A dynamic and static soc estimation system and method for an electric vehicle power battery

Abstract

The application discloses a kind of static SOC estimation system and estimation method of electric vehicle power battery, estimate the health status SOH (n) under the current cycle number of battery;Determine the total effective capacity C 总有效 (n) under the current cycle number of battery;Estimate the total useful capacity C 总有用 (t j ,n) under the current state of battery;Estimate the static SOC 静态 (t j ,n) and dynamic SOC 动态 (t j ,n) under the current state of battery;The static SOC static estimation method of proposed power battery considers the degradation problem of battery, its value can reflect how much the actual remaining effective capacity of battery under current aging state, in addition, the influence of battery temperature and operating current on battery discharge capacity is also considered, so the available amount of battery can be accurately estimated in full working condition or full life cycle, the maximum cruising range of electric vehicle under current driving state and road condition can be predicted using the value, solve the technical problems of large SOC estimation error in the prior art in the full working condition range or full life cycle of battery.

Description

Technical Field

[0001] This invention belongs to the field of electric vehicle technology and relates to a monitoring system and estimation method, specifically a dynamic and static SOC estimation system and method for electric vehicle power batteries. Background Technology

[0002] Guided by my country's "carbon peaking and carbon neutrality" strategy, vehicle electrification has become a major direction for the transformation and upgrading of my country's automotive industry, and also an important strategic measure to ensure my country's energy security. The Battery Management System (BMS), as one of the key technologies restricting the development of the current electric vehicle industry, directly affects the output characteristics, lifespan, and safety of electric vehicle power batteries, and is a crucial technical guarantee for the large-scale promotion and application of electric vehicles. Typically, a BMS has functions such as monitoring battery state parameters (voltage, current, temperature, etc.), estimating battery state of charge (SOC), charging and discharging management, equalization control, battery fault diagnosis, and alarms. Among these, real-time display of the remaining battery power is crucial for its charging and discharging control, energy management, and equalization control. For lithium-ion batteries widely used in electric vehicles, their State of Charge (SOC) is related to many factors (such as current, temperature, and discharge history) and exhibits a complex nonlinear relationship, making accurate SOC estimation very difficult. Simultaneously, battery performance gradually degrades over service life, exhibiting characteristics such as reduced capacity and increased internal resistance. Furthermore, the numerous influencing factors and complex degradation mechanisms make it difficult for current SOC estimation methods to maintain high accuracy throughout the battery's entire lifespan, thus affecting the overall performance of the Battery Management System (BMS). In addition, the SOC of the power battery needs to be monitored in real time during electric vehicle operation, thus requiring estimation methods with low complexity and computational power requirements.

[0003] Furthermore, current methods for estimating the State of Charge (SOC) of electric vehicle (EV) batteries typically involve detecting dynamic values ​​during the discharge process. When an EV operates under high-power conditions or in low-temperature environments, its discharge capacity decreases significantly, causing the SOC to not reach 0% when the battery reaches its discharge cutoff voltage. For example, when a battery discharges at a high current constant current to the cutoff condition, it can still discharge with a smaller current. Therefore, current research focuses on how to synchronize the discharge cutoff condition of an EV battery with its 0% SOC. However, this approach to SOC can prevent drivers from accurately assessing the actual remaining battery capacity in real time, potentially misleading them into making inappropriate driving decisions.

[0004] Currently, although the Ah integral method has drawbacks such as the inability to estimate initial values, the cumulative effect of errors, and the high requirements for current acquisition accuracy, it remains the most widely used battery SOC estimation method in electric vehicles due to its simple principle and ease of implementation. Its general expression is (see "Wu Daoming et al., Method for Improving the Accuracy of Power Battery SOC Estimation Based on Ah Integral Method, ZL 202011445349.8"):

[0005]

[0006] In the formula: t0 represents the initial time / s; t j Represents the current time in seconds; η represents the coulomb efficiency; C batt This represents the current battery discharge capacity in Ah; I represents the charging / discharging current (positive for charging, negative for discharging) in A. Battery capacity is related to temperature and battery aging status, and its calculation expression can be written as:

[0007] C batt (t j ) = C batt_N ·ε T (t j )·ε A (t j (2)

[0008] In the formula: C batt_N Indicates the battery's rated capacity in Ah; ε T Indicates the battery temperature coefficient; ε A This indicates the battery aging factor.

[0009] In actual electric vehicle operation, in addition to the complex and varied operating conditions, the power battery also experiences temperature changes and performance degradation. Although developers of current SOC estimation methods have taken note of these issues and have used coulombic efficiency η and battery temperature coefficient ε... T and battery aging coefficient ε A Three factors, namely current, temperature, and aging, were considered (see formulas (1) to (2)). Typically, η and ε... T and ε A The values ​​were obtained based on fitting data from certain battery charge-discharge experiments. However, because the battery charge-discharge process involves multiple physicochemical processes such as ion transport, electron transport, heat transport, and electrochemical reaction kinetics, and is affected by factors such as current, temperature, service time, and charge-discharge mode, it is difficult to accurately obtain η and ε solely from charge-discharge experimental data. T and ε A The calculation formula.

[0010] The aforementioned shortcomings result in significant estimation errors in the traditional Ah integral method for SOC estimation across the entire operating range or the entire lifespan of the battery (see "Fu Shiyi, Lü Taolin, Min Fanqi, et al. A review of SOC estimation methods for lithium-ion batteries in electric vehicles, Energy Storage Science and Technology, 2021(10)3:1127-1136"). Furthermore, current SOC algorithms for automotive power batteries only focus on estimating dynamic values ​​during battery use in real time, without estimating the actual usable capacity of the battery SOC (i.e., static values). This prevents drivers from accurately judging the actual remaining charge of the power battery in real time, potentially misleading them into making inappropriate driving choices.

[0011] Therefore, establishing a method that can accurately display the current battery charge status and reflect the actual remaining battery charge will be of great significance for optimizing the functions of the power battery management system and driver operation choices. Summary of the Invention

[0012] To address the shortcomings of existing technologies, the present invention aims to provide a dynamic and static SOC estimation system and method for electric vehicle power batteries, thereby solving the technical problem of large SOC estimation errors in existing technologies across the entire battery operating range or throughout its entire life cycle.

[0013] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0014] A method for estimating the dynamic and static state of charge (SOC) of an electric vehicle power battery specifically includes the following steps:

[0015] Step 1: Estimate the state of health (SOH)(n) of the battery at the current cycle number;

[0016] Step 2: Determine the total effective capacity C of the battery at the current number of cycles. 总有效 (n);

[0017] Step 3: Determine the initial SOC(t0,n) of the battery at the current cycle number;

[0018] Step 4: Estimate the total usable capacity C of the battery in its current state. 总有用 (t j ,n);

[0019] Step 5: Estimate the static SOC of the battery in its current state. 静态 (t j (n) and dynamic SOC 动态 (t j ,n);

[0020] Step 5.1, calculate the total effective capacity C of the battery at the current cycle number obtained in Step 2. 总有效Substituting (n) and the initial SOC(t0,n) of the battery obtained in step 3 into formula (5-1), we obtain the static SOC of the battery at the current moment. 静态 (t j ,n);

[0021]

[0022] in:

[0023] t0 represents the initial charging / discharging time in seconds for the current cycle number;

[0024] j represents the current time step;

[0025] t j This represents the current time in seconds, and its value is equal to t0 + jΔt, where Δt is the time step, which is set by the user in the BMS as needed.

[0026] t represents the time variable in seconds;

[0027] n represents the current cycle number, i.e., the current number of charging or discharging cycles;

[0028] I(t,n) represents the current battery operating current in A, and its value varies with time t and the number of cycles n.

[0029] C 总有效 (n) represents the total effective capacity of the battery in Ah, and its value changes with the number of cycles n.

[0030] Step 5.2, combine the initial SOC(t0,n) of the battery obtained in Step 3 with the total usable capacity C of the battery in its current state obtained in Step 4. 总有用 (t j Substituting n into formula (5-2), we obtain the current battery dynamic SOC. 动态 (t j ,n):

[0031]

[0032] in:

[0033] C 总有用 (t j ,n) represents the total usable capacity of the battery in the current state, in Ah.

[0034] Step 1: Estimate the state of health (SOH)(n) of the battery at the current cycle number, which includes the following steps:

[0035] Step 1.1: Measure the charging capacity C of the new battery after charging using the standard charging method. 充_新电池 And input it into the BMS in advance;

[0036] Step 1.2: Record the total charging capacity C of the battery before the current discharge begins, when charged using the standard charging method. 充 (n), and the new battery charging capacity C obtained in step 1.1 充_新电池 Substituting into formula (1-1), the health status SOH(n) of the battery at the current cycle number is calculated;

[0037]

[0038] Step 2: Determine the total effective capacity C of the battery at the current number of cycles. 总有效 (n) includes the following operations: the total effective capacity C of a new battery at the time of manufacture. 新电池 The C obtained is equal to the discharge capacity of a new battery when it is fully charged and discharged at a standard discharge current. 新电池 Substituting the SOH(n) obtained in step one into formula (2-1), the total effective capacity C of the battery at the current cycle number can be calculated. 总有效 (n):

[0039] C 总有效 (n)=SOH(n)·C 新电池 (2-1).

[0040] In step three, determining the initial SOC(t0,n) of the battery under the current cycle number specifically includes the following operations: when the battery completes the charging process under the current cycle number, the battery is in a fully charged state, and its initial SOC(t0,n) under the current cycle is set to 100%; when the battery is discharging from a state that has never been fully charged, the initial SOC(t0,n) of the battery is equal to the SOC value recorded in the BMS at the previous moment.

[0041] In step four, estimate the total usable capacity C of the battery in its current state. 总有用 (t j The specific steps include:

[0042] Step 4.1: Collect the battery operating current I(t,n) and battery temperature T online;

[0043] Step 4.2: Using the initial SOC (t0,n) of the battery under the current cycle obtained in Step 3, the battery operating current I (t,n) obtained in Step 4.1, and the battery temperature T, the unusable active lithium capacity Q at the current moment at the battery negative electrode is obtained. 不可脱嵌 (t j ,n);

[0044] Step 4.3, take the Q obtained in step 4.2 不可脱嵌 (t j Substituting n into formula (4-1) yields the real-time unavailable effective capacity C of the battery in its current state. 不可用 (tj ,n);

[0045] C 不可用 (t j (n) = 26.8·Q 不可脱嵌 (t j (4-1)

[0046] Step 4.4, take C obtained from step 4.3 不可用 (t j The total effective capacity C obtained in step two is (n) and (n) 总有效 Substituting (n) into formula (4-2), we obtain the total usable capacity C of the battery at the current moment for the current number of cycles. 总有用 (t j ,n);

[0047] C 总有用 (t j ,n)=C 总有效 (n)-C 不可用 (t j ,n) (4-2).

[0048] Step 4.2 specifically includes the following steps:

[0049] Step 4.2.1: Substitute the initial SOC (t0,n) of the battery under the current cycle obtained in Step 3, the battery operating current I (t,n) obtained in Step 4.1, and the battery temperature T into formulas (4-3) to (4-6) in real time to obtain the current time t. j negative electrode lithium intercalation concentration [c s (r1,t j ),c s (r2,t j ),…,c s (r m ,t j )] T ;

[0050]

[0051] Initial conditions are

[0052] c s (r,t0)=c s_max SOC(t0,n) (4-4)

[0053] Boundary conditions are

[0054]

[0055]

[0056] In the formula:

[0057] t represents the time variable in seconds;

[0058] t0 represents the initial time in seconds;

[0059] D s Represents the lithium diffusion coefficient of the electrode material / m 2 ·s -1 , varies with battery temperature T;

[0060] c s (r,t) represents the lithium intercalation concentration of the negative electrode active particles in mol·m -3 ;

[0061] c s_max This indicates the maximum lithium intercalation concentration of the negative electrode active particles (mol·m). -3 ;

[0062] r s This represents the average radius of the negative electrode active particles in meters.

[0063] a 负 This indicates the specific surface area of ​​the negative electrode active particles (m²). -1 ;

[0064] F represents the Faraday constant, which is equal to 26.8 Ah·mol⁻¹. -1 ;

[0065] Specifically, it includes the following sub-steps:

[0066] Step 4.2.1.1: Discretize equation (4-3) using the finite difference method, focusing on the internal nodes r along the radius r of the battery negative electrode particles. i Above, the partial derivatives of the spatial step size Δr with respect to the spatial r are subjected to a second-order central difference; at time node t j The above implicitly differs the partial derivative of time step Δt with respect to time t;

[0067] in:

[0068] m is in (0, r) s The number of discrete nodes within the BMS is preset by the OEM.

[0069] i represents the node number along the direction of the negative electrode particle radius r, which is equal to 2, 3, ..., m-2, m-1 here;

[0070] Δr represents the spatial step size along the radius r of the negative electrode particle, and its value is equal to r. s / (m-1);

[0071] Δt represents the time step for estimating SOC, which is set by the user in the BMS as needed, and its value is equal to t. j -t j-1, t j Indicates the current time, t j-1 This indicates the previous time step, and j is the current time step number, with values ​​equal to 1, 2, ...;

[0072] Step 4.2.1.2: At the boundary node r1 along the radius r of the battery negative electrode particles, apply a first-order backward difference to equation (4-5), where r1 = 0; at the boundary node r m Above, a first-order forward difference is applied to equation (4-6), where r m =r s ;

[0073] Step 4.2.1.3: At the initial time t0, all grid nodes along the radius r of the battery negative electrode particles satisfy equation (11), thus obtaining the negative electrode lithium intercalation concentration [c] at all grid nodes. s (r1,t0),c s (r2,t0),…,c s (r m ,t0)] T All equal to c s_max SOC(t0,n);

[0074] Step 4.2.1.4 yields the discrete equation (4-7) for the concentration of all grid nodes along the radius r of the negative electrode particles. This is then used to calculate the concentration at the previous time step t. j-1 negative electrode lithium intercalation concentration [c s (r1,t j-1 ),c s (r2,t j-1 ),…,c s (r m ,t j-1 )] T Substituting into the discrete equation (4-7), we obtain the current time t. j negative electrode lithium intercalation concentration [c s (r1,t j ),c s (r2,t j ),…,c s (r m ,t j )] T ;

[0075]

[0076] Step 4.2.2, based on the current time t obtained in step 4.2.1 j Negative electrode lithium intercalation concentration [c] s (r1,t j ),c s (r2,t j ),…,cs (r m ,t j )] T This will give you the current time t. j Surface lithium intercalation concentration c of negative electrode particles s_表面 (t j Minimum lithium intercalation concentration c s_当前最小 (t j ) and average lithium intercalation concentration c s_平均 (t j Substituting this into formula (4-8), we obtain the current unusable active lithium capacity Q at the battery's negative electrode. 不可脱嵌 (t j ,n);

[0077]

[0078] in:

[0079] Q 不可脱嵌 (t j (n) represents the current unusable active lithium capacity at the negative electrode of the battery in mol.

[0080] V 负 Indicates the volume of the negative electrode active material / m 3 ;

[0081] c s_表面 (t j () represents the surface lithium intercalation concentration of the negative electrode active particles at the current moment / mol·m -3 That is: c s (r m ,t j );

[0082] c s_当前最小 (t j () represents the minimum lithium intercalation concentration of the negative electrode active particles at the current moment / mol·m -3 That is: min[c s (r1,t j ),c s (r2,t j ),…,c s (r m ,t j )];

[0083] c s_表面最小 (t j () represents the surface lithium intercalation concentration of the negative electrode active particles when discharged to the cutoff voltage at the current current, in mol·m⁻¹. -3 ;

[0084] c s_Minimum (n) represents the minimum lithium intercalation concentration (mol·m) of the negative electrode active particles at the current cycle number. -3 ;

[0085] c s_平均 (t j () represents the average lithium intercalation concentration of the negative electrode active particles at the current moment / mol·m -3 ,Right now:

[0086] In step 4.2.2, the minimum lithium intercalation concentration c of the negative electrode active particles at the current cycle number. s_最小 (n) is obtained through formula (14);

[0087] c s_最小 (n)=c smin_0 ·(a1+a2·SOH) (4-9)

[0088] in:

[0089] c smin_0 The minimum lithium intercalation concentration, expressed in mol, represents the new battery electrode material.

[0090] a1 and a2 are dimensionless fitting parameters.

[0091] In step 4.2.2, the surface lithium intercalation concentration c of the negative electrode active particles when discharged to the cutoff voltage at the current is... s_表面最小 (t j It is calculated using formula (4-10);

[0092]

[0093] in:

[0094] a3, a4, and a5 are dimensionless fitting parameters;

[0095] I dis Indicates discharge current in A;

[0096] I 1C This indicates the current (A) corresponding to a 1C battery capacity.

[0097] E a Activation energy is expressed in J·mol⁻¹ -1 Its value is obtained by fitting discharge experimental data;

[0098] R represents the gas molar constant, which is equal to 8.314 J·mol⁻¹. -1 ·K -1 ;

[0099] T ref This indicates a reference temperature, usually taken as 298.15K;

[0100] T represents the battery temperature in K.

[0101] A dynamic and static SOC estimation system for an electric vehicle power battery includes a SOH estimation module, a total effective capacity estimation module, an initial SOC estimation module, a total usable capacity estimation module, a battery dynamic and static SOC estimation module, and a display module. The SOH estimation module, the total effective capacity estimation module, and the battery dynamic and static SOC estimation module are connected in sequence. The total usable capacity estimation module is connected to the initial SOC estimation module and the battery dynamic and static SOC estimation module, respectively. The battery dynamic and static SOC estimation module is also connected to a display module.

[0102] The SOH estimation module is used to estimate the state of health (SOH)(n) of the battery at the current cycle number.

[0103] The total effective capacity estimation module is used to determine the total effective capacity C of the battery at the current cycle number. 总有效 (n);

[0104] The initial SOC estimation module is used to determine the initial SOC(t0,n) of the battery at the current cycle number;

[0105] The total usable capacity estimation module is used to estimate the total usable capacity C of the battery in its current state. 总有用 (t j ,n);

[0106] The battery dynamic and static SOC estimation module is used to estimate the static SOC of the battery in its current state. 静态 (t j (n) and dynamic SOC 动态 (t j ,n);

[0107] The display module is used to display the remaining effective capacity and remaining effective usable capacity of the battery in its current state.

[0108] Compared with the prior art, the beneficial technical effects of this invention are:

[0109] (I) The static SOC estimation method for power batteries proposed in this application takes into account the battery degradation problem. Its value can reflect the actual remaining effective capacity of the battery under the current aging state. Using this value, the current theoretical maximum driving range of electric vehicles can be predicted. In addition, the influence of battery temperature and operating current on battery discharge capacity is also considered. Therefore, the amount of usable electricity when the battery is continuously discharged at the current current under the current temperature and aging state can be accurately estimated under all operating conditions or the whole life cycle. Using this value, the maximum driving range of electric vehicles under the current driving state and road conditions can be predicted, which solves the technical problem of large SOC estimation error in the existing technology under the whole operating conditions or the whole life cycle of the battery.

[0110] (II) The dynamic SOC estimation method for power batteries proposed in this application is based on lithium intercalation concentration. When the discharge power of the electric vehicle power battery changes abruptly, the dynamic SOC estimated by this method can better track the transient law of the battery. Compared with the traditional ampere-hour estimation method, it has higher estimation accuracy. Attached Figure Description

[0111] Figure 1 This is a flowchart of the method of the present invention;

[0112] Figure 2 This is a structural diagram of the system of the present invention;

[0113] Figure 3 This is a schematic diagram showing the total embedded active lithium capacity of the new battery in this invention;

[0114] Figure 4 This is a schematic diagram of the total active lithium embedded in the battery in this invention;

[0115] Figure 5 This is a schematic diagram illustrating the current battery capacity for deintercalation and deintercalation of active lithium in this invention;

[0116] Figure 6 Voltage, current, and dynamic / static SOC variation curves during battery charging;

[0117] Figure 7 The curves show the changes in voltage, current, and dynamic / static SOC during the battery discharge process.

[0118] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0119] It should be noted that the full name of BMS in this invention is Battery Management System.

[0120] It should be noted that the battery charging methods in this invention all adopt the standard charging methods recommended by the manufacturer, which are usually constant current and constant voltage charging at room temperature. The constant current charging current is 0.3C, the charging cut-off voltage is 4.2V (3.65V for lithium iron phosphate batteries), and the constant voltage charging cut-off current is 0.02C.

[0121] It should be noted that the current state in this invention refers to the current cycle number, battery temperature, and operating current.

[0122] It should be noted that, unless otherwise specified, all components in this invention are those known in the art.

[0123] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0124] A method for estimating the dynamic and static state of charge (SOC) of an electric vehicle power battery specifically includes the following steps:

[0125] Step 1: Estimate the state of health (SOH)(n) of the battery at the current cycle number;

[0126] Step 2: Determine the total effective capacity C of the battery at the current number of cycles. 总有效 (n);

[0127] Step 3: Determine the initial SOC(t0,n) of the battery at the current cycle number;

[0128] Step 4: Estimate the total usable capacity C of the battery in its current state. 总有用 (t j ,n);

[0129] Step 5: Estimate the static SOC of the battery in its current state. 静态 (t j (n) and dynamic SOC 动态 (t j ,n);

[0130] Step 5.1, calculate the total effective capacity C of the battery at the current cycle number obtained in Step 2. 总有效 Substituting (n) and the initial SOC(t0,n) of the battery obtained in step 3 into formula (5-1), we obtain the static SOC of the battery at the current moment. 静态 (t j ,n);

[0131]

[0132] in:

[0133] t0 represents the initial charging / discharging time in seconds for the current cycle number;

[0134] j represents the current time step;

[0135] t j This represents the current time in seconds, and its value is equal to t0 + jΔt, where Δt is the time step, which is set by the user in the BMS as needed.

[0136] t represents the time variable in seconds;

[0137] n represents the current cycle number, i.e., the current number of charging or discharging cycles;

[0138] I(t,n) represents the current battery operating current in A, and its value varies with time t and the number of cycles n.

[0139] C 总有效 (n) represents the total effective capacity of the battery in Ah, and its value changes with the number of cycles n.

[0140] Step 5.2, combine the initial SOC(t0,n) of the battery obtained in Step 3 with the total usable capacity C of the battery in its current state obtained in Step 4. 总有用 (t j Substituting n into formula (5-2), we obtain the current battery dynamic SOC. 动态 (t j ,n):

[0141]

[0142] in:

[0143] C 总有用 (t j ,n) represents the total usable capacity of the battery in the current state, in Ah.

[0144] In this scheme, the method for estimating the dynamic and static SOC of the electric vehicle power battery is a real-time estimation method. 'n' represents the number of cycles, meaning the battery can undergo multiple charge-discharge cycles. During one discharge cycle, the current time t is estimated using Δt as the time step. j The battery undergoes multiple static and dynamic estimations, with each estimation consisting of steps one through five.

[0145] In the above technical solution, the static SOC estimation method for power batteries proposed in this application takes into account the battery degradation problem. Its value can reflect the actual remaining effective capacity of the battery under the current aging state. Using this value, the current theoretical maximum driving range of the electric vehicle can be predicted. In addition, the influence of battery temperature and operating current on battery discharge capacity is also considered. Therefore, it can accurately estimate the amount of electricity that the battery can use when continuously discharging at the current current under the current temperature and aging state throughout the entire operating condition or the entire life cycle. Using this value, the maximum driving range of the electric vehicle under the current driving state and road conditions can be predicted, thus solving the technical problem of large SOC estimation error in the existing technology across the entire operating condition or the entire life cycle of the battery.

[0146] Furthermore, the dynamic SOC estimation method for power batteries proposed in the above technical solution is based on lithium intercalation concentration. When the discharge power of the electric vehicle power battery changes abruptly, the SOC dynamic estimation method can better track the transient law of the battery, and has higher estimation accuracy than the traditional ampere-hour estimation method.

[0147] This invention also includes the following technical features:

[0148] Specifically, step one involves estimating the battery's state of health (SOH(n)) at the current cycle number, which includes the following steps:

[0149] Step 1.1: Measure the charging capacity C of the new battery after charging using the standard charging method. 充_新电池 And input it into the BMS in advance;

[0150] Step 1.2: Record the total charging capacity C of the battery before the current discharge begins, when charged using the standard charging method. 充 (n), and the new battery charging capacity C obtained in step 1.1 充_新电池 Substituting into formula (1-1), the health status SOH(n) of the battery at the current cycle number is calculated;

[0151]

[0152] Specifically, in step two, determine the total effective capacity C of the battery at the current number of cycles. 总有效 (n) includes the following operations: the total effective capacity C of a new battery at the time of manufacture. 新电池 The C obtained is equal to the discharge capacity of a new battery when it is fully charged and discharged at a standard discharge current. 新电池 Substituting the SOH(n) obtained in step one into formula (2-1), the total effective capacity C of the battery at the current cycle number can be calculated. 总有效 (n):

[0153] C 总有效(n)=SOH(n)·C 新电池 (2-1).

[0154] In the above scheme, the total effective capacity C of the battery can generally be considered as... 新电池 Equal to its rated capacity, see Figure 3 and Figure 4 , Figure 3 C represents the total effective capacity of the new battery, corresponding to the total intercalated active lithium capacity of the new battery. Figure 4 The total effective capacity C of the battery in its current state. 总有效 The corresponding total embedded active lithium capacity shows that the battery has lost active lithium due to aging.

[0155] Specifically, in step three, determining the initial SOC(t0,n) of the battery under the current cycle number includes the following operations: when the battery completes the charging process under the current cycle number, the battery is in a fully charged state, and its initial SOC(t0,n) under the current cycle is set to 100%; when the battery has never been discharged from a fully charged state, the initial SOC(t0,n) of the battery is equal to the SOC value recorded in the BMS at the previous moment.

[0156] Specifically, in step four, the total usable capacity C of the battery in its current state is estimated. 总有用 (t j The specific steps include:

[0157] Step 4.1: Collect the battery operating current I(t,n) and battery temperature T online;

[0158] Step 4.2: Using the initial SOC (t0,n) of the battery under the current cycle obtained in Step 3, the battery operating current I (t,n) obtained in Step 4.1, and the battery temperature T, the unusable active lithium capacity Q at the current moment at the battery negative electrode is obtained. 不可脱嵌 (t j ,n);

[0159] Step 4.3, take the Q obtained in step 4.2 不可脱嵌 (t j Substituting n into formula (4-1) yields the real-time unavailable effective capacity C of the battery in its current state. 不可用 (t j ,n);

[0160] C 不可用 (t j (n) = 26.8·Q 不可脱嵌 (t j (4-1)

[0161] Step 4.4, take C obtained from step 4.3 不可用 (tj The total effective capacity C obtained in step two is (n) and (n) 总有效 Substituting (n) into formula (4-2), we obtain the total usable capacity C of the battery at the current moment for the current number of cycles. 总有用 (t j ,n);

[0162] C 总有用 (t j ,n)=C 总有效 (n)-C 不可用 (t j ,n) (4-2).

[0163] See Figure 5 , Figure 5 Let C be the total usable capacity of the battery under the current state, corresponding to the total intercalated active lithium capacity. It can be seen that not only is there a loss of active lithium due to battery aging, but also some active lithium cannot be intercalated due to the lithium intercalation concentration gradient inside the battery active particles.

[0164] In the above technical solution, based on lithium intercalation concentration, when the discharge power of the electric vehicle power battery changes abruptly, the SOC dynamics estimated by this method can better track the transient law of the battery, and it has higher estimation accuracy than the traditional ampere-hour estimation method.

[0165] Specifically, step 4.2 includes the following steps:

[0166] Step 4.2.1: Substitute the initial SOC (t0,n) of the battery under the current cycle obtained in Step 3, the battery operating current I (t,n) obtained in Step 4.1, and the battery temperature T into formulas (4-3) to (4-6) in real time to obtain the current time t. j negative electrode lithium intercalation concentration [c s (r1,t j ),c s (r2,t j ),…,c s (r m ,t j )] T ;

[0167]

[0168] Initial conditions are

[0169] c s (r,t0)=c s_max SOC(t0,n) (4-4)

[0170] Boundary conditions are

[0171]

[0172]

[0173] In the formula:

[0174] t represents the time variable in seconds;

[0175] t0 represents the initial time in seconds;

[0176] D s Represents the lithium diffusion coefficient of the electrode material / m 2 ·s -1 As the battery temperature T changes, the Arrhenius equation is usually used, and the equation coefficients are determined by half-cell impedance spectroscopy experiments. The temperature T is measured in real time by the current sensor in the BMS.

[0177] c s (r,t) represents the lithium intercalation concentration of the negative electrode active particles in mol·m -3 ;

[0178] c s_max This indicates the maximum lithium intercalation concentration of the negative electrode active particles (mol·m). -3 ;

[0179] r s This represents the average radius of the negative electrode active particles in meters.

[0180] a 负 This indicates the specific surface area of ​​the negative electrode active particles (m²). -1 ;

[0181] F represents the Faraday constant, which is equal to 26.8 Ah·mol⁻¹. -1 ;

[0182] Specifically, it includes the following sub-steps:

[0183] Step 4.2.1.1: Discretize equation (4-3) using the finite difference method, focusing on the internal nodes r along the radius r of the battery negative electrode particles. i Above, the partial derivatives of the spatial step size Δr with respect to the spatial r are subjected to a second-order central difference; at time node t j The above implicitly differs the partial derivative of time step Δt with respect to time t;

[0184] in:

[0185] m is in (0, r) s The number of discrete nodes within the BMS is preset by the OEM.

[0186] i represents the node number along the direction of the negative electrode particle radius r, which is equal to 2, 3, ..., m-2, m-1 here;

[0187] Δr represents the spatial step size along the radius r of the negative electrode particle, and its value is equal to r. s / (m-1);

[0188] Δt represents the time step for estimating SOC, which is set by the user in the BMS as needed, and its value is equal to t. j -t j-1 , t j Indicates the current time, t j-1 This indicates the previous time step, and j is the current time step number, with values ​​equal to 1, 2, ...;

[0189] Step 4.2.1.2: At the boundary node r1 along the radius r of the battery negative electrode particles, apply a first-order backward difference to equation (4-5), where r1 = 0; at the boundary node r m Above, a first-order forward difference is applied to equation (4-6), where r m =r s ;

[0190] Step 4.2.1.3: At the initial time t0, all grid nodes along the radius r of the battery negative electrode particles satisfy equation (11), thus obtaining the negative electrode lithium intercalation concentration [c] at all grid nodes. s (r1,t0),c s (r2,t0),…,c s (r m ,t0)] T All equal to c s_max SOC(t0,n);

[0191] Step 4.2.1.4 yields the discrete equation (4-7) for the concentration of all grid nodes along the radius r of the negative electrode particles. This is then used to calculate the concentration at the previous time step t. j-1 negative electrode lithium intercalation concentration [c s (r1,t j -1), c s (r2,t j-1 ),…,c s (r m ,t j-1 )] T Substituting into the discrete equation (4-7), we obtain the current time t. j negative electrode lithium intercalation concentration [c s (r1,t j ),c s (r2,t j ),…,c s (r m ,t j )] T ;

[0192]

[0193] Step 4.2.2, based on the current time t obtained in step 4.2.1 j Negative electrode lithium intercalation concentration [c] s (r1,t j ),c s (r2,t j ),…,c s (r m ,t j )] T This will give you the current time t. j Surface lithium intercalation concentration c of negative electrode particles s_表面 (t j Minimum lithium intercalation concentration c s_当前最小 (t j ) and average lithium intercalation concentration c s_平均 (t j Substituting this into formula (4-8), we obtain the current unusable active lithium capacity Q at the battery's negative electrode. 不可脱嵌 (t j ,n);

[0194]

[0195] in:

[0196] Q 不可脱嵌 (t j (n) represents the current unusable active lithium capacity at the negative electrode of the battery in mol.

[0197] V 负 Indicates the volume of the negative electrode active material / m 3 ;

[0198] c s_表面 (t j () represents the surface lithium intercalation concentration of the negative electrode active particles at the current moment / mol·m -3 That is: c s (r m ,t j );

[0199] c s_当前最小 (t j () represents the minimum lithium intercalation concentration of the negative electrode active particles at the current moment / mol·m -3 That is: min[c s (r1,t j ),c s (r2,t j ),…,c s (r m ,t j )];

[0200] c s_表面最小 (t j () represents the surface lithium intercalation concentration of the negative electrode active particles when discharged to the cutoff voltage at the current current, in mol·m⁻¹. -3 ;

[0201] c s_最小 (n) represents the minimum lithium intercalation concentration of the negative electrode active particles at the current cycle number, in mol·m⁻¹. -3 ;

[0202] c s_平均 (t j () represents the average lithium intercalation concentration of the negative electrode active particles at the current moment / mol·m -3 ,Right now:

[0203] Specifically, in step 4.2.2, the minimum lithium intercalation concentration c of the negative electrode active particles at the current cycle number is... s_最小 (n) is obtained through formula (14);

[0204] c s_最小 (n)=c smin_0 ·(a1+a2·SOH) (4-9)

[0205] in:

[0206] c smin_0 The minimum lithium intercalation concentration, expressed in mol, represents the new battery electrode material.

[0207] a1 and a2 are dimensionless fitting parameters.

[0208] Specifically, in step 4.2.2, the surface lithium intercalation concentration c of the negative electrode active particles when discharged to the cutoff voltage at the current is... s_表面最小 (t j It is calculated using formula (4-10);

[0209]

[0210] in:

[0211] a3, a4, and a5 are dimensionless fitting parameters;

[0212] I dis Indicates discharge current in A;

[0213] I 1C This indicates the current (A) corresponding to a 1C battery capacity.

[0214] E a Activation energy is expressed in J·mol⁻¹ -1 Its value is obtained by fitting discharge experimental data;

[0215] R represents the gas molar constant, which is equal to 8.314 J·mol⁻¹. -1 ·K -1 ;

[0216] T ref This indicates a reference temperature, usually taken as 298.15K;

[0217] T represents the battery temperature in K.

[0218] This invention also provides a dynamic and static SOC estimation system for electric vehicle power batteries, such as... Figure 2 As shown, it includes a SOH estimation module, a total effective capacity estimation module, an initial SOC estimation module, a total usable capacity estimation module, a battery dynamic and static SOC estimation module, and a display module. The SOH estimation module, the total effective capacity estimation module, and the battery dynamic and static SOC estimation module are connected in sequence. The total usable capacity estimation module is connected to the initial SOC estimation module and the battery dynamic and static SOC estimation module, respectively. The battery dynamic and static SOC estimation module is also connected to a display module.

[0219] The SOH estimation module is used to estimate the battery's state of health (SOH(n)) at the current cycle number.

[0220] The total effective capacity estimation module is used to determine the total effective capacity C of the battery at the current cycle number. 总有效 (n);

[0221] The initial SOC estimation module is used to determine the initial SOC(t0,n) of the battery at the current cycle number;

[0222] The total usable capacity estimation module is used to estimate the total usable capacity C of the battery in its current state. 总有用 (t j ,n);

[0223] The battery dynamic and static SOC estimation module is used to estimate the static SOC of the battery under its current state. 静态 (t j (n) and dynamic SOC 动态 (t j ,n);

[0224] The display module is used to display the remaining effective capacity and remaining effective available capacity of the battery in its current state.

[0225] Example:

[0226] This embodiment presents a method for estimating the dynamic and static SOC of an electric vehicle power battery. It uses a pouch-type lithium-ion battery (NCM positive electrode material, graphite negative electrode material) manufactured by CALB Co., Ltd., with a rated capacity of 26 Ah. The minimum lithium intercalation concentration c at the battery negative electrode is... s_最小The minimum lithium intercalation concentration c at the surface of the battery negative electrode is 513 mol·m⁻³. s_表面最小 The coefficients in the calculation formula are a3 = 513, a4 = 211.6, a5 = 42.6, and Ea = 6480 J·mol⁻¹. -1 T ref =298.15K;

[0227] In this embodiment, the battery is first subjected to standard constant current and constant voltage charging. After charging is completed, the battery capacity C 充 The capacity is 25.89 Ah, and the charging capacity C is taken as the standard charging capacity of the new battery. 充_新电池 Given a rated capacity of 26Ah, according to formula (1-1), the current state of equilibrium (SOH) of the battery is 99.6%; taking the total effective capacity C of the new battery... 新电池 With a rated capacity of 26Ah, the current total effective capacity C of the battery can be obtained according to formula (2-1). 总有效 The battery capacity is 25.89 Ah; the initial SOC before charging is 2.41%; after charging is completed, the battery is left to stand for 600 seconds, and then discharged at a constant current of 2C. When the battery voltage reaches 2.8V, the battery continues to discharge at a constant current of 0.5C until the battery voltage reaches 2.8V and then the discharge stops.

[0228] During battery charging and discharging, the battery's average temperature and operating current are input into formula (4-2) in real time. Using formula (4-2), the total usable capacity C of the battery can be calculated in real time. 总有用 Calculation results show that during the charging process, the total usable capacity C of the lithium-ion battery... 总有用 Equal to its current total effective capacity C 总有效 Therefore, the estimated battery SOC 静态 Equal to SOC 动态 ,like Figure 6 As shown; during discharge, the total usable capacity C of the lithium-ion battery... 总有用 Less than its current total effective capacity C 总有效 Therefore, the estimated battery SOC 静态 Higher than SOC 动态 ,like Figure 7 As shown.

[0229] from Figure 7 It can be seen that when the battery discharges to the cutoff voltage with a large current, its dynamic SOC... 动态 The value is exactly 0%, but its static SOC 静态 The value is still above 0% (5.5%), indicating that although the battery cannot continue to discharge at the current discharge current (2C) in the current state, it still has 5.5% of its effective capacity, which can be utilized by reducing the discharge current.

[0230] from Figure 7 It can be seen that when the battery continues to discharge at a small current of 0.5C, the battery's SOC... 动态 The value first rises and then falls. When the battery terminal voltage reaches the cutoff voltage again, the battery SOC (State of Charge) is restored. 动态 The value also dropped to 0% again, at which point the battery's static SOC... 静态 A reading of 0.7% indicates that the battery's effective capacity is basically fully utilized, and the battery should be charged promptly.

Claims

1. A method for estimating the dynamic and static SOC of a power battery for an electric vehicle, characterized in that, Specifically, the following steps are included: Step 1: Estimate the battery's health status at the current cycle count. ; Step 2: Determine the total effective capacity of the battery at the current number of cycles. ; The total effective capacity of a new battery at the time of manufacture This equals the discharge capacity of a new battery when discharged at a standard discharge current from a fully charged state. And obtained in step one Substituting into formula (2-1), the total effective capacity of the battery at the current cycle number can be calculated. : （2-1） Step 3: Determine the initial battery cycle count for the current number of cycles. ; Step 4: Estimate the total usable capacity of the battery in its current state. ; Step 4.1: Online acquisition of battery operating current and battery temperature T ; Step 4.2, using the initial battery configuration obtained in Step 3 for the current cycle. The battery operating current obtained in step 4.1 and battery temperature T Obtain the current unusable active lithium capacity at the battery's negative electrode. ; Step 4.3, take the result obtained in step 4.2 Substituting into formula (4-1), we obtain the real-time unavailable effective capacity of the battery in its current state. ; （4-1） Step 4.4, take the result obtained in step 4.3 The total effective capacity obtained in step two Substituting into formula (4-2), we obtain the total usable capacity of the battery at the current moment for the current number of cycles. ; （4-2）； Step 5: Estimate the static state of the battery in its current condition. and dynamic ; Step 5.1: Calculate the total effective capacity of the battery at the current cycle number obtained in Step 2. And the initial battery obtained in step three Substituting into formula (5-1), we obtain the battery static state at the current moment. ; （5-1） in: t 0 indicates the initial charging / discharging time in seconds for the current cycle number; j Represents the number of time steps at the current moment. ； This represents the current time in seconds, and its value is equal to... , The time step is set by the user in the BMS as needed; t Represents the time variable / seconds; n This indicates the current cycle number, i.e., the current number of charging or discharging cycles; This represents the current battery operating current in A, and its value varies with time. t and number of loops n change; This represents the total effective capacity of the battery in Ah, and its value varies with the number of cycles. n change; Step 5.2, initialize the battery obtained in Step 3. The total usable capacity of the battery in its current state obtained in step four. Substituting into formula (5-2), we obtain the battery dynamics at the current moment. : （5-2） in: This represents the total usable capacity of the battery in its current state, expressed in Ah.

2. The method for estimating the dynamic and static SOC of an electric vehicle power battery as described in claim 1, characterized in that, Step 1: Estimate the battery's health status at the current cycle count. Specifically, it includes the following steps: Step 1.1: Measure the charging capacity of the new battery after charging using the standard charging method. And input it into the BMS in advance; Step 1.2: Record the total charging capacity of the battery before the current discharge begins, when charged using the standard charging method. and the new battery charging capacity obtained in step 1.1 Substituting into formula (1-1), the health status of the battery at the current cycle number is calculated. ; （1-1）。 3. The method for estimating the dynamic and static SOC of an electric vehicle power battery as described in claim 1, characterized in that, In step three, the initial discharge time for the battery at the current cycle number is determined. Specifically, this includes the following operations: When the battery completes the charging process for the current cycle, the battery is in a fully charged state, and its initial charge level for the current cycle is set. It is 100%; when the battery has never been discharged from a fully charged state, the battery's initial state is 100%. It equals the SOC value recorded in the BMS at the previous moment.

4. The method for estimating the dynamic and static SOC of an electric vehicle power battery as described in claim 1, characterized in that, Step 4.2 specifically includes the following steps: Step 4.2.1, initialize the battery under the current cycle as obtained in Step 3. The battery operating current obtained in step 4.1 and battery temperature T Substitute the current time into formulas (4-3) to (4-6) to obtain the current time. negative electrode lithium intercalation concentration ; （4-3） Initial conditions are （4-4） Boundary conditions are （4-5） （4-6） In the formula: The time variable is / s; Indicates the initial time in seconds; Represents the lithium diffusion coefficient of the electrode material / m 2 ·s -1 With battery temperature T change; The concentration of lithium intercalation in the negative electrode active particles is expressed as mol·m⁻². -3 ; This indicates the maximum lithium intercalation concentration of the negative electrode active particles (mol·m). -3 ; r represents the radius of the negative electrode particle in meters; This represents the average radius of the negative electrode active particles in meters. This indicates the specific surface area of ​​the negative electrode active particles (m²). -1 ; F represents the Faraday constant, which is equal to 26.8 Ah·mol⁻¹. -1 ; Specifically, it includes the following sub-steps: Step 4.2.1.1: Discretize equation (4-3) using the finite difference method, within the radius of the battery negative electrode particles. r Internal nodes of the direction Above, with spatial step size space r The partial derivatives are obtained using the second-order central difference; at time node Above, by time step Regarding time t Implicit difference is performed using the partial derivatives; in: m For in (0, The number of discrete nodes within the BMS is preset by the OEM. i Indicates the radius along the negative electrode particle r The ordinal number of the node in the direction, which here equals 2, 3, ... m -2, m -1; Indicates the radius along the negative electrode particle r The spatial step size in the direction is equal to the value of ; This indicates the estimated SOC time step, which is set by the user in the BMS as needed, and its value is equal to... , Indicates the current moment. Indicates the previous moment, j This is the current time step number, and its value is 1, 2, ...; Step 4.2.1.2, within the radius of the battery negative electrode particles r Boundary nodes of direction Above, a first-order backward difference is applied to equation (4-5), where =0; at the boundary node Above, a first-order forward difference is applied to equation (4-6), where ; Step 4.2.1.3, at the initial moment Battery negative electrode particle radius r All grid nodes in the direction satisfy equation (11), thus obtaining the negative electrode lithium insertion concentration at all grid nodes. All equal to ; Step 4.2.1.4: Obtain the negative electrode particle radius according to steps 4.2.1.1 to 4.2.1.

3. r The discrete equation (4-7) for the concentration of all grid nodes in the direction is used to calculate the concentration of the previous time step. negative electrode lithium intercalation concentration Substituting into the discrete equation (4-7), we obtain the current time. negative electrode lithium intercalation concentration ; （4-7） Step 4.2.2, based on the current time obtained in step 4.2.1 Negative electrode lithium intercalation concentration You can get the current time. Surface lithium intercalation concentration of negative electrode particles Minimum lithium intercalation concentration and average lithium intercalation concentration Substituting this into formula (4-8), we obtain the current unusable active lithium capacity at the battery's negative electrode. ; （4-8） in: This indicates the current unusable active lithium capacity at the battery's negative electrode, expressed in mol. Indicates the volume of the negative electrode active material / m 3 ; This indicates the surface lithium intercalation concentration of the negative electrode active particles at the current moment (mol·m). -3 ,Right now: ; This represents the minimum lithium intercalation concentration of the negative electrode active particles at the current moment, expressed as / mol·m -3 ,Right now: ; This represents the surface lithium intercalation concentration (mol·m) of the negative electrode active particles when discharged to the cutoff voltage at the current. -3 ; This represents the minimum lithium intercalation concentration of the negative electrode active particles at the current cycle number, expressed as / mol·m -3 ; This represents the average lithium intercalation concentration of the negative electrode active particles at the current moment, expressed as / mol·m -3 ,Right now: .

5. The method for estimating the dynamic and static SOC of an electric vehicle power battery as described in claim 4, characterized in that, In step 4.2.2, the minimum lithium intercalation concentration of the negative electrode active particles at the current cycle number. It is obtained through formula (14); （4-9） in: The minimum lithium intercalation concentration, expressed in mol, represents the new battery electrode material. and These are dimensionless fitting parameters.

6. The method for estimating the dynamic and static SOC of an electric vehicle power battery as described in claim 4, characterized in that, In step 4.2.2, the surface lithium intercalation concentration of the negative electrode active particles when discharged to the cutoff voltage at the current is... It is calculated using formula (4-10); （4-10） in: , and These are dimensionless fitting parameters; Indicates discharge current in A; This indicates the current (A) corresponding to a 1C battery capacity. E a Activation energy is expressed in J·mol⁻¹ -1 Its value is obtained by fitting discharge experimental data; R represents the gas molar constant, which is equal to 8.314 J·mol⁻¹. -1 ·K -1 ; T ref This indicates a reference temperature, usually taken as 298.15K; T Indicates battery temperature in K.

7. A dynamic and static SOC estimation system for an electric vehicle power battery, based on the dynamic and static SOC estimation method for an electric vehicle power battery according to any one of claims 1 to 6, characterized in that, It includes a SOH estimation module, a total effective capacity estimation module, an initial SOC estimation module, a total usable capacity estimation module, a battery dynamic and static SOC estimation module, and a display module. The SOH estimation module, the total effective capacity estimation module, and the battery dynamic and static SOC estimation module are connected in sequence. The total usable capacity estimation module is connected to the initial SOC estimation module and the battery dynamic and static SOC estimation module, respectively. The battery dynamic and static SOC estimation module is also connected to a display module. The SOH estimation module is used to estimate the battery's health status at the current cycle number. ; The total effective capacity estimation module is used to determine the total effective capacity of the battery at the current cycle number. ; The initial SOC estimation module is used to determine the initial SOC of the battery at the current cycle number. ; The total usable capacity estimation module is used to estimate the total usable capacity of the battery in its current state. ; The battery dynamic and static SOC estimation module is used to estimate the static SOC of the battery in its current state. and dynamic ; The display module is used to display the remaining effective capacity and remaining effective usable capacity of the battery in its current state.

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