A modeling method for electric vehicle battery operating characteristics considering the influence of low temperature

Abstract

The present invention relates to the field of battery modeling and discloses a method for modeling the operating characteristics of an electric vehicle battery taking into account the influence of low temperatures, comprising: calculating the operating temperature of an electric vehicle battery in idle, discharging, charging and preheating states; establishing a relationship between the operating temperature of the electric vehicle battery and energy availability; establishing operating constraints of the electric vehicle battery taking into account the preheating process; and linearizing the electric vehicle battery operating characteristic model. The present invention has the beneficial effect of being able to more accurately estimate the energy of the available electric vehicle battery during and after charging in extremely cold weather by using the electric vehicle battery operating characteristic model taking into account the influence of low temperatures, while more effectively managing the uncertainty of the electric vehicle departure time and ensuring the flexibility of the electric vehicle operation.

Description

Technical Field

[0001] The present invention relates to the field of battery modeling, and in particular to a method for modeling operating characteristics of an electric vehicle battery taking into account the influence of low temperature. Background Art

[0002] In extremely cold weather, low temperatures can significantly reduce the charge and discharge performance of electric vehicle batteries. Unlike stationary batteries, electric vehicle batteries are often parked outdoors, where their operating temperatures often approach the cold ambient temperature, which can affect their performance. Therefore, the impact of low temperatures on the charge and discharge performance of electric vehicle batteries must be considered. For example, lithium-ion batteries, one of the most common battery types used in electric vehicles, significantly increase charging time and energy consumption in cold weather. Charging at sub-zero temperatures can increase battery wear, degradation, and safety risks.

[0003] Therefore, an additional preheating process is performed before charging to raise the EV battery temperature to above 0°C. According to existing literature, it takes 20 minutes to raise the operating temperature of an EV battery from -20°C to 0°C, and 48 minutes to raise it from -19.3°C to -2.4°C.

[0004] Regarding discharge performance, although lithium-ion batteries can be discharged in a temperature range of -30°C to 40°C, the energy that can be released is significantly reduced at cold temperatures. For example, when a lithium-ion battery is discharged at -20°C, there is a reduction of approximately 40% in energy compared to 20°C. This decrease is because the lithium-ion battery reaches its cutoff voltage too early, preventing the complete release of the stored energy. This conclusion also applies to other electrochemical cells, such as lead-acid batteries and supercapacitor batteries. Ignoring the impact of low temperatures on the operating characteristics of electric vehicle batteries will overestimate the available energy of electric vehicle batteries, resulting in unfeasible energy management optimization schemes in extremely cold weather. Therefore, establishing an improved electric vehicle battery operating characteristic model that considers the impact of low temperatures is very important to ensure accurate energy assessment.

[0005] To reflect the effects of low temperatures, some studies have developed temperature-dependent battery operation models. For example, some studies have proposed a linear function based on data fitting to reflect the impact of low temperatures on the discharge / charging power of electric vehicle batteries. In contrast, some studies have explored the impact of low temperatures on battery energy availability, incorporating energy limits and energy variation constraints into their operation models. For example, some studies have proposed a temperature-aware energy limit constraint by modeling the rated energy as a polynomial function of the ambient temperature. However, these studies only used the daily average ambient temperature and ignored temperature fluctuations throughout the day. Some studies have developed a temperature-aware energy variation model, but the battery state of charge modeling in these studies ignores adaptability to the battery's idle state. This limitation can lead to inaccurate estimates of energy availability when idle states exist. Some studies have proposed a new battery state of charge variation formula that considers both the static battery state of charge (unaffected by temperature) and the operating battery state of charge (affected by temperature). However, the electrothermal coupling model employed involves nonlinear relationships, increasing computational complexity. Furthermore, some of these models ignore the EV battery preheating process required to ensure safe charging. Some studies have considered the optimal preheating temperature of electric vehicle batteries, but the preheating process is not included in the electric vehicle battery operating characteristic model.

[0006] In summary, existing EV battery operating states fail to simultaneously consider energy limitations, energy variations, and preheating processes. Inaccurate modeling may lead to inaccurate performance evaluations of EV batteries in cold temperatures. Summary of the Invention

[0007] The purpose of the present invention is to propose a method for modeling the operating characteristics of electric vehicle batteries that takes into account the influence of low temperatures, so as to solve the technical problem that the existing technology fails to consider energy limitations, energy changes and preheating processes when modeling the battery operating status, resulting in inaccurate evaluation of battery performance in extremely cold weather.

[0008] Specifically, the present invention provides a method for modeling the operating characteristics of an electric vehicle battery taking into account the influence of low temperature, comprising the following steps:

[0009] S1. Calculate the operating temperature of electric vehicle batteries in idle, discharging, charging and preheating states;

[0010] S2: Establish the relationship between the operating temperature of electric vehicle batteries and energy availability;

[0011] S3: Establishing the battery operation constraints of electric vehicles considering the preheating process;

[0012] S4: Linearize the electric vehicle battery operating characteristic model.

[0013] A storage medium stores instructions and data for implementing a method for modeling the operating characteristics of an electric vehicle battery taking into account the influence of low temperatures.

[0014] A device for modeling the operating characteristics of an electric vehicle battery taking into account the influence of low temperature comprises: a processor and a storage medium; the processor loads and executes instructions and data in the storage medium to implement a method for modeling the operating characteristics of an electric vehicle battery taking into account the influence of low temperature.

[0015] The beneficial effects provided by the present invention are: being able to more accurately estimate the energy of the available electric vehicle battery during and after charging through an electric vehicle battery operation characteristic model that takes into account the influence of low temperature in extremely cold weather, while more effectively managing the uncertainty of the electric vehicle departure time and ensuring the flexibility of the electric vehicle operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the process of the method of the present invention;

[0017] Figure 2 Representing the energy state transitions of an electric vehicle battery in idle mode;

[0018] Figure 3 Indicates the energy state transition of the battery of an electric vehicle in V2R mode;

[0019] Figure 4 Represents the energy state transition of the battery of an electric vehicle in R2V mode;

[0020] Figure 5 It is a schematic diagram of the working of the hardware device of an embodiment of the present invention. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0022] Before formally explaining the present invention, the scheme of the present invention is first generally explained for easy understanding.

[0023] Please refer to Figure 1 The present invention provides a method for modeling the operating characteristics of an electric vehicle battery taking into account the influence of low temperature, including:

[0024] S1. Calculate the operating temperature of electric vehicle batteries in idle, discharging, charging and preheating states;

[0025] The specific process of step S1 is as follows:

[0026] The operating temperature of electric vehicle batteries is greatly affected by their four working states. The four working states include idle state ( )、Discharge state( )、Charging status( ) and preheating state ( ). The energy availability of EV batteries depends on the operating temperature, so evaluating the operating temperature of EV batteries is the first step in establishing an EV battery operating characteristic model.

[0027] The operating temperature formula for electric vehicle batteries is as follows:

[0028] (1)

[0029] (2)

[0030] (3)

[0031] (4)

[0032] (5)

[0033] (6)

[0034] Wherein, formula (1) is the battery operating temperature of the electric vehicle in the idle state The modeling formula, Equal to ambient temperature , A binary variable indicating whether it is in idle state;

[0035] Formula (2) is the battery operating temperature of the electric vehicle under discharge state According to the modeling formula, in the discharge state, when using a bidirectional charger, the operating temperature of the electric vehicle battery will rise slightly, but it can be ignored. Therefore, It is also equal to , A binary variable indicating whether it is in the discharge state;

[0036] Formula (3) is the battery operating temperature of the electric vehicle under charging state Modeling formula, in the charging state, if Above the charging threshold temperature , Can be equal to Otherwise, a grid-powered heater is needed to preheat the EV battery to Raised to threshold , A binary variable indicating whether it is in charging state;

[0037] Formula (4) is the battery operating temperature in the preheating state of the electric vehicle The modeling formula, A binary variable indicating whether it is in the preheating state;

[0038] Formula (5) is the change in the operating temperature of the electric vehicle battery in the preheating state The modeling formula, Is the heater in time t The power consumed when is the heater efficiency, is the number of battery cells, is the mass of each battery cell, is the specific heat capacity of the battery, is the duration of each time interval;

[0039] Formula (6) is the electric vehicle battery The temperature is represented by the modeling formula of the state correlation function.

[0040] S2: Establish the relationship between the operating temperature of electric vehicle batteries and energy availability;

[0041] As an embodiment, the present invention defines four key energy state parameters to describe the effect of temperature on the energy availability of electric vehicle batteries, including rated energy , store energy , unavailable energy and available energy .

[0042] Specifically, rated energy refers to the battery's rated energy at a specific operating temperature. The maximum amount of energy that can be stored and delivered.

[0043] Stored energy: t The total energy stored in a battery at any given moment, affected only by charging and discharging activity.

[0044] Unusable energy: At low temperatures, part of the energy will freeze and This energy cannot be released, it is only affected by Although this energy is still stored in the battery, the cutoff voltage is reached too early in the discharge process, preventing the battery from discharging further.

[0045] Available energy: refers to the energy consumed at operating temperature The stored energy that can be released under the and the effects of charge / discharge activity.

[0046] The effects of temperature on the energy availability of electric vehicle batteries are as follows:

[0047] (7)

[0048] (8)

[0049] (9)

[0050] (10)

[0051] Among them, formula (7) converts the unavailable energy Fitted to operating temperature Compared with the rated energy of the battery at room temperature Nonlinear function of

[0052] Formula (8) represents the operating temperature Rated energy under Compared with the rated energy of the battery at room temperature and unavailable energy the relationship between;

[0053] Formula (9) represents the available energy and stored energy and unavailable energy the relationship between;

[0054] Formula (10) shows t Battery charging status at all times Equal to available energy With rated energy ratio.

[0055] S3: Establishing the battery operation constraints of electric vehicles considering the preheating process;

[0056] It should be noted that the electric vehicle battery operation constraints during the preheating process include energy change constraints, energy limit constraints, discharge limit constraints, preheating constraints and charging limit constraints.

[0057] As an example, the energy change constraint is as follows

[0058] (11)

[0059] (12)

[0060] Figure 2 Represents the energy state transitions of an electric vehicle battery in idle mode.

[0061] Among them, constraint (11) represents the energy change constraint of the electric vehicle in idle mode. In this mode, the battery only experiences a temperature drop without any charging or discharging activity. The electric vehicle battery experiences arrive When the temperature changes, the energy state changes from point B to point C, and the unavailable energy changes. is a negative value, which means that the difference in unavailable energy is negative, that is, the unavailable energy increases. Among them, constraint (12) indicates that when the temperature changes The available energy after Although the total stored energy in the electric vehicle battery remains unchanged, the available energy increases from point B to point C due to the increase in unavailable energy at lower temperatures. Reduce to point C .

[0062] (13)

[0063] Figure 3 Represents the energy state conversion of electric vehicle batteries in V2R mode (power from electric vehicle batteries flows to residential power grid).

[0064] Among them, constraint (13) indicates that the battery of electric vehicle in V2R mode experiences discharge process and temperature change. Available energy afterwards The available energy from point D Change to point E The change in available energy can be divided into two independent parts: (I) is the change in available energy due to temperature change, (II) The change in available energy caused by discharge. For the first part, during the transition from point D to point Q The change of is defined in constraint (11). For the second part, the electric vehicle battery releases electricity, resulting in a decrease in the available energy from point D to point P, is a negative value. express t Discharge power at all times, Indicates discharge efficiency.

[0065] (14)

[0066] Figure 4 Represents the energy state conversion of the electric vehicle battery in the R2V mode (power from the residential grid flows to the electric vehicle battery).

[0067] Among them, constraint (14) represents the available energy of the electric vehicle battery after the preheating and charging process in R2V mode. If the battery temperature of the electric vehicle Below threshold temperature The preheating process will first reduce the temperature from point F to Raise to point G , which will increase the available energy, i.e. Then, the electric vehicle battery is charged, causing the available energy to further increase from point G to point H. is a positive value. express t Charging power at all times, Indicates charging efficiency.

[0068] (15)

[0069] Wherein, constraint (15) represents the change of available energy in the electric vehicle battery taking into account the three operating modes and temperature changes. represents the change in available energy due to temperature change, Represents the change in available energy caused by charging and discharging activities.

[0070] The energy limit constraints are as follows:

[0071] (16)

[0072] (17)

[0073] (18)

[0074] Among them, constraint (16) represents the upper and lower limit constraints of available energy, and constraint (17) represents the upper limit of available energy and Constraint (18) represents the lower limit of available energy and The relationship between represents the upper limit of available energy, Indicates the upper limit of the battery charge state, where represents the lower limit of available energy, Indicates the lower limit of the battery charge state.

[0075] The discharge limit constraints are as follows:

[0076] (19)

[0077] (20)

[0078] Wherein, constraint (19) represents the discharge power The maximum power of the bidirectional charger should not be exceeded , constraint (20) prevents the temperature from dropping to Discharge at the following times. It is a binary state variable representing whether discharge is performed.

[0079] The preheating and charging limits are as follows:

[0080] (twenty one)

[0081] (twenty two)

[0082] (twenty three)

[0083] (twenty four)

[0084] (25)

[0085] (26)

[0086] (27)

[0087] (28)

[0088] Among them, constraint (21) means that in R2V mode, the power flowing into the electric vehicle battery should be less than , is a binary state variable that represents whether the electric vehicle battery is in R2V mode;

[0089] Constraint (22) indicates that the electric vehicle battery cannot be in idle mode, R2V mode and V2R mode at the same time. Since the electric vehicle battery is only discharged in V2R mode, A binary state variable representing whether the electric vehicle battery is in V2R mode;

[0090] Constraint (23) is used to ensure that preheating and charging cannot occur simultaneously;

[0091] Constraint (24) indicates that in R2V mode, when the operating temperature of the electric vehicle battery is lower than the defined At the same time greater than Preheating will only occur when

[0092] Constraint (25) indicates that when the operating temperature of the electric vehicle battery is higher than the defined At the same time less than When it is on, it will be charged;

[0093] Constraint (26) indicates that the preheating power should not exceed the rated power of the heater ;

[0094] Constraint (27) indicates that the charging power cannot exceed ;

[0095] Constraint (28) indicates that both the preheating power and the charging power should satisfy the power relationship of the bidirectional charger.

[0096] S4: Linearize the electric vehicle battery operating characteristic model.

[0097] It should be noted that the linearization method of the electric vehicle battery operating characteristic model is as follows:

[0098] (29)

[0099] (30)

[0100] (31)

[0101] (32)(32a)

[0102] (32b)

[0103] (32c)

[0104] (32d)

[0105] (32e)

[0106] (32f)

[0107] (33)

[0108] (34)

[0109] (35)

[0110] Based on the relationship in formula (22), formula (6) can be transformed into the form of formula (29), but formula (29) still has a bilinear term 、 , according to formula (26), the bilinear term Can be used Instead of; bilinear term is a binary variable and continuous variables The product can be linearized using the big-M method, introducing auxiliary variables ,Will Replace by constraint (30); for equation (7) and The nonlinear function is linearized using the piecewise function shown in formula (31); formula (32) introduces the continuous variable { }with binary variables { } to further describe the choice of piecewise function; the bilinear terms in equations (24) and (25) By linearizing using the big-M method in equation (33), equations (24) and (25) can be transformed into equations (34) and (35) respectively.

[0111] In summary, the electric vehicle battery operation characteristic model consists of continuous variables { , }、Binary variable{ } and constraints (8), (10), (15)-(23), (26)-(35).

[0112] See Figure 5 , Figure 5 4 is a schematic diagram of the working of the hardware device of an embodiment of the present invention, wherein the hardware device specifically includes: an electric vehicle battery operating characteristic modeling device 401 considering the influence of low temperature, a processor 402 and a storage medium 403.

[0113] An electric vehicle battery operating characteristic modeling device 401 considering the influence of low temperature: The electric vehicle battery operating characteristic modeling device 401 considering the influence of low temperature implements the electric vehicle battery operating characteristic modeling method considering the influence of low temperature.

[0114] Processor 402: The processor 402 loads and executes the instructions and data in the storage medium 403 to implement the electric vehicle battery operating characteristics modeling method considering the influence of low temperature.

[0115] Storage medium 403: The storage medium 403 stores instructions and data; the storage medium 403 is used to implement the electric vehicle battery operating characteristics modeling method considering the influence of low temperature.

[0116] The beneficial effects of the present invention are: it is able to more accurately estimate the energy of the available electric vehicle battery during and after charging by considering the electric vehicle battery operation characteristic model affected by low temperature in extremely cold weather, while more effectively managing the uncertainty of the electric vehicle departure time and ensuring the flexibility of the electric vehicle operation.

[0117] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for modeling the operating characteristics of electric vehicle batteries considering the effects of low temperatures, characterized by: include: S1. Calculate the operating temperature of electric vehicle batteries in idle, discharging, charging and preheating states; S2: Establish the relationship between the operating temperature of electric vehicle batteries and energy availability; S3: Establishing the battery operation constraints of electric vehicles considering the preheating process; S4: Linearize the electric vehicle battery operating characteristic model; Step S1 is as follows: The operating temperature formula for electric vehicle batteries is as follows: (1) (2) (3) (4) (5) (6) Wherein, formula (1) is the battery operating temperature of the electric vehicle in the idle state The modeling formula, Equal to ambient temperature , A binary variable indicating whether it is in idle state; Formula (2) is the battery operating temperature of the electric vehicle in the discharge state The modeling formula, in the discharge state, and The difference does not exceed the preset value. A binary variable indicating whether it is in the discharge state; Formula (3) is the battery operating temperature of the electric vehicle in the charging state Modeling formula, in the charging state, if Above the charging threshold temperature ,but and The difference does not exceed the preset value, otherwise, a grid-powered heater is needed to preheat the electric vehicle battery to Raised to threshold , A binary variable indicating whether it is in the charging state; Formula (4) is the battery operating temperature in the preheating state of the electric vehicle The modeling formula, A binary variable indicating whether it is in the preheating state; Formula (5) is the change in the operating temperature of the electric vehicle battery in the preheating state The modeling formula, Is the heater in time t The power consumed when is the heater efficiency, is the number of battery cells, is the mass of each battery cell, is the specific heat capacity of the battery, is the duration of each time interval; Formula (6) is the electric vehicle battery The temperature is represented by the modeling formula of the state correlation function.

2. The electric vehicle battery operating characteristics modeling method considering low temperature effects according to claim 1, characterized in that: Step S2 is specifically as follows: The effects of temperature on the energy availability of electric vehicle batteries are as follows: (7) (8) (9) (10) Among them, formula (7) converts the unavailable energy Fitted to operating temperature Compared with the rated energy of the battery at room temperature A nonlinear function of; Equation (8) represents the operating temperature Rated energy under Compared with the rated energy of the battery at room temperature and unavailable energy The relationship between the available energy and stored energy and unavailable energy The relationship between t Battery charging status at all times Equal to available energy With rated energy ratio.

3. The electric vehicle battery operating characteristics modeling method considering low temperature effects according to claim 2, characterized in that: In step S3, the electric vehicle battery operation constraints during the heating process include: energy change constraints, energy limit constraints, discharge limit constraints, preheating constraints, and charging limit constraints.

4. The method for modeling the operating characteristics of an electric vehicle battery considering the influence of low temperature according to claim 3, characterized in that: The energy change constraints are as follows: (11) (12) (13) (14) (15) Constraint (11) represents the energy variation constraint of the electric vehicle in idle mode; Constraint (12) indicates that the temperature changes The available energy after Modeling formula of Constraint (13) indicates that the battery of an electric vehicle undergoes a discharge process and temperature changes in the V2R mode. Available energy afterwards The modeling formula is: where the change in available energy can be divided into two independent parts, is the change in available energy caused by a change in temperature, is the change in available energy caused by the discharge; Constraint (14) represents the available energy of the electric vehicle battery after the preheating and charging process in R2V mode. Modeling formula of Constraint (15) represents the variation of available energy in the EV battery considering the three operating modes and temperature variation simultaneously.

5. The method for modeling the operating characteristics of an electric vehicle battery considering the influence of low temperature according to claim 4, characterized in that: The energy limit constraints are as follows: (16) (17) (18) Among them, constraint (16) represents the upper and lower limit constraints of available energy, and constraint (17) represents the upper limit of available energy and Constraint (18) represents the lower limit of available energy and relationship, in which represents the upper limit of available energy, Indicates the upper limit of the battery charge state, where represents the lower limit of available energy, Indicates the lower limit of the battery charge state.

6. The electric vehicle battery operating characteristics modeling method considering low temperature effects according to claim 5, characterized in that: The discharge limit constraints are as follows: (19) (20) Wherein, constraint (19) represents the discharge power The maximum power of the bidirectional charger should not be exceeded , constraint (20) prevents the temperature from dropping to Discharge when: It is a binary state variable representing whether discharge is performed.

7. The method for modeling the operating characteristics of an electric vehicle battery considering the influence of low temperature according to claim 6, characterized in that: The preheating and charging limits are as follows: (21) (22) (23) (24) (25) (26) (27) (28) Among them, constraint (21) means that in R2V mode, the power flowing into the electric vehicle battery should be less than , is a binary state variable that represents whether the electric vehicle battery is in R2V mode; Constraint (22) indicates that the electric vehicle battery cannot be in idle mode, R2V mode and V2R mode at the same time. Since the electric vehicle battery is only discharged in V2R mode, A binary state variable representing whether the electric vehicle battery is in V2R mode; Constraint (23) is used to ensure that preheating and charging cannot occur simultaneously; Constraint (24) indicates that in R2V mode, when the operating temperature of the electric vehicle battery is lower than the defined At the same time greater than Preheating will only occur when Constraint (25) indicates that when the operating temperature of the electric vehicle battery is higher than the defined At the same time less than When it is on, it will be charged; Constraint (26) indicates that the preheating power should not exceed the rated power of the heater ; Constraint (27) indicates that the charging power cannot exceed ; Constraint (28) indicates that both the preheating power and the charging power should satisfy the power relationship of the bidirectional charger.

8. A storage medium, characterized in that: The storage medium stores instructions and data for implementing a method for modeling the operating characteristics of an electric vehicle battery taking into account the influence of low temperature as described in any one of claims 1 to 7.

9. A device for modeling the operating characteristics of electric vehicle batteries taking into account the effects of low temperatures, characterized by: include: A processor and a storage medium; the processor loads and executes instructions and data in the storage medium to implement a method for modeling the operating characteristics of an electric vehicle battery taking into account the influence of low temperature as described in any one of claims 1 to 7.

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