A battery thermal management system and control method for pure electric vehicles in high temperature environments

Abstract

The present invention discloses a battery thermal management system and control method for pure electric vehicles in medium- and high-temperature environments. The system compares the driving characteristic parameters of a preceding vehicle with the real-time driving characteristic parameters of the vehicle itself to obtain instantaneous speed weights and average speed weights that vary with the vehicle's driving, thereby determining the vehicle's future driving conditions. The system also determines the impact of the vehicle's future driving conditions on the charge and discharge currents during the battery reaction process, thereby determining the battery temperature corresponding to the vehicle's future driving conditions. The battery temperature is then compared with a threshold to determine whether the battery enters a radiator cooling mode or a chiller cooling mode. The system uses minimizing the difference between the lithium-ion battery temperature and the target temperature and optimizing the thermal management system actuator energy consumption as optimization goals to determine the optimal output speeds of the water pump and fan in the cooling mode. The present invention takes into account actuator energy consumption and switching between different modes, resulting in high control accuracy and reduced energy consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal management of new energy vehicles, and specifically relates to a battery thermal management system and a control method thereof in a medium-high temperature environment of a pure electric vehicle. Background Art

[0002] With the development of my country's automotive industry, sales have continued to rise. While this industry has brought economic growth, it has also created a series of environmental and energy issues. As the power source of pure electric vehicles, the temperature of the battery has a significant impact on the safety and reliability of pure electric vehicles.

[0003] Research shows that the optimal operating temperature for batteries is between 15°C and 35°C. Exceeding this range accelerates the diffusion of lithium ions within the battery, speeding up reactions within the battery. This results in a slight increase in battery capacity, but also in some side reactions. This increases the thickness of the SEI film and increases the rate of battery aging. As heat accumulates within the battery, the battery temperature continues to rise, ultimately leading to thermal runaway. When gases from side reactions accumulate within the battery, exceeding a certain threshold can cause an explosion and lead to thermal safety issues.

[0004] Currently, commonly used battery cooling optimization methods can be divided into two categories: classical control methods and intelligent optimization methods. Classical control methods often formulate battery cooling optimization strategies based on rules, such as segmented control, proportional-integral-derivative (PID) control, and fuzzy control. These methods have the advantages of simple design and easy implementation, but their control rules are often derived from practical experience. When experience is insufficient, it is difficult to achieve satisfactory cooling effects, and accurate energy consumption evaluation standards are not provided. To compensate for the shortcomings of classical control algorithms, intelligent optimization algorithms have gradually been applied to battery cooling systems. During the battery cooling process, intelligent optimization algorithms do not consider actuator energy consumption and switching between different modes, resulting in low control accuracy and high energy consumption. Summary of the Invention

[0005] In view of the shortcomings in the prior art, the present invention provides a battery thermal management system and a control method thereof for a pure electric vehicle in a medium-high temperature environment.

[0006] The present invention achieves the above technical objectives through the following technical means.

[0007] A control method for a battery thermal management system in a pure electric vehicle under a medium-high temperature environment:

[0008] Compare the driving characteristic parameters of the preceding vehicle with the real-time driving characteristic parameters of the own vehicle to obtain the instantaneous speed weight that changes with the driving of the own vehicle and average speed weight Based on the weights, the formula Obtain the driving characteristic parameter value of the next state of the vehicle, and then determine the future driving condition of the vehicle; where v t+1,1n represents the instantaneous speed of the next state of the nth target vehicle, v t+1,2n Indicates the average speed of the nth target vehicle in the next state;

[0009] Determining the impact of the vehicle's future driving conditions on the battery thermal management system, specifically the impact on the charge and discharge currents during the lithium-ion battery reaction process; the charge and discharge currents during the lithium-ion battery reaction process and the lithium-ion battery temperature satisfy a centralized thermal model of a lithium-ion battery under liquid cooling conditions, thereby determining the lithium-ion battery temperature corresponding to the vehicle's future driving conditions, and comparing the lithium-ion battery temperature with a battery operating temperature threshold to determine whether the battery enters a radiator cooling mode or a chiller cooling mode;

[0010] Taking the minimum difference between the lithium-ion battery temperature and the target temperature and the optimal energy consumption of the thermal management system actuator as the optimization objectives, the optimal output speed of the water pump and fan in the cooling mode is solved.

[0011] Furthermore, the instantaneous speed weight and average speed weight Satisfy respectively: Where: v 1n is the instantaneous speed of the preceding vehicle, v 2n is the average speed of the preceding vehicle, n=1,2…m, n represents the nth target preceding vehicle, m represents the total number of preceding vehicles; v1 is the instantaneous speed of the vehicle, v2 is the average speed of the vehicle.

[0012] Furthermore, the impact of the future driving conditions of the vehicle on the charge and discharge current during the lithium-ion battery reaction process is specifically as follows:

[0013]

[0014] Where: I is the charge and discharge current during the lithium-ion battery reaction process, U0 is the open circuit voltage of the lithium-ion battery, R0 is the sum of the ohmic internal resistance and polarization internal resistance of the lithium-ion battery, P p is the traction power of electric vehicles, P s is the power of the electric vehicle thermal management system, V v is the vehicle speed, F r is the rolling resistance of the vehicle, F a is the vehicle's air resistance, M v is the total mass of the vehicle, η s is the traction efficiency, △V v is the change in vehicle speed.

[0015] Furthermore, the concentrated heat model of the lithium-ion battery under the liquid cooling condition is:

[0016]

[0017] Where: ΔT b is the temperature change of the lithium-ion battery, T b is the temperature of the lithium-ion battery, m b is the concentrated mass of the battery, c b is the battery specific heat capacity, A b is the contact area between the lithium-ion battery and the coolant, g1 is the intermediate amount, G l is the coolant mass flow rate, T l is the coolant temperature.

[0018] Furthermore, when T b low ≤T b ≤T b high , the battery enters the radiator cooling mode: the second port (2032) of the three-way valve is closed, the first port (2031) of the three-way valve and the third port (2033) of the three-way valve are connected, the fan (301) is turned on, and the water pump (201) is turned on; when T b >T b high , the battery enters the chiller cooling mode: the first port (2031) of the three-way valve is closed, the second port (2032) of the three-way valve and the third port (2033) of the three-way valve are connected, the fan (301) is turned off, and the water pump (201) is turned on.

[0019] Furthermore, the objective function corresponding to the optimization goal is:

[0020]

[0021] Among them: O1 and O2 are weights, T br is the target temperature, N p represents the prediction time domain and the control time domain, and P s =N pump T pump η pump +N fan T fan η fan , where T pump Represents the water pump torque, η pump Indicates the pump efficiency, T fan represents the fan torque, η fan Indicates fan efficiency.

[0022] Furthermore, the constraints satisfied by the battery temperature, water pump speed, and fan speed are:

[0023] T b1 ≤T b ≤T b 2

[0024]

[0025]

[0026] Among them, T b 1 Is the lower limit of the battery's optimal operating temperature; T b 2 It is the lower limit of the optimal operating temperature of the battery; is the minimum pump speed, is the maximum speed of the water pump; is the minimum fan speed, The maximum fan speed.

[0027] A battery thermal management system for a pure electric vehicle in a medium- and high-temperature environment includes a water chiller, a water pump, a power battery, a three-way valve, a radiator, and a fan. The first port and the second port of the water chiller are respectively connected to a refrigerant circuit, the fourth port of the water chiller is connected to the second port of the three-way valve, the third port of the three-way valve is connected to the first port of the power battery, the second port of the power battery is connected to the first port of the water pump, the second port of the water pump is connected to an endpoint A, and endpoint A is also connected to the third port of the water chiller and the first port of the radiator. The second port of the radiator is connected to the first port of the three-way valve. The fan is arranged at the radiator.

[0028] The beneficial effects of the present invention are:

[0029] (1) The present invention can improve control accuracy by estimating the weight of the preceding vehicle's driving characteristic parameters of the vehicle's future driving conditions in real time and determining the impact of the vehicle's future driving conditions on the lithium-ion battery cooling process;

[0030] (2) The present invention utilizes model predictive control, takes the minimum difference between the lithium-ion battery temperature and the target temperature and the optimal energy consumption of the thermal management system actuator as the objective function, performs temperature tracking and energy consumption optimization, and considers the switching between the battery radiator cooling and the chiller cooling mode, thereby ensuring the thermal safety of the battery in medium and high temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a structural block diagram of the battery thermal management system in a medium to high temperature environment according to the present invention;

[0032] Figure 2 Schematic diagram of the battery thermal management system optimization method under medium and high temperature environments according to the present invention;

[0033] Figure 3This is a flow chart of the battery thermal management system control method under medium and high temperature environments according to the present invention;

[0034] In the figure: 100-battery thermal management system, 101-chiller, 201-water pump, 202-power battery, 203-three-way valve, 204-radiator, 301-fan, 1011-chiller first port, 1012-chiller second port, 1013-chiller third port, 1014-chiller fourth port, 2011-water pump first port, 2012-water pump second port, 2021-power battery first port, 2022-power battery second port, 2031-three-way valve first port, 2032-three-way valve second port, 2033-three-way valve third port, 2041-radiator first port, 2042-radiator second port. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0036] Figure 1 : This is a structural block diagram of the battery thermal management system 100 of the present application. The battery thermal management system 100 includes a chiller 101, a water pump 201, a power battery 202, a three-way valve 203, a radiator 204 and a fan 301. The fan 301 is arranged at the radiator 204; the first port 1011 of the chiller is connected to the refrigerant circuit (for example, an electronic expansion valve), and the second port 1012 of the chiller is connected to the refrigerant circuit (for example, a gas-liquid separator). The refrigeration circuit is not shown in the figure and is only represented by a dotted line; the fourth port 1014 of the chiller is connected to the second port 2032 of the three-way valve, the third port 2033 of the three-way valve is connected to the first port 2021 of the power battery, the second port 2022 of the power battery is connected to the first port 2011 of the water pump, and the second port 2012 of the water pump is connected to the terminal A. The terminal A is also connected to the third port 1013 of the chiller and the first port 2041 of the radiator. The second port 2042 of the radiator is connected to the first port 2031 of the three-way valve; Figure 1 The solid line represents the coolant circuit, and the dotted line represents the refrigerant circuit. In this embodiment, the power battery 202 is composed of a plurality of lithium-ion single cells.

[0037] The battery thermal management system of the present application includes two operating modes: battery radiator cooling and battery chiller cooling. In a medium-temperature environment, the ambient temperature is suitable and the battery heat generation is not large. The battery can dissipate heat through the radiator, thereby reducing the compressor load and reducing compressor energy consumption. In this mode, the second port 2032 of the three-way valve is closed, and the first port 2031 of the three-way valve is connected to the third port 2033 of the three-way valve. Heat is dissipated through the radiator to ensure the thermal safety of the battery in the medium-temperature environment and reduce the thermal management energy consumption. In a high-temperature environment, the high-temperature coolant of the battery cannot exchange heat with the ambient air through the radiator, so it needs to be cooled by a chiller. In this mode, the first port 2031 of the three-way valve is closed, and the second port 2032 of the three-way valve is connected to the third port 2033 of the three-way valve. The high-temperature coolant of the battery thermal management exchanges heat with the low-temperature refrigerant through the chiller 101, and forms low-temperature coolant at the outlet of the chiller third port 1013, thereby cooling the battery in the high-temperature environment. The battery chiller solves the problem of insufficient heat dissipation of the battery radiator cooling at high temperatures, ensuring the thermal safety of the battery.

[0038] Figure 2 This is a schematic diagram of the battery thermal management system optimization method under medium and high temperature environments described in this application. Figure 3 This is a flow chart of the battery thermal management system control method for medium- and high-temperature environments described in the present invention. When an electric vehicle is in operation, the vehicle network system acquires real-time driving characteristic parameter information of the vehicle and preceding vehicles to predict future driving conditions. The system then determines the impact of these predicted driving conditions on the battery thermal management system based on these conditions. The system then considers switching between battery radiator cooling and chiller cooling models. Finally, through a model predictive control method, the battery target temperature is used as the optimization target value. With the optimization objectives of minimizing the difference between the actual battery temperature and the target temperature and optimizing the thermal management system actuator energy consumption, the system determines the optimal actuator output speed, achieving optimal battery cooling in medium- and high-temperature environments.

[0039] The specific design of the battery thermal management system optimization method under medium and high temperature environments is as follows:

[0040] 1. Predicting the vehicle's future driving conditions

[0041] The driving characteristic parameter information of the vehicle and the preceding vehicle is called up through the vehicle networking system, including instantaneous speed and average speed. At the same time, the vehicle and the preceding vehicle interact with each other through the vehicle networking system, and the driving characteristic parameter information of the vehicle and the preceding vehicle is stored in the vehicle networking system.

[0042] Based on the obtained driving characteristic parameters of the preceding vehicle and the vehicle, the following formula is determined: The weight of each driving characteristic parameter of each preceding vehicle is shown. Since the driving information of pure electric vehicles changes in real time, the weight of each driving characteristic parameter of each preceding vehicle is real-time. 1n and v 2n , where n = 1, 2...m, n represents the nth target vehicle ahead, and m represents the total number of vehicles ahead; these driving characteristic parameters are compared with the real-time driving characteristic parameters of the vehicle to obtain the instantaneous speed weight that changes with the vehicle's driving and average speed weight Where v1 represents the instantaneous speed of the vehicle, and v2 represents the average speed of the vehicle.

[0043] The influence weight of each characteristic parameter of each preceding vehicle is used to determine the characteristic parameter of the future driving condition of the vehicle, thereby determining the driving condition. The driving characteristic parameter value of the next state of the vehicle can be obtained by multiplying the next state driving characteristic parameter value of each preceding vehicle with the obtained weight and summing them up, as shown in the following formula: As shown, v t+1,1n and v t+1,2n Indicates the driving characteristic parameter value of the next state of the nth target vehicle, and Represents the influence weight of the nth target vehicle in front, which can determine the driving characteristic parameter value of the next state of the vehicle, thereby determining the future driving condition sequence V v (k+i), i=1:N p , k represents the kth moment of vehicle operation, i represents the driving condition prediction time domain N p The i-th driving condition prediction time node.

[0044] 2. Establishing a Battery Thermal Management System Model

[0045] The present invention utilizes a cooling structure consisting of a battery-side coolant circulation loop and a heat pump air conditioning refrigerant circulation loop. Based on this structure, to optimize the cooling process, a predictive model is required to simulate the battery's electrothermal characteristics and the heat exchange characteristics of each actuator.

[0046] (1) Battery centralized heating model

[0047] When a new energy vehicle is in operation, the lithium-ion battery outputs a certain discharge rate current, which generates a certain amount of heat per unit time, causing the lithium-ion battery temperature to rise. Heat generated within the lithium-ion battery mainly comes from Joule heat, polarization heat, reaction heat, and side reaction heat. Side reaction heat is very small and can be ignored.

[0048] The chemical reaction process of lithium-ion batteries during charge and discharge is:

[0049]

[0050] The chemical reaction inside the lithium-ion battery is reversible, and the thermodynamic equation of the lithium-ion battery can be expressed as:

[0051] ΔG=ΔH-T b ΔS=-nFU0

[0052] Among them, ΔG is the energy released by the lithium-ion battery during the chemical reaction, ΔH is the enthalpy change of the lithium-ion battery during the chemical reaction, and T b is the temperature of the lithium-ion battery, ΔS is the entropy change of the lithium-ion battery during the chemical reaction, n is the number of charges related to the chemical reaction of the lithium battery, F is the Faraday constant, and U0 is the open circuit voltage of the lithium-ion battery.

[0053] Reaction heat Q of the chemical reaction process of lithium-ion batteries r for:

[0054]

[0055] Where I is the charge and discharge current during the lithium-ion battery reaction process.

[0056] The sum of the ohmic internal resistance and polarization internal resistance of a lithium-ion battery is R0, so the sum of the Joule heat and polarization heat of the lithium-ion battery can be obtained as:

[0057] Q j +Q p =I 2 R0

[0058] In summary, the relationship between the heat generated by lithium-ion batteries and the charge and discharge current during the lithium-ion battery reaction process is:

[0059]

[0060] The heat dissipation methods of lithium-ion batteries are divided into heat conduction, heat convection and heat radiation.

[0061] During vehicle operation, the heat transferred from the lithium-ion battery to the surrounding coolant is:

[0062] Q s =hA b (T b -T l )

[0063] Among them, Q s is the heat dissipated by the lithium-ion battery, h is the heat transfer coefficient, A b is the contact area between lithium-ion battery and coolant, T b is the temperature of the lithium-ion battery, T l is the temperature of the coolant; the heat transfer coefficient h is:

[0064] h=g1G l

[0065] Among them, the intermediate ρ l is the coolant density, Pr f The Prandtl number is a dimensionless constant representing the heat exchange in fluid flow, μ f The dynamic viscosity is obtained from the average temperature of the coolant in the pipe, μ ω is the dynamic viscosity obtained from the wall temperature of the coolant in the pipe, G l is the coolant mass flow rate.

[0066] The relationship between the heat change per unit time of a lithium-ion battery and the temperature of the lithium-ion battery is:

[0067] Q b =c b m b ΔT b

[0068] Where ΔT b Represents the temperature change of lithium-ion battery, m b is the concentrated mass of the battery, c b is the specific heat capacity of the battery.

[0069] Heat change per unit time of lithium battery Q b It can also be expressed as:

[0070] Q b =Q c -Q s

[0071] Therefore, the concentrated heat dissipation model of lithium-ion batteries under liquid cooling conditions can be obtained:

[0072]

[0073] The model input is the charge and discharge current I during the lithium-ion battery reaction and the temperature T of the coolant. l , the output is the temperature change of the lithium-ion battery ΔT b .

[0074] (2) Chiller model

[0075] At the chiller, the heat exchange between the refrigerant and the coolant is:

[0076] Q e =h e A e ΔT e =G com q k

[0077] Among them, h e is the heat transfer coefficient between the coolant and the refrigerant at the chiller, A e is the heat transfer area of ​​the chiller, G com is the refrigerant flow rate, q k is the heat generated per unit mass, ΔT e is the average heat transfer temperature difference change of the chiller, expressed as:

[0078]

[0079] Among them, T e is the average heat transfer temperature difference of the chiller, T lei is the coolant temperature at the chiller inlet, T leo is the coolant temperature at the chiller outlet.

[0080] According to the law of thermodynamic equilibrium, the average heat transfer temperature difference of the chiller is equal to the change in the coolant temperature at the inlet and outlet of the chiller. Therefore, the coolant temperature at the chiller outlet is:

[0081]

[0082] Among them, c l is the specific heat capacity of the coolant.

[0083] (3) Water pump model

[0084] In the battery cooling circuit, the water pump provides the power required for coolant flow. The water pump speed is:

[0085]

[0086] Among them, V pump is the pump displacement, η pump is the pump efficiency, ρ l is the coolant density.

[0087] (4) Radiator model

[0088] The heat transfer capacity of the radiator is:

[0089] Q rad =|T rad,a,i -T rad,a,out |·G air c air =|T rad,l,i -T rad,l,o |·G l c l

[0090] Among them, Q rad Heat exchange for the radiator, T rad,a,i is the air inlet temperature of the radiator, T rad,a,outis the air outlet temperature of the radiator, T rad,l,i is the temperature of the radiator coolant inlet (i.e., the radiator second port 2042), T rad,l,o is the temperature of the radiator cooling outlet (i.e., the first radiator port 2041), G air is the air mass flow rate, c air is the specific heat capacity of air.

[0091] (5) Fan model

[0092] Fan air volume V fan for:

[0093]

[0094] Among them, A fan is the fan blade area, N fan is the fan speed, η fan is the fan efficiency, P fan Fan pressure.

[0095] 3. Impact of driving conditions on battery thermal management systems

[0096] During the driving process of electric vehicles, the heat generated by the battery changes with the changes in the vehicle driving conditions, so the driving conditions will have a certain impact on the cooling of the battery. The power output of the battery mainly depends on the traction power required for the operation of the electric vehicle and the power required for system thermal management. The expression related to the charge and discharge current and power during the reaction process of lithium-ion batteries is:

[0097]

[0098] Among them, P p is the traction power of electric vehicles, V v is the vehicle speed, F r is the rolling resistance of the vehicle, F a is the vehicle's air resistance, M v is the total mass of the vehicle, η s is the traction efficiency, P s is the power of the electric vehicle thermal management system, △V v is the change in vehicle speed;

[0099] Further:

[0100]

[0101] From this we can see that changes in driving conditions can not only affect the changes in the charging and discharging current during the lithium-ion battery reaction process, thereby affecting the heat generation of the battery, but also affect the air mass flow rate, thereby affecting the radiator cooling.

[0102] 4. Battery radiator cooling and chiller cooling mode switching

[0103] When the ambient temperature is appropriate and the battery does not generate much heat, the battery can be cooled by the radiator, thereby reducing the load on the compressor and reducing the energy consumption of the system. When the ambient temperature is high, the high-temperature coolant of the battery cannot exchange heat with the ambient air through the radiator, so a chiller is required to ensure the thermal safety of the battery. Therefore, it is necessary to comprehensively consider the driving conditions and the temperature of the lithium-ion battery to switch between the two modes. Since the vehicle driving conditions have a certain impact on the thermal management of the battery, the battery temperature and driving conditions must be taken into account during the mode switching process. The acquired driving conditions and battery temperature information are input into the vehicle controller to determine the lithium-ion battery temperature corresponding to the driving conditions, and the temperature is compared with the battery operating temperature threshold. According to the comparison result, it is determined whether the battery enters the radiator cooling mode or the chiller cooling mode. For example Figure 3 As shown, T b low 、T b high They correspond to the minimum and maximum temperature values ​​of the battery at the time of radiator cooling. b <T b low , the battery enters heating mode; when T b low ≤T b ≤T b high , the battery enters the radiator cooling mode: the second port 2032 of the three-way valve is closed, the first port 2031 of the three-way valve and the third port 2033 of the three-way valve are connected, the fan 301 is turned on, and the water pump 201 is turned on. This working mode ensures the thermal comfort of the cabin and the safety of battery thermal management under medium and high temperature conditions. The battery radiator cooling avoids the additional compressor load and energy consumption caused by the battery chiller cooling; when T b >T b high The battery enters the chiller cooling mode: the first port 2031 of the three-way valve is closed, the second port 2032 of the three-way valve and the third port 2033 of the three-way valve are connected, the fan 301 is turned off, and the water pump 201 is turned on. This working mode ensures the thermal comfort of the cabin and the thermal management safety of the battery under high temperatures. The battery chiller cooling solves the problem of insufficient heat dissipation of the battery radiator at high temperatures.

[0104] 5. Model Predictive Control Method Design

[0105] The heat generated by the battery will change with the driving conditions. If it can be predicted and the corresponding control quantity is solved according to the battery target temperature, the battery temperature will be very close to the designed battery temperature target value. At the same time, the energy consumption of the battery thermal management system will be improved accordingly. Therefore, the present invention uses model predictive control to design a control strategy for the battery thermal management system.

[0106] The present invention adopts the state space equation form to construct the model predictive controller. The model needs to be discretized and the system is affected by other external interference factors. The system discretized state space model is expressed as follows:

[0107]

[0108] Among them, x(k+1), x(k), u(k), r(k), and y(k) represent the state quantity at time k+1 and the state variable, control variable, measurable disturbance variable, and output variable at time k, respectively. A, B u 、B d , C are state matrix, input matrix, measurable matrix and output matrix respectively. The present invention regards the state space equation of the battery thermal management system as a black box model, that is, matrix A and matrix B are regarded as unknown parameters, and matrix C is regarded as the unit matrix.

[0109] For the battery thermal management system of the present invention, the state variables are:

[0110] x=[T b T l T leo Q rad ]

[0111] The system control variables are:

[0112] u=[N pump N fan ]

[0113] The input disturbance of the battery thermal management system model is the vehicle driving condition, that is:

[0114] r=[V v ]

[0115] If the controlled object target is the battery temperature, the system output value is:

[0116] y=[T b P s ]

[0117] The optimization goal of the objective function is to minimize the function value of the cost function:

[0118] min[J(z k )]

[0119] The objective function is:

[0120]

[0121] Among them: O1 and O2 are weights; P s To evaluate the energy consumption index during battery cooling, specifically P s is the power of the electric vehicle thermal management system, which can be expressed as the water pump speed N pum and fan speed N fan The function of P s =N pump T pump η pump +N fan T fan η fan , where T pump Represents the water pump torque, η pump Indicates the pump efficiency, T fan represents the fan torque, η fan Indicates fan efficiency; both the prediction time domain and the control time domain are set to N p The first term of the objective function is expressed as the lithium-ion battery temperature and the target temperature T br The difference between the actual and target battery temperatures indicates that the battery is operating near its optimal temperature. The second term represents the cooling energy consumption of the battery thermal management system; a smaller value indicates lower actuator energy consumption during battery cooling. Based on the difference between the actual and target battery temperatures, the energy consumption of both the water pump and fan actuators is considered to solve the corresponding control variable of the objective function.

[0122] In addition, the battery temperature, water pump speed, and fan speed should all be controlled within a reasonable range, so they are constrained:

[0123] T b 1 ≤T b ≤T b 2

[0124]

[0125]

[0126] Among them, T b 1 Is the lower limit of the battery's optimal operating temperature; T b 2 It is the lower limit of the optimal operating temperature of the battery; is the minimum pump speed, is the maximum speed of the water pump; is the minimum fan speed, The maximum fan speed.

[0127] The embodiments described are preferred implementations of the present invention, but the present invention is not limited to the above implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention are within the scope of protection of the present invention.

Claims

1. A control method for a battery thermal management system in a pure electric vehicle under high temperature conditions, characterized by: Compare the driving characteristic parameters of the preceding vehicle with the real-time driving characteristic parameters of the own vehicle to obtain the instantaneous speed weight that changes with the driving of the own vehicle and average speed weight Based on the instantaneous speed weight and the average speed weight, the formula Obtain the driving characteristic parameter value of the next state of the vehicle, and then determine the future driving condition of the vehicle; where v t+1,1n represents the instantaneous speed of the next state of the nth target vehicle, v t+1,2n Indicates the average speed of the nth target vehicle in the next state; Determining the impact of the vehicle's future driving conditions on the battery thermal management system, specifically the impact on the charge and discharge currents during the lithium-ion battery reaction process; the charge and discharge currents during the lithium-ion battery reaction process and the lithium-ion battery temperature satisfy a centralized thermal model of a lithium-ion battery under liquid cooling conditions, thereby determining the lithium-ion battery temperature corresponding to the vehicle's future driving conditions, and comparing the lithium-ion battery temperature with a battery operating temperature threshold to determine whether the battery enters a radiator cooling mode or a chiller cooling mode; Taking the minimum difference between the lithium-ion battery temperature and the target temperature and the optimal energy consumption of the thermal management system actuator as the optimization goals, the optimal output speed of the water pump and fan in the cooling mode is solved; The instantaneous speed weight satisfy Where: v 1n is the instantaneous speed of the preceding vehicle, n=1,2……m, n represents the nth target preceding vehicle, m represents the total number of preceding vehicles, and v1 is the instantaneous speed of the own vehicle; The average speed weight satisfy Where: v 2n is the average speed of the preceding vehicle, n=1,2……m, n represents the nth target preceding vehicle, m represents the total number of preceding vehicles, and v2 is the average speed of the vehicle; The concentrated heat dissipation model of lithium-ion batteries under the liquid cooling condition is: Where: ΔT b is the temperature change of the lithium-ion battery, T b is the temperature of the lithium-ion battery, m b is the concentrated mass of the battery, c b is the battery specific heat capacity, A b is the contact area between the lithium-ion battery and the coolant, g1 is the intermediate amount, G l is the coolant mass flow rate, T l is the coolant temperature.

2. The control method according to claim 1, characterized in that: The impact of the future driving conditions of the vehicle on the charge and discharge current during the lithium-ion battery reaction process is specifically as follows: Where: I is the charge and discharge current during the lithium-ion battery reaction process, U0 is the open circuit voltage of the lithium-ion battery, R0 is the sum of the ohmic internal resistance and polarization internal resistance of the lithium-ion battery, P p is the traction power of electric vehicles, P s is the power of the electric vehicle thermal management system, V v is the vehicle speed, F r is the rolling resistance of the vehicle, F a is the vehicle's air resistance, M v is the total mass of the vehicle, η s is the traction efficiency, △V v is the change in vehicle speed.

3. The control method according to claim 1, characterized in that: when The battery enters the radiator cooling mode: the second port (2032) of the three-way valve is closed, the first port (2031) of the three-way valve and the third port (2033) of the three-way valve are connected, the fan (301) is turned on, and the water pump (201) is turned on; wherein: is the minimum temperature of the battery when the radiator is cooling. It is the maximum temperature of the battery when the radiator is cooling.

4. The control method according to claim 1, wherein: when The battery enters the chiller cooling mode: the first port (2031) of the three-way valve is closed, the second port (2032) of the three-way valve and the third port (2033) of the three-way valve are connected, the fan (301) is turned off, and the water pump (201) is turned on; wherein It is the maximum temperature of the battery when the radiator is cooling.

5. The control method according to claim 2, characterized in that: The objective function corresponding to the optimization goal is: Among them: O1 and O2 are weights, T br is the target temperature, N p represents the prediction time domain and the control time domain, and P s =N pump T pump η pump +N fan T fan η fan , where N pump Indicates the pump speed, T pump Represents the water pump torque, η pump Indicates the pump efficiency, N fan Indicates the fan speed, T fan represents the fan torque, η fan represents the fan efficiency, and k represents the kth moment of vehicle operation.

6. The control method according to claim 5, characterized in that: The constraints satisfied by the battery temperature, water pump speed, and fan speed are: in, It is the lower limit of the optimal operating temperature of the battery; It is the upper limit of the optimal operating temperature of the battery; is the minimum pump speed, is the maximum speed of the water pump; is the minimum fan speed, The maximum fan speed.

7. A battery thermal management system that implements the control method according to any one of claims 1 to 6, characterized in that: The invention comprises a chiller (101), a water pump (201), a power battery (202), a three-way valve (203), a radiator (204) and a fan (301); the first port (1011) and the second port (1012) of the chiller are respectively connected to the refrigerant circuit; the fourth port (1014) of the chiller is connected to the second port (2032) of the three-way valve; the third port (2033) of the three-way valve is connected to the first port (2021) of the power battery; the second port (2022) of the power battery is connected to the first port (2011) of the water pump; the second port (2012) of the water pump is connected to the end point A; the end point A is also connected to the third port (1013) of the chiller and the first port (2041) of the radiator; the second port (2042) of the radiator is connected to the first port (2031) of the three-way valve; and the fan (301) is arranged at the radiator (204).

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