery pack is introduced into the original series-connected multiple batteries, so that multiple batteries can be connected in a combination of series and parallel connection.

[0055] The controller involved in this application embodiment is used to calibrate the SOC of the batteries in the series battery pack (referred to as series batteries, such as battery 1) based on the SOC change of a portion of the batteries in the parallel battery pack (referred to as parallel batteries, such as battery 2) due to charging and discharging.

[0056] In this embodiment, the State of Charge (SOC) of the series-connected batteries (before calibration) is obtained using a conventional SOC detection method (hereinafter referred to as the SOC detection method). The calibration operation in this application reduces the errors introduced by the conventional SOC detection method. Conventional SOC detection methods include the ampere-hour integration method and the open-circuit voltage detection method, which can be referred to in the foregoing description and will not be repeated here.

[0057] The controllers involved in the embodiments of this application include one or more controllers for managing battery charging and discharging. For example... Figure 2 As shown, the controller can be located in the battery management system (BMS) of the energy storage system. The controller includes, but is not limited to, at least one of the following: a main controller and a battery control unit (BCU). The main controller can be a smart array controller unit (SACU) or an energy management system (EMS). The following description uses the controller in the energy storage system as an example of a main controller. Other situations can be referred to this description, and will not be repeated in the embodiments of this application.

[0058] It should be noted that the number M of individual cells in the parallel battery corresponding to the SOC change is the same as the number M of individual cells in the series battery whose SOC is being calibrated, where M is an integer greater than or equal to 1. Alternatively, it can be understood that the parallel battery corresponding to the SOC change and the series battery whose SOC is being calibrated can be individual cells or battery packs with multiple individual cells; this application does not limit this.

[0059] It should also be noted that a parallel battery pack includes multiple batteries in which the positive terminals can be connected to each other and the negative terminals can be connected to each other (e.g., batteries 2 and 3). A series battery pack includes multiple batteries in a battery pack other than those in a parallel battery pack (e.g., batteries 0, 1, 4, and 5), in which the positive and negative terminals of different batteries are connected.

[0060] The current flowing through series-connected batteries can be distributed among the different batteries in a parallel battery pack. Therefore, batteries in a parallel battery pack are less prone to overcharging or over-discharging compared to those in a series battery pack. This can also be understood as the charging and discharging of multiple batteries being constrained by the State of Charge (SOC) of the batteries in the series battery pack. Based on this, the controller can determine the SOC of the battery pack by using the calibrated SOC of the series batteries and manage the charging and discharging of the multiple batteries in the pack accordingly. This prevents overcharging or over-discharging of the batteries in the series battery pack, and also ensures that the batteries in the parallel battery pack are not overcharged or over-discharged. This is beneficial for maintaining the efficient operation and safe use of the energy storage system.

[0061] The aforementioned controller is used to calibrate the SOC of a series-connected battery (e.g., battery 1) based on the SOC change of the parallel-connected battery (e.g., battery 2) due to charging and discharging. This process includes... Figure 3 The content involved in steps S101-S104.

[0062] S101. The controller determines the change in SOC of the parallel batteries due to charging and discharging, denoted as ΔSOC2.

[0063] The charging and discharging time is denoted as Time 1 - Time 2. Here, the charging and discharging of parallel batteries refers to the charging and discharging of parallel batteries through the DC bus. The charging and discharging of parallel batteries and other batteries in the battery pack on the DC bus are synchronized. That is, multiple batteries in the battery pack are simultaneously charged and discharged through their connected DC bus, including: multiple batteries in the battery pack are simultaneously charged through their connected DC bus, and / or, multiple batteries in the battery pack are simultaneously discharged through their connected DC bus.

[0064] like Figure 4As shown, the controller obtains the SOC (SOC2#) of the parallel battery at time 2, and subtracts the SOC of the parallel battery at time 1 (denoted as SOC2) from the SOC (SOC2#) at time 2 to obtain the change in SOC of the parallel battery due to charging and discharging, denoted as ΔSOC2. This can be understood as ΔSOC2 = SOC2# - SOC2.

[0065] S102. The controller determines that the SOC of the series-connected battery changes to SOC1# due to the charge and discharge cycle.

[0066] refer to Figure 4 The controller determines the SOC of the series battery at time 2, denoted as SOC1#.

[0067] It should be noted here that before step S102, the controller also determines the SOC of the series battery at time 1, denoted as SOC1. For simplicity, Figure 4 The example given uses the condition that SOC1 equals SOC2. In reality, SOC1 and SOC2 may not be equal.

[0068] It should also be noted that the SOC values ​​of the series battery at time 1 (SOC1), the series battery at time 2 (SOC1#), the parallel battery at time 1 (SOC2), and the parallel battery at time 2 (SOC2#) mentioned above are all SOC detection values ​​obtained using traditional SOC detection methods. For example, after being detected by the battery controller using a traditional SOC detection method, the values ​​are transmitted to the main controller (here, the controller). It can also be understood that the SOC change (ΔSOC2) of the parallel battery due to charging and discharging is obtained based on the ampere-hour integration method or the open-circuit voltage detection method.

[0069] like Figure 2 As shown, taking battery 2 (parallel connected) and battery 1 (series connected) as an example, this illustrates how the battery controller detects SOC1# and SOC2#. The detection of SOC1 and SOC2 can be found in the relevant descriptions and will not be repeated here. When the battery controller uses the ampere-hour integration method to measure the SOC (SOC1#) of the series-connected battery at time 2, the battery controller executes... This is denoted by formula (1). Wherein, the current I1 is the current flowing through the series-connected batteries, which can be measured by a current sensor installed in the series circuit. When the battery controller uses the ampere-hour integration method to measure the SOC (SOC2#) of the parallel batteries at time 2, the battery controller executes... This is denoted as Formula (2). Wherein, the current I2 is the current flowing through the parallel batteries, which can be measured by a current sensor installed on the parallel circuit. Alternatively, if the batteries are idle after time 2 (e.g., when charging and discharging stops), the battery controller can use an open-circuit detection method to detect the SOC (SOC1#) of the series battery at time 2, and the SOC (SOC2#) of the parallel battery at time 2. This includes: the battery controller detecting the open-circuit voltage of the series and parallel batteries respectively, then consulting the OCV-SOC table to determine the SOC (SOC1#) of the series battery at time 2, and the SOC (SOC2#) of the parallel battery at time 2.

[0070] S103. The controller determines the estimated value of the SOC of the series battery at time 2 by using the SOC of the series battery at time 1 (SOC1), the change in SOC of the parallel battery due to charging and discharging (ΔSOC2), and the SOC change multiple N of the parallel and series batteries during charging and discharging. This value is denoted as SOC′1#.

[0071] Wherein, the SOC change factor N during charging and discharging of parallel and series batteries represents the total number of batteries in the parallel battery pack. For example, Figure 2 The total number of batteries in the parallel battery pack shown is 2. It is not limited to 2; N is an integer greater than or equal to 2.

[0072] refer to Figure 4 Optionally, SOC′1#=SOC1+N×ΔSOC2, denoted as formula (3).

[0073] In formula (3), SOC′1# is the estimated SOC of the series battery at time 2, SOC1 is the SOC of the series battery at time 1, and N×ΔSOC2 is the estimated SOC change of the series battery due to charging and discharging (ΔSOC1), i.e., ΔSOC1=N×ΔSOC2. Here, N×ΔSOC2 is determined based on the principle of parallel current splitting. Since the current flowing through the series battery is N times that flowing through the parallel battery, the SOC change of the parallel battery due to charging and discharging (e.g., ΔSOC2) is used as a reference, and the SOC change of the series battery due to charging and discharging is N times ΔSOC2.

[0074] S104. The controller determines a value between the estimated SOC (SOC′1#) of the series battery at time 2 and the detected SOC (SOC1#) of the series battery at time 2, which is the calibrated SOC of the series battery. The main controller uses the calibrated SOC as the SOC of the series battery at time 2.

[0075] Continue to refer to Figure 4This can also be understood as the range of SOC values ​​after calibration for a series-connected battery being between SOC′1# and SOC1#. For example, the SOC after calibration for a series-connected battery could be the average of SOC′1# and SOC1#.

[0076] It's important to note that parallel batteries offer better interference immunity compared to series batteries. For example, the SOC (State of Charge) of parallel batteries is less affected by factors like temperature and noise compared to series batteries, making the SOC changes caused by discharge more reliable. Specifically, the less temperature-dependent SOC testing in parallel batteries stems from the fact that they form a more uniform temperature field with other batteries in the parallel battery pack, significantly reducing the interference of temperature rise on SOC detection. Furthermore, the less noise-dependent SOC testing in parallel batteries is due to the fact that the current flowing through a parallel battery is only 1 / N of the current flowing through a series battery; therefore, when using the ampere-hour integration method to test the SOC, noise in the current has a smaller impact on the SOC detection of parallel batteries compared to a series structure.

[0077] Therefore, the change in SOC caused by the discharge of parallel batteries provides a reliable reference for calculating the estimated SOC of series batteries. By using the estimated SOC of series batteries to calibrate the detected SOC of series batteries, the accuracy of the SOC of series batteries can be improved.

[0078] It should be noted that, not limited to formula (3), the formula for the controller to determine the estimated SOC of the series battery at time 2 can also be other formulas, including but not limited to SCO′1#=SOC1+β×N×ΔSOC2. Wherein, β is the scaling factor, the value of which is affected by factors such as temperature, and can be a value close to 1, for example, a value between [0.95-1.05].

[0079] It should also be noted that the aforementioned steps S101-S104 use the SOC detection value (e.g., SOC1#) of the series-connected battery as an example to illustrate how to calibrate the SOC of the series-connected battery. In practice, when calibrating the SOC of the series-connected battery based on the SOC change caused by charging and discharging of the parallel-connected battery, the calibrated object is not limited to the SOC detection value of the series-connected battery, but can also be the detected SOC change caused by charging and discharging of the series-connected battery (denoted as ΔSOC1#).

[0080] When the object to be calibrated is the aforementioned ΔSOC1#, the controller is used to calibrate the SOC of the series battery based on the SOC change of the parallel battery due to charging and discharging. This includes: the controller estimating the SOC change of the series battery due to charging and discharging (the aforementioned ΔSOC1, ΔSOC1 = N × ΔSOC2) based on the SOC change of the parallel battery due to charging and discharging (denoted as ΔSOC2). Based on the estimated SOC change of the series battery (ΔSOC1), the controller calibrates the measured SOC change ΔSOC1# of the series battery. The calibrated SOC change is a value between ΔSOC1 and ΔSOC1#, for example, the average of ΔSOC1 and ΔSOC1#. The controller adds the calibrated SOC change to the SOC of the series battery before charging and discharging, and uses this as the SOC of the series battery. The detected SOC change of the series battery due to charging and discharging (ΔSOC1#) can be obtained by the controller using the ampere integration method. Here, the SOC of the series-connected battery before charging and discharging includes the initial SOC of the series-connected battery or the SOC obtained by the (i-1)th time using the ampere-hour integration method. Again, taking a charging / discharging time of time 1 to time 2 as an example, the SOC obtained by the (i-1)th time using the ampere-hour integration method is: the SOC of the series-connected battery at time 1 obtained by using the ampere-hour integration method.

[0081] Based on the foregoing, the energy storage system provided in this application embodiment includes a controller and a battery pack, the battery pack comprising multiple batteries. The multiple batteries are connected in parallel (e.g., ...). Figure 2 Battery 2) and other parallel batteries (e.g. Figure 2 After battery 3) is connected in parallel, it is connected in series with other batteries in the plurality of batteries, which include series-connected batteries (e.g., batteries connected in series with each other). Figure 2 Battery 1 in the middle.

[0082] The controller is used to control the charging and discharging of the multiple batteries through the DC bus to which they are connected, and to determine the amount of SOC change (e.g., ΔSOC2 mentioned above) of the parallel batteries due to charging and discharging.

[0083] The controller is also used to calibrate the SOC of a series battery based on the SOC change of the parallel battery.

[0084] Optionally, before calibrating the SOC of the series-connected batteries, the controller is further configured to determine the SOC of the series-connected batteries due to the change in charge and discharge, resulting in a first SOC (which is the detected SOC value of the series-connected batteries, such as the aforementioned SOC1#). The aforementioned calibration of the SOC of the series-connected batteries from the first SOC to the second SOC based on the change in SOC of the parallel-connected batteries includes: calibrating the SOC of the series-connected batteries from the first SOC to the second SOC based on the change in SOC of the parallel-connected batteries.

[0085] The controller is used to determine that the SOC of the series-connected battery changes to a first SOC due to charging and discharging, including: the controller determines that the SOC of the series-connected battery changes from a third SOC (e.g., the aforementioned SOC1) to a first SOC due to charging and discharging.

[0086] The controller is used to calibrate the SOC of the series-connected battery from a first SOC to a second SOC based on the SOC change of the parallel-connected battery. This includes: the controller determining a fourth SOC (an estimated value of the SOC of the series-connected battery, such as the aforementioned SOC′1#) using a third SOC (e.g., SOC1 mentioned above), the SOC change of the parallel-connected battery, and the SOC change factor N between the series-connected and parallel-connected batteries during charging and discharging. Then, the controller determines the calibrated second SOC, which is a value between the first SOC and the fourth SOC. A description of this process can be found in the foregoing description of steps S101-S104.

[0087] Optionally, the controller is also used to determine the SOC of the battery pack based on a second SOC. For example, the second SOC can be used as the SOC of the battery pack. The SOC of the battery pack can be used by the controller to manage the charging and discharging of multiple batteries in the battery pack, enabling power scheduling between the energy storage system and external devices. Figure 2 As shown, the energy storage system includes a controller, a battery pack, a DC / DC converter, and an energy storage inverter. The energy storage inverter receives charge / discharge control commands from the main controller and then controls the charging and discharging of multiple batteries in the battery pack via the DC / DC converter. Optionally, the charge / discharge control commands are generated based on the battery pack's SOC and power scheduling commands from external devices. Further details regarding this process can be found in the aforementioned section. Figure 1 The relevant descriptions are omitted here.

[0088] It should be noted here that... Figure 2 It can be seen as based on Figure 1 A schematic diagram of the improved energy storage system. Figure 2 Compared to energy storage systems in China Figure 1 Improvements to the medium-sized energy storage system include: Figure 2 The controller of the energy storage system can calibrate the battery's state of charge (SOC). Figure 2 Compared to Figure 1 For similarities, please refer to the aforementioned [references to] Figure 1 The description of the embodiments in this application will not be repeated.

[0089] The foregoing Figure 2As shown, the connection relationship of the batteries in the parallel battery pack is fixed, which leads to a waste of power in each battery within the parallel battery pack. This is because when the batteries in the parallel battery pack are considered as a whole and connected in series with other batteries not connected in parallel (series battery packs), the total capacity of the batteries in the parallel battery pack is greater than the capacity of a single battery in the series battery pack. This means that the usable capacity of the multiple batteries depends on the capacity of the single battery in the series battery pack. When a single battery in the series battery pack is fully charged or discharged first, even if the batteries in the parallel battery pack still have remaining capacity, the multiple batteries in the battery pack must stop charging and discharging, resulting in a waste of power in each battery within the parallel battery pack.

[0090] To fully utilize the power of each battery in a parallel battery pack, some possible implementations refer to... Figure 5 and Figure 6 As shown, the connection relationship of the batteries in the parallel battery pack is not fixed, allowing for adjustments when calibration is required. Figure 5 The serial switching shown is Figure 6 The parallel connection shown also allows for switching from [the previous connection] after calibration is complete. Figure 6 The parallel switching shown is Figure 5 The series connection shown.

[0091] Optional, see reference Figure 5 and Figure 6 As shown, the batteries in the parallel battery pack can be connected in parallel via conductive busbar 1 (e.g., an aluminum busbar), and can be connected in series via conductive busbar 2 (e.g., an aluminum busbar). Conductive busbar 1 connects the positive terminals of the batteries in the parallel battery pack to each other, and the negative terminals to each other. For example, the conductive busbars between the positive terminals of batteries 2 and 3, and between the negative terminals of batteries 2 and 3, can both be conductive busbar 1 for parallel connection. Conductive busbar 2 connects the positive and negative terminals of the batteries in the parallel battery pack sequentially, switching to a series battery pack. For example, the conductive busbars between the negative terminal of battery 2 and the positive terminal of battery 3 can both be conductive busbar 2 for series connection. Both conductive busbar 1 and conductive busbar 2 are equipped with isolating switches to control the opening and closing of the conductive busbars. These isolating switches include, but are not limited to, circuit breakers, relays, etc.

[0092] The conduction states of busbar 1 and busbar 2 are opposite, which means that at the same time, the connection mode of each battery in the parallel battery pack is either parallel or switched to series.

[0093] Continue to refer to Figure 5 and Figure 6 The conduction states of conductor 1 and conductor 2 are controlled by a controller (e.g., a main controller). The controller can set the conduction states of conductor 1 and conductor 2 based on whether battery SOC calibration is required. Figure 5 As shown, multiple batteries in the default battery pack are connected in series. In this case, the controller issues a switch control command to open both disconnecting switches Q1 and Q2 on conductor 1, and turn on (close) disconnecting switch Q2 on conductor 2. Optionally, this switch control command is generated by the main controller and transmitted to the battery controller, which then executes the switch control command.

[0094] Here, the default is that multiple batteries in the battery pack are connected in series, including when all batteries in the battery pack are fully charged.

[0095] In a battery pack with multiple batteries connected in series, when these batteries are charged and discharged through the DC bus they are connected to, the SOC (State of Charge) of the batteries obtained by the controller is obtained using the ampere-hour integration method. As charging and discharging proceeds, the error in the SOC obtained by the controller gradually accumulates. At this point, the controller is also used to, upon determining that multiple batteries have stopped charging and discharging through the DC bus they are connected to, adjust the SOC of each battery in the parallel battery pack (e.g., ...). Figure 5 Battery 2 and Figure 5 The battery in section 3) is switched from series connection to parallel connection. For example... Figure 6 As shown, the controller issues a switch control command to turn on (close) both isolating switches Q1 and Q2 on conductor 1, and to open isolating switch Q2 on conductor 2, thereby switching the batteries in the parallel battery pack from series connection to parallel connection. When a parallel battery pack is introduced among multiple batteries in the battery stack, the controller performs a calibration operation to calibrate the SOC of the series batteries. This calibration operation includes: the controller calibrating the SOC of the batteries in the series battery pack (referred to as series batteries, such as battery 1) based on the SOC changes caused by charging and discharging of the batteries in the parallel battery pack (referred to as parallel batteries, such as battery 2). For details regarding the calibration operation, please refer to the aforementioned descriptions; they will not be repeated here.

[0096] The controller is configured to switch the batteries in a parallel battery pack from series connection to parallel connection when it is determined that multiple batteries have stopped charging and discharging through the DC bus they are connected to. This includes: if a first condition is met, when it is determined that multiple batteries have stopped charging and discharging through the DC bus they are connected to, the controller switches the batteries in the parallel battery pack (e.g., ...) from series connection to parallel connection. Figure 5 Battery 2 and Figure 5 The battery 3) in the battery pack is switched from series connection to parallel connection. The first condition includes at least one of the following: the state of charge (SOC) of the battery pack is less than a first threshold (e.g., 90%), and the multiple batteries in the battery pack are continuously charged and discharged through the DC bus to which they are connected for a first time.

[0097] When the first condition is met, it indicates that the SOC error obtained by the controller as charging and discharging proceeds has become significant, or will become significant. For example, if multiple batteries in the battery pack have been continuously charging and discharging for a first time (an example of meeting the first condition) before ceasing charging and discharging through their connected DC bus, the SOC obtained by the controller can be detected based on the ampere-hour integration method. However, the error of the ampere-hour integration method gradually accumulates during the first time, eventually leading to a significant error. If, after the first condition is met, multiple batteries continue to charge and discharge through their connected DC bus, the SOC detected based on the time integration method will become increasingly larger. As another example, if the SOC of the battery pack is less than a first threshold (e.g., 90%), and multiple batteries in the battery pack stop charging and discharging through their connected DC bus and the SOC is detected using an open-circuit detection method, the aforementioned plateau region will appear, making it impossible to accurately obtain the battery's SOC, resulting in a significant error.

[0098] Therefore, the controller will initiate the calibration operation only if the first condition is met. If the first condition is not met, it indicates that the error is small and negligible, and the controller may not initiate the calibration operation, instead switching the batteries in the parallel battery pack to series connection and then connecting them in series with the batteries in the series battery pack. In this way, all the batteries in the battery pack are connected in series, which helps to fully utilize the power of each battery in the parallel battery pack, allowing for balanced battery SOC calibration and efficient use of the power of each battery in the parallel battery pack.

[0099] Optionally, after switching the batteries in the parallel battery pack from series connection to parallel connection when it is determined that multiple batteries in the battery pack have stopped charging and discharging through the DC bus they are connected to, the controller is further configured to switch the batteries in the parallel battery pack from parallel connection to series connection again when it is determined that multiple batteries have stopped charging and discharging through the DC bus they are connected to. This indicates that after the calibration operation is performed, when the SOC of the batteries obtained by the controller is accurate (accumulated errors have been eliminated) to support the precise management of battery charging and discharging by the energy storage system, the controller then restores the batteries in the parallel battery pack to series connection to fully utilize the capacity of each battery in the parallel battery pack.

[0100] As can be seen from the foregoing, when the connection of each battery in the parallel battery pack supports series-parallel switching, the controller can dynamically perform calibration operations to avoid the continuous amplification of the cumulative error of the battery SOC, while also taking into account the full utilization of the power of each battery in the parallel battery pack.

[0101] Optionally, before switching the batteries in the parallel battery pack from parallel to series connection, the controller also determines that the calibrated SOC of the parallel batteries is equal to the SOC of the series batteries. This operation ensures that when the batteries in the battery pack are restored to a series connection, the SOC of each battery in the battery pack is consistent. This also ensures that the voltage of each battery in the battery pack remains consistent during subsequent charging and discharging processes, avoiding voltage imbalance problems caused by inconsistent SOCs after switching from parallel to series connection.

[0102] Optionally, after determining that multiple batteries in the battery pack have stopped charging and discharging through the DC bus they are connected to, if the SOC of the series batteries and the SOC of the parallel batteries are inconsistent, before the controller switches each battery in the parallel battery pack from parallel to series, the controller is also used to control the series batteries to discharge through a non-DC bus, or to control each battery in the parallel battery pack to discharge through a non-DC bus, so that the calibrated SOC of the series batteries is equal to the SOC of the parallel batteries.

[0103] The controller is used to control the discharge of each battery in a series-connected battery pack or a parallel-connected battery pack through a non-DC bus, including: when the calibrated SOC of the series-connected battery is greater than the SOC of the parallel-connected battery, the controller controls the series-connected battery to discharge through the non-DC bus; when the calibrated SOC of the series-connected battery is less than the SOC of the parallel-connected battery, the controller controls the discharge of each battery in the parallel-connected battery pack through the non-DC bus.

[0104] The battery discharges on the non-DC bus, including discharging through a resistor connected to it, consuming electrical energy through the resistor. The circuit between the battery and the resistor is usually open. When balancing is required, the controller can control the circuit between the battery and the resistor to open; the opening time depends on the SOC difference between the series-connected and parallel-connected batteries.

[0105] It should be noted that the series-parallel switching of individual batteries in a parallel battery pack can only be performed when multiple batteries have stopped charging and discharging through the DC bus they are connected to. This avoids the influence of current when the isolating switch switches from open to closed, making the switching operation safer and more controllable.

[0106] It should be noted here that... Figure 5 and Figure 6 It can be seen as based on Figure 1 A schematic diagram of the improved energy storage system. Figure 5 and Figure 6 Compared to energy storage systems in China Figure 1 Improvements to the medium-sized energy storage system include: Figure 5 and Figure 6 The controller of the energy storage system can dynamically calibrate the SOC of the battery. Figure 5 and Figure 6 Compared to Figure 1 For similarities, please refer to the aforementioned [references to] Figure 1 The description of the embodiments in this application will not be repeated.

[0107] It should be understood that, Figure 2 , Figure 5 and Figure 6 The energy storage system shown is merely an example; in reality, an energy storage system may include more or fewer components. Figure 2 , Figure 5 and Figure 6 The different components shown can also be combined. For example, a DC / DC converter can be combined into a PCS. Figure 2 , Figure 5 and Figure 6 The energy storage system shown should not be construed as limiting the embodiments of this application.

[0108] This application also provides a state-of-charge calibration method, applied to the aforementioned energy storage system, specifically to a controller within the energy storage system. The energy storage system also includes a battery pack containing multiple batteries. The multiple batteries are connected in parallel (e.g., Figure 2 Battery 2) and other parallel batteries (e.g. Figure 2 After battery 3) is connected in parallel, it is connected in series with other batteries in the plurality of batteries, which include series-connected batteries (e.g., batteries connected in series with each other). Figure 2 The state-of-charge (SOC) calibration method in this application embodiment includes: controlling the multiple batteries to charge and discharge through the DC bus to which they are connected, determining the SOC change of the parallel batteries due to charging and discharging (e.g., ΔSOC2 mentioned above), and determining the SOC of the series batteries due to the charging and discharging change to a first SOC (which is the SOC detection value of the series batteries, such as SOC1# mentioned above). The controller is also used to calibrate the SOC of the series batteries from the first SOC to a second SOC based on the SOC change of the parallel batteries.

[0109] The process of the SOC of the series-connected battery changing to the first SOC due to charging and discharging includes: the controller determining that the SOC of the series-connected battery changes from the third SOC (e.g., the aforementioned SOC1) to the first SOC due to charging and discharging.

[0110] Based on the SOC change of the parallel batteries, the SOC of the series batteries is calibrated from a first SOC to a second SOC. This includes: the controller determining a fourth SOC (an estimated value of the series batteries' SOC, such as SOC′1# mentioned above) using a third SOC (e.g., SOC1 mentioned above), the SOC change of the parallel batteries, and the SOC change factor N between the series and parallel batteries during charging and discharging. Then, the controller determines the calibrated second SOC, which is a value between the first and fourth SOCs. A description of this process can be found in the previous descriptions of steps S101-S104, and will not be repeated here.

[0111] This application also provides an energy storage system, which includes a controller and a memory. The memory is coupled to the controller and is used to store computer program code, which includes computer instructions. The controller calls the computer instructions to cause the energy storage system to execute the state of charge calibration method in this application embodiment.

[0112] The various embodiments of this application can be combined arbitrarily to achieve different technical effects.

[0113] In the description of the embodiments of this application, unless otherwise stated, " / " means "or". For example, A / B can mean A or B. The "and / or" in the text is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, in the description of the embodiments of this application, "multiple" means two or more.

[0114] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. This program can be stored in a computer-readable storage medium, and when executed, it can include the processes described in the above method embodiments. The aforementioned storage medium includes various media capable of storing program code, such as ROM or random access memory (RAM), magnetic disks, or optical disks.

[0115] In summary, the above description is merely an embodiment of the technical solution of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made based on the disclosure of this application should be included within the scope of protection of this application.

Claims

1. An energy storage system, characterized by, The energy storage system comprises a controller and a battery pack, the battery pack comprising a plurality of batteries, first and second batteries of the plurality of batteries being connected in parallel, the first and second batteries being connected in series with other batteries of the plurality of batteries except the first and second batteries, the other batteries comprising a third battery, wherein The controller is configured to control the plurality of batteries to charge and discharge through a DC bus to which the plurality of batteries are connected, and determine a state of charge (SOC) variation of the first battery caused by charging and discharging. The controller is further configured to calibrate the SOC of the third battery based on the SOC variation of the first battery.

2. The energy storage system of claim 1, wherein, Before calibrating the SOC of the third battery, The controller is further configured to determine that the SOC of the third battery changes to a first SOC caused by charging and discharging. The controller is configured to calibrate the SOC of the third battery, comprising: The controller is configured to calibrate the SOC of the third battery from the first SOC to a second SOC based on the SOC variation of the first battery.

3. The energy storage system of claim 2, wherein The controller is further configured to determine that the SOC of the third battery changes to a first SOC caused by charging and discharging, comprising: The controller determines that the SOC of the third battery changes from a third SOC to the first SOC caused by charging and discharging; The controller is configured to calibrate the SOC of the third battery from the first SOC to a second SOC based on the SOC variation of the first battery, comprising: The controller determines the fourth SOC through the third SOC, the SOC variation of the first battery, and a SOC variation multiple N of the third battery and the first battery during charging and discharging; The controller determines the calibrated second SOC, the second SOC being a value between the first SOC and the fourth SOC.

4. The energy storage system of claim 2, wherein, The fourth SOC and the third SOC satisfy: SOC4 = SOC3 + N x ΔSOC; wherein the SOC4 is the fourth SOC, the SOC3 is the third SOC, the N is a total number of batteries of the first battery and the second battery, the second battery is at least one battery connected in parallel with the first battery, and the ΔSOC is the SOC variation of the first battery.

5. The energy storage system of any one of claims 1-4, wherein The controller is further configured to take the second SOC as the SOC of the battery pack.

6. The energy storage system of any one of claims 1-5, wherein, Before the first and second batteries of the plurality of batteries are connected in parallel, The controller is further configured to switch the first and second batteries of the plurality of batteries connected in series from series connection to parallel connection when it is determined that the plurality of batteries stop charging and discharging through the DC bus to which the plurality of batteries are connected.

7. The energy storage system of claim 6, wherein, The first battery and the second battery are connected in parallel through a first conductive row and a second conductive row, the first conductive row is used to connect the first battery and the second battery in parallel, the second conductive row is used to connect the first battery and the second battery in series, a first switch is arranged on the first conductive row, a second switch is arranged on the second conductive row, and the first switch and the second switch are in opposite conducting states. The controller is further configured to switch the first battery and the second battery in series to parallel connection, including: The controller controls the first switch on the first conductive row to switch from off to on, and controls the second switch on the second conductive row to switch from on to off.

8. The energy storage system of claim 7, wherein, The controller is configured to switch the first battery and the second battery in series to parallel connection in a case where the plurality of batteries stop charging and discharging through the DC bus to which they are connected, including: If a first condition is met, the controller switches the first battery and the second battery in series to parallel connection in a case where the plurality of batteries stop charging and discharging through the DC bus to which they are connected; the first condition includes at least one of the following: the SOC of the battery pack is less than a first threshold, and the plurality of batteries have been continuously charging and discharging through the DC bus for a first time.

9. The energy storage system of claim 8, wherein, After the first battery and the second battery are connected in parallel, The controller is further configured to switch the first battery and the second battery from parallel connection back to series connection in a case where the plurality of batteries stop charging and discharging through the DC bus to which they are connected again.

10. The energy storage system of claim 9, wherein, Before the first battery and the second battery are switched from parallel connection to series connection, The controller is further configured to determine that the SOC of the third battery after calibration is equal to the SOC of the first battery.

11. The energy storage system of claim 10, wherein, Before the first battery and the second battery are switched from parallel connection to series connection, The controller is further configured to control the first battery and the second battery to discharge through a non-DC bus, or control the third battery to discharge through a non-DC bus, so that the SOC of the third battery after calibration is equal to the SOC of the first battery.

12. A state-of-charge calibration method, characterized by, The method is applied to an energy storage system, the energy storage system includes a battery pack, the battery pack includes a plurality of batteries, a first battery and a second battery in the plurality of batteries are connected in parallel, and the first battery and the second battery are connected in series with other batteries in the plurality of batteries except the first battery and the second battery, the other batteries include a third battery, and the method includes: Controlling the plurality of batteries to charge and discharge through a DC bus to which they are connected, and determining a state of charge (SOC) variation of the first battery caused by charging and discharging; Calibrating the SOC of the third battery based on the SOC variation of the first battery.

13. The method of claim 12, wherein, Before calibrating the SOC of the third battery, the method further includes: Determining that the SOC of the third battery changes to a first SOC due to charging and discharging; Calibrating the SOC of the third battery, specifically including: Calibrating the SOC of the third battery from the first SOC to a second SOC based on the SOC variation of the first battery.

14. The method of claim 13, wherein, The SOC of the third battery is determined to be a first SOC due to charging and discharging, specifically comprising: The SOC of the third battery is determined to change from a third SOC to the first SOC due to charging and discharging; Based on the SOC change amount of the first battery, the SOC of the third battery is calibrated from the first SOC to a second SOC, specifically comprising: The fourth SOC is determined through the third SOC, the SOC change amount of the first battery, and the SOC change multiple N of the third battery and the first battery during charging and discharging; The calibrated second SOC is determined, and the second SOC is a value between the first SOC and the fourth SOC.

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