A method of estimating battery peak power in real time, a battery management system, a battery and a software product

Abstract

The application belongs to the technical field of battery management system, and particularly relates to a method for real-time estimation of battery peak power by using off-line calculated peak current, a battery management system, a battery system and a computer software product. The method identifies battery parameters by a third-order equivalent circuit model off-line, estimates the extreme current of the battery in an open circuit state by using the off-line identified battery parameters, and estimates the peak power of the battery in real time by using the estimated extreme current of the battery in the open circuit state.

Description

Technical Field

[0001] This invention belongs to the field of battery management system technology, and particularly relates to a method for real-time estimation of battery peak power using offline calculated peak current, a battery management system, a battery system, and computer software products. Background Technology

[0002] In battery management systems, equivalent circuit models of the battery are frequently used for offline parameter identification. The identified parameters are then used to estimate the battery's operating state. A schematic diagram of the model used for offline battery parameter identification is shown below. Figure 1 The formulas used are (1) to (6).

[0003] U(t)=OCV(t)+Vp(t)+Vr(t) (1)

[0004] Vr(t)=I(t)×R0(t) (2)

[0005] Vp(t)=Vp1(t)+Vp2(t)+Vp3(t) (3)

[0006]

[0007]

[0008]

[0009] Where t represents a certain moment, t-1 represents the moment before a certain moment, and t is an integer greater than or equal to 1. U(t) is the battery terminal voltage, OCV(t) is the battery open-circuit voltage, Vp(t) is the battery polarization voltage, which is divided into first-order polarization voltage Vp1(t), second-order polarization voltage Vp2(t), and third-order polarization voltage Vp3(t). Vr(t) is the battery ohmic voltage, I(t) is the battery current, and R0(t) is the battery ohmic internal resistance. The battery model time constant τ is divided into first-order time constant τ1, second-order time constant τ2, and third-order time constant τ3. The battery polarization internal resistance Rp(t) is divided into first-order polarization internal resistance Rp1(t), second-order polarization internal resistance Rp2(t), and third-order polarization internal resistance Rp3(t). dt is the battery data sampling time interval, which can be customized, such as 0.1 seconds. The variables in formulas (1) to (6) are all related to time t.

[0010] Because it is difficult to estimate the peak power of a battery in real time under actual operating conditions, the state of power estimation of the battery peak power is subject to significant deviations. To address the problem of inaccurate battery peak power estimation, a method for online estimation of battery peak power based on offline parameter identification is proposed. Summary of the Invention

[0011] The purpose of this invention is to address the problems existing in the prior art by providing a method for real-time online estimation of battery peak power based on offline parameter identification. This method identifies battery parameters offline using a third-order RC equivalent circuit model. Using the offline identified battery parameters, it estimates the extreme current Im when the battery transitions from a stable open-circuit state to a charge / discharge state. Finally, it uses the extreme current Im to estimate the battery's peak power in real time.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] A method for real-time estimation of battery peak power using offline calculated peak current, the method comprising the following steps:

[0014] S1, using the battery parameters identified offline, and using the formula of the third-order RC equivalent circuit model, calculate the extreme current Im of the battery when the battery voltage reaches the target voltage U1(t+Δt) from time t to time t+Δt when the battery transitions from a stable open-circuit state to a charge-discharge state.

[0015] S2, using the extreme current Im to calculate the extreme current Im_dyn when the battery voltage reaches the target voltage U1(t+Δt) from time t to time t+Δt under actual operating conditions;

[0016] S3, using the calculated extreme current Im_dyn of the battery under actual operating conditions and the target battery voltage U1(t+Δt), calculate the battery peak power SOP in real time. The formula for calculating the battery peak power SOP is as follows:

[0017] SOP = Im_dyn × U1(t + Δt).

[0018] Preferably, the formula for the third-order RC equivalent circuit model includes:

[0019] Formula (1): U(t)=OCV(t)+Vp(t)+Vr(t)

[0020] Formula (2): Vr(t)=I(t)×R0(t)

[0021] Formula (3): Vp(t) = Vp1(t) + Vp2(t) + Vp3(t)

[0022] Formula (4):

[0023] Formula (5):

[0024] Formula (6):

[0025] Where t represents a certain moment, t-1 represents the moment before a certain moment, and t is an integer greater than or equal to 1;

[0026] U(t) is the battery terminal voltage, OCV(t) is the battery open-circuit voltage, and Vp(t) is the battery polarization voltage, which is divided into first-order polarization voltage Vp1(t), second-order polarization voltage Vp2(t), and third-order polarization voltage Vp3(t).

[0027] Vr(t) is the ohmic voltage of the battery, I(t) is the current of the battery, and R0(t) is the ohmic internal resistance of the battery.

[0028] The time constant τ of the battery model is divided into first-order time constant τ1, second-order time constant τ2, and third-order time constant τ3.

[0029] The polarization resistance Rp(t) of the battery is divided into first-order polarization resistance Rp1(t), second-order polarization resistance Rp2(t), and third-order polarization resistance Rp3(t); the time interval between two moments before and after dt.

[0030] Preferably, step S1 includes the following steps:

[0031] S11, offline battery parameter identification; under different temperatures, currents, and SOCs, the identified parameters are ohmic internal resistance R0(t), polarization internal resistance Rp1(t), polarization internal resistance Rp2(t), polarization internal resistance Rp3(t), and time constants (τ1, τ2, τ3), presented in a three-dimensional table. Under different temperatures and SOCs, the identified parameter is the open-circuit voltage OCV(t), presented in a two-dimensional table.

[0032] S12, set the minimum and maximum values ​​of the extreme current; the minimum value is denoted as Im_lb, and the maximum value is denoted as Im_ub. The minimum value is uniformly set to zero, and the maximum value can be adjusted according to the maximum allowable charging and discharging current of the battery.

[0033] S13, Set the initial value of the extreme current; The initial value of the extreme current is denoted as Im_0, and the initial value of Im_0 is between Im_lb and Im_ub, and the initial value is the average value of Im_lb and Im_ub;

[0034] S14. Assign Im_0 to the extreme current Im. Using the extreme current Im, the current battery temperature T, and the current battery SOC, calculate the battery's ohmic internal resistance and polarization internal resistance by looking up the parameter table in the parameters identified offline in step S11. The calculation method for the time constant τ is the same as the calculation method for the battery internal resistance.

[0035] S15, use the current battery temperature T and the current battery SOC to look up the parameter table in the offline identification parameter OCV(t) in step S11 to calculate the battery open circuit voltage OCV(t);

[0036] S16, using the battery internal resistance R0(t) and Rp(t) and time constant τ(t) calculated by looking up the table in S14, replace I(t) with the extreme current Im calculated at the current moment, and substitute them into formulas (2), (3), (4), (5) and (6) to calculate the ohmic voltage Vr(t) and polarization voltage Vp(t).

[0037] S17. Using the calculation results of S15 and S16, substitute them into formula (1) to calculate the voltage value U(t). Record the calculated voltage U(t) as U1(t). Calculate the extreme current Im corresponding to the time when U1(t) reaches the battery target voltage U1(t+Δt) from time t to time t+Δt.

[0038] Note: When calculating the value of U1(t), the value of U1(t) is calculated multiple times. The calculation of U1(t) ends when the calculated value of U1(t) is equal to the target voltage U1(t+Δt) at time t+Δt.

[0039] Step S2 includes the following steps:

[0040] S21, Under the actual operating conditions of the battery, the current time is t, and the polarization voltage Vp(t) at point B2 corresponding to time t. B Calculate Vp(t) by replacing Im with the current sampling current, sampling battery temperature T, and battery SOC, following the steps and methods in S14 and S16. B calculate;

[0041] S22, Under actual battery operating conditions, the current time is t, and the open-circuit voltage OCV(t+Δt) at point X2 corresponding to time t+Δt is calculated; OCV(t+Δt) is the open-circuit voltage based on OCV(t) after time Δt, and the sampling temperature and SOC at time t are denoted as T. t SOC t The temperature and SOC at time t+Δt are denoted as T. t+Δt SOC t+Δt From time t to time t+Δt, SOC t To SOC t+Δt T is calculated using ampere-hour integration. t+Δt Approximately equal to T t ;OCV(t+Δt) is calculated according to method S15, with T t+Δt and SOC t+Δt Substitute into the calculation;

[0042] S23, Under the actual operating conditions of the battery, the current time is time t, and the extreme current Im at point B2 corresponding to time t is calculated; Im calculated by S1 is a lookup function of temperature T and SOC, and Im is denoted as f(T, SOC). Using the temperature T and SOC at point B2 as input variables, the extreme current Im at point B2 is calculated according to the method in step S14.

[0043] S24, Determine the target voltage U1(t+Δt); refer to the description method in step S1 for determination;

[0044] S25, Under actual battery operating conditions, at time t, calculate the real-time extreme current Im_dyn from point B2 corresponding to time t+Δt to point X2 corresponding to time t+Δt; The relationship between the extreme current Im identified offline in S1 and the battery extreme current Im_dyn under actual operating conditions is as follows:

[0045] U1(t+Δt)=OCV(t+Δt)-Vp(t+Δt)-R0(t+Δt)×Im_dyn

[0046]

[0047]

[0048]

[0049]

[0050] Vp(t) B The value is calculated according to step S21, the OCV(t+Δt) value is calculated according to step S22, and the target voltage U1(t+Δt) value is calculated according to step S1.

[0051] Furthermore, the present invention also discloses a battery management system, which includes a built-in or external offline identification basic data storage module and a calculation module; the offline identification basic data storage module and the calculation module use the method described above to estimate the battery peak power in real time.

[0052] Furthermore, the present invention also discloses a battery system, including the aforementioned battery management system.

[0053] Furthermore, the present invention also discloses a computer program product, including a computer program or instructions that, when executed by a processor, implement the method. The computer program product described in this invention includes a computer program that enables a computer to perform a certain function or effect during operation, a computer-readable storage medium storing the computer program, a computer program product or manufacture containing the computer-readable storage medium or the computer program, and electronic (digital) signals for transmitting computer program instruction codes, etc. The computer-readable storage medium includes, for example, optical discs, magnetic disks, optical fibers, ROMs, PROMs, VCDs, DVDs, and other storage devices.

[0054] By employing the above-mentioned technical solution, this invention identifies battery parameters offline using a third-order RC equivalent circuit model. Using the offline identified battery parameters, it estimates the extreme current Im when the battery transitions from a stable open-circuit state to a charge / discharge state. Using the extreme current Im of the battery, it estimates the peak power of the battery in real time. Attached Figure Description

[0055] Figure 1 Third-order RC equivalent circuit model diagram.

[0056] Figure 2 A graph showing the fitting effect of battery voltage during the discharge process.

[0057] Figure 3 Schematic diagram for calculating discharge voltage curve.

[0058] Figure 4 Flowchart for calculating the voltage curve U1(t) from time t to time t+Δt.

[0059] Figure 5 Schematic diagram for calculating discharge voltage curve.

[0060] Figure 6 Flowchart for calculating the voltage curve U1(t) from time t to time t+Δt.

[0061] Figure 7 A schematic diagram showing the real-time calculation of the discharge voltage curve to the target voltage U1(t+Δt).

[0062] Figure 8 A flowchart for real-time estimation of battery peak power using peak current Im.

[0063] Figure 9 Application structure diagram of the present invention. Detailed Implementation

[0064] The present invention will be further described in detail below with reference to the accompanying drawings: This embodiment is implemented under the premise of the technical solution of the present invention, and detailed implementation methods are given, but the protection scope of the present invention is not limited to the following embodiments.

[0065] like Figure 8 The method shown is a real-time estimation of battery peak power using offline calculated peak current. The method includes the following steps:

[0066] S1. Using the battery parameters identified offline, the extreme current Im is calculated when the battery voltage reaches the target voltage U1(t+Δt) based on time t to time t+Δt when the battery transitions from a stable open-circuit state to a charge / discharge state using the formula of the third-order RC equivalent circuit model.

[0067] S2, using the extreme current Im to calculate the extreme current Im_dyn when the battery voltage reaches the target voltage U1(t+Δt) from time t to time t+Δt under actual operating conditions;

[0068] S3, using the calculated extreme current Im_dyn of the battery under actual operating conditions and the target battery voltage U1(t+Δt), calculate the battery peak power SOP in real time; the formula for calculating the battery peak power SOP is as follows:

[0069] SOP = Im_dyn × U1(t + Δt).

[0070] Note 1: The offline identification basic data storage module contains the objects and parameter tables for offline identification of battery parameters.

[0071] 1) The objects of offline battery parameter identification are the battery current curves and voltage curves when the battery is in a stable open circuit state and transitioning to a charge / discharge state under different temperatures, currents, and SOCs. The sampling time interval is at least 0.5 seconds (preferably 0.1 seconds), and three decimal places are retained.

[0072] 2) Parameter table, which is the output of parameters after offline identification. The identified parameter table values ​​are retained to three decimal places; the specific parameter table is divided into three-dimensional table and two-dimensional table.

[0073] Three-dimensional table: a table showing the correspondence between ohmic internal resistance R0, polarization internal resistance Rp1, polarization internal resistance Rp2, polarization internal resistance Rp3, and time constants (τ1, τ2, τ3) under different temperatures, currents, and SOCs.

[0074] Two-dimensional table: a table showing the correspondence between open-circuit voltage (OCV) at different temperatures and SOCs.

[0075] If new battery parameters are identified offline, the objects can be retrieved again and identified offline to create a new parameter table. The identified parameter table values ​​are independent of time and do not change over time.

[0076] Note 2: Target voltage U1(t+Δt): It is related to battery temperature, current and type, and can be set according to requirements, such as 2.0 volts or 2.7 volts for discharging and 3.6 volts or 4.2 volts for charging.

[0077] in:

[0078] S1. Utilize the battery parameters identified offline. The parameters include the ohmic internal resistance R0(t), the polarization internal resistance Rp(t), and the time constant τ. Substitute these parameters into formulas (1) to (6) to calculate the extreme current Im when the battery voltage reaches the target voltage U1(t+Δt) from time t to time t+Δt when the battery transitions from a stable open-circuit state to a charge / discharge state.

[0079] S11, offline identification of battery parameters. Identified parameters include ohmic internal resistance R0(t), polarization internal resistance Rp1(t), polarization internal resistance Rp2(t), polarization internal resistance Rp3(t), time constants τ1, τ2, τ3, and open-circuit voltage OCV(t). Ohmic internal resistance R0(t) and polarization internal resistance Rp(t) are related to SOC, temperature, and current, while OCV(t) is related to SOC and temperature.

[0080] Offline parameter identification refers to the method of calculating parameters when a battery transitions from a stable open-circuit state to a charge / discharge state using the collected voltage and current data from the time interval t before the first moment of the transition to the charge / discharge state to t+Δt. Since the open-circuit voltage OCV(t) can be directly measured, the calculation process will not be described further. The offline identification methods for ohmic internal resistance, polarization internal resistance, and time constant are as follows.

[0081] The measured voltage curve of the battery is denoted as U0(t), and the fitted voltage curve of the battery is denoted as Uf(t). Battery parameter identification uses the least squares method. Formulas (1) to (6) are used to fit the battery terminal voltage curve Uf(t). Taking battery discharge as an example, the specific fitting process is as follows: Figure 2 (a) As shown in Table 1 and Table 2. Figure 2 (b) is a graph showing the effect of the battery charging voltage fitting process. The principle, process and method of voltage fitting are the same as those of discharge, and will not be repeated here.

[0082] Table 1. Schematic diagram of collected voltage U0(t) and fitted voltage Uf(t) data.

[0083]

[0084]

[0085] like Figure 2 As shown in (a) and Table 1, Uf(t) is fitted multiple times, and the fitted curve Uf(t) continuously approaches the measured voltage curve U0(t) until the objective function F between the fitted curve Uf(t) and the measured voltage curve U0(t) is minimized in the nth fitting. At this point, the fitting is complete, and the battery identification parameters corresponding to the nth fitted curve Uf(t) are used as the final identification parameters. The battery parameter identification process can be represented by Table 2.

[0086] Table 2. Schematic diagram of battery parameter identification process

[0087]

[0088] When fitting Uf(t) using parameters, initial values ​​for the battery parameters to be identified and the range of the fitted values ​​need to be given. For example, the initial values ​​of R0(t) and Rp(t) are shown in Table 2, and the fitted values ​​range from 0 to 100 milliohms. The initial values ​​of the time constant are also shown in Table 2, and the fitted values ​​range from 0 to 100 seconds. When the true values ​​of the parameters cannot be predicted in advance, the initial values ​​can be set as hypothetical values. During each fitting of the voltage Uf(t), the fitted parameters continuously approach the true values. Before the first fitting begins, the initial parameters are substituted into formulas (1) to (6), and the first calculation result of the F value is obtained through function calculation. This corresponds to the first fitted voltage in Table 1 and the first parameter fitting result in Table 2. Before the second fitting begins, the first parameter fitting result is substituted into formulas (1) to (6), and the second calculation result of the F value is obtained through function calculation. This corresponds to the second fitted voltage in Table 1 and the second parameter fitting result in Table 2. This process is repeated, and each time Uf(t) is calculated, the parameters are adjusted within the range of the parameter fitting values ​​until the nth fitting. The calculated objective function F value is the minimum value of the first to the last calculated value F. The formulas for calculating the objective function F are shown in (7) and (8).

[0089]

[0090]

[0091] L is the length of the voltage sampling point array [A,B,C,…,X] in Table 1. U0(t) contains L voltage sampling points, and Uf(t) contains L voltage fitting points. i is the index of an element in the sampling point array [A,B,C,…,X], U0(t) i and Uf(t) i Let U and Uf represent a single element in U0(t) and Uf(t), respectively. F is the minimum value of the objective function f(x), which is the minimum value of the objective function F obtained by the least squares method.

[0092] S12 sets the minimum and maximum values ​​of the extreme current. The minimum value is denoted as Im_lb, and the maximum value is denoted as Im_ub. The minimum value is uniformly set to zero, while the maximum value can be adjusted according to the battery's maximum allowable charge and discharge current. For example, if the battery's rated capacity is 50Ah and the maximum allowable charge and discharge current is 10C (where C is the battery rate symbol), Im_ub is designed to be 500A in the calculation. If the battery's maximum allowable charge and discharge current is 5C, Im_ub is designed to be 250A in the calculation.

[0093] S13, Set the initial value of the extreme current. The initial value of the extreme current is denoted as Im_0. The initial value of Im_0 is between Im_lb and Im_ub, and the initial value is the average value of Im_lb and Im_ub.

[0094] In step S14, Im_0 is assigned to the extreme current Im. Using the extreme current Im, the current battery temperature T, and the current battery SOC, the ohmic internal resistance and polarization internal resistance of the battery are calculated by looking up a table in the offline identification parameters in S11. The calculation method for the time constant τ is the same as that for the battery internal resistance, and will not be repeated here.

[0095] To facilitate the explanation of the method and process of calculating the battery internal resistance by looking up the table, the internal resistance identification value is not taken. Instead, a random assumed internal resistance value is selected and rounded to one decimal place. The assumed internal resistance value data is shown in the table below.

[0096] Table 3 Discharge internal resistance at 10 degrees Celsius (T1) Measuring gauge (unit: milliohms)

[0097]

[0098] Table 4 Discharge internal resistance at 40 degrees Celsius (T2) Measuring gauge (unit: milliohms)

[0099]

[0100] The specific steps for calculating the battery internal resistance by referring to the table are as follows, which are carried out in three steps. Here, the internal resistance includes polarization internal resistance and ohmic internal resistance.

[0101] The first step is to perform SOC interpolation at the same temperature T1 or T2 and the same current I1 or I2 or I3.

[0102]

[0103] When SOC takes different values, R1(I i Different values ​​of R1(I) i The internal resistance is calculated based on Tables 3 and 4, under different currents I1, I2, and I3, when the state of charge (SOC) is different. The corresponding current is I iSOC corresponds to SOC j The internal resistance below, The data are from Tables 3 and 4. Where i ∈ [1, 3], SOC ∈ [SOC...]. j SOC j+1 ], j∈[1,2], the interpolation results of R1 under currents I1, I2, and I3 are denoted as R1(I1), R1(I2), and R1(I3), respectively. When Greater than When the condition is met, the plus sign is used in formula (3), and vice versa.

[0104] The second step is to interpolate the current Imax at the same temperature T1 or T2 and the same state of charge (SOC).

[0105] R2=R1(I i )±|R1(I i+1 )―R1(I i )|*(Im―I i ) / (I i+1 —I i (10)

[0106] R2 is based on R1(I) calculated in the first step. i The result of current interpolation is calculated. Where Im∈[I i ,I i+1 ], i∈[1,2]. The interpolation result of R2 at temperature T1 is denoted as R2(T1), and the interpolation result at temperature T2 is denoted as R2(T2). When R1(I i+1 ) greater than R1(I i When ), take the plus sign in formula (4), otherwise take the minus sign.

[0107] The third step is to interpolate the temperature T at the same current and the same state of charge (SOC).

[0108] R3=R2(T1)±|R2(T1)―R2(T2)|*(T2―T) / (T2―T1) (11)

[0109] R3 is the result of the final calculation of the battery's internal resistance using a lookup table. Where T∈[T1,T2]. When R2(T1) is greater than R2(T2), the minus sign is used in formula (3), and vice versa. R3 can be either the polarization resistance or the ohmic resistance.

[0110] Tables 3 and 4 are example reference tables for linear interpolation of internal resistance. The actual internal resistance identification value is adjusted according to the actual SOC, temperature, and current. When calculating R3, at each moment, there is a corresponding SOC, current Imax, and temperature T, and a corresponding value of R3.

[0111] Here are three specific steps for calculating the battery's internal resistance using a table: Assumption 1: Current extreme current Im is 0.5C, current temperature T is 10 degrees Celsius, current battery SOC is 50%, internal resistance (from the table) is 0.7 milliohms; Assumption 2: Current extreme current Im is 0.5C, current temperature T is 10 degrees Celsius, current battery SOC is 25%, internal resistance (from the table) is 0.8 milliohms; Assumption 3: Current extreme current Im is 0.75C, current temperature T is 10 degrees Celsius, current battery SOC is 50%, internal resistance (from the table) is 0.65 milliohms; Assumption 4: Current extreme current Im is 0.5C, current temperature T is 25 degrees Celsius, current battery SOC is 50%, internal resistance (from the table) is 0.65 milliohms; Assumption 5: Current extreme current Im is 1.5C, current temperature T is 10 degrees Celsius, current battery SOC is 50%, internal resistance (from the table) is 0.6 milliohms.

[0112] When the actual temperature T, SOC, and current of the battery exceed the test value range of the base table (see Tables 3 and 4), the internal resistance is calculated using the method of looking up the boundary values ​​of the base table. That is, when Im is greater than I3, the table is looked up according to I3; when Im is less than I1, the table is looked up according to I1. The SOC and temperature are handled in the same way. The reason for this is that the offline identification parameters are identified under our designed test conditions. During actual operation, the actual SOC, current, and temperature of the battery may exceed the test range of the SOC, current, and temperature corresponding to the offline identification parameters. When using the actual temperature T, SOC, and current of the battery to look up the table to calculate the battery internal resistance, the linear difference method is used, as shown in formulas (9) to (11).

[0113] S15, using the battery's current temperature T and current SOC, the battery open-circuit voltage OCV(t) is calculated by looking up a two-dimensional table in the offline identification parameter OCV(t) from step S11. When calculating the battery OCV(t) using the battery's actual temperature T and SOC from the battery OCV base table, a linear interpolation method is used. When calculating OCV(t), the interpolation method in S14 is referenced to adjust the current I... i Simply replace it with temperature T, and refer to formulas (9) and (10) to complete the OCV(t) lookup table calculation.

[0114] S16. Using the battery internal resistance calculated from the table in S14, substitute it into formulas (2)(3)(4)(5)(6) to calculate the ohmic voltage Vr(t) and polarization voltage Vp(t).

[0115] When calculating the polarization voltage and ohmic voltage, Im from step S14 is taken as I(t). R3 calculated by interpolation in S14, the time constant identified in S11, and OCV(t) calculated by interpolation in S15 are substituted into formulas (2) to (6) for calculation. dt is taken as 0.1 seconds. To facilitate the explanation of the calculation method and process of polarization voltage and ohmic voltage, the identified values ​​of internal resistance and time constant are not taken. Instead, assumed values ​​of internal resistance and time constant are randomly selected and retained to two decimal places. The calculation of the first-order polarization voltage and ohmic voltage is shown in the table below, and the calculation results are retained to two decimal places. The calculation of the second-order polarization voltage and the third-order polarization voltage is similar to that of the first-order polarization voltage and will not be described again.

[0116] Table 5 shows the ohmic voltage and first-order polarization voltage calculated using formulas (2) and (4).

[0117]

[0118] As shown in Table 5, in each calculation, the input constant is the invariant when calculating the polarization voltage and ohmic voltage using the formula, and the input variable is the variable when calculating the polarization voltage and ohmic voltage using the formula. In each calculation, R3 is interpolated once, that is, the polarization internal resistance Rp1(t) and the ohmic internal resistance R0(t) are interpolated once through step S14. The initial polarization voltage is Vp1(t-1). The Vp1(t-1) calculated in the first calculation is zero. The Vp1(t-1) calculated in the second calculation is the final voltage of the first calculation. The Vp1(t-1) calculated in the third calculation is the final voltage of the second calculation. And so on, the polarization voltage is calculated iteratively using formula (4).

[0119] S17. Using the calculation results of S15 and S16, substitute them into formula (1) to calculate the voltage value U(t). Record the calculated voltage U(t) as U1(t). Calculate the extreme current Im corresponding to the time when U1(t) reaches the battery target voltage U1(t+Δt) from time t to time t+Δt.

[0120] Note: When calculating the value of U1(t), the value of U1(t) is calculated multiple times. The calculation of U1(t) ends when the calculated value of U1(t) is equal to the target voltage U1(t+Δt) at time t+Δt.

[0121] Time t corresponds to the moment before the first calculation of the polarization voltage in Table 5 of S16. Time t is the moment before the current is generated. For example, if the current is zero at the first moment and not zero at the second moment (corresponding to the first calculation in Table 5), the first moment is time t. When recording time t, the polarization voltage of the battery must be zero before time t, and the same applies below. The extreme current Im is calculated multiple times. When the voltage U1(t) calculated by the extreme current Im can reach the target voltage U1(t+Δt) from time t to time t+Δt, the calculation of the extreme current is terminated.

[0122] In the first scenario, before time t+Δt, the voltage U1(t) calculated using the extreme current Im reaches the target voltage U1(t+Δt). In this case, the calculation of U1(t) is stopped, and the ohmic voltage Vr(t), polarization voltage Vp(t), and open-circuit voltage OCV(t) are cleared to zero. The magnitude of the extreme current Im is adjusted, and its value is assigned to Im_ub. Then, Im_ub and Im_lb are divided by two to obtain the new extreme current Im. The battery voltage U1(t) is then calculated again using the new extreme current Im. Taking battery discharge as an example... Figure 3 As shown.

[0123] Figure 3 In the diagram, the values ​​of the horizontal and vertical axes can be adjusted according to different battery types. Figure 3 In this diagram, point A0 corresponds to the first moment, denoted as t(1), point B0 corresponds to the second moment, denoted as t(t), point C0 corresponds to the third moment, which is usually the moment when the current is not zero, denoted as t(t+1), and so on. The last point X0 corresponds to the moment t+Δt, denoted as t(t+Δt). The voltage at this moment is the target voltage of the battery, denoted as U1(t+Δt). The total time from point B0 to point X0 is Δt, which can be 2 seconds, 10 seconds, etc. Figure 3 In the process, the time interval dt between any two sampling points from point B0 to point X0 is equal and can be freely designed as needed, for example, 0.1 seconds. Figure 3 The variables corresponding to each point are shown in the table below.

[0124] Table 6. Relevant Variables

[0125]

[0126] Starting from point A0 to point X0, the battery SOC changes from SOC(1) to SOC(t+Δt), calculated using the ampere-hour integration method. The battery temperature T is collected by a temperature sensor, and the battery extreme current Im is given an initial value by S13 and S14. Point B0 is set as the initial point, and the polarization voltage is zero. At time t, point C0 corresponds to the moment when the polarization voltage just starts to be generated, which is also the moment when the current value starts to be non-zero.

[0127] Assume that the calculated U1(t+2) at point D0 represents the point at which the target voltage U1(t+Δt) is reached. At points C0 and D0, the values ​​calculated multiple times using SOC, Im, and T are: battery internal resistance R3, open-circuit voltage OCV(t), polarization voltage Vp(t), ohmic voltage Vr(t), and battery terminal voltage U1(t). The calculation time interval is dt, and the calculation methods for each variable are as described in S11 to S16. The calculated value of the battery terminal voltage U1(t) at point D0 is U1(t+2), which means U1(t+2) = U1(t+Δt) at point D0. Assume Δt is 2 seconds and dt is 0.1 seconds. Starting from point B0, assume that the battery terminal voltage U1(t) reaches the target voltage U1(t+Δt) ahead of schedule at 0.5 seconds. Figure 3 The voltage curve U1(t) calculated at point D0 reaches the target voltage U1(t+Δt). Within a 0.5-second time interval, the polarization resistance is negligible due to the influence of SOC, T, and Im when calculating the polarization voltage. From formulas (4), (5), and (6), it can be seen that the value of Im is too large, leading to a larger calculated value of the polarization voltage. Voltage U1(t+2) reaches the target voltage U1(t+Δt) earlier. During the calculation process from point C0 to point D0, Im remains unchanged, i.e., Im(t+1) = Im(t+2) = Im. Assuming that U1(t+3) calculated at point E0 is the point where the target voltage U1(t+Δt) is reached, the calculation process is similar to that at point D0 and will not be repeated.

[0128] When the calculated value of Im is too large, the ohmic voltage Vr(t), polarization voltage Vp(t), and OCV(t) need to be reset to zero, and the calculation needs to be restarted at point C0. Before restarting the calculation, the current calculated Im is added to the design minimum boundary value Im_lb, and then divided by two to complete the adjustment calculation of Im. The initial value of Im is assumed to be 25 amperes, and Im_lb is zero. The adjustment process is shown in the table below.

[0129] Table 7. Schematic diagram of extreme current Im adjustment process

[0130]

[0131] The calculations for each adjustment of the extreme current Im in Table 7 must be performed sequentially from point A onwards, following the calculations for the relevant variables in Table 6. Each time the extreme current Im is reduced, the ohmic internal resistance value calculated from the table is less affected by the battery's SOC and T, but more significantly affected by the extreme current Im. The calculated ohmic voltage gradually decreases, as... Figure 3The voltage difference between points B0 and C0 gradually decreases from the first curve to the third curve. Similarly, the method for calculating polarization resistance by looking up the table is the same as that for ohmic resistance, but the polarization voltage calculation is iterative. As shown in Table 5, although the polarization resistance calculated by looking up the table will change, the main factor affecting the value of the calculated polarization voltage is the magnitude of the extreme current Im. As can be seen from formulas (4), (5), and (6), the increment of the polarization voltage value decreases with each calculation. Figure 3 As shown in the first, second, and third curves, the calculation effect after Im adjustment is that the voltage curve U1(t) is closer to the center of the curve in each calculation. Figure 3 The third voltage curve corresponds to a calculation time length close to Δt. For example, the calculation time interval between each pair of points C0D0, C0E0, and C0X0 represents the time length for U1(t) to reach the target voltage U1(t+Δt) during the first, second, and last calculations. The ranges of SOC and temperature T within these time lengths are denoted as [SOC1, SOC2] and [T1, T2], representing the minimum and maximum values ​​of SOC and temperature T, respectively, as shown in Table 7. Starting from point B0, the calculation process for the terminal voltages at other points such as C0, D0, and E0 is as follows... Figure 4 As shown.

[0132] In the second scenario, at time t+Δt, the voltage U1(t) calculated from the extreme current Im does not reach the target voltage U1(t+Δt). (See below.) Figure 5 As shown, there are three calculated voltage curves U1(t). The first and second calculated voltage curves do not reach the target voltage U1(t+Δt) at time t+Δt, while the third calculated voltage curve reaches the target voltage U1(t+Δt) at time t+Δt.

[0133] Before reaching time t+Δt, following the method of the first case, calculate the battery terminal voltage U1(t) at C1, D1, E1, F1 and other points in sequence. When reaching time t+Δt, the corresponding position is point X1.

[0134] When the calculated value of Im is too small, the ohmic voltage Vr(t), polarization voltage Vp(t), and OCV(t) need to be reset to zero, and the calculation needs to be restarted at point C1. Before restarting the calculation, the current calculated value of Im is added to the maximum design boundary value Im_ub, and then divided by two to complete the adjustment calculation of Im. The initial value of Im is assumed to be 5 amperes, and Im_ub is assumed to be 10 amperes. The adjustment process is shown in the table below.

[0135] Table 8. Schematic diagram of extreme current Im adjustment process

[0136]

[0137]

[0138] The calculations for each adjustment of the extreme current Im in Table 8 must be performed sequentially from point A1 onwards, following the calculations for the relevant variables in Table 4. Each time the extreme current Im is increased, the ohmic internal resistance value calculated from the table is less affected by the battery's SOC and T, but more significantly affected by the extreme current Im. The calculated ohmic voltage gradually increases, as... Figure 5 The voltage difference between points B1 and C1 gradually increases from the first curve to the third curve. Similarly, the method for calculating polarization resistance by looking up the table is the same as that for ohmic resistance, but the polarization voltage calculation is iterative. As shown in Table 5, although the polarization resistance calculated by looking up the table will change, the main factor affecting the magnitude of the calculated polarization voltage is the magnitude of the extreme current Im. As can be seen from formulas (4), (5), and (6), the increment of the polarization voltage value increases with each calculation. Figure 5 As shown in the first, second, and third curves, the calculation effect after Im adjustment is that the voltage curve U1(t) is closer to the center of the curve in each calculation. Figure 5 The third voltage curve has a calculation time of Δt for each calculation. For example, the calculation time interval between points C1 and C1 is the time length for U1(t) to reach the target voltage U1(t+Δt) in the first, second, and third calculations. The range of SOC and temperature T within the time length Δt is denoted as [SOC1, SOC2] and [T1, T2], respectively, representing the minimum and maximum values ​​of SOC and temperature T within the time length Δt, as shown in Table 8.

[0139] From time t to time t+Δt, the calculated battery terminal voltage U1(t) value is continuously adjusted by Im to approach the calculated value of the third curve. At point X1, it is determined whether the difference between the extreme current Im used in the previous voltage curve calculation and the extreme current Im used in the current voltage curve calculation is less than the set threshold dI. If it is less than the set threshold dI, it means that the extreme current Im calculated this time is the final calculation result. If it is greater than the set threshold, it means that the extreme current Im calculated this time is too small. The extreme current Im calculated this time is assigned to Im_lb. The sum of Im_ub and Im_lb is divided by two to obtain the extreme current Im for the next calculation. The battery U1(t) is recalculated until the difference between the extreme current Im used in the previous voltage curve calculation and the extreme current Im calculated this time is less than the set threshold dI. The extreme current Im calculation ends when this process is completed. The above process can be represented by the data in the table below.

[0140] Table 9. Voltage curve analysis for each calculation (taking discharge as an example)

[0141]

[0142]

[0143] For Table 9, set dI = 1.5A. The initial current Im is 50.00 (A) in the first calculation, with Im_lb = 0 (A) and Im_ub = 100 (A). The extreme current Im calculated in each subsequent calculation is given using the previous method. The difference between the extreme currents is 25.00 (A) for the second calculation and 12.50 (A) for the third, 6.25 (A) for the fourth, 3.13 (A) for the fifth, 1.56 (A) for the sixth, and 0.78 (A) for the seventh. In the seventh calculation, the difference between the current extreme current and the previous calculated value (0.78) is less than the threshold dI. When the extreme current Im is 99.22 (A), the calculated voltage U1(t) of the battery reaches the target voltage U1(t+Δt) at time t+Δt from time t to time t+Δt.

[0144] Figure 5 The voltage curve calculated each time from point B1 to point X1 can be used... Figure 6 The process is shown in the diagram.

[0145] S2, using the extreme current Im to calculate the extreme current Im_dyn when the battery voltage reaches the target voltage U1(t+Δt) from time t to time t+Δt under actual operating conditions;

[0146] Figure 7 This is a schematic diagram of calculating the target voltage U1(t+Δt) using the real-time extreme current Im_dyn during the discharge process.

[0147] Figure 7 In the diagram, point B2 represents the battery terminal voltage U1(t), which includes the battery's real-time polarization voltage. The voltage at point B2 is obtained by a voltage sensor. The voltage calculation from C2 to X2 requires the extreme current Im calculated in S1, the target voltage U1(t+Δt) at point X2, the open-circuit voltage OCV(t+Δt) at point X2, and the polarization voltage Vp(t) at point B2. B The joint calculation completes the calculation of the real-time extreme current Im_dyn. Specifically, S2 can be divided into the following steps.

[0148] S21, Under the actual operating conditions of the battery, the current time is t, and the polarization voltage Vp(t) at point B2 corresponding to time t. B Calculate Vp(t) by replacing Im with the current sampling current, sampling battery temperature T, and battery SOC, following the steps and methods in S14 and S16. B calculate;

[0149] S22, Under actual battery operating conditions, the current time is t, and the open-circuit voltage OCV(t+Δt) at point X2 corresponding to time t+Δt is calculated; OCV(t+Δt) is the open-circuit voltage based on OCV(t) after time Δt, and the sampling temperature and SOC at time t are denoted as T. t SOC t The temperature and SOC at time t+Δt are denoted as T. t+Δt SOC t+Δt From time t to time t+Δt, SOC t To SOC t+Δt T is calculated using ampere-hour integration. t+Δt Approximately equal to T t ;OCV(t+Δt) is calculated according to method S15, with T t+Δt and SOC t+Δt Substitute into the calculation;

[0150] S23, Under the actual operating conditions of the battery, the current time is time t, and the extreme current Im at point B2 corresponding to time t is calculated; Im calculated by S1 is a lookup function of temperature T and SOC, and Im is denoted as f(T, SOC). Using the temperature T and SOC at point B2 as input variables, the extreme current Im at point B2 is calculated according to the method in step S14.

[0151] S24, Determine the target voltage U1(t+Δt); refer to the description method in step S1 for determination;

[0152] S25, Under the actual operating conditions of the battery, the current time is t, and the calculation of the real-time extreme current Im_dyn from point B2 corresponding to time t+Δt to point X2 corresponding to time t+Δt is performed.

[0153] Figure 7 In the process of time changing from time t to time t+Δt, that is, from point B2 to point X2, the following formula is used to calculate point X2.

[0154] U1(t+Δt)=OCV(t+Δt)-Vp(t+Δt)-R0(t+Δt)×Im_dyn (12)

[0155]

[0156] In the formula, U1(t+Δt), Vp(t+Δt), R0(t+Δt), and Rp(t+Δt) are the calculated voltage, calculated polarization voltage, calculated ohmic internal resistance, and calculated polarization internal resistance of the battery at point X2. Substituting formula (13) into (12), we can obtain the formula (14) for calculating Im_dyn.

[0157]

[0158] When the battery system is left idle for a long time, the battery's polarization voltage disappears, such as... Figure 7 After a long period of stillness before point B2, the polarization voltage Vp(t) at point B2 is... B When the value is zero, the extreme current Im_dyn of the battery is the extreme current Im identified offline in S1. According to formula (14), the formula for calculating the extreme current Im is as follows.

[0159]

[0160] By combining formulas (14) and (15), the relationship between the extreme current Im identified offline in S1 and the extreme current Im_dyn of the battery under actual operating conditions can be obtained as follows.

[0161]

[0162] In formula (16), Vp(t) B Calculate according to step S21, calculate OCV(t+Δt) according to step S22, and calculate U1(t+Δt) according to step S24.

[0163] In steps S1 and S2 Figures 3 to 7 This is a schematic diagram of a battery transitioning from a stable open-circuit state to a discharge state. Tables 1 to 9 are schematic tables illustrating the transition from a stable open-circuit state to a discharge state. The principle, process, and method for calculating Im and Im_dyn when a battery transitions from a stable open-circuit state to a charging state are the same as those when transitioning from a stable open-circuit state to a discharge state, and will not be repeated here.

[0164] S3 calculates the battery peak power in real time using the extreme current Im_dyn calculated under actual operating conditions and the battery target voltage U1(t+Δt).

[0165] The formula for calculating the peak power of the battery is as follows: as time changes from time t to time t+Δt, the calculated value is the product of the extreme current Im_dyn of the battery calculated by S2 and the design value of the target voltage U1(t+Δt). SOP represents the real-time peak power of the battery.

[0166] SOP=Im_dyn×U1(t+Δt) (17)

[0167] The foregoing description of embodiments of the present invention, through which those skilled in the art are able to implement or use the present invention, will be readily apparent to those skilled in the art. Various modifications to these embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novelty disclosed herein.

Claims

1. A method for real-time estimation of battery peak power using off-line calculated peak current, characterized in that, The method includes the following steps: S1, using the battery parameters identified offline, calculates the battery's transition from a stable open-circuit state to a charge / discharge state using a third-order RC equivalent circuit model formula, based on... Time to At time [time], the battery calculated voltage reaches the target voltage. Extreme current at time ; S2, utilizing extreme current Calculate when the battery voltage reaches the target voltage from time t to time t+∆t under actual operating conditions. Extreme current at time ; Extreme current Extreme battery current under actual operating conditions The relationship between them is as follows: ； in, The time constant of the battery model. The polarization voltage of point B2 at time t, under the actual operating conditions of the battery. Under actual battery operating conditions, the current time is time t. The open-circuit voltage at point X2 corresponding to the given time; S3 utilizes the extreme current of the battery under actual operating conditions. Calculated values ​​and target battery voltage Real-time calculation of battery peak power Battery peak power The calculation formula is as follows: 。 2. The method according to claim 1, characterized in that, The formula for the third-order RC equivalent circuit model includes: Official (1): , Official (2): , Official (3): , Official (4): , Official (5): , Official (6): ; in, Indicates a certain moment, It refers to the moment before a certain moment. It is an integer greater than or equal to 1; This is the battery's terminal voltage. This is the battery open-circuit voltage. The polarization voltage of a battery is divided into first-order polarization voltage. Second-order polarization voltage Third-order polarization voltage ; This refers to the ohmic voltage of the battery. For the battery current, The internal resistance of the battery is ohms. Time constant of battery model Divided into first-order time constants Second-order time constant Third-order time constant ; Battery polarization internal resistance It is divided into first-order polarization internal resistance Second-order polarization internal resistance Third-order polarization internal resistance ; The time interval between two consecutive moments.

3. The method according to claim 2, characterized in that, Step S1 includes the following steps: S11, offline battery parameter identification; the parameter identified under different temperatures, currents, and SOCs is the ohmic internal resistance. Polarization internal resistance Polarization internal resistance Polarization internal resistance Time constant , , The identified parameters are presented in a three-dimensional table; the parameters identified at different temperatures and SOCs are open-circuit voltages. The identified parameters are in a two-dimensional table; S12 sets the minimum and maximum values ​​of the extreme current; the minimum value is denoted as... The maximum value is denoted as The minimum value is uniformly set to zero, and the maximum value can be adjusted according to the battery's maximum allowable charging and discharging current; S13, Set the initial value of the extreme current; the initial value of the extreme current is denoted as... , The initial value is between and Between, the initial value is taken and The average value; S14, Assigned to extreme current Utilizing extreme currents Current battery temperature Battery current Three variables: the ohmic internal resistance and polarization internal resistance of the battery are calculated by looking up the parameter table from the parameters identified offline in step S11; time constant. The calculation method is the same as the calculation method for battery internal resistance; S15, utilizing the current battery temperature Battery current In step S11, offline parameter identification Calculate the battery open-circuit voltage by referring to the parameter table. ; S16. Using the battery internal resistance calculated from the table in S14, substitute it into formulas (2), (3), (4), (5) and (6) to calculate the ohmic voltage. and polarization voltage ; S17, using the calculation results of S15 and S16, substitute them into formula (1) to calculate the voltage value. Calculate the voltage Recorded as Calculate when from Time's up time, Reaching the target battery voltage The corresponding extreme current .

4. The method according to claim 3, characterized in that, The measured voltage curve of the battery in step S11 is denoted as follows: The fitted voltage curve of the battery is denoted as ; Battery parameter identification employs the least squares method, using formulas (1) to (6) to fit the battery terminal voltage. curve; After multiple fitting operations, the fitted curve was obtained. Continuously approaching the measured voltage curve until the The second fitting yields the fitted curve. and measured voltage curve The objective function associated with each other When the minimum is reached, the fitting is completed and the first... The fitted curve The corresponding battery identification parameters are used as the final identification parameters.

5. The method according to claim 3, characterized in that, The assumed internal resistance values ​​in step S14 are shown in Tables 3 and 4 below, in milliohms. The internal resistance includes polarization internal resistance and ohmic internal resistance. Table 3: 10 degrees Celsius Discharge internal resistance Measurement table: ， Table 4: 40 degrees Celsius Discharge internal resistance Measurement table: ， The specific steps for calculating the battery polarization resistance and ohmic resistance by referring to tables are as follows, and are performed in three steps: The first step is to maintain the same temperature. or same current or or Down, Interpolation; ； when When taking different values, Different values, Based on Tables 3 and 4, the calculated values ​​correspond to... , , Next, when The internal resistance calculated at different times; The corresponding current is , Corresponding to The internal resistance below, The data are from Tables 3 and 4; among them, , , , In current , , The interpolation results are denoted as follows: , , ;when Greater than When the condition is met, the plus sign is used in formula (3); otherwise, the minus sign is used. The second step is to maintain the same temperature. or In the same Below, current Interpolation; ， Based on the calculation in the first step The results of current interpolation calculations; among which, , ; At temperature The interpolation result is denoted as At temperature The interpolation result is denoted as ;when Greater than When the condition is met, the plus sign is used in formula (4); otherwise, the minus sign is used. The third step is to apply the same current at the same temperature. Below, temperature Interpolation; ， The final result of the table lookup calculation for the battery's internal resistance; where, ;when Greater than When the condition is met, the minus sign is used in formula (3); otherwise, the plus sign is used. It can be either polarization resistance or ohmic resistance.

6. The method according to claim 3, characterized in that, In step S15, the actual temperature of the battery is used. , Check battery Base meter calculation battery When calculating, the linear interpolation method is used; At that time, referring to the interpolation method in S14, the current is... Replace with temperature You can then complete the task by referring to formulas (3) and (4). Calculate by looking up a table.

7. The method according to any one of claims 3-6, characterized in that, Step S2 uses the discharge voltage curve for calculation, where point A is defined as corresponding to the first moment, denoted as... Define point B as corresponding to the second time step, which is... Time, recorded as Let point C correspond to the third moment, which is usually the moment when the current is not zero, denoted as . And so on, the last point X corresponds to Time, recorded as At time t, the voltage at this moment is the battery's cutoff voltage, denoted as . ; Step S2 includes the following steps: S21, Polarization voltage at point B2 when the current value changes under actual battery operating conditions. Calculation; replaced by the current sampling current. Collect battery temperature ,Battery Complete according to the steps and methods in S14 and S16. calculate; S22, Open-circuit voltage at the target voltage time (point X2) under actual battery operating conditions. calculate; Based on go through Open-circuit voltage over time Temperature at any given time and They are respectively denoted as , , Temperature at any moment and They are respectively denoted as , ;from Time to time, to Calculated by ampere-hour integration. Approximately equal to ; According to method S15, and Substitute into the calculation; S23, the extreme current at point B2 when the current value changes under actual battery operating conditions. Calculated; calculated via S1 It's about temperature. and The lookup table function will Recorded as Utilizing the temperature at that point and As an input variable, calculate the extreme current at this point according to the method in step S14. ; S24, Determine the target voltage ; Refer to the description in step S1; S25, Real-time extreme current from point B2 to point X2 when the target voltage is reached under actual battery operating conditions. Calculate the extreme currents identified offline in S1. Extreme battery current under actual operating conditions The relationship between them is as follows: ， ， ， ， ； The value is calculated according to step S21. The value is calculated according to step S22, target voltage. The value is calculated according to step S1.

8. A battery management system, characterized in that, The battery management system includes a built-in or external offline identification basic data storage module and a calculation module; the offline identification basic data storage module and the calculation module estimate the battery peak power in real time using the method described in any one of claims 1-7.

9. A battery system comprising the battery management system of claim 8.

10. A computer program product comprising a computer program or instructions, characterized in that, When the computer program or instructions are executed by a processor, they implement the method of any one of claims 1-7.

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