Coupling thermal management system and control method for extended-range automobile and extended-range automobile

Abstract

The invention provides an extended-range automobile coupling thermal management system, a control method and an extended-range automobile, the extended-range automobile coupling thermal management system comprises a range extender for generating electric energy and heat by consuming fuel oil; the three thermostats are used for adjusting circulation of cooling liquid and are mainly responsible for arranging a range extender radiator and a heat exchanger in different circulation loops, if the range extender radiator and the heat exchanger are located in the same circulation loop, in the heat exchange process of the range extender and the power battery, external airflow can take away a large amount of heat through the radiator, the temperature rise speed of the range extender and the battery is reduced, and the service life of the range extender is prolonged. The oil consumption of the range extender and the aging damage of the battery in the cold start process are further increased; the two water pumps are used for pumping the cooling liquid and ensuring that the cooling liquid circularly flows in the system; the two radiators are used for discharging redundant heat; and the heat exchanger is used for transferring the heat generated by the range extender to the power battery, so that the temperature of the battery is rapidly increased to reduce the aging damage of the battery.

Description

Technical Field

[0001] The present invention relates to a whole vehicle thermal management system, and in particular to a coupled thermal management system for an extended-range vehicle based on a deep deterministic policy gradient algorithm, and a control method for a cold start condition, and also to an extended-range vehicle comprising the coupled thermal management system for the extended-range vehicle. Background Art

[0002] As the global greenhouse effect, environmental pollution and energy problems become increasingly severe, promoting the electrification of automobiles and developing hybrid vehicles have become important trends in the automotive field. Extended-range electric vehicles are a series hybrid vehicle that runs on pure electric power. They combine the environmental advantages of pure electric vehicles with the endurance of traditional fuel vehicles, showing many unique advantages. By carrying a small internal combustion engine (range extender) as a generator, it does not directly drive the vehicle, but charges the battery or directly supplies power to the motor, thereby significantly extending the total mileage of the vehicle and solving the range anxiety problem of pure electric vehicles. It can be used as an effective transitional solution before the maturity of pure electric vehicle technology.

[0003] For power batteries, their performance is greatly affected by temperature, especially under low temperature conditions. Low temperature slows down the power of charge transfer, reduces the conductivity of the electrolyte and the diffusion rate of lithium ions, thereby seriously reducing the available energy and power of the battery. In addition, the lithium plating phenomenon inside the lithium battery under low temperature conditions will cause permanent damage to the capacity and power capacity of the battery. Fuel economy tests show that in urban conditions, the fuel consumption of hybrid vehicles at -7°C increases by about 30-34% compared to 25°C, and the emission performance and endurance performance also drop sharply. Based on the temperature conditions in recent years, the lowest temperature in northern my country is below -7°C, the lowest temperature in the area north of the Yellow River is below -10°C, and the extreme low temperature in 12 northern provinces is even below -30°C. The performance of current extended-range vehicles cannot meet the market demand in large areas of my country.

[0004] Moreover, the current energy management strategy for extended-range electric vehicles mainly focuses on the output power distribution of the power source. During the optimization process, it is assumed that the power source and battery are at an ideal temperature state. Since the cold start process of the power source and the performance degradation of the power battery at low temperatures are ignored, these strategies have poor energy-saving effects in low-temperature environments. Summary of the invention

[0005] The present invention provides a coupled thermal management system for extended-range electric vehicles by studying the cold-start energy management strategy for extended-range electric vehicles in low-temperature environments and considering the coupling relationship between the power system and the thermal management system. The system can achieve comprehensive and optimal allocation of the power source and heat source of the entire vehicle, and can effectively improve the vehicle's fuel economy, battery life and low-temperature adaptability.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A coupled thermal management system for an extended-range vehicle includes the following five circulation loops and circulation loop controllers:

[0008] The first circulation loop is an engine heating cycle: the engine water pump outlet is connected to the range extender cooling water circuit inlet, the range extender cooling water circuit outlet is connected to the engine thermostat inlet, and the engine thermostat first outlet is connected to the engine water pump inlet;

[0009] The second circulation loop is the engine heat exchange cycle: the other outlet of the engine thermostat is connected to the inlet of the engine heat exchanger thermostat, the first outlet of the engine heat exchanger thermostat is connected to the first inlet of the heat exchanger, and the first outlet of the heat exchanger is connected to the inlet of the engine water pump;

[0010] The third circulation loop is the engine cooling cycle: the other outlet of the engine heat exchanger thermostat is connected to the engine radiator inlet, and the engine radiator outlet is connected to the engine water pump inlet;

[0011] The fourth circulation loop is a power battery heating and heat exchange cycle: the power battery cooling water outlet is connected to the battery thermostat inlet, the battery thermostat outlet is connected to the other inlet of the heat exchanger, and the other outlet of the heat exchanger is connected to the battery water pump inlet;

[0012] The fifth circulation loop is the power battery cooling cycle: the other outlet of the battery thermostat is connected to the inlet of the battery radiator, the outlet of the battery radiator is connected to the inlet of the battery water pump, and the outlet of the battery water pump is connected to the inlet of the power battery cooling water circuit.

[0013] The circulation loop controller is used to control the working state of the circulation loop according to different cooling and / or heat demand modes of the extended-range vehicle, and is communicatively connected with the battery radiator, the engine radiator, the battery thermostat, the engine thermostat, the engine heat exchanger thermostat, the engine water pump and the battery water pump.

[0014] Another object of the present invention is to provide a method for controlling a coupled thermal management system of an extended-range vehicle, comprising the following steps:

[0015] Step 1: Define the environment and parameters of the coupled thermal management system model, with the coolant flow in the circulation loop as the state, and changing the water pump speed, thermostat opening, and radiator fan speed as the action;

[0016] Step 2: Construct Actor network and Critic network: The Actor network accepts the current state as input and outputs actions, where the output actions are the range extender output power, water pump speed, radiator fan speed, and thermostat opening; the Critic network accepts the observed value of the current state and the output action of the Actor network as input and outputs the action value, while initializing the network weights;

[0017] Step 3: Define the compromise between power battery aging damage, fuel consumption, actuator energy consumption and battery SOC stability cost as the cost function;

[0018] Step 4: Store the sequences within a period of time into the experience pool, and then randomly sample from the experience pool to train and update the Actor and Critic networks;

[0019] Step 5: Evaluate the performance and generalization ability of the model by testing the model at different startup temperatures. If the model performs poorly, adjust the model parameters and return to step S4 for iterative training until the model reaches the optimal coupled thermal management system control strategy.

[0020] As a more optimal technical solution of the present invention, the step 4 also includes using experience replay and target network technology to stabilize training; and simultaneously conducting tests in various possible environments to ensure the generalization ability of the model;

[0021] As a more optimal technical solution of the present invention, the fuel cost f f , Power battery life cost b , actuator energy cost f a and SOC stability cost f s The total cost of

[0022]

[0023] Constant ω f ,ω b ,ω a and ω s is the weight factor.

[0024] As a more optimal technical solution of the present invention, the fuel cost is as follows:

[0025]

[0026] As a more optimal technical solution of the present invention, the life cost of the power battery is as follows:

[0027]

[0028] As a more optimal technical solution of the present invention, the energy consumption cost of the actuator is as follows:

[0029] P pump (u) = m1u 3 +m2u 2 +m3u,u=V p,en ,V p，bat

[0030] P fan (u) = m4u 3 +m5u 2 +m6u,u=V airE , V airB

[0031] f a =P pump (V p，en )+P pump (V p,bat )+P fan (V airE )+P fan (V airB ) (3)

[0032] As a more optimal technical solution of the present invention, the SOC stability cost is as follows:

[0033]

[0034] Another object of the present invention is to provide an extended-range electric vehicle, which includes the above-mentioned extended-range electric vehicle coupled thermal management system and a control method for executing the above-mentioned extended-range electric vehicle coupled thermal management system.

[0035] The beneficial effects are as follows:

[0036] The coupled thermal management system control method provided by the present invention aims at the cold start problem in a low temperature environment. It can minimize the power battery life loss and fuel consumption while meeting the vehicle driving power requirements, while reducing the energy consumption of the actuator as much as possible and ensuring the stability of the battery SOC. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the structure of the coupled thermal management system provided by the present invention, wherein: 1. engine thermostat; 2. engine radiator thermostat; 3. heat exchanger; 4. engine radiator; 5. range extender; 6. engine water pump; 7. battery water pump; 8. power battery; 9. battery thermostat; 10. battery radiator; A. heating cycle; B. heat exchange cycle; C. cooling cycle.

[0038] Figure 2 is the control amount P in embodiment 1 of the present invention gen Result graph.

[0039] Figure 3 is the control amount v in Example 1 of the present invention p，en Result graph.

[0040] Figure 4 is the control amount V in Example 1 of the present invention p，bat Result graph.

[0041] Figure 5 This is a state quantity SOC result diagram in Example 1 of the present invention.

[0042] Figure 6 is the state quantity T in the embodiment 1 of the present invention en，c Result graph.

[0043] Figure 7 is the state quantity T in the embodiment 1 of the present invention bat Result graph.

[0044] Figure 8 is the state quantity Q in embodiment 1 of the present invention exh Result graph. DETAILED DESCRIPTION

[0045] The present invention is further described in detail below through specific embodiments and drawings.

[0046] The coupled thermal management system provided by the present invention includes a range extender, which generates electricity and heat by consuming fuel; three thermostats, which are used to adjust the circulation of coolant and are mainly responsible for placing the radiator of the range extender and the heat exchanger in different circulation loops. If they are in the same circulation loop, during the heat exchange process between the range extender and the power battery, the external airflow passes through the radiator and takes away a large amount of heat, reducing the temperature rise rate of the range extender and the battery, thereby increasing the fuel consumption of the range extender and the aging damage of the battery during the cold start process; two water pumps, which are used to pump coolant to ensure that the coolant circulates in the system; two radiators, which are used to discharge excess heat; and a heat exchanger, which is used to transfer the heat generated by the range extender to the power battery, so that the battery temperature rises rapidly to reduce the aging damage of the battery.

[0047] Example 1

[0048] A method for controlling a coupled thermal management system of an extended-range vehicle comprises the following steps:

[0049] Step 1: Define the environment and parameters of the coupled thermal management system model, with the coolant flow in the circulation loop as the state, and changing the water pump speed, thermostat opening, and radiator fan speed as the action;

[0050] Step 2: Construct Actor network and Critic network: The Actor network accepts the current state as input and outputs actions, where the output actions are the range extender output power, water pump speed, radiator fan speed, and thermostat opening; the Critic network accepts the observed value of the current state and the output action of the Actor network as input and outputs the action value, while initializing the network weights;

[0051] Step 3: Define the compromise between power battery aging damage, fuel consumption, actuator energy consumption and battery SOC stability cost as the cost function;

[0052] Step 4: Store the sequences within a period of time into the experience pool, and then randomly sample from the experience pool to train and update the Actor and Critic networks;

[0053] Step 5: Evaluate the performance and generalization ability of the model by testing the model at different startup temperatures. If the model performs poorly, adjust the model parameters and return to step S4 for iterative training until the model reaches the optimal coupled thermal management system control strategy.

[0054] The above method is as follows:

[0055] 1. System Modeling

[0056] The lumped parameter thermal model is used to describe the dynamic response of the coupled thermal management system. The temperature dynamics equations of the range extender coolant and the power battery can be expressed as:

[0057]

[0058] Where C en，c , C bat，c , C bat are the heat capacities of the range extender coolant, battery coolant, and battery, respectively. en，c 、T bat，c 、T bat They are range extender coolant, battery coolant, battery temperature, Q en，clt , R bat are the heating power of the range extender on the coolant and the heat power generated by the battery, Q ra，en , Q ra，bat , Q exh They are the cooling power of the range extender radiator, the cooling power of the battery radiator and the heat transfer power of the heat exchanger. en，clt and Q bat It is determined by the specific operating conditions and energy management strategies of REEVs. ra，en , Q ra，bat , Q exh , Q en，clt and Q bat It can be expressed as follows:

[0059] Q ra,en =h1(V airE ,V flow,en1 )S ra (T en,c -T amb )

[0060] Q ra,bat =h1(V airB ,V flow,bot1 )S ra (T bat,c -T amb )

[0061] Q exh =h2(V flow,en2 ,V flow,but2 )S exh (T en，c -T bat，c )

[0062]

[0063] Among them, S ra and S exh is the heat transfer area of ​​the radiator and heat exchanger, V airE and V airB Represent the wind speed generated by the range extender and battery radiator fans, V flow，en1 Indicates the coolant flow rate of the cooling circuit of the range extender cooling system, V flow，en2 V represents the coolant flow rate flowing through the heat exchanger in the range extender heat exchange cycle. flow，bat1 and V flow，bat2 is the coolant flow rate of the cooling circuit and heating circuit of the battery cooling system, h1 and h2 are the convective heat transfer coefficients, which can be described as a function of the coolant flow rate and wind speed. LHV =4.6×10 7 (J / kg), P gen is the output power of the range extender, η g is the generator efficiency, fuel is the mass of gasoline consumed per unit time, I bat is the charge and discharge current of the power battery, R bat is the internal resistance of the power battery, which varies with SOC and T bat Change and change, fuel, I bat and It can be expressed as follows:

[0064]

[0065] Where λ is the temperature correction coefficient, U oc is the open circuit voltage of the power battery, P tracis the required power on the power bus, Q max is the battery capacity, and the λ expression is as follows:

[0066]

[0067] Wherein T0=80℃ is the setting parameter.

[0068] The coupled thermal management system is modeled in AMEsim. Through the trend analysis of each variable on h1 and h2, the fitting model is summarized as follows:

[0069]

[0070] The coolant flow rate circulating in the cooling circuit and heating circuit of the cooling system is determined by the speed of the water pump and the opening of the thermostat, which can be described by the following formula:

[0071] V flow,en1 =K1V p,en H en1 ,H en1 ∈[0,1]

[0072] V flow,en2 =V flow,en1 H en2 ,H en2 ∈[0,1]

[0073] V flow,bat1 =K2V p，bat H bat

[0074] V flow，bat2 =K2V p，bat (1-H bat ),H bat ∈[0,1] (10)

[0075] Where V p，en and V p，bat are the pump speeds of the range extender cooling system and the battery cooling system, H en1 , H en2 and H bat They are the thermostat openings of the range extender, range extender radiator and battery radiator respectively, and K1 and K2 are proportional coefficients.

[0076] 2. Battery Life Model

[0077] The experimental results show that under low temperature conditions (especially -20°C), lithium metal deposition occurs during the charging process of the battery, which is related to the accelerated aging of the battery, and the battery cycled at low temperature has a lower Coulombic efficiency. The Arrhenius diagram in (3) is equivalent to the functional relationship between the aging rate and the temperature A ge (bat):

[0078]

[0079] 3. Network Structure

[0080] DDPG can be divided into two large networks: the policy network and the value network. DDPG continues the idea of ​​DQN with a fixed target network, and each network is further divided into a target network and a reality network. However, the update of the target network is somewhat different.

[0081] The policy network, also known as Actor, outputs a deterministic action. The network that produces this deterministic action is defined as a = μ θ (s). The previous policy gradient adopted a random strategy, and each action required sampling the distribution of the current optimal strategy, while DDPG adopts a deterministic strategy, which is directly determined by the function μ. The actor's estimation network is μ θ (s), θ is the parameter of the neural network. This estimation network is used to output real-time actions. In addition, the Actor has a target network with the same structure but different parameters, which is used to update the value network Critic. Both networks output action action. The action output by the Actor is P gen 、V p，en 、V p，bat 、V airE 、V airB , H en1 , H en2 and H bat

[0082] The value network, or Critic, is used to fit the value function. It also has an estimation network and a target network. Both networks output the value q-value of the current state at the output, but they are different at the input. The target network input of Critic has two parameters, namely the observed value of the current state and the action action output by the Actor's target network. The input of Critic's estimation network is the action action output by the current Actor's estimation network. The target network is used to calculate Q target .

[0083] The update of the value network is based on the gradient descent of TD-error. As a judge, Critic does not know whether the action output by Actor is good enough at the beginning. It also needs to learn step by step to give accurate scores. Therefore, with the help of the value of the next moment fitted by the target network and the real benefit, we can get, let minus the current mean square error, then we can construct. The update method is actually similar to DQN. The only difference is that the parameters of the target network are updated slowly in the DDPG algorithm, instead of directly copying the parameters of the existing network every N steps in DQN.

[0084] The update of the policy network (Actor) is based on gradient ascent, because the goal of the Actor is to find an action a that can maximize the output value Q, so optimizing the gradient of the policy network is to maximize the Q value output by the value network. The Loss function adds a negative sign to minimize the error. It is worth noting that DDQG also borrows the experience replay technique of DQN. DDPG also stores a sequence of a period of time in the experience pool. Each time training, a minibatch is randomly sampled from the experience pool for training.

[0085] 4. Cost Function

[0086] The optimization of DDPG must reach a compromise between power battery aging damage, fuel consumption, actuator energy consumption, and battery SOC stability. The vehicle operating condition is selected as UDDS condition, and the selected optimization time range is the first 400 seconds. The total cost is given by the following formula:

[0087]

[0088] The total cost is composed of four intermediate functions: fuel cost (f f ), power battery life cost (f b ), actuator energy consumption cost f a and SOC stability cost f s The constant ω f ,ω b ,ω a and ω s is the weight factor.

[0089] Fuel cost:

[0090]

[0091] Power battery life cost:

[0092]

[0093] Actuator energy cost:

[0094] P pump (u) = m1u 3 +m2u 2 +m3u,u=V p，en ,V p，bat

[0095] P fan (u) = m4u 3 +m5u 2 +m6u,u=V airE , V airB

[0096] f a =P pump (V p，en )+P pump (V p，bat )+P fan (V airE )+P fan (V airB ) (15)

[0097] SOC stability cost:

[0098]

[0099] The simulation and results are as follows:

[0100] Table 1. Parameter settings of DDPG strategy

[0101]

[0102] The control volume results are as follows Figures 2 to 4 shown.

[0103] Remaining control amount: V airE 、V airB and H bat Always equal to 0, H en1 , H en2 It is always equal to 1, that is, the engine radiator fan and the battery radiator fan are not working, and all the heat generated by the engine is transferred to the power battery through the heat exchanger, reducing energy loss.

[0104] The state quantity results are as follows Figures 5 to 8 shown.

[0105] At the beginning of the journey, the range extender is enabled at maximum power to provide power and heat requirements for the vehicle. At the same time, the engine coolant temperature rises rapidly, the power battery is in a charging state, and the SOC rises. The output power of the heat exchanger gradually increases to about 28kW as the engine coolant temperature rises, and the battery is quickly preheated with a large heat exchange power to reduce battery aging damage caused by low temperature. When the engine temperature rises to about 80°C, the output power of the range extender drops to about 20kW, maintaining the engine coolant temperature at about 75°C. When the power battery temperature increases to 20°C, the output power of the heat exchanger gradually decreases, and the battery temperature rises slowly. In the later stage of the journey, the range extender stops working, and the power battery basically provides all the power and heat requirements. The SOC gradually decreases and finally converges to the expected value (0.5). The heat exchanger no longer outputs heat power to the power battery. Since the battery's self-generated heat power is less than the heat exchange power between the power battery pack shell and the external environment, the battery temperature slowly drops.

[0106] In summary, the present invention takes into account the coupling relationship between the power system and the thermal management system, studies the cold start energy management strategy of extended-range electric vehicles for low-temperature environments, and comprehensively optimizes the allocation of the power source and heat source of the whole vehicle, which can effectively improve the vehicle's fuel economy, battery life and low-temperature adaptability.

[0107] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A coupled thermal management system for an extended-range vehicle, characterized in that: It includes the following five circulation loops and circulation loop controllers: The first circulation loop is an engine heating cycle: the engine water pump outlet is connected to the range extender cooling water circuit inlet, the range extender cooling water circuit outlet is connected to the engine thermostat inlet, and the engine thermostat first outlet is connected to the engine water pump inlet; The second circulation loop is the engine heat exchange cycle: the other outlet of the engine thermostat is connected to the inlet of the engine heat exchanger thermostat, the first outlet of the engine heat exchanger thermostat is connected to the first inlet of the heat exchanger, and the first outlet of the heat exchanger is connected to the inlet of the engine water pump; The third circulation loop is the engine cooling cycle: the other outlet of the engine heat exchanger thermostat is connected to the engine radiator inlet, and the engine radiator outlet is connected to the engine water pump inlet; The fourth circulation loop is a power battery heating and heat exchange cycle: the power battery cooling water outlet is connected to the battery thermostat inlet, the battery thermostat outlet is connected to the other inlet of the heat exchanger, and the other outlet of the heat exchanger is connected to the battery water pump inlet; The fifth circulation loop is the power battery cooling cycle: the other outlet of the battery thermostat is connected to the inlet of the battery radiator, the outlet of the battery radiator is connected to the inlet of the battery water pump, and the outlet of the battery water pump is connected to the inlet of the power battery cooling water circuit. The circulation loop controller is used to control the working state of the circulation loop according to different cooling and / or heat demand modes of the extended-range vehicle, and is communicatively connected with the battery radiator, the engine radiator, the battery thermostat, the engine thermostat, the engine heat exchanger thermostat, the engine water pump and the battery water pump.

2. A control method for a coupled thermal management system of an extended-range vehicle, characterized in that: The steps include: Step 1: Define the environment and parameters of the coupled thermal management system model, with the coolant flow in the circulation loop as the state, and changing the water pump speed, thermostat opening, and radiator fan speed as the action; Step 2: Construct Actor network and Critic network: The Actor network accepts the current state as input and outputs actions, where the output actions are the range extender output power, water pump speed, radiator fan speed, and thermostat opening; the Critic network accepts the observed value of the current state and the output action of the Actor network as input and outputs the action value, while initializing the network weights; Step 3: Define the compromise between power battery aging damage, fuel consumption, actuator energy consumption and battery SOC stability cost as the cost function; Step 4: Store the sequences within a period of time into the experience pool, and then randomly sample from the experience pool to train and update the Actor and Critic networks; Step 5: Evaluate the performance and generalization ability of the model by testing the model at different startup temperatures. If the model performs poorly, adjust the model parameters and return to step S4 for iterative training until the model reaches the optimal coupled thermal management system control strategy.

3. The method for controlling a coupled thermal management system for an extended-range vehicle as claimed in claim 2, characterized in that: The step 4 also includes using experience replay and target network technology to stabilize training; at the same time, testing is performed in various possible environments to ensure the generalization ability of the model.

4. The method for controlling a coupled thermal management system for an extended-range vehicle as claimed in claim 2, characterized in that: The fuel cost f in step 3 f , Power battery life cost b , actuator energy cost f a and SOC stability cost f s The total cost of Constant ω f ,ω b ,ω a and ω s is the weight factor.

5. The method for controlling a coupled thermal management system for an extended-range vehicle as claimed in claim 2, characterized in that: The fuel costs are as follows:

6. The method for controlling a coupled thermal management system for an extended-range vehicle as claimed in claim 2, characterized in that: The life cost of the power battery is as follows:

7. The method for controlling a coupled thermal management system for an extended-range vehicle as claimed in claim 2, characterized in that: The energy cost of the actuator is as follows: P pump (u)=m1u 3 +m2u 2 +m3u,u=V p,en ,V p，bat P fan (u)=m4u 3 +m5u 2 +m6u,u=V airE ,V airB f a =P pump (V p,en )+P pump (V p，bat )+P fan (V airE )+P fa (V airB ) (3) 8. The method for controlling a coupled thermal management system for an extended-range vehicle as claimed in claim 2, characterized in that: The SOC stability cost is as follows:

9. An extended-range electric vehicle, characterized in that: The extended-range electric vehicle includes the above-mentioned extended-range electric vehicle coupled thermal management system and a control method for executing the above-mentioned extended-range electric vehicle coupled thermal management system.

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