Energy storage system, state of charge detection device, and state of charge detection method

Abstract

The embodiment of the invention provides an energy storage system, a state of charge detection device and a state of charge detection method, the energy storage system comprises a battery cluster, a power conversion circuit and a controller, and a calibration cell is connected in series between the battery cluster and the power conversion circuit. And the power conversion circuit is used for carrying out voltage transformation or inversion conversion on the input direct current and then outputting the direct current to a load. The controller calibrates a second charge state of the battery cluster according to the charge state variable quantity of the calibration battery core from the first moment to the second moment and the first charge state of the battery cluster, the second moment is after the first moment, and the first charge state is the charge state of the battery cluster at the first moment; the second state of charge is the state of charge of the battery cluster at the second moment. At the second moment, the change rate of the voltage at the two ends of the calibration battery cell is a characteristic value of the change rate of the voltage at the two ends of the calibration battery cell, and the characteristic value is a maximum value, a minimum value or an inflection point value. By adopting the method and the device, accumulative errors in the state of charge estimation process can be reduced, and the state of charge detection precision is high.

Description

Technical Field

[0001] The present application relates to the field of power electronics, and in particular to an energy storage system, a state of charge detection device, and a state of charge detection method. Background Art

[0002] State of Charge (SOC) is an important state in the energy storage system, providing an important reference for the safety management, charge and discharge control, energy management and other functions of the energy storage system. In order to ensure the normal operation of the energy storage system, high-precision state of charge estimation is the key. In the prior art, the state of charge is usually estimated by the ampere-hour integration method, the open circuit voltage method, the internal resistance method, and the model-based estimation method. Among them, the open circuit voltage method has a large error in the estimation of lithium iron phosphate batteries due to inaccurate estimation of the voltage platform area. The integration of the ampere-hour integration method is easily affected by the degree of battery aging, the current battery pack temperature, and the performance of the hardware sampling circuit, so that there will be cumulative errors in the estimation process, and the state of charge error can only be corrected at the beginning and end of charging and discharging. If the energy storage system is in a shallow charge and discharge working mode for a long time, the error calibration cannot be triggered. Other model-based estimation methods, such as fuzzy logic and artificial neural networks, require a lot of data support and the model is complex. Summary of the invention

[0003] The embodiments of the present application provide an energy storage system, a state of charge detection device, and a state of charge detection method, which reduce the cumulative error in the state of charge estimation process and avoid the problem of only being able to correct the state of charge error at the beginning and end of the battery cluster charging and discharging. The state of charge detection has high accuracy and strong applicability.

[0004] In a first aspect, the present application provides an energy storage system, which includes a battery cluster, a power conversion circuit, and a controller. A calibration cell is connected in series between the battery cluster and the power conversion circuit. The power conversion circuit is used to transform or invert the input direct current and then output it to the load. The controller is used to calibrate the second state of charge of the battery cluster according to the change in the state of charge of the calibration cell from the first moment to the second moment and the first state of charge of the battery cluster. The second moment is after the first moment, the first state of charge is the state of charge of the battery cluster at the first moment, the second state of charge is the state of charge of the battery cluster at the second moment, and at the second moment, the rate of change of the voltage across the calibration cell is a characteristic value of the rate of change of the voltage across the calibration cell, and the characteristic value is a maximum value, a minimum value, or an inflection point value.

[0005] In the present application, at the second moment when the rate of change of the voltage across the calibration cell reaches a characteristic value, the controller in the energy storage system calibrates the second state of charge of the battery cluster according to the change in the state of charge of the calibration cell from the first moment to the second moment and the first state of charge of the battery cluster, wherein the second moment is after the first moment, and the first state of charge is the state of charge of the battery cluster at the first moment, and the second state of charge is the state of charge of the battery cluster at the second moment. Specifically, the controller may use the difference between the fourth state of charge and the third state of charge as the change in state of charge, the fourth state of charge being the state of charge of the calibration cell corresponding to the maximum value of the rate of change of the voltage across the calibration cell, and since the state of charge corresponding to the characteristic value on the curve of the rate of change of the calibration cell voltage is relatively stable, the problem of error caused by the state of charge corresponding to the characteristic value being disturbed by operating conditions such as temperature and cell attenuation and aging can be avoided, and the state of charge is used for subsequent calibration of the state of charge of the battery cluster, thereby improving the calibration reliability of the state of charge of the battery cluster, solving the cumulative error in the state of charge estimation method such as the ampere-hour integration method, and avoiding the problem of being able to correct the state of charge error only at the beginning and end of charging and discharging of the battery cluster, and having high accuracy in state of charge detection and strong applicability.

[0006] In a possible implementation, the controller is used to obtain a target change amount according to the state of charge change amount, the capacity of the battery cluster, and the capacity of the calibration cell, and calibrate the second state of charge of the battery cluster to the first state of charge plus the target change amount. Here, the controller obtains the target change amount according to the state of charge change amount of the calibration cell from the first moment to the second moment, the capacity of the battery cluster, and the capacity of the calibration cell, and calibrates the second state of charge of the battery cluster to the first state of charge plus the target change amount, eliminating the cumulative error in the state of charge estimation method using the ampere-hour integration method and other methods.

[0007] In one possible implementation, the controller is used to multiply the ratio of the capacity of the calibration cell to the capacity of the battery cluster by the charge state change to obtain a target change. The target change is obtained by combining the ratio of the capacity of the calibration cell to the capacity of the battery cluster, and the second state of charge of the battery cluster is calibrated to the first state of charge plus the target change, so as to more accurately calibrate the second state of charge of the battery cluster.

[0008] In a possible implementation, there are multiple calibration cells, and the multiple calibration cells are connected in parallel. Here, the battery cluster is connected in series with the multiple calibration cells in parallel, and the total capacity of the multiple calibration cells in parallel is higher, which can prevent the calibration cells from being overcharged during the charging and discharging process and extend the cycle life of the calibration cells.

[0009] In a possible implementation, a bypass switch is connected in parallel at both ends of the calibration cell, and the bypass switch is used to be turned on when the calibration cell fails. When the calibration cell fails or a spare part is replaced, the branch where the calibration cell is located can be short-circuited by turning on the bypass switch without affecting the operation of the entire energy storage system.

[0010] In a possible implementation, the controller is also used to control the state of charge of the calibration cell to change within a set interval before calibrating the second state of charge of the battery cluster to obtain the rate of change of the voltage across the calibration cell during the change of the state of charge of the calibration cell. Based on the change of the state of charge of the calibration cell within the set interval, the change rates of multiple voltages corresponding to the multiple states of charge of the calibration cell are obtained. The characteristic value of the change rate of the voltage across the calibration cell during the change process and the state of charge of the calibration cell corresponding to the characteristic value are obtained. The change amount of the state of charge is the difference between the fourth state of charge and the third state of charge, the fourth state of charge is the state of charge of the calibration cell corresponding to the characteristic value, and the third state of charge is the state of charge of the calibration cell at the first moment. Since the state of charge on the horizontal axis corresponding to the maximum, minimum and inflection point values ​​on the voltage change rate curve is relatively stable, the maximum, minimum and inflection point values ​​can realize stable marking of the state of charge, that is, the state of charge corresponding to the maximum, minimum and inflection point values ​​are stored in a preset table, etc., for subsequent calibration of the state of charge of the battery cluster. The state of charge corresponding to the subsequent maximum, minimum and inflection point values ​​will not change much, avoiding the problem of errors caused by the state of charge corresponding to the maximum, minimum and inflection point values ​​being disturbed by temperature and battery cell attenuation and aging conditions. The above-mentioned state of charge is used for subsequent calibration of the state of charge of the battery cluster, thereby improving the calibration reliability of the state of charge of the battery cluster.

[0011] In a possible implementation, the amount of change in the state of charge is the difference between the fourth state of charge and the third state of charge, the fourth state of charge is the state of charge of the calibration cell corresponding to the characteristic value, and the third state of charge is the state of charge of the calibration cell at the first moment. The fourth state of charge is obtained according to the characteristic value and the preset table, and the preset table includes the characteristic value and the state of charge corresponding to the characteristic value. Since the horizontal coordinate state of charge corresponding to the maximum value, minimum value and inflection point value on the voltage change rate change curve has a relatively stable characteristic, the maximum value, minimum value and inflection point value can realize a stable marking of the state of charge, that is, the state of charge corresponding to the maximum value, minimum value and inflection point value is stored in the preset table, etc., for subsequent calibration of the state of charge of the battery cluster, and the state of charge corresponding to the subsequent maximum value, minimum value and inflection point value will not change too much, avoiding the problem of error caused by the state of charge corresponding to the maximum value, minimum value and inflection point value being disturbed by temperature and cell attenuation aging conditions, and the above-mentioned state of charge is used for subsequent calibration of the state of charge of the battery cluster, thereby improving the calibration reliability of the state of charge of the battery cluster.

[0012] In a possible implementation, the calibration cell is a cell composed of a polyanion sodium positive electrode. Specifically, the polyanion sodium positive electrode may include sodium vanadium phosphate, sodium iron pyrophosphate, composite sodium iron pyrophosphate, sodium iron sulfate, etc. By utilizing the slow decay characteristics of the polyanion sodium positive electrode material, the horizontal axis charge state corresponding to the maximum value, minimum value and inflection point value on the voltage change rate change curve is not easy to fluctuate, thereby improving the calibration reliability of the charge state of the battery cluster.

[0013] In a second aspect, the present application provides a state of charge detection device, the state of charge detection device includes a controller and a calibration cell, the calibration cell is used to be connected in series with the battery. The controller is used to calibrate the second state of charge of the battery according to the change in the state of charge of the calibration cell from the first moment to the second moment and the first state of charge of the battery, the second moment is after the first moment, the first state of charge is the state of charge of the battery at the first moment, the second state of charge is the state of charge of the battery at the second moment, and at the second moment, the rate of change of the voltage across the calibration cell is a characteristic value of the rate of change of the voltage across the calibration cell, and the characteristic value is a maximum value, a minimum value or an inflection point value.

[0014] In the present application, at the second moment when the rate of change of the voltage across the calibration cell reaches a characteristic value, the controller in the state of charge detection device calibrates the second state of charge of the battery cluster according to the change in the state of charge of the calibration cell from the first moment to the second moment and the first state of charge of the battery cluster, wherein the second moment is after the first moment, and the first state of charge is the state of charge of the battery cluster at the first moment, and the second state of charge is the state of charge of the battery cluster at the second moment. Specifically, the controller may use the difference between the fourth state of charge and the third state of charge as the change in state of charge, the fourth state of charge being the state of charge of the calibration cell corresponding to the maximum value of the rate of change of the voltage across the calibration cell, and since the state of charge corresponding to the characteristic value on the curve of the rate of change of the calibration cell voltage is relatively stable, the problem of error caused by the state of charge corresponding to the characteristic value being disturbed by operating conditions such as temperature and cell attenuation and aging can be avoided, and the state of charge is used for subsequent calibration of the state of charge of the battery cluster, thereby improving the calibration reliability of the state of charge of the battery cluster, solving the cumulative error in the state of charge estimation method such as the ampere-hour integration method, and avoiding the problem of being able to correct the state of charge error only at the beginning and end of charging and discharging of the battery cluster, and having high accuracy in state of charge detection and strong applicability.

[0015] In a possible implementation, the controller is used to obtain a target change amount according to the state of charge change amount, the capacity of the battery, and the capacity of the calibration cell, and calibrate the second state of charge of the battery to the first state of charge plus the target change amount. The controller obtains the target change amount according to the state of charge change amount of the calibration cell from the first moment to the second moment, the capacity of the battery cluster, and the capacity of the calibration cell, and calibrates the second state of charge of the battery cluster to the first state of charge plus the target change amount, eliminating the cumulative error in the state of charge estimation method using the ampere-hour integration method and other methods.

[0016] In one possible implementation, the controller is used to multiply the ratio of the capacity of the calibration cell to the capacity of the battery by the charge state change to obtain a target change. The target change is obtained by combining the ratio of the capacity of the calibration cell to the capacity of the battery cluster, and the second state of charge of the battery cluster is calibrated to the first state of charge plus the target change, so as to more accurately calibrate the second state of charge of the battery cluster.

[0017] In a possible implementation, the controller is also used to control the state of charge of the calibration cell to change within a set interval before calibrating the second state of charge of the battery to obtain the rate of change of the voltage across the calibration cell during the change of the state of charge of the calibration cell. Based on the change of the state of charge of the calibration cell within the set interval, the change rates of multiple voltages corresponding to the multiple states of charge of the calibration cell are obtained, and the characteristic value of the change rate of the voltage across the calibration cell during the change process and the state of charge of the calibration cell corresponding to the characteristic value are obtained. The change in the state of charge is the difference between the fourth state of charge and the third state of charge, the fourth state of charge is the state of charge of the calibration cell corresponding to the characteristic value, and the third state of charge is the state of charge of the calibration cell at the first moment. Since the state of charge on the horizontal axis corresponding to the maximum, minimum and inflection point values ​​on the voltage change rate curve is relatively stable, the maximum, minimum and inflection point values ​​can realize stable marking of the state of charge, that is, the state of charge corresponding to the maximum, minimum and inflection point values ​​are stored in a preset table, etc., for subsequent calibration of the state of charge of the battery cluster. The state of charge corresponding to the subsequent maximum, minimum and inflection point values ​​will not change much, avoiding the problem of errors caused by the state of charge corresponding to the maximum, minimum and inflection point values ​​being disturbed by temperature and battery cell attenuation and aging conditions. The above-mentioned state of charge is used for subsequent calibration of the state of charge of the battery cluster, thereby improving the calibration reliability of the state of charge of the battery cluster.

[0018] In a possible implementation, the amount of change in the state of charge is the difference between the fourth state of charge and the third state of charge, the fourth state of charge is the state of charge of the calibration cell corresponding to the characteristic value, and the third state of charge is the state of charge of the calibration cell at the first moment. The fourth state of charge is obtained according to the characteristic value and the preset table, and the preset table includes the characteristic value and the state of charge corresponding to the characteristic value. Since the horizontal coordinate state of charge corresponding to the maximum value, minimum value and inflection point value on the voltage change rate change curve has a relatively stable characteristic, the maximum value, minimum value and inflection point value can realize a stable marking of the state of charge, that is, the state of charge corresponding to the maximum value, minimum value and inflection point value is stored in the preset table, etc., for subsequent calibration of the state of charge of the battery cluster, and the state of charge corresponding to the subsequent maximum value, minimum value and inflection point value will not change too much, avoiding the problem of error caused by the state of charge corresponding to the maximum value, minimum value and inflection point value being disturbed by temperature and cell attenuation aging conditions, and the above-mentioned state of charge is used for subsequent calibration of the state of charge of the battery cluster, thereby improving the calibration reliability of the state of charge of the battery cluster.

[0019] In a possible implementation, the calibration cell is a cell composed of a polyanion sodium positive electrode. Specifically, the polyanion sodium positive electrode may include sodium vanadium phosphate, sodium iron pyrophosphate, composite sodium iron pyrophosphate, sodium iron sulfate, etc. By utilizing the slow decay characteristics of the polyanion sodium positive electrode material, the horizontal axis charge state corresponding to the maximum value, minimum value and inflection point value on the voltage change rate change curve is not easy to fluctuate, thereby improving the calibration reliability of the charge state of the battery cluster.

[0020] In a third aspect, the present application provides a state of charge detection method, the method comprising calibrating the second state of charge of the battery based on the change in the state of charge of the calibration cell from a first moment to a second moment and the first state of charge of the battery, wherein the calibration cell is connected in series with the battery, the second moment is after the first moment, the first state of charge is the state of charge of the battery at the first moment, the second state of charge is the state of charge of the battery at the second moment, and at the second moment, the rate of change of the voltage across the calibration cell is a characteristic value of the rate of change of the voltage across the calibration cell, and the characteristic value is a maximum value, a minimum value or an inflection point value.

[0021] In the present application, at the second moment when the rate of change of the voltage across the calibration cell reaches a characteristic value, the second state of charge of the battery cluster is calibrated according to the change in the state of charge of the calibration cell from the first moment to the second moment and the first state of charge of the battery cluster, wherein the second moment is after the first moment, and the first state of charge is the state of charge of the battery cluster at the first moment, and the second state of charge is the state of charge of the battery cluster at the second moment. Specifically, the difference between the fourth state of charge and the third state of charge can be used as the change in state of charge. The above-mentioned fourth state of charge is the state of charge of the calibration cell corresponding to the maximum value of the rate of change of the voltage across the calibration cell. Since the state of charge corresponding to the characteristic value on the curve of the rate of change of the calibration cell voltage is relatively stable, the problem of error caused by the state of charge corresponding to the characteristic value being disturbed by operating conditions such as temperature and cell attenuation and aging can be avoided. The above-mentioned state of charge is used for subsequent calibration of the state of charge of the battery cluster, which improves the calibration reliability of the state of charge of the battery cluster, solves the cumulative error in the state of charge estimation method such as the ampere-hour integration method, and avoids the problem of being able to correct the state of charge error only at the beginning and end of charging and discharging of the battery cluster. The state of charge detection has high accuracy and strong applicability.

[0022] In a possible implementation, the second state of charge of the battery is calibrated according to the change in the state of charge of the calibration cell from the first moment to the second moment and the first state of charge of the battery, including obtaining a target change according to the change in the state of charge, the capacity of the battery and the capacity of the calibration cell, and calibrating the second state of charge of the battery to the first state of charge plus the target change. The target change is obtained according to the change in the state of charge of the calibration cell from the first moment to the second moment, the capacity of the battery cluster and the capacity of the calibration cell, and the second state of charge of the battery cluster is calibrated to the first state of charge plus the target change, eliminating the cumulative error in the state of charge estimation method using the ampere-hour integration method and the like.

[0023] In a possible implementation, a target change is obtained according to the state of charge change, the capacity of the battery, and the capacity of the calibration cell, including multiplying the ratio of the capacity of the calibration cell to the capacity of the battery by the state of charge change to obtain the target change. The target change is obtained by combining the ratio of the capacity of the calibration cell to the capacity of the battery cluster, and the second state of charge of the battery cluster is calibrated to the first state of charge plus the target change, so as to more accurately calibrate the second state of charge of the battery cluster.

[0024] In a possible implementation, before calibrating the second state of charge of the battery, the method further includes controlling the state of charge of the calibration cell to change within a set interval to obtain a rate of change of the voltage across the calibration cell during the change of the state of charge of the calibration cell. Based on the change of the state of charge of the calibration cell within the set interval, the rates of change of multiple voltages corresponding to multiple states of charge of the calibration cell are obtained, and a characteristic value in the rate of change of the voltage across the calibration cell during the change process, as well as the state of charge of the calibration cell corresponding to the characteristic value, are obtained. The change in the state of charge is the difference between the fourth state of charge and the third state of charge, the fourth state of charge is the state of charge of the calibration cell corresponding to the characteristic value, and the third state of charge is the state of charge of the calibration cell at the first moment. Since the state of charge on the horizontal axis corresponding to the maximum, minimum and inflection point values ​​on the voltage change rate curve is relatively stable, the maximum, minimum and inflection point values ​​can realize stable marking of the state of charge, that is, the state of charge corresponding to the maximum, minimum and inflection point values ​​are stored in a preset table, etc., for subsequent calibration of the state of charge of the battery cluster. The state of charge corresponding to the subsequent maximum, minimum and inflection point values ​​will not change much, avoiding the problem of errors caused by the state of charge corresponding to the maximum, minimum and inflection point values ​​being disturbed by temperature and battery cell attenuation and aging conditions. The above-mentioned state of charge is used for subsequent calibration of the state of charge of the battery cluster, thereby improving the calibration reliability of the state of charge of the battery cluster.

[0025] In a possible implementation, the amount of change in the state of charge is the difference between the fourth state of charge and the third state of charge, the fourth state of charge is the state of charge of the calibration cell corresponding to the characteristic value, and the third state of charge is the state of charge of the calibration cell at the first moment. The fourth state of charge is obtained according to the characteristic value and the preset table, and the preset table includes the characteristic value and the state of charge corresponding to the characteristic value. Since the horizontal coordinate state of charge corresponding to the maximum value, minimum value and inflection point value on the voltage change rate change curve has a relatively stable characteristic, the maximum value, minimum value and inflection point value can realize a stable marking of the state of charge, that is, the state of charge corresponding to the maximum value, minimum value and inflection point value is stored in the preset table, etc., for subsequent calibration of the state of charge of the battery cluster, and the state of charge corresponding to the subsequent maximum value, minimum value and inflection point value will not change too much, avoiding the problem of error caused by the state of charge corresponding to the maximum value, minimum value and inflection point value being disturbed by temperature and cell attenuation aging conditions, and the above-mentioned state of charge is used for subsequent calibration of the state of charge of the battery cluster, thereby improving the calibration reliability of the state of charge of the battery cluster.

[0026] In a possible implementation, the calibration cell is a cell composed of a polyanion sodium positive electrode. Specifically, the polyanion sodium positive electrode may include sodium vanadium phosphate, sodium iron pyrophosphate, composite sodium iron pyrophosphate, sodium iron sulfate, etc. By utilizing the slow decay characteristics of the polyanion sodium positive electrode material, the horizontal axis charge state corresponding to the maximum value, minimum value and inflection point value on the voltage change rate change curve is not easy to fluctuate, thereby improving the calibration reliability of the charge state of the battery cluster. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of an application scenario of the energy storage system provided by this application;

[0028] Figure 2 is a schematic diagram of another application scenario of the energy storage system provided by the present application;

[0029] Figure 3 is a schematic diagram of another application scenario of the energy storage system provided by the present application;

[0030] Figure 4 It is a curve diagram of the relationship between the state of charge and voltage change rate of the calibration cell provided by the present application;

[0031] Figure 5 is another curve diagram of the relationship between the state of charge and the voltage change rate of the calibration cell provided in the present application;

[0032] Figure 6 is another curve diagram of the relationship between the state of charge and the voltage change rate of the calibration cell provided in the present application;

[0033] Figure 7 It is a flow chart of the charge state detection method provided in this application. DETAILED DESCRIPTION

[0034] See also Figure 1 , Figure 1 It is a schematic diagram of an application scenario of the energy storage system provided by the present application. The energy storage system provided by the present application may include multiple battery clusters. Among them, each battery cluster may include multiple battery packs connected in series, and the multiple battery packs connected in series are connected to one end of the power conversion circuit. The other end of each power conversion circuit is connected in parallel to connect one end of the converter, and the other end of the converter is used to connect the AC load. Here, the power conversion circuit can be a DC conversion circuit or an inverter circuit. Taking the power conversion circuit as a DC conversion circuit as an example, the DC conversion circuit can perform voltage conversion (which can be boost, buck, etc.) on the DC power output by the battery pack in the battery cluster, and the converter performs inversion conversion on the DC power output by the DC conversion circuit, and outputs the AC power obtained after the inversion conversion to the AC load to power the AC load.

[0035] exist Figure 1 In the application scenario of the energy storage system shown, in the process of the energy storage system supplying power to the AC load, in order to ensure the normal operation of the energy storage system, the state of charge of each battery cluster in the energy storage system is detected and estimated, thereby providing an important reference for the safety management, charge and discharge control, energy management and other functions of the energy storage system. At present, the state of charge is usually estimated by the ampere-hour integration method, the open circuit voltage method, the internal resistance method, and the model-based estimation method. However, due to the inaccurate estimation of the voltage platform area, the open circuit voltage method has a large error in estimating the state of charge of the battery cluster. The estimation of the state of charge by the ampere-hour integration method is easily affected by the aging degree of the battery pack in the battery cluster, the current battery pack temperature, and the performance of the hardware sampling circuit, so that there will be cumulative errors in the estimation process, and the state of charge error can only be corrected at the beginning and end of the battery cluster charging and discharging. If the energy storage system is in a shallow charge and discharge working mode for a long time, the error calibration cannot be triggered. Other model-based estimation methods, such as fuzzy logic and artificial neural networks, require a large amount of data support and have complex models.

[0036] In the energy storage system provided in the present application, the energy storage system includes a battery cluster, a power conversion circuit and a controller. Among them, each battery cluster is connected to the power conversion circuit through at least one calibration cell. Specifically, each battery cluster is connected in series with at least one calibration cell. During the operation of the energy storage system, that is, when the battery packs in each battery cluster are charged or discharged, the calibration cells connected in series to the battery cluster are also charged or discharged synchronously, and when the state of charge of the calibration cell changes, the rate of change of the voltage across the calibration cell also changes accordingly. The rate of change of the voltage across the calibration cell can also be referred to as the first-order derivative of the voltage across the calibration cell to the state of charge, expressed as dV / dQ. The above-mentioned controller is used to detect the state of charge of the battery cluster and the state of charge of the calibration cell. At the same time, the controller also detects the rate of change of the voltage across the calibration cell. When it is detected that the rate of change of the voltage across the calibration cell reaches a characteristic value, the controller calibrates the state of charge of the battery cluster at the moment when the rate of change of the voltage across the calibration cell reaches the characteristic value. Specifically, the controller calibrates the second state of charge of the battery cluster according to the change in the state of charge of the calibration cell from the first moment to the second moment and the first state of charge of the battery cluster, wherein the second moment is after the first moment, and the first state of charge is the state of charge of the battery cluster at the first moment, and the second state of charge is the state of charge of the battery cluster at the second moment. Among them, at the second moment, the rate of change of the voltage across the calibration cell is a characteristic value of the rate of change of the voltage across the calibration cell, and the characteristic value may be a maximum value, a minimum value, or an inflection point value, and then, the controller calibrates the second state of charge at the second moment to the first state of charge plus the target change. Alternatively, when the difference between the first state of charge plus the target change and the second state of charge at the second moment exceeds a set threshold, the controller may calibrate the second state of charge at the second moment to the first state of charge plus the target change, thereby calibrating the state of charge of the battery cluster. Here, the controller calibrates the state of charge of the battery cluster based on the moment when the rate of change of the voltage across the calibration cell reaches the characteristic value, which solves the cumulative error in the state of charge estimation method using the ampere-hour integration method, and avoids the problem of correcting the state of charge error only at the beginning and end of the battery cluster charging and discharging. The state of charge detection has high accuracy and strong applicability.

[0037] In some feasible implementations, each battery cluster in the energy storage system is connected in series with a calibration cell, see Figure 2 , Figure 2 is another application scenario diagram of the energy storage system provided by this application. Figure 2As shown, the energy storage system may include multiple battery clusters, namely, battery cluster a, battery cluster b, ..., battery cluster n, a total of n battery clusters, battery cluster a, battery cluster b, ..., battery cluster n are respectively connected in series with calibration cell 11, calibration cell 21, ..., calibration cell n1, and calibration cell 11, calibration cell 21, ..., calibration cell n1 are respectively connected to DC conversion circuit a, DC conversion circuit b, ..., DC conversion circuit n. During the operation of the energy storage system, that is, when the battery packs in each battery cluster are charged or discharged, the calibration cells connected in series to the battery clusters are also charged or discharged synchronously, and when the charge state of the calibration cells changes, the rate of change of the voltage across the calibration cells also changes accordingly. Controller ( Figure 2 (not shown) is used to detect the state of charge of each battery cluster and the corresponding calibration cell. At the same time, the controller also detects the rate of change of the voltage across the calibration cell. For example, the controller detects the state of charge of the battery cluster a and the corresponding calibration cell 11, and detects the rate of change of the voltage across the calibration cell 11. When the controller detects that the state of charge of the battery cluster a is the first state of charge at the first moment, and detects that the rate of change of the voltage across the calibration cell 11 reaches the characteristic value at the second moment, the controller detects that the state of charge of the battery cluster a is the second state of charge at the second moment, and the second moment is after the first moment. Then, the controller obtains the target change amount according to the change amount of the state of charge of the calibration cell 11 from the first moment to the second moment, the capacity of the battery cluster a, and the capacity of the calibration cell 11, and calibrates the second state of charge of the battery cluster a to the first state of charge plus the target change amount, thereby calibrating the state of charge of the battery cluster a. It can be understood that the controller detects the state of charge of other battery clusters and the calibration process is similar to the above-mentioned detection process of the battery cluster a, and will not be repeated here. In addition, each calibration cell in the energy storage system can be connected in parallel with a bypass switch. When a calibration cell fails, such as failing to charge and discharge normally, or when a spare part is being replaced, the bypass switch can be turned on to short-circuit the branch where the calibration cell is located, without affecting the operation of the entire energy storage system. The controller calibrates the state of charge of the battery cluster based on the time when the rate of change of the voltage across the calibration cell reaches the characteristic value, that is, when the rate of change of the voltage across the calibration cell reaches the maximum value, minimum value or inflection point value, which solves the cumulative error in the state of charge estimation method using the ampere-hour integration method, and avoids the problem of only being able to correct the state of charge error at the beginning and end of the battery cluster charging and discharging. The state of charge detection has high accuracy and strong applicability.

[0038] Optionally, each of the above battery clusters may be connected in series with a plurality of calibration cells. For example, each battery cluster may be connected in series with a plurality of calibration cells connected in parallel. For example, a battery cluster connected in series with two calibration cells connected in parallel. Figure 3 , Figure 3 is another application scenario diagram of the energy storage system provided by this application. Figure 3As shown, the energy storage system may include multiple battery clusters, namely, battery cluster a, battery cluster b, ..., battery cluster n, a total of n battery clusters. Each battery cluster is connected in series with two parallel calibration cells, for example, battery cluster a is connected in series with parallel calibration cells 11 and 12, and battery cluster b is connected in series with parallel calibration cells 21 and 22. The connection method of other battery clusters and calibration cells is similar. Controller ( Figure 3 The controller (not shown) is used to detect the state of charge of each battery cluster and the corresponding calibration cell. At the same time, the controller also detects the rate of change of the voltage across the calibration cell. For example, the controller detects the state of charge of the battery cluster a and the corresponding calibration cells 11 and 12, and detects the rate of change of the voltage across the calibration cells 11 and 12. When the controller detects that the state of charge of the battery cluster a is the first state of charge at the first moment, and detects that the rate of change of the voltage across the calibration cells 11 and 12 reaches a characteristic value at the second moment, the controller detects that the state of charge of the battery cluster a is the second state of charge at the second moment, and the second moment is after the first moment. Then, the controller obtains the target change amount according to the change amount of the state of charge of the calibration cells 11 and 12 from the first moment to the second moment, the capacity of the battery cluster a, and the capacity of the calibration cells 11 and 12, and calibrates the second state of charge of the battery cluster a to the first state of charge plus the target change amount, thereby calibrating the state of charge of the battery cluster a. It is understandable that the controller detects the state of charge of other battery clusters and the calibration process is similar to the above-mentioned detection process of battery cluster a, which will not be repeated here. Here, each battery cluster is connected in series with multiple calibration cells in parallel. The total capacity of the multiple calibration cells in parallel is higher, which can avoid overcharging of the calibration cells during the charging and discharging process and extend the cycle life of the calibration cells. The controller calibrates the state of charge of the battery cluster based on the moment when the rate of change of the voltage across the calibration cell reaches the characteristic value, that is, when the rate of change of the voltage across the calibration cell reaches the maximum value, minimum value or inflection point value, which solves the cumulative error in the state of charge estimation method using the ampere-hour integration method, and avoids the problem of only being able to correct the state of charge error at the beginning and end of the battery cluster charging and discharging. The state of charge detection has high accuracy and strong applicability.

[0039] In some feasible embodiments, when it is detected that the rate of change of the voltage across the calibration cell reaches a characteristic value, the controller obtains the target change amount according to the change amount of the state of charge of the calibration cell from the first moment to the second moment, the capacity of the battery cluster, and the capacity of the calibration cell. Specifically, the controller multiplies the ratio of the capacity of the calibration cell to the capacity of the battery cluster by the above-mentioned change amount of the state of charge to obtain the target change amount. The above-mentioned characteristic value can be a maximum value, a minimum value, or an inflection point value. Taking the case where the rate of change of the voltage across the calibration cell reaches a maximum value as an example, the controller can use the difference between the fourth state of charge and the third state of charge as the change amount of the state of charge. The above-mentioned fourth state of charge is the state of charge of the calibration cell corresponding to the rate of change of the voltage across the calibration cell reaching a maximum value, and the above-mentioned third state of charge is the state of charge of the calibration cell at the first moment. The change amount of the state of charge is multiplied by the ratio of the capacity of the calibration cell to the capacity of the battery cluster to obtain the target change amount. Finally, the controller calibrates the state of charge of the battery cluster detected at the second moment when the rate of change of the voltage across the calibration cell reaches the characteristic value, that is, calibrates the second state of charge detected at the second moment to the first state of charge plus the target change amount. Calibration of the battery cluster state of charge corresponding to the moment when the rate of change of the voltage across the calibration cell reaches the characteristic value solves the cumulative error in the state of charge estimation method using the ampere-hour integration method, and avoids the problem of only being able to correct the state of charge error at the beginning and end of the battery cluster charge and discharge. The state of charge detection has high accuracy and strong applicability.

[0040] In some feasible implementations, before calibrating the second state of charge of the battery cluster, the controller is also used to control the state of charge of the calibration cell to change within a set interval to obtain the rate of change of the voltage across the calibration cell during the change of the state of charge of the calibration cell. Then, the controller obtains the rate of change of multiple voltages corresponding to multiple states of charge of the calibration cell based on the change of the state of charge of the calibration cell within the set interval, obtains the characteristic value in the rate of change of the voltage across the calibration cell during the change, and the state of charge of the calibration cell corresponding to the characteristic value. In other words, before calibrating the second state of charge of the battery cluster, the controller controls the state of charge of the calibration cell to change within a set interval to obtain the state of charge corresponding to the maximum value, minimum value or inflection point value when the rate of change of the voltage across the calibration cell is a maximum value, a minimum value or an inflection point value, so as to be used for the subsequent calibration of the state of charge of the battery cluster. Specifically, the controller can control the state of charge of the calibration cell from 0% to 100%, or from 100% to 0% before detecting the state of charge of the battery cluster, and obtain the rate of change of the voltage across the calibration cell when the calibration cell is any state of charge between 0% and 100%. Please also see Figure 4 , Figure 4 is a curve diagram showing the relationship between the state of charge and voltage change rate of the calibration cell provided in this application. Figure 4As shown, by controlling the charge state of the calibration cell from 0% to 100%, and detecting the change rate of the voltage across the calibration cell under different charge states, a curve diagram showing the change rate of voltage as a function of charge state is obtained. Figure 4 The curve graph in includes a maximum value, that is, the voltage change rate dV / dQ_1 corresponding to the peak P1, then the state of charge S1 corresponding to the voltage change rate dV / dQ_1 can be stored in a preset table, etc., for subsequent calibration of the state of charge of the battery cluster. For example, during the process of detecting the state of charge of the battery cluster by the controller, the state of charge of the battery cluster is detected as the first state of charge at the first moment, and the state of charge of the calibration cell is the third state of charge, and at the second moment after the first moment, it is detected that the change rate of the voltage across the calibration cell reaches a maximum value. The controller obtains (for example, from a preset table) the state of charge S1 corresponding to the maximum value of the change rate of the voltage across the calibration cell, obtains the target change amount according to the change amount of the state of charge of the calibration cell from the first moment to the second moment, the capacity of the battery cluster, and the capacity of the calibration cell, and calibrates the state of charge of the battery cluster detected at the second moment to the first state of charge plus the target change amount, thereby calibrating the state of charge of the battery cluster, and the above-mentioned state of charge change amount is the difference between the state of charge S1 and the third state of charge. In addition, Figure 4 The curve graph in also includes a minimum value, that is, the voltage change rate dV / dQ_2 corresponding to the trough P2, then the state of charge S2 corresponding to the voltage change rate dV / dQ_2 can also be stored in a preset table, etc., for subsequent calibration of the state of charge of the battery cluster. For example, during the process of detecting the state of charge of the battery cluster by the controller, the state of charge of the battery cluster is detected as the first state of charge at the first moment, the state of charge of the calibration cell is the third state of charge, and the change rate of the voltage across the calibration cell reaches a minimum value at the second moment after the first moment. The controller obtains (for example, from the preset table) the state of charge S2 corresponding to the minimum value of the change rate of the voltage across the calibration cell, obtains the target change amount according to the change amount of the state of charge of the calibration cell from the first moment to the second moment, the capacity of the battery cluster, and the capacity of the calibration cell, and calibrates the state of charge of the battery cluster detected at the second moment to the first state of charge plus the target change amount, thereby calibrating the state of charge of the battery cluster, and the above-mentioned state of charge change amount is the difference between the state of charge S2 and the third state of charge.

[0041] Optionally, the controller obtains the change rates of multiple voltages corresponding to multiple states of charge of the calibration cell based on the change of the state of charge of the calibration cell within a set interval, and stores the states of charge corresponding to the inflection point values ​​in the change rates of the multiple voltages in a preset table, etc., for subsequent calibration of the state of charge of the battery cluster. Please also refer to Figure 5 , Figure 5 is another curve diagram of the relationship between the state of charge and voltage change rate of the calibration cell provided in this application. Figure 5As shown, by controlling the charge state of the calibration cell from 0% to 100%, and detecting the change rate of the voltage across the calibration cell under different charge states, a curve diagram showing the change rate of voltage as a function of charge state is obtained. Figure 5 The curve graph in includes an inflection point value, that is, the voltage change rate dV / dQ_3 corresponding to the connection point P3 of the convex curve and the concave curve on the curve, then the state of charge S3 corresponding to the inflection point value dV / dQ_3 can be stored in a preset table, etc., for subsequent calibration of the state of charge of the battery cluster. For example, during the process of detecting the state of charge of the battery cluster by the controller, the state of charge of the battery cluster is detected as the first state of charge at the first moment, the state of charge of the calibration cell is the third state of charge, and the change rate of the voltage across the calibration cell reaches the inflection point value at the second moment after the first moment. The controller obtains (for example, from the preset table) the state of charge S3 corresponding to the change rate of the voltage across the calibration cell reaching the inflection point value, obtains the target change amount according to the change amount of the state of charge of the calibration cell from the first moment to the second moment, the capacity of the battery cluster, and the capacity of the calibration cell, calibrates the state of charge of the battery cluster detected at the second moment to the first state of charge plus the target change amount, thereby calibrating the state of charge of the battery cluster, and the above-mentioned state of charge change amount is the difference between the state of charge S3 and the third state of charge. Here, the state of charge of the battery cluster is calibrated based on the time when the rate of change of the voltage across the calibration cell reaches the characteristic value, which solves the cumulative error in the state of charge estimation method using the ampere-hour integration method, and avoids the problem that the error calibration can only be triggered when the battery cluster is fully charged and discharged. In addition, the state of charge is marked by the characteristic point (maximum value, minimum value or inflection point value) of the change rate of the voltage of the calibration cell during the charge and discharge process. Compared with the traditional method of judging the state of charge based on the absolute value of the voltage, it suppresses the errors caused by temperature fluctuations, charge and discharge times, and changes in health status. Figure 6 , Figure 6 is another curve diagram of the relationship between the state of charge and the voltage change rate of the calibration cell provided in the present application, such as Figure 6 As shown, Figure 6The curves include the rate of change of the calibration cell voltage as the state of charge after the calibration cell is charged and discharged once, 300 times, and 1000 times. Due to the attenuation and aging of the cell, the rate of change of the calibration cell voltage after different charge and discharge cycles is significantly different. If the state of charge is predicted by the absolute value of the rate of change of the calibration cell voltage, a complex electrochemical model needs to be established for compensation. Although the absolute value of the rate of change of the calibration cell voltage changes with the number of charge and discharge cycles, the horizontal axis state of charge corresponding to the maximum, minimum and inflection point values ​​on the voltage change rate curve has a relatively stable characteristic. The maximum, minimum and inflection point values ​​can achieve stable marking of the state of charge. The state of charge corresponding to the maximum, minimum and inflection point values ​​are stored in a preset table, etc., for subsequent calibration of the state of charge of the battery cluster. The subsequent state of charge corresponding to the maximum, minimum and inflection point values ​​will not change much, avoiding the problem of errors caused by the state of charge corresponding to the maximum, minimum and inflection point values ​​being disturbed by temperature and cell attenuation and aging conditions. The above-mentioned state of charge is used for subsequent calibration of the state of charge of the battery cluster to improve the calibration reliability of the state of charge of the battery cluster.

[0042] In some feasible embodiments, the calibration cell contains a cell composed of a polyanionic sodium positive electrode. The polyanionic sodium positive electrode may include sodium vanadium phosphate, sodium iron pyrophosphate, composite sodium iron pyrophosphate, sodium iron sulfate, etc. Specifically, when the calibration cell contains a cell composed of a polyanionic sodium positive electrode, the slow decay characteristics of the polyanionic sodium positive electrode material are utilized so that the horizontal axis charge state corresponding to the maximum, minimum and inflection point values ​​on the voltage change rate change curve is not easy to fluctuate. In addition, when the calibration cell contains a cell composed of a polyanionic sodium positive electrode, the calibration cell has a cycle decay rate that is less than the cycle decay rate of the battery pack in the battery cluster to which it is connected within the operating voltage range. For example, when the battery pack in the battery cluster adopts a lithium iron phosphate type, the cycle decay rate of the calibration cell is less than that of the lithium iron phosphate cell, and the calibration cell has excellent cycle performance, so that the calibration cell can have a longer cycle life without affecting the service life of the cluster unit. Furthermore, when active ion loss occurs in the calibration cell, the full charge potential of the positive electrode is often raised. Here, the voltage at both ends of the calibration cell corresponding to the state of charge of 100% satisfies that the capacity fluctuation is less than 1% within the range of ±50mV, thereby avoiding the above phenomenon causing the state of charge position corresponding to the characteristic value (maximum, minimum or inflection point value) of the rate of change of the calibration cell voltage to fluctuate, and achieving that when the full charge potential of the positive electrode fluctuates within a certain range, the impact on the capacity is less than 1%, reducing the interference caused by the loss of active ions in the calibration cell on the calibration of the state of charge of the subsequent battery cluster.

[0043] The embodiment of the present application also provides a state of charge detection device, which includes a controller and at least one calibration cell, and at least one calibration cell is used to be connected in series with a battery. Here, the controller in the state of charge detection device may include a first controller and a second controller, the first controller is used to detect the state of charge of the calibration cell and the change rate of the voltage across the calibration cell, and the second controller is used to detect the state of charge of the battery. When the first controller detects that the change rate of the voltage across the calibration cell reaches a characteristic value, the first controller obtains a target change amount according to the change amount of the state of charge of the calibration cell from the first moment to the second moment, the capacity of the battery, and the capacity of the calibration cell. Among them, the second moment is after the first moment, and the first state of charge is the state of charge of the battery at the first moment, and the second state of charge is the state of charge of the battery at the second moment. Among them, at the second moment, the change rate of the voltage across the calibration cell is a characteristic value of the change rate of the voltage across the calibration cell, and the characteristic value can be one of a maximum value, a minimum value, or an inflection point value. Then, the first controller calibrates the second state of charge at the second moment to the first state of charge plus the target change amount, and sends it to the second controller. Alternatively, when the difference between the first state of charge plus the target change and the second state of charge at the second moment exceeds a set threshold, the first controller can calibrate the second state of charge at the second moment to the first state of charge plus the target change and send it to the second controller, thereby calibrating the battery state of charge.

[0044] In some feasible implementations, when the first controller detects that the rate of change of the voltage across the calibration cell reaches a characteristic value, the first controller obtains a target change amount according to the charge state change amount of the calibration cell from the first moment to the second moment, the capacity of the battery, and the capacity of the calibration cell. Specifically, the controller multiplies the ratio of the capacity of the calibration cell to the capacity of the battery by the charge state change amount to obtain the target change amount.

[0045] In some feasible embodiments, before the second controller calibrates the second state of charge of the battery, the first controller controls the state of charge of the calibration cell to change within a set interval to obtain the rate of change of the voltage across the calibration cell during the change of the state of charge of the calibration cell. Then, the first controller obtains the rate of change of multiple voltages corresponding to the multiple states of charge of the calibration cell based on the change of the state of charge of the calibration cell within the set interval, obtains the characteristic value of the rate of change of the voltage across the calibration cell during the change, and the state of charge of the calibration cell corresponding to the characteristic value. In other words, before calibrating the second state of charge of the battery, the first controller controls the state of charge of the calibration cell to change within a set interval to obtain the state of charge corresponding to the maximum value, minimum value or inflection point value when the rate of change of the voltage across the calibration cell is the maximum value, minimum value or inflection point value, for subsequent calibration of the state of charge of the battery. The specific process of obtaining the state of charge corresponding to the characteristic value can be referred to the above Figure 4 and Figure 5 The description of is not repeated here. Here, the state of charge of the horizontal axis corresponding to the maximum value, minimum value and inflection point value on the voltage change rate curve has a relatively stable characteristic. The maximum value, minimum value and inflection point value can realize stable marking of the state of charge, that is, the state of charge corresponding to the maximum value, minimum value and inflection point value is stored in a preset table, etc., for subsequent calibration of the battery state of charge. The state of charge corresponding to the subsequent maximum value, minimum value and inflection point value will not change much, avoiding the problem of error caused by the state of charge corresponding to the characteristic value being disturbed by temperature and cell attenuation aging conditions, and the state of charge corresponding to the above characteristic value is used for subsequent calibration of the battery state of charge, thereby improving the calibration reliability of the battery state of charge.

[0046] See also Figure 7 , Figure 7 The charge state detection method provided in this application is applicable to the above Figures 1 to 3 The state of charge detection of the battery cluster in any energy storage system shown. Figure 7 As shown, the charge state detection method provided in the present application includes the steps of:

[0047] S901, detecting the state of charge of the battery, and detecting the state of charge of the calibration cell and the rate of change of the voltage across the calibration cell.

[0048] In some feasible embodiments, the above-mentioned battery is connected in series with at least one calibration cell. When the battery is charged or discharged, the calibration cell connected in series with the battery is also charged or discharged synchronously, and when the state of charge of the calibration cell changes, the rate of change of the voltage across the calibration cell also changes accordingly. The state of charge of the battery cluster is detected and the state of charge of the calibration cell is detected. At the same time, the rate of change of the voltage across the calibration cell is also detected. When it is detected that the rate of change of the voltage across the calibration cell reaches a characteristic value, the state of charge of the battery cluster at the moment when the rate of change of the voltage across the calibration cell reaches the characteristic value is calibrated. Specifically, the above-mentioned characteristic value can be one of a maximum value, a minimum value or an inflection point value.

[0049] S902, calibrate whether the rate of change of the voltage across the battery cell reaches a characteristic value. If the judgment result is yes, execute step S903; if the judgment result is no, execute step S901.

[0050] S903, obtaining a target change amount according to the charge state change amount of the calibration cell, the capacity of the battery, and the capacity of the calibration cell.

[0051] S904: Calibrate the state of charge of the battery currently being detected to the first state of charge plus the target change amount.

[0052] In some feasible implementations, when it is detected that the rate of change of the voltage across the calibration cell reaches a characteristic value, the state of charge of the battery cluster at the moment when the rate of change of the voltage across the calibration cell reaches the characteristic value is calibrated. The target change amount is obtained according to the change amount of the state of charge of the calibration cell from the first moment to the second moment, the capacity of the battery cluster and the capacity of the calibration cell. Among them, the above-mentioned second moment is after the first moment, and the first state of charge is the state of charge of the battery cluster at the first moment, and the second state of charge is the state of charge of the battery cluster at the second moment. Among them, at the second moment, the rate of change of the voltage across the calibration cell is the characteristic value of the rate of change of the voltage across the calibration cell, and the characteristic value can be one of a maximum value, a minimum value or an inflection point value. Then, the second state of charge at the second moment is calibrated to the first state of charge plus the target change amount. Alternatively, when the difference between the value of the first state of charge plus the target change amount and the second state of charge at the second moment exceeds a set threshold, the second state of charge at the second moment is calibrated to the first state of charge plus the target change amount and sent to the second controller, thereby calibrating the state of charge of the battery cluster. Here, the state of charge of the battery cluster is calibrated based on the moment when the rate of change of the voltage across the calibration cell reaches the characteristic value, which solves the cumulative error in the state of charge estimation method using the ampere-hour integration method and avoids the problem of correcting the state of charge error only at the beginning and end of the battery cluster charging and discharging. The state of charge detection has high accuracy and strong applicability.

[0053] In some feasible implementations, when it is detected that the rate of change of the voltage across the calibration cell reaches a characteristic value, the target change is obtained according to the change in the state of charge of the calibration cell from the first moment to the second moment, the capacity of the battery cluster, and the capacity of the calibration cell. Specifically, the ratio of the capacity of the calibration cell to the capacity of the battery cluster is multiplied by the above-mentioned change in the state of charge to obtain the target change. The above-mentioned characteristic value may be a maximum value, a minimum value, or an inflection point value. Taking the case where the rate of change of the voltage across the calibration cell reaches a maximum value as an example, the difference between the fourth state of charge and the third state of charge may be used as the change in the state of charge. The above-mentioned fourth state of charge is the state of charge of the calibration cell corresponding to the rate of change of the voltage across the calibration cell reaching a maximum value. The above-mentioned third state of charge is the state of charge of the calibration cell at the first moment. The change in the state of charge is multiplied by the ratio of the capacity of the calibration cell to the capacity of the battery cluster to obtain the target change. Finally, the state of charge of the battery cluster detected at the second moment when the rate of change of the voltage across the calibration cell reaches the characteristic value is calibrated, that is, the second state of charge detected at the second moment is calibrated to the first state of charge plus the target change amount. The state of charge of the battery cluster corresponding to the moment when the rate of change of the voltage across the calibration cell reaches the characteristic value is calibrated, which solves the cumulative error in the state of charge estimation method using the ampere-hour integration method, and avoids the problem of only being able to correct the state of charge error at the beginning and end of the battery cluster charging and discharging. The state of charge detection has high accuracy and strong applicability.

[0054] In some feasible embodiments, before detecting the state of charge of the battery cluster, the state of charge of the calibration cell is controlled to change within a set interval to obtain the rate of change of the voltage across the calibration cell during the change of the state of charge of the calibration cell. Next, based on the change of the state of charge of the calibration cell within the set interval, the change rates of multiple voltages corresponding to the multiple states of charge of the calibration cell are obtained, and the characteristic value of the rate of change of the voltage across the calibration cell during the change process, and the state of charge of the calibration cell corresponding to the characteristic value are obtained. In other words, before calibrating the second state of charge of the battery cluster, the state of charge of the calibration cell is controlled to change within a set interval to obtain the state of charge corresponding to the maximum value, minimum value or inflection point value when the rate of change of the voltage across the calibration cell is the minimum value or the inflection point value, so as to be used for the subsequent calibration of the state of charge of the battery cluster. The specific process of obtaining the state of charge corresponding to the characteristic value can be referred to the above Figure 4 and Figure 5 The description of is not repeated here. Here, the state of charge of the horizontal coordinate corresponding to the maximum value, minimum value and inflection point value on the voltage change rate curve has a relatively stable characteristic, and the maximum value, minimum value and inflection point value can realize stable marking of the state of charge, that is, the state of charge corresponding to the maximum value, minimum value and inflection point value is stored in a preset table, etc., for subsequent calibration of the state of charge of the battery cluster, and the state of charge corresponding to the subsequent maximum value, minimum value and inflection point value will not change much, avoiding the problem of error caused by the calibration state of charge being disturbed by temperature and cell attenuation aging conditions, and the above calibration state of charge is used for the subsequent calibration of the state of charge of the battery cluster, so as to improve the calibration reliability of the state of charge of the battery cluster.

Claims

1. An energy storage system, characterized in that: The energy storage system includes a battery cluster, a power conversion circuit and a controller, wherein the battery cluster and the power conversion circuit are connected in series with calibration cells, and the power conversion circuit is used to transform or invert the input direct current and then output it to the load; The controller is used to calibrate the second state of charge of the battery cluster according to the change in the state of charge of the calibration cell from the first moment to the second moment and the first state of charge of the battery cluster, the second moment is after the first moment, the first state of charge is the state of charge of the battery cluster at the first moment, the second state of charge is the state of charge of the battery cluster at the second moment, and at the second moment, the rate of change of the voltage across the calibration cell is a characteristic value of the rate of change of the voltage across the calibration cell, and the characteristic value is a maximum value, a minimum value or an inflection point value.

2. The energy storage system according to claim 1, characterized in that: The controller is used to obtain a target change amount according to the charge state change amount, the capacity of the battery cluster and the capacity of the calibration cell, and calibrate the second charge state of the battery cluster to the first charge state plus the target change amount.

3. The energy storage system according to claim 2, characterized in that: The controller is used for multiplying the ratio of the capacity of the calibration cell to the capacity of the battery cluster by the charge state change amount to obtain the target change amount.

4. The energy storage system according to any one of claims 1 to 3, characterized in that: There are multiple calibration cells, and the multiple calibration cells are connected in parallel.

5. The energy storage system according to any one of claims 1 to 4, characterized in that: A bypass switch is connected in parallel at both ends of the calibration cell, and the bypass switch is used to be turned on when the calibration cell fails.

6. The energy storage system according to any one of claims 1 to 5, characterized in that: The controller is further configured to, before calibrating the second state of charge of the battery cluster: Controlling the state of charge of the calibration cell to change within a set interval to obtain a rate of change of the voltage across the calibration cell during the change of the state of charge of the calibration cell; Obtaining change rates of multiple voltages corresponding to multiple states of charge of the calibration cell based on changes in the state of charge of the calibration cell within a set interval; Acquire a characteristic value of a change rate of the voltage across the calibration cell during the change process, and a state of charge of the calibration cell corresponding to the characteristic value; The state of charge change is the difference between a fourth state of charge and a third state of charge, the fourth state of charge is the state of charge of the calibration cell corresponding to the characteristic value, and the third state of charge is the state of charge of the calibration cell at the first moment.

7. The energy storage system according to any one of claims 1 to 5, characterized in that: The change in state of charge is a difference between a fourth state of charge and a third state of charge, the fourth state of charge is the state of charge of the calibration cell corresponding to the characteristic value, and the third state of charge is the state of charge of the calibration cell at the first moment; The fourth state of charge is obtained according to the characteristic value and a preset table, wherein the preset table includes the characteristic value and the state of charge corresponding to the characteristic value.

8. The energy storage system according to any one of claims 1 to 7, characterized in that: The calibration cell is a cell composed of a polyanion sodium positive electrode.

9. A charge state detection device, characterized in that: The state of charge detection device includes a controller and a calibration cell, wherein the calibration cell is used to be connected in series with the battery; The controller is used to calibrate the second state of charge of the battery according to the change in the state of charge of the calibration cell from the first moment to the second moment and the first state of charge of the battery, the second moment is after the first moment, the first state of charge is the state of charge of the battery at the first moment, the second state of charge is the state of charge of the battery at the second moment, and at the second moment, the rate of change of the voltage across the calibration cell is a characteristic value of the rate of change of the voltage across the calibration cell, and the characteristic value is a maximum value, a minimum value or an inflection point value.

10. The charge state detection device according to claim 9, characterized in that: The controller is used to obtain a target change amount according to the charge state change amount, the capacity of the battery and the capacity of the calibration cell, and calibrate the second charge state of the battery to the first charge state plus the target change amount.

11. The charge state detection device according to claim 10, characterized in that: The controller is used for multiplying the ratio of the capacity of the calibration cell to the capacity of the battery by the charge state change to obtain the target change.

12. The charge state detection device according to any one of claims 9 to 11, characterized in that: The controller is further configured to, before calibrating the second state of charge of the battery: Controlling the state of charge of the calibration cell to change within a set interval to obtain a rate of change of the voltage across the calibration cell during the change of the state of charge of the calibration cell; Obtaining change rates of multiple voltages corresponding to multiple states of charge of the calibration cell based on changes in the state of charge of the calibration cell within a set interval; Acquire a characteristic value of a change rate of the voltage across the calibration cell during the change process, and a state of charge of the calibration cell corresponding to the characteristic value; The state of charge change is the difference between a fourth state of charge and a third state of charge, the fourth state of charge is the state of charge of the calibration cell corresponding to the characteristic value, and the third state of charge is the state of charge of the calibration cell at the first moment.

13. The charge state detection device according to any one of claims 9 to 11, characterized in that: The change in state of charge is a difference between a fourth state of charge and a third state of charge, the fourth state of charge is the state of charge of the calibration cell corresponding to the characteristic value, and the third state of charge is the state of charge of the calibration cell at the first moment; The fourth state of charge is obtained according to the characteristic value and a preset table, wherein the preset table includes the characteristic value and the state of charge corresponding to the characteristic value.

14. The charge state detection device according to any one of claims 9 to 13, characterized in that: The calibration cell is a cell composed of a polyanion sodium positive electrode.

15. A method for detecting a state of charge, characterized in that: The method comprises: The second state of charge of the battery is calibrated according to the change in the state of charge of the calibration cell from the first moment to the second moment and the first state of charge of the battery, wherein the calibration cell is connected in series with the battery, the second moment is after the first moment, the first state of charge is the state of charge of the battery at the first moment, the second state of charge is the state of charge of the battery at the second moment, and at the second moment, the rate of change of the voltage across the calibration cell is a characteristic value of the rate of change of the voltage across the calibration cell, and the characteristic value is a maximum value, a minimum value or an inflection point value.

16. The method according to claim 15, characterized in that The step of calibrating the second state of charge of the battery according to the change in the state of charge of the calibration cell from the first moment to the second moment and the first state of charge of the battery comprises: A target change is obtained according to the state of charge change, the capacity of the battery and the capacity of the calibration cell, and the second state of charge of the battery is calibrated to the first state of charge plus the target change.

17. The method according to claim 16, characterized in that The obtaining a target change amount according to the charge state change amount, the capacity of the battery and the capacity of the calibration cell includes: The target change is obtained by multiplying the ratio of the capacity of the calibration cell to the capacity of the battery by the charge state change.

18. The method according to any one of claims 15 to 17, characterized in that: Before calibrating the second state of charge of the battery, the method further includes: Controlling the state of charge of the calibration cell to change within a set interval to obtain a rate of change of the voltage across the calibration cell during the change of the state of charge of the calibration cell; Obtaining change rates of multiple voltages corresponding to multiple states of charge of the calibration cell based on changes in the state of charge of the calibration cell within a set interval; Acquire a characteristic value of a change rate of the voltage across the calibration cell during the change process, and a state of charge of the calibration cell corresponding to the characteristic value; The state of charge change is the difference between a fourth state of charge and a third state of charge, the fourth state of charge is the state of charge of the calibration cell corresponding to the characteristic value, and the third state of charge is the state of charge of the calibration cell at the first moment.

19. The method according to any one of claims 15 to 17, characterized in that: The change in state of charge is a difference between a fourth state of charge and a third state of charge, the fourth state of charge is the state of charge of the calibration cell corresponding to the characteristic value, and the third state of charge is the state of charge of the calibration cell at the first moment; The fourth state of charge is obtained according to the characteristic value and a preset table, wherein the preset table includes the characteristic value and the state of charge corresponding to the characteristic value.

20. The method according to any one of claims 15 to 19, characterized in that: The calibration cell is a cell composed of a polyanion sodium positive electrode.

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