Charge capacity calculation device and method for energy storage system

Abstract

The invention relates to a charge capacity calculation device and method for an energy storage system. A method of calculating a charge capacity of an energy storage system according to one embodiment of the present invention. The method includes: a current application step of applying a predetermined current having a constant value to the energy storage system; a first voltage measurement step of measuring a voltage of the energy storage system while a predetermined current having a constant value is applied to the energy storage system; a second voltage measurement step of measuring a voltage of the energy storage system after blocking a predetermined current having a constant value applied to the energy storage system; and a resistance (R) and capacitance (C) calculation step for calculating the resistance (R) and capacitance (C) of the energy storage system on the basis of the voltage of the energy storage system measured in the first voltage measurement step, the voltage of the energy storage system measured in the second voltage measurement step, and a predetermined current having a constant value.

Description

[0001] This application is a divisional application of Chinese invention patent application "Agency and Method for Calculating Charging Capacity of Energy Storage System", which entered the Chinese national phase on February 20, 2020, with PCT application number PCT / KR2019 / 002070, international application date of February 20, 2019, and Chinese application number 201980003996.2. Technical Field

[0002] This invention relates to an apparatus and method for calculating the charging capacity of an energy storage system.

[0003] More specifically, the present invention relates to an apparatus and method for accurately calculating the charging capacity of an energy storage system by increasing the accuracy of the voltage model used in an extended Kalman filter. Background Technology

[0004] With industrial development, the demand for electricity is increasing, and the differences in electricity consumption between day and night, seasons, and days are becoming increasingly pronounced. Recently, for this reason, many technologies have been rapidly developed to reduce peak loads by utilizing excess power in the system.

[0005] A typical example of these technologies is an energy storage system, in which excess power is stored in a battery, or insufficient power is supplied from the battery.

[0006] In order to maintain the lifespan of an energy storage system and ensure its safe use over a long period of time, the energy storage system must operate within an appropriate charging capacity range, and the lifespan of the energy storage system varies greatly depending on the number of charge / discharge cycles.

[0007] Therefore, it is important to understand the state of an energy storage system by measuring its current, voltage, and temperature, and by accurately measuring its state of charge (SOC).

[0008] The traditional method for calculating the state of charge (SOC) of an energy storage system is the current integration method. However, in the traditional current integration method, there are errors in the current sensor used to measure the current, and these errors accumulate during the integration process, making it difficult to calculate the accurate charging capacity.

[0009] As another traditional technique for solving this traditional problem, there is a method for calculating the charging capacity of an energy storage system by substituting a current integration method based on the current measured by a current sensor and the voltage model of the energy storage system into an extended Kalman filter.

[0010] However, even in techniques that use the current integration method and the voltage model of the energy storage system in the traditional extended Kalman filter, there is still a problem of errors in the final charging capacity due to the low accuracy of the resistor (R) and capacitor (C) used to calculate the voltage model of the energy storage system.

[0011] Therefore, the present invention proposes an apparatus and method for reducing the charging capacity error of an energy storage system by accurately calculating the resistance (R) and capacitance (C) used to calculate the voltage model of the energy storage system and performing the final calculation using a Kalman filter of the voltage model with high specific weights.

[0012] (Patent Document 1) KR2013-0105123A Summary of the Invention

[0013] Technical issues

[0014] This invention provides an apparatus and method for accurately calculating the charging capacity of an energy storage system by precisely calculating the voltage model of the energy storage system.

[0015] More specifically, the present invention provides an apparatus and method for accurately calculating charging capacity by precisely calculating the resistors (R) and capacitors (C) used in the voltage model of an energy storage system and substituting the accurate voltage model into an extended Kalman filter.

[0016] Technical solutions

[0017] Embodiments of the present invention provide a method for calculating the resistance (R) and capacitance (C) of an energy storage system. The method includes: a current application step, which applies a predetermined current having a constant value to the energy storage system; a first voltage measurement step, which measures the voltage of the energy storage system while the predetermined current having a constant value is applied to the energy storage system; a second voltage measurement step, which measures the voltage of the energy storage system after the predetermined current having a constant value is blocked from being applied to the energy storage system; and a resistance (R) and capacitance (C) calculation step, which calculates the resistance (R) and capacitance (C) of the energy storage system based on the voltage of the energy storage system measured in the first voltage measurement step, the voltage of the energy storage system measured in the second voltage measurement step, and the predetermined current having a constant value.

[0018] The predetermined current with a constant value applied in the current application step can be a low-c rate current.

[0019] The method may further include: a state variable calculation step, which uses the resistance R and capacitance C of the energy storage system, calculated using a low-c rate current, to calculate the state variables of the extended Kalman filter; and an energy storage system charging capacity calculation step, which substitutes the state variables into the extended Kalman filter to calculate the charging capacity of the energy storage system.

[0020] The extended Kalman filter can repeatedly perform the following steps: updating the state variables over time; updating the error covariance of the state variables over time; calculating the Kalman gain of the extended Kalman filter; using the gain to estimate the state variables; and using the gain to correct the error covariance of the state variables.

[0021] The state variable calculation steps may include: a charging capacity state variable calculation step, which generates a state variable for the charging capacity of the energy storage system; and a voltage state variable calculation step, which generates a state variable for the voltage of the energy storage system.

[0022] The charging capacity state variable can be calculated using the current integration method, which integrates the current measured in the energy storage system. The calculated charging capacity state variable can be updated over time according to Equation 1 below.

[0023] (Equation 1)

[0024]

[0025] (Where, Q_capacity: the capacity of the secondary battery, k: time index, I[k]: the current measured at time index k, t: time)

[0026] The voltage state variable calculation steps can use a voltage model circuit to calculate the voltage state variable of the energy storage system. The calculated voltage state variable can be updated over time according to Equation 2 below.

[0027] (Equation 2)

[0028]

[0029] (where R1 and C1 are) Figure 5 The circuit model includes resistor and capacitor values, k: time index, I[k]: current measured at time index k, t: time.

[0030] In other embodiments of the present invention, an energy storage system includes: a plurality of battery racks; and a battery compartment controller (BSC) for controlling the plurality of battery racks, wherein the BSC includes: a voltage measurement unit for measuring the output voltage of the energy storage system; a current measurement unit for measuring the output current of the energy storage system; a storage unit for storing a lookup table of resistance (R) and capacitance (C) of the temperature-dependent energy storage system calculated using a predetermined current with a constant value; and a charging capacity calculation unit for calculating the charging capacity of the energy storage system based on the lookup table.

[0031] The voltage measurement unit can measure: a first voltage, which is the voltage of the energy storage system when a predetermined current is applied to the energy storage system; and a second voltage, which is the voltage of the energy storage system after the current applied to the energy storage system is cut off.

[0032] The charging capacity calculation unit may include: a voltage state variable calculation unit for calculating the voltage state variable of the energy storage system based on the resistance and capacitance of a lookup table; and a charging capacity state variable calculation unit for calculating the charging capacity state variable of the energy storage system using a current integration method for integrating the measured output current, wherein the calculated voltage state variable and charging capacity state variable can be substituted into a Kalman filter to calculate the charging capacity of the energy storage system.

[0033] Function of the present invention

[0034] This invention can accurately calculate the voltage model of an energy storage system by precisely calculating the resistors (R) and capacitors (C) used in the voltage model of the energy storage system.

[0035] Furthermore, the present invention can accurately calculate the charging capacity of an energy storage system by calculating an accurate voltage model of the energy storage system. Attached Figure Description

[0036] Figure 1 This is a flowchart illustrating a method for calculating the resistance (R) and capacitance (C) of the voltage model of the energy storage system of the present invention.

[0037] Figure 2 This is a flowchart illustrating the operation of an extended Kalman filter according to an embodiment of the present invention.

[0038] Figure 3 This is a view illustrating a practical experimental method (DCPR) for calculating the resistance R and capacitance C used to calculate the voltage model of an energy storage system, according to an embodiment of the present invention.

[0039] Figure 4 It is a graph comparing the change in charging capacity after discharge calculated based on the traditional voltage model with the change in charging capacity calculated using the voltage model calculation method of the present invention.

[0040] Figure 5 It is a voltage model circuit used to calculate the voltage of an energy storage system according to an embodiment of the present invention.

[0041] Figure 6 This is a view for comparing the charging capacity calculated using the method for calculating the charging capacity of the energy storage system by means of the resistance and capacitance calculation method used to calculate the voltage model of the energy storage system of the present invention with the charging capacity calculated by means of the prior art (using only the current integration method).

[0042] Figure 7 This is a view of the charging capacity calculated by the method for calculating the charging capacity of the energy storage system using the resistance and capacitance calculation method for calculating the voltage model of the energy storage system of the present invention, and the charging capacity calculated by the conventional algorithm (a conventional technique using a voltage model calculated at a high c-rate and a voltage model with a low weight algorithm in a Kalman filter) by reflecting error conditions.

[0043] Figure 8 This is a view of capacity test results used to compare the charging capacity estimation method of the present invention with that of existing algorithms.

[0044] Figure 9 This is a view illustrating the configuration of an energy storage system according to an embodiment of the present invention. Detailed Implementation

[0045] In the following, embodiments of the invention will be described in detail with reference to the accompanying drawings, enabling those skilled in the art to readily implement the invention. However, the invention may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. For clarity of description, parts irrelevant to the description are omitted in the drawings, and the same reference numerals refer to the same elements.

[0046] Although the terms "initial," "second," etc., may be used herein to describe various elements, these elements should not be limited by these terms. The terms above are used only to distinguish one component from another. For example, an initial component may be referred to as a second component without departing from the scope of the invention, and vice versa. The terminology used in this specification is for describing specific embodiments and is not intended to limit the scope of the invention. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0047] Throughout this specification, when one part is referred to as "connected" to another part, this includes not only "direct connection" but also "electrical connection" to another element therebetween. Furthermore, when describing something as including (or containing or having) some elements, it should be understood that it may include only (or contain or have) those elements, or, if no specific limitation exists, it may include (or contain or have) other elements as well as those elements. The terms "...operation" or "...operation" as used throughout this specification do not mean "operation for...".

[0048] In consideration of the functions of this invention, the terminology used in this specification may be currently widely used general terms, but may vary depending on the intent of those skilled in the art, precedents, or the emergence of new technologies. Furthermore, in some cases, terms may be arbitrarily chosen by the applicant, and in such cases, their meanings are described in the corresponding descriptive sections of this invention. Therefore, the terminology used in this invention should be defined based on the meaning of the terms and the entirety of this invention, rather than simply the terminology's name.

[0049] 1. A method for calculating the resistance (R) and capacitance (C) of a voltage model for an energy storage system according to an embodiment of the present invention.

[0050] As a method for calculating the charging capacity of conventional energy storage systems, the current integration method is used. This method determines the charging capacity by integrating the charging and discharging currents over time. However, errors exist in the current sensors used to measure the charging and discharging currents. These errors accumulate as time is used for current integration, thus reducing the accuracy of the charging capacity ultimately calculated using this method.

[0051] Traditionally, to address this issue, both the voltage model and the current integration method of the energy storage system are substituted into the extended Kalman filter to obtain a more accurate charging capacity.

[0052] However, traditionally, because the resistance R and capacitance C used to calculate the voltage model of the energy storage system substituted into the extended Kalman filter are not calculated accurately, there are still errors in the charging capacity of the energy storage system.

[0053] Therefore, this invention proposes a method for accurately calculating the resistance (R) and capacitance (C) for calculating the voltage model of an energy storage system.

[0054] Figure 1 This is a method for calculating the resistance (R) and capacitance (C) of the voltage model used to calculate the energy storage system of the present invention.

[0055] This invention uses the resistance (R) and capacitance (C) of the energy storage system to calculate the voltage model of the energy storage system.

[0056] The method for calculating the resistance (R) and capacitance (C) of an energy storage system according to the present invention is characterized by using a low-c rate current.

[0057] In this invention, as can be used... Figure 3 The DCPR method shown is a method for calculating the resistance (R) and capacitance (C) of an energy storage system.

[0058] In the following text, reference will be made to Figure 1 and Figure 3 A method for calculating the resistance (R) and capacitance (C) of the energy storage system of the present invention is described.

[0059] 1-1. Current application step S110: Applying a predetermined current with a constant value to the energy storage system.

[0060] The present invention applies a predetermined current with a constant value to an energy storage system, measures the voltage change of the energy storage system, and calculates the resistance (R) and capacitance (C) of the energy storage system based on this.

[0061] The current application step is the process of applying a predetermined current of constant value to an energy storage system charged to a predetermined charging capacity. After applying the predetermined current of constant value to the energy storage system in this manner, a first voltage measurement step is performed. At this time, the predetermined current of constant value to be applied is a current with a low c-rate. The c-rate can refer to the intensity of the current.

[0062] The applied current, having a constant value, uses a current with a total rate of 2 to 3 c or higher. However, the inventors of this invention have discovered that by applying a c-rate current with a rate less than 2 to 3 c, the resistance and capacitance values ​​of the energy storage system can be calculated more accurately.

[0063] Therefore, in this invention, the low-c rate current can be a current having a value between the minimum current value that can measure the resistance and capacitance of the energy storage system and the 2c rate value.

[0064] Preferably, the current with a low c-rate can be a current with a c-rate of 0.1, which corresponds to 1 / 10 of the current with a c-rate of 1.

[0065] When a current with a high c-rate is applied, the voltage of the energy storage system changes after the current is applied. In contrast, when a current with a low c-rate is applied, the voltage of the energy storage system can be stabilized quickly after the current is applied, and the resistance (R) and capacitance (C) of the energy storage system can be calculated more accurately.

[0066] 1-2. The first voltage measurement step S120 involves measuring the voltage of the energy storage system while a predetermined current of constant value is applied to the energy storage system.

[0067] The first voltage measurement step of the present invention is to measure the voltage of the energy storage system while a predetermined current with a constant value flows through the energy storage system.

[0068] Specifically, when a predetermined current with a constant value is applied to an energy storage system charged to a predetermined charging capacity during the voltage application step, the voltage of the energy storage system changes by a predetermined value. The voltage of the energy storage system measured at this time is used in the steps of calculating the resistance (R) and capacitance (C), which will be described later.

[0069] 1-3. Second voltage measurement step S130: After interrupting the predetermined current with a constant value applied to the energy storage system, the voltage of the energy storage system is measured.

[0070] The second voltage measurement step of the present invention is the step of terminating the application of a predetermined current with a constant value and measuring the voltage of the energy storage system after the first voltage measurement step.

[0071] Specifically, when a predetermined current of constant value is applied to and then cut off from the energy storage system, the voltage of the energy storage system changes. For example, when current is applied in the charging direction and then cut off, the voltage of the energy storage system may decrease, and when current is applied in the discharging direction and then cut off, the voltage of the energy storage system may increase. The voltage change of the energy storage system measured at this time is used in the steps of calculating the resistance (R) and capacitance (C), which will be described later.

[0072] 1-4. Calculation step S140: Calculating the resistance (R) and capacitance (C) of the energy storage system based on the voltage of the energy storage system measured in the first voltage measurement step, the voltage of the energy storage system measured in the second voltage measurement step, and a predetermined current with a constant value.

[0073] The resistance (R) and capacitance (C) calculation steps are based on the voltage of the energy storage system measured in the first voltage measurement step, the voltage of the energy storage system measured in the second voltage measurement step, and a predetermined current with a constant value. Specifically, since the predetermined current with a constant value applied to the energy storage system and the voltage corresponding to the flow of the predetermined current with a constant value are known, the resistance (R) and capacitance (C) of the energy storage system can be calculated.

[0074] For example, in Figure 5 In the circuit, V cell It is the sum of the OCV voltage, the voltage applied to R0, and the voltage applied to C1. On the other hand, the OCV value is a preset value based on the charging capacity of the individual battery cells. The resistance value of R0 is determined by the voltage V measured at time t. cell Voltage V t Compared with V measured at time t + 1 cell Voltage V t + 1 The difference between the two values ​​is obtained by dividing the current flowing at a low rate (c) in the circuit. The voltage applied to R0 is also known. Therefore, since the voltage and current applied to C1 are known, the values ​​of R1 and C1 can be calculated.

[0075] In this way, the resistance (R) and capacitance (C) of the energy storage system, which are repeatedly calculated while the temperature of the energy storage system is changed, can be stored in the form of a resistance and capacitance lookup table for the energy storage system.

[0076] Meanwhile, because a current with a low c-rate (0.1c-rate) is used in this invention, the voltage of the energy storage system measured in the second voltage measurement step stabilizes rapidly after the current stops flowing, so the voltage of the energy storage system when the current is flowing and the voltage of the energy storage system when the current is not flowing are accurately measured.

[0077] Therefore, if the voltage model of the energy storage system is calculated using the resistance (R) and capacitance (C) of the energy storage system, and the charging capacity of the energy storage system is calculated based on this model, the charging capacity of the energy storage system can be calculated accurately.

[0078] Meanwhile, in this invention, a predetermined rest time may exist between the current application step and the first voltage measurement step, as well as between the first voltage measurement step and the second voltage measurement step.

[0079] The following describes a method for accurately calculating the voltage model of an energy storage system using the resistance (R) and capacitance (C) calculation method of the present invention, and for calculating the charging capacity of the energy storage system based thereon.

[0080] 2. A method for calculating the charging capacity of the energy storage system of the present invention.

[0081] The charging capacity of a conventional energy storage system is calculated by substituting the voltage and current integral models into the state variables of an extended Kalman filter. However, traditionally, the values ​​of the resistance (R) and capacitance (C) used to calculate the voltage model cannot be calculated accurately, leading to errors in the calculated charging capacity.

[0082] Specifically, traditionally, when calculating the resistance (R) and capacitance (C) used to calculate the voltage model, a high c-rate current of approximately 2 to 3c is used to calculate the resistance (R) and capacitance (C).

[0083] However, in this invention, when calculating the resistance (R) and capacitance (C) used in the voltage calculation model, the calculation accuracy of the resistance (R) and capacitance (C) is increased by using a low c-rate current.

[0084] On the other hand, the low-c rate current can be the value between the minimum current value that can be used to measure the resistance and capacitance of the energy storage system and the 2c rate.

[0085] Preferably, the current with a low c-rate can be a current with a 0.1 c-rate, which corresponds to 1 / 10 of the current with a 1 c-rate. Figure 4It is a graph comparing the change in charging capacity after discharge calculated based on the traditional voltage model with the change in charging capacity calculated using the voltage model calculation method of the present invention.

[0086] refer to Figure 4 When the voltage model is calculated based on the resistance R and capacitance C calculated by conventional methods, the rate of change of charging capacity (3%) calculated by the extended Kalman filter after discharge is relatively large.

[0087] Normally, the charging capacity does not change after discharging, but the traditional method has a 3% change rate, making it inaccurate.

[0088] However, as in the present invention described above, when the voltage model is calculated based on the resistor R and capacitor C calculated using a low-c rate current, the rate of change of the charging capacity calculated by the extended Kalman filter after discharge (0.5%) is relatively small.

[0089] That is, because the rate of change in charging capacity after discharge is small, the present invention has the effect of more accurately calculating charging capacity.

[0090] Therefore, by using the energy storage system charging capacity calculation method of the present invention, the charging capacity can be calculated more accurately than the traditional method.

[0091] Figure 2 This is a flowchart illustrating the operation of an extended Kalman filter according to an embodiment of the present invention.

[0092] On the other hand, the extended Kalman filter is an adaptive software algorithm that can statistically estimate the state of a system by taking into account external measurable variables and system disturbances (external errors).

[0093] Specifically, the extended Kalman filter repeatedly performs time updates on the state variables, time updates on the error covariance of the state variables, calculates the Kalman gain of the extended Kalman filter, estimates the state variables using the calculated Kalman gain, and corrects the error covariance of the state variables using the gain.

[0094] In other words, the extended Kalman filter can be a method to reduce errors by repeatedly performing estimation -> correction -> estimation -> correction.

[0095] In this invention, the state equation of the extended Kalman filter is configured to include state variables and update these state variables over time. The charging capacity state variable and the voltage state variable of the energy storage system are used as the state variables.

[0096] 2.1 Calculate the charging capacity state variable of the energy storage system as one of the state variables.

[0097] The method for calculating the charging capacity among the state variables of the energy storage system of the present invention calculates the charging capacity of the energy storage system by measuring the current of the energy storage system and integrating the measured current.

[0098] The method for measuring the current of an energy storage system can use the current information of the energy storage system measured by the energy storage system control unit that controls and manages the energy storage system.

[0099] In other words, the initial value of the charging capacity state variable can be calculated by measuring the current in the energy storage system and integrating it using the logarithmic integration method.

[0100] The charging capacity state variable of the energy storage system calculated by the above method can be updated over time in the extended Kalman filter using the following Equation 1.

[0101] (Equation 1)

[0102]

[0103] (Where, Q_capacity: the capacity of the secondary battery, k: time index, I[k]: the current measured at time index k, t: time)

[0104] 2.2 Method for calculating the voltage state variable of the energy storage system among the state variables

[0105] It can be used Figure 5 The voltage model circuit is used to calculate the voltage state variables of the energy storage system in the state variables of this invention.

[0106] Figure 5 The voltage model circuit includes: an open-circuit voltage source 210, which varies according to a predetermined current value flowing in the energy storage system; at least one of resistors R0 (220) and R1 (230); and at least one capacitor C1. The values ​​of resistors R0 (220) and R1 (230) and capacitor C1 constituting the voltage model circuit can be detected in a resistance and capacitance lookup table for the energy storage system at each temperature, which is calculated and stored using a constant current with a low c-rate according to an embodiment of the invention.

[0107] When the values ​​of the resistors and capacitors constituting the voltage model circuit are checked for each temperature in the resistance and capacitance lookup table of the energy storage system, the value V1, which is the initial value of the voltage state variable, can be calculated.

[0108] Specifically, since the values ​​of R1, C1, and R0, as well as the current flowing through R1, C1, and R0, are known respectively, the value of V1, which is the voltage applied to C1, can be calculated.

[0109] On the other hand, the charging capacity state variable of the energy storage system calculated by the above method can be updated in the extended Kalman filter using the following equation 2.

[0110] (Equation 2)

[0111]

[0112] (where R1 and C1 are) Figure 5 The circuit model includes resistor and capacitor values, k: time index, I[k]: current measured at time index k, t: time.

[0113] 2.3 Steps for calculating the charging capacity of an energy storage system

[0114] On the other hand, Equation 3 is an equation that expresses the state variables of the extended Kalman filter used in this invention, namely Equation 1 (the equation for time updating the charging capacity state variable) and Equation 2 (the equation for time updating the voltage state variable), through a vector state equation.

[0115] (Equation 3)

[0116]

[0117] (Where, Capacity: the capacity of the secondary battery, R1 and C1 are...) Figure 5 The circuit model includes resistor and capacitor values, k: time index, I[k]: current measured at time index k, t: time.

[0118] The charging capacity of the energy storage system can be accurately calculated by inserting Equation 3 into the initial values ​​of the extended Kalman filter (when k = 0).

[0119] The extended Kalman filter used in this invention can reduce the error in the calculated charging capacity by repeatedly performing the following process (time update (estimation) -> measurement update (correction) -> time update (estimation) -> measurement update (correction)).

[0120]

[0121] (P: error covariance, H: transform coefficient, K: Kalman gain, Q: standard deviation relative to the true value, A: state variable (Equation 3), z: observation value, R: error relative to the observed true value, k: step size, u: additional input value, I: identity matrix)

[0122] Then, as the error of the input state variable decreases, the error of the extended Kalman filter can be calculated more accurately.

[0123] In other words, in this invention, an accurate voltage model is calculated based on the values ​​of resistance (R) and capacitance (C) calculated using a current with a low c-rate, and then substituted into an extended Kalman filter, thereby reducing errors compared to voltage models calculated using existing techniques.

[0124] <Specific experimental data>

[0125] In the following text, the voltage model of the energy storage system is generated using the resistance (R) and capacitance (C) of the energy storage system measured at a low c-rate, which is a feature of the present invention, and the resulting data of the energy storage system's charging capacity calculated based on this model are compared and described with the resulting data of the charging capacity calculated by conventional techniques.

[0126] Table 1 and Figure 6 This is a table and view for comparing the charging capacity calculated by the method for calculating the charging capacity of the energy storage system using the resistance and capacitance calculation method used to calculate the voltage model of the energy storage system of the present invention with the charging capacity calculated by the prior art (using only the current integration method).

[0127] [Table 1]

[0128]

[0129] In Table 1, the external error is the error caused by the current sensor. On the other hand, the temperature-related error value, depending on whether the external error exists or not, is the difference between the actually measured charging capacity value and the charging capacity value calculated by the calculation method according to the present invention or a conventional method.

[0130] Refer to Table 1 and Figure 6 If there are no external errors (no errors in the current sensor), it can be confirmed that the error in the State of Charge (SOC) calculated using conventional techniques is smaller than the SOC error calculated using the method of this invention. In contrast, if external errors exist, it can be confirmed that the SOC error calculated using the method of this invention is smaller than the SOC error calculated using conventional techniques. Furthermore, when external errors exist, even considering the rate of increase in SOC error, the maximum SOC error calculated using the method of this invention is approximately 3%, while the SOC error calculated using existing techniques is more than twice that, exceeding 7% at its maximum.

[0131] Therefore, in the absence of external errors, the prior art is more accurate. However, in the actual environment in which energy storage systems are used, errors occur in the current sensor. Thus, in the actual use environment, the method of the present invention for calculating the charging capacity of the energy storage system is more accurate than the method of the prior art.

[0132] Meanwhile, Table 2 and Figure 7 This is a table and view used to compare the charging capacity of the energy storage system calculated by the resistance and capacitance calculation method used to calculate the voltage model of the energy storage system of the present invention with the charging capacity calculated by the conventional algorithm (a conventional technique using a voltage model calculated at a high c-rate and a voltage model with a low-weight algorithm in a Kalman filter) by reflecting error conditions.

[0133] [Table 2]

[0134]

[0135] Refer to Table 2 and Figure 7 When the current sensor has an error of ±3% (external error) Figure 7 (a) When using the existing algorithm, the maximum error in calculating the charging capacity is 2.5%, but when using the charging capacity (SOC) calculation method of this invention ( Figure 7 (b) When the maximum error in charging capacity is 1%, it can be confirmed that the charging capacity calculation method of the present invention has a smaller error than that of existing algorithms. Furthermore, when the system degradation (SOH) error (external error) of the energy storage system is ±5% and the tolerance range (external error) of the processing capacity generated within a fixed range is ±2.5%, the maximum error in charging capacity calculated by existing algorithms is 9%, but when using the charging capacity calculation method of the present invention, it can be confirmed that the maximum error in charging capacity is 1.5%.

[0136] As a result, when the external error is large, it can be confirmed that the error generated by the charging capacity calculation method of the present invention is smaller compared with the use of existing algorithms to measure charging capacity.

[0137] On the other hand, Table 3 and Figure 8 These are tables and views used to compare the results of capacity tests using existing algorithms and the charging capacity estimation method of this invention.

[0138] [Table 3]

[0139]

[0140] As shown in Table 3 and Figure 8 As shown, based on capacity testing using existing algorithms, the maximum error in the charging direction is confirmed to be 3.9%, and the maximum error in the discharging direction is 5%. In contrast, based on the results of capacity testing using the charging capacity calculation method of the present invention, the maximum error in the charging direction is confirmed to be 2%, and the maximum error in the discharging direction is 2%.

[0141] As a result, it can be confirmed that the charging capacity calculation method of the present invention leads to a small error in the capacity test results for both charging and discharging.

[0142] On the other hand, in traditional algorithms, when the maximum error described above occurs, the current charging capacity may not be accurately determined, causing the energy storage system to continue charging or discharging for up to one minute. If charging or discharging continues in this manner, even within the maximum charging or discharging capacity of the energy storage system, the charging or discharging process may continue and damage the energy storage system.

[0143] 3. An energy storage system according to an embodiment of the present invention.

[0144] Figure 9 This is a view illustrating the configuration of an energy storage system according to an embodiment of the present invention.

[0145] In the following text, reference will be made to Figure 9 An energy storage system according to an embodiment of the present invention is described.

[0146] The energy storage system 10 according to an embodiment of the present invention may include a plurality of battery racks 11 and a battery section controller (BSC) 110 for controlling the plurality of battery racks.

[0147] Specifically, the BSC 110 can be configured to include a voltage measurement unit 120 for measuring the output voltage of the energy storage system; a current measurement unit 130 for measuring the output current of the energy storage system; a storage unit 140 storing a lookup table of the resistance and capacitance of the energy storage system calculated using a predetermined current with a constant value; and a charging capacity calculation unit 150 for calculating the charging capacity of the energy storage system based on the measured voltage and current and the calculated resistance and capacitance.

[0148] A constant current is used when a current with a total rate of 2 to 3 c or higher is applied. However, the inventors of this invention have found that the resistance and capacitance values ​​of the energy storage system can be calculated more accurately by applying a c-rate current with a rate lower than 2 to 3 c.

[0149] Therefore, in this invention, the low-c rate current can be a current having a value between the minimum current value that can measure the resistance and capacitance of the energy storage system and the 2c rate value.

[0150] Preferably, the current with a low c-rate can be a current with a 0.1 c-rate, which corresponds to 1 / 10 of the current with a 1 c-rate.

[0151] Simultaneously, the voltage measurement unit 120 can measure a first voltage, which is the voltage of the energy storage system when a predetermined current is applied to the energy storage system; and a second voltage, which is the voltage of the energy storage system after the current applied to the energy storage system is cut off.

[0152] Simultaneously, the current measurement unit 130 measures the output current of the energy storage system, and the measured output current of the energy storage system is used to calculate the state variable value of the charging capacity of the energy storage system.

[0153] The lookup table stored in storage unit 140 can be executed and stored according to the method of calculating the resistance (R) and capacitance (C) of the voltage model of the energy storage system according to the above embodiment of the present invention.

[0154] Meanwhile, the charging capacity calculation unit 150 can be configured to include a voltage state variable calculation unit 151, which is used to calculate the voltage state variable of the energy storage system based on the resistance and capacitance of the lookup table; and a charging capacity state variable calculation unit 152, which is used to calculate the state variable for the charging capacity of the energy storage system using a current integration method for integrating the measured output current of the energy storage system, and can calculate the charging capacity of the energy storage system by substituting the calculated voltage state variable and the charging capacity state variable into a Kalman filter.

[0155] The charging capacity of a specific energy storage system can be calculated by performing the process of calculating the charging capacity of the energy storage system of the present invention described above.

[0156] For example, the charging capacity state variable calculated in the charging capacity state variable calculation unit can be updated over time according to Equation 1 below.

[0157] (Equation 1)

[0158]

[0159] (Where, Q_capacity: the capacity of the secondary battery, k: time index, I[k]: the current measured at time index k, t: time)

[0160] Meanwhile, the calculated voltage state variables in the voltage state variable calculation unit can be updated over time according to Equation 2 below.

[0161] (Equation 2)

[0162]

[0163] (where R1 and C1 are) Figure 5 The circuit model includes resistor and capacitor values, k: time index, I[k]: current measured at time index k, t: time.

[0164] On the other hand, although the technical concept of the present invention has been specifically described with reference to the above embodiments, it should be noted that the above embodiments are for illustrative purposes and not for limiting purposes. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from its spirit and scope.

Claims

1. A method for calculating the charging capacity of an energy storage system, the method comprising: A current application step, wherein a predetermined current having a constant value is applied to the energy storage system; The first voltage measurement step measures the voltage of the energy storage system while a predetermined current with a constant value is applied to the energy storage system. The second voltage measurement step measures the voltage of the energy storage system after blocking a predetermined current with a constant value applied to the energy storage system. The resistance (R) and capacitance (C) calculation steps are based on the voltage of the energy storage system measured in the first voltage measurement step, the voltage of the energy storage system measured in the second voltage measurement step, and the predetermined current having the constant value, to calculate the resistance (R) and capacitance (C) of the energy storage system. The voltage state variable calculation step calculates the voltage state variable for the energy storage system based on the calculated resistance and capacitance. The charging capacity state variable calculation step uses a current integration method to integrate the measured output current to calculate the state variable for the charging capacity of the energy storage system. The energy storage system charging capacity calculation step involves substituting the voltage state variable and the charging capacity state variable into the extended Kalman filter to calculate the charging capacity of the energy storage system. The predetermined current with a constant value applied in the current application step is a current between the minimum current value capable of measuring the resistance and capacity of the energy storage system and a rate of 0.1c.

2. The method according to claim 1, wherein, The extended Kalman filter is executed repeatedly: Update the state variables over time; The error covariance of the state variables is updated over time; Calculate the Kalman gain of the extended Kalman filter; The gain is used to estimate the state variables; and The gain is used to correct the error covariance of the state variable.

3. The method according to claim 1, wherein, The calculated charging capacity state variable is updated over time according to Equation 1 below. Equation 1 Where Q_capacity is the capacity of the energy storage system, k is the time index, I[k] is the current measured at time index k, and t is the time.

4. The method according to claim 1, wherein, The voltage state variable calculation step uses a voltage model circuit to calculate the voltage state variable of the energy storage system. The calculated voltage state variables are updated over time according to Equation 2 below. Equation 2 Where R1 and C1 are the resistance and capacitance values ​​included in the voltage model circuit, k: time index, I[k]: current measured at time index k, and t: time.

5. The method according to claim 4, wherein, The voltage model circuit includes: An open-circuit voltage source, wherein the open-circuit voltage source is used to output a predetermined voltage based on the current value flowing through the energy storage system; One or more resistors; and One or more capacitors.

6. An energy storage system, comprising: Multiple battery holders; and A battery compartment controller (BSC) is used to control the plurality of battery racks. The BSC includes: A voltage measurement unit is used to measure the output voltage of the energy storage system when a predetermined current with a constant value is applied to the energy storage system. A current measurement unit, wherein the current measurement unit is used to measure the output current of the energy storage system; and A charging capacity calculation unit, wherein the charging capacity calculation unit is used to calculate the charging capacity of the energy storage system using the resistance (R) and capacitance (C) of the energy storage system calculated by the predetermined current and the output voltage, the charging capacity calculation unit comprising: A voltage state variable calculation unit, used to calculate the voltage state variable of the energy storage system based on the calculated resistance and capacitance; and A charging capacity state variable calculation unit is provided, which is used to calculate the state variables of the charging capacity of the energy storage system using a current integration method for integrating the measured output current. The charging capacity calculation unit substitutes the calculated voltage state variable and the charging capacity state variable into the Kalman filter to calculate the charging capacity of the energy storage system. The predetermined current having the constant value is a current between the minimum current value and a rate of 0.1c that can be used to measure the resistance and capacitance of the energy storage system.

7. The energy storage system according to claim 6, wherein, The voltage measurement unit measures: The first voltage is the voltage of the energy storage system when the predetermined current is applied to the energy storage system. as well as The second voltage is the voltage of the energy storage system after the predetermined current applied to the energy storage system is cut off.

8. The energy storage system according to claim 6, wherein, The charging capacity state variable calculated in the charging capacity state variable calculation unit is updated over time according to Equation 1 below. Equation 1 Where Q_capacity is the capacity of the energy storage system, k is the time index, I[k] is the current measured at time index k, and t is the time.

9. The energy storage system according to claim 6, wherein, The voltage state variables calculated in the voltage state variable calculation unit are updated over time according to Equation 2 below. Equation 2 Where R1 and C1 are the resistance and capacitance values ​​included in the voltage model circuit, k: time index, I[k]: current measured at time index k, and t: time.

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