An integrated fuel cell thermal management system and control method thereof based on hybrid theory

Abstract

The present invention discloses an integrated fuel cell thermal management system based on hybrid theory and a control method thereof, which belongs to the technical field of thermal management of fuel cell vehicles. The present invention includes multiple working modes including fuel cell coolant large and small circulation, electric drive coolant circulation and electric drive waste heat heating fuel cell coolant circulation, covering a variety of thermal management needs under all-weather conditions, and reducing energy consumption through reasonable waste heat utilization. In addition, the connection relationship between the various components in the integrated fuel cell thermal management system of the present application is easy to implement, and the control logic is simple and clear; the present invention adopts the hybrid logic dynamic model in the hybrid theory to model the mode switching process in the integrated fuel cell thermal management system, and develops a hybrid model predictive control based on the hybrid logic dynamic model mode switching model to improve the performance of the mode switching process.

Description

Technical Field

[0001] The present invention relates to the field of thermal management technology for fuel cell vehicles, and in particular to thermal management architecture design and hybrid control related to integrated fuel cells. Background Art

[0002] As an important component of fuel cell vehicles, the efficiency of the fuel cell thermal management system has a huge impact on the vehicle's range. In winter, most fuel vehicles use the heat generated by the fuel cell stack to quickly increase its internal temperature to above 0°C, thereby avoiding ice and frost caused by cold starts.

[0003] In order to increase the heating speed of the fuel cell, most of the existing technologies use the method of shutting down the water pump and fan, which will cause local overheating of the stack and other problems, and easily cause thermal runaway of the fuel cell, which is not conducive to the service life of the stack. In addition, as a complex system, the fuel cell thermal management system contains both continuous and discrete dynamic characteristics, but the existing technology only uses continuous mathematical models or discrete mathematical models to describe the system, which is difficult to reflect the real physical characteristics of the system and has high energy consumption. Therefore, it is necessary to establish a model that can describe the complex dynamic characteristics of the system and reduce energy consumption.

[0004] Therefore, there is an urgent need to develop an efficient fuel cell thermal management system and its control method, which can perform cold start through waste heat recovery at low temperatures, ensure the thermal safety of the fuel cell stack, fully cool the fuel cell stack at medium and high temperatures, and meet various thermal management needs with low energy consumption under all-weather conditions. Summary of the invention

[0005] In order to achieve the above objectives, the present application provides an integrated fuel cell thermal management system, including a fuel cell coolant large and small circulation, an electric drive coolant circulation, and an electric drive waste heat heating fuel cell coolant circulation.

[0006] According to the above-mentioned integrated fuel cell thermal management system: the fuel cell coolant small cycle includes a fuel cell, a thermostat and a first water pump. The fuel cell coolant large cycle includes a fuel cell, a thermostat, a first water pump, a first radiator and a fan. The electric drive coolant cycle includes a second water pump, an inverter, a motor, a second radiator and a fan. The electric drive waste heat heating fuel cell coolant cycle includes a fuel cell, a thermostat, a first switch valve, a plate heat exchanger, a second water pump, an inverter, a motor and a second switch valve. The fan provides the required air flow for the heat exchange between the radiator coolant and the air. The integrated fuel cell thermal management system of the present application provides multiple possible working modes through a simple topological structure, thereby meeting different thermal management requirements.

[0007] In order to establish an integrated fuel cell thermal management system that includes both discrete and continuous characteristics and reduce the problem of excessive system energy consumption caused by the prior art, the present invention adopts the hybrid logic dynamic model in the hybrid theory to model the mode switching process in the integrated fuel cell thermal management system, and develops a hybrid model predictive control based on the hybrid logic dynamic model mode switching model to improve the performance of the mode switching process.

[0008] This paper adopts a hybrid logic dynamic model to model the mode switching process of the integrated fuel cell thermal management system. The main modeling process is:

[0009] 1. Establish a linear state space model for each stage of mode switching;

[0010] 2. The division basis of each stage of mode switching is expressed as propositional logic, and auxiliary logic variables are introduced to express the switching process, and the logical relationship is converted into a linear integer inequality;

[0011] 3. By combining the logical variables that express the current stage of the system and the continuous auxiliary variables that express the system state changes in the current stage, the continuous state changes and discrete stage switching of the system are described in a unified framework.

[0012] The specific form of the hybrid dynamic model of the integrated fuel cell thermal management system established based on the hybrid logic dynamic modeling method is:

[0013] Where k is the discrete step length; x(k) is the system state variable, including the coolant temperature at the fuel cell outlet, the coolant temperature at the first radiator outlet, the coolant temperature at the motor outlet, and the coolant temperature at the second radiator outlet; u(k) is the input variable of the system, including the on-off state of the first switch valve, the second switch valve, the on-off state of the thermostat, and the on-off state of the fan; y(k) is the system output variable, including the coolant temperature at the first radiator outlet and the coolant temperature at the second radiator outlet. δ(k) and z(k) are auxiliary discrete variables and auxiliary continuous variables introduced by the system in hybrid logic modeling.

[0014] Based on the hybrid logic dynamic mode switching model, a hybrid model predictive control objective function is developed, which consists of a state quantity objective function and a control quantity objective function. The state quantity-related objective function can be expressed as: The objective function related to the control quantity Δu can be expressed as: By optimizing certain performance indicators at each time step, the mode switching coordinated control is transformed into a finite level optimal control problem. Then, the following finite level optimal control problem is solved at each time step:

[0015]

[0016] Where J is the control objective function value, N is the prediction time domain, and J x (k+i|k) is the system prediction output objective function, Q is the weight system matrix of the output value, J Δu (k+i|k) is the difference objective function of the control quantity at the two sampling moments before and after, and R is the corresponding weight coefficient matrix of the control quantity. Only the first control quantity will be applied to the system at time k, and a new round of prediction and optimization will be carried out at time k+1.

[0017] Finally, the hybrid controller design based on the integrated fuel cell thermal management system can be transformed into a mixed integer linear programming optimal problem, and the auxiliary variable ε is introduced to express the upper and lower limits of the objective function, which is expressed as the following inequality group:

[0018]

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention includes multiple working modes including fuel cell coolant large and small circulation, electric drive coolant circulation and electric drive waste heat heating fuel cell coolant circulation, covering various thermal management requirements under all-weather conditions, and reducing energy consumption through reasonable waste heat utilization; in addition, the connection relationship between the various components in the integrated fuel cell thermal management system of the present application is easy to implement, and the control logic is simple and clear;

[0021] The present invention adopts a hybrid logic dynamic model in hybrid theory to model the mode switching process in an integrated fuel cell thermal management system, and develops a hybrid model predictive control based on the hybrid logic dynamic model mode switching model to improve the performance of the mode switching process. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a system diagram of an integrated fuel cell thermal management system according to an embodiment of the present application;

[0023] Figure 2 yes Figure 1 The system diagram of the integrated fuel cell thermal management system shown in the fuel cell system coolant small circulation and electric drive radiator cooling mode;

[0024] Figure 3 yes Figure 1 The system diagram of the integrated fuel cell thermal management system in the fuel cell system coolant large circulation and electric drive radiator cooling mode is shown;

[0025] Figure 4 yes Figure 1 The system diagram of the integrated fuel cell thermal management system in the electric drive waste heat recovery heating fuel cell mode under low temperature environment;

[0026] Figure 5 yes Figure 1 The control method flow chart of the integrated fuel cell thermal management system is shown.

[0027] In the figure: a fuel cell 101 , a thermostat 102 , a first water pump 103 , a first radiator 104 , a first switch valve 105 , a plate heat exchanger 106 , a second water pump 201 , an inverter 202 , a motor 203 , a second switch valve 204 , a second radiator 205 , and a fan 301 . DETAILED DESCRIPTION

[0028] Through the following specific embodiments, drawings and claims, other features, advantages and implementation cases of the present application can be set forth or become apparent. In addition, the above-mentioned invention content and the following specific embodiments are exemplary and are intended to provide further explanations without limiting the scope of the present application for protection. However, the specific embodiments and specific examples only indicate the preferred implementation cases of the present application. For those skilled in the art, various changes and modifications within the spirit and scope of the present application will become apparent through this specific embodiment.

[0029] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. For example, the thermostat can be replaced by a three-way valve or other reasonable valve types. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. Various specific embodiments of the present invention will be described below with reference to the drawings that constitute a part of this specification. It should be understood that ordinal numbers such as "first" and "second" used in this application are only used for distinction and identification, and do not have any other meanings. If not specifically specified, they do not represent a specific order and do not have a specific association. For example, the term "first water pump" itself does not imply the existence of a "third water pump", and the term "second switch valve" itself does not imply the existence of a "first switch valve".

[0030] Attached Figure 1 FIG. 1 is a system diagram of an integrated fuel cell thermal management system according to an embodiment of the present application, which illustrates the components and their connection relationships in the thermal management system. Figure 1 As shown, the thermal management system includes a fuel cell 101, a thermostat 102, a first water pump 103, a first radiator 104, a first switch valve 105, a plate heat exchanger 106, a second water pump 201, an inverter 202, a motor 203, a second switch valve 204, a second radiator 205 and a fan 301, as well as connecting pipes between the various components represented by connecting lines.

[0031] The selection and function of each component of the thermal management system are described as follows. Among them, the thermostat 102 controls the opening and closing of the valve hole by accepting the coolant temperature accuracy. Among them, the water pump type used in the first water pump 103 and the second water pump 201 is an electric water pump, which drives the coolant to flow in the coolant circulation system. Among them, the first switch valve 105 and the second switch valve 204 can be solenoid valve switch valves or electric switch valves to control the opening and closing of the valves. Among them, the fan 301 can be different types of fans to provide the required air flow for the heat exchange between the coolant and the air of the first radiator 104 and the second radiator 205.

[0032] Attached Figure 2-4 Yes Figure 1 The system diagram of the integrated fuel cell thermal management system shown in the figure shows the fluid flow state of the thermal management system in different working modes, wherein the hollow arrows represent the flow direction and flow path of the electric drive coolant, and the bold solid arrows represent the flow direction and flow path of the fuel cell coolant. Figure 2-4 The various operating modes are shown.

[0033] Attached Figure 2 Yes Figure 1 The system diagram of the integrated fuel cell thermal management system in the fuel cell system coolant small circulation and electric drive radiator cooling mode is shown. When the ambient temperature is suitable and the heat generated by the fuel cell is not large, the fuel cell system performs a small coolant circulation to meet its own heat dissipation needs and maintain low energy consumption operation. The coolant pumped out by the first water pump 103 passes through the fuel cell 101 and the thermostat 102 in the closed state in turn, and then returns to the first water pump 103 to form a fuel cell coolant small circulation. At the same time, the coolant pumped out by the second water pump 201 passes through the inverter 202, the motor 203 and the second radiator 205 in turn, and then returns to the second water pump 201 to form an electric drive radiator cooling cycle. Under the wind speed control of the fan 301, the high-temperature coolant at the inlet of the radiator 104 undergoes heat exchange and cooling with the air, and forms a low-temperature coolant at the outlet of the radiator 104.

[0034] Attached Figure 3 Yes Figure 1 The system diagram of the integrated fuel cell thermal management system shown is in the fuel cell system coolant large circulation and electric drive radiator cooling mode. When the ambient temperature is too high and the fuel cell itself generates too much heat, the fuel cell system performs a coolant large circulation to ensure the thermal safety of the fuel cell, and at the same time performs an electric drive radiator cooling cycle. The coolant pumped out by the first water pump 103 passes through the fuel cell 101 and the thermostat 102 in the open state in turn, and then passes through the first radiator 104, and then returns to the first water pump 103 to form a fuel cell coolant large circulation. At this time, the first switch valve 105 is in the closed state. Electric drive radiator cooling cycle and Figure 2 The above described modes are consistent and will not be repeated here.

[0035] Attached Figure 4 Yes Figure 1 The system diagram of the integrated fuel cell thermal management system in the electric drive waste heat recovery and fuel cell heating mode under low temperature environment is shown. In low temperature environment, the cold start of the fuel cell is prone to cause the problem of local overheating of itself, and at the same time, the waste heat of the electric drive is not efficiently utilized, so it evaporates into the air. This design recovers the waste heat of the electric drive to heat the fuel cell to ensure the thermal safety of the fuel cell under cold start. The first water pump 103 The coolant pumped out by the first water pump 103 passes through the fuel cell 101 and the thermostat 102 in the open state in turn. At this time, the first switch valve 105 is opened. Due to the pressure difference, the coolant will flow to the first switch valve 105 channel, and then flow through the plate heat exchanger 106 and return to the first water pump 103. At the same time, the second switch valve 205 is opened, and the coolant from the second water pump 201 passes through the inverter 202, the motor 203, the second switch valve 204 and the plate heat exchanger 106 in turn, and then returns to the second water pump 201, forming an electric drive waste heat recovery cycle. The high-temperature electric drive coolant exchanges heat with the lower-temperature fuel cell coolant in the plate heat exchanger 106, and forms high-temperature coolant at the outlet of the fuel cell coolant channel of the plate heat exchanger 106, thereby achieving the purpose of heating the fuel cell with the electric drive waste heat.

[0036] Attached Figure 5 Yes Figure 1 The control method flow chart of the integrated fuel cell thermal management system is shown in FIG. First, the vehicle is started and the ambient temperature T is obtained according to the temperature sensor. amb The system is judged to be in cold start mode or self-cooling cycle in low temperature environment. amb ≤0, the fuel cell is cold started, and the attached Figure 4 The electric drive waste heat recovery heating fuel cell mode in the low temperature environment is shown. amb >0, a self-cooling cycle is performed. Further, according to the fuel cell temperature T obtained by the temperature sensor st Thermostat opening threshold T 1 For comparison, when T st ≥T 1 When Figure 3 The fuel cell system coolant circulation and electric drive radiator cooling mode shown. Otherwise, perform the additional Figure 2 The fuel cell system coolant small circulation and electric drive radiator cooling mode are shown.

[0037] In order to determine the model of the integrated fuel cell thermal management system, the general method of establishing mathematical models in the industry is referred to, and the mathematical models of fuel cell thermal management and electric drive system thermal management are established based on thermodynamic theory. The final expression of the mathematical model of the integrated fuel cell thermal management system is:

[0038]

[0039] Among them is C st Fuel cell specific heat capacity, J / (kg*K); M st is the fuel cell mass, kg; Q r is the heat removed by the radiator, kW; Q amb is the heat exchanged with the environment, kW; C r1 is the specific heat capacity of the first radiator, J / (kg*K); M r1 is the mass of the first radiator, kg; ΔT is the temperature difference between the outlet temperature of the first radiator and the ambient temperature, K; is the relationship between the air volume of the first radiator and the fan speed; T rad,in is the first radiator inlet temperature, K; C ω1 is the flow rate of coolant flowing through the first radiator, kg / s; C m is the specific heat capacity of the motor, J / (kg*K); M m is the motor mass, kg; Q in is the heat generated by the motor, kW; ρ w is the coolant density, kg / m 3 ; C ω2 is the specific heat capacity of the coolant, J / (kg*K); q v is the flow rate of coolant flowing through the second radiator, L / min; C r2 is the specific heat capacity of the motor, J / (kg*K); M r2 is the motor mass, kg; T α is the ambient temperature, K; V f is the fan air flow rate, m 3 / s; γ α is the air density, kg / m 3 ; C p,a is the specific heat capacity of air at constant pressure, J / (kg*K); Δt α is the inlet and outlet temperature of the second radiator, K.

[0040] The heat transfer capacity of the plate heat exchanger can be expressed as:

[0041]

[0042] Where ò is the average heat exchange system of the hot and cold sides of the plate heat exchanger, W / (m 2 *K); A cis the heat exchange area on the cold side, m 2 ; is the logarithmic mean temperature difference between the cold and hot side inlets.

[0043] By the attached Figure 2-4 It can be seen that the mode switching of the thermal management system will change with the current state of the thermostat 102, the first switch valve 105 and the second switch valve 204. The criteria for judging the current state are the comparison between the coolant temperature at the outlet of the fuel cell 101 and the coolant temperature at the outlet of the motor 203 and the valve threshold. 1 ,δ 2 and δ 3 represents the switch state of the thermostat 102, the first switch valve 105 and the second switch valve 204. 1 ∈{0,1},δ 2 ∈{0,1} and δ 3 ∈{0,1}. When the system working mode is attached Figure 2 When the fuel cell coolant small circulation and electric drive radiator coolant mode are shown, δ 1 =0,δ 2 =0,δ 3 = 0. When the system working mode is Figure 3 When the fuel cell coolant is in large circulation and the electric drive radiator cooling mode is shown, δ 1 =1,δ 2 =0,δ 3 = 0. When the system working mode is attached Figure 4 When the electric drive waste heat is used to heat the fuel cell, δ 1 =1,δ 2 =1,δ 3 =1.

[0044] Taking the fuel cell small cycle as an example, the criteria for judging the mode are: the temperature T of the fuel cell 101 st The thermostat 102 opening threshold T 1 When entering the small cycle, T st ≤T 1 , the inequality relation is combined with the binary δ 1 The correlation is:

[0045]

[0046] in The linear inequalities of other working modes can be obtained by the same method, which will not be repeated here.

[0047] Similarly, for the fuel cell coolant small circulation mode, the state space equation corresponding to its working mode is given by δ 1 Determined, the corresponding auxiliary continuous variable z is:

[0048]

[0049] With z 1 As an example, convert the above nonlinear integer mixed integer equality into an equivalent linear mixed integer inequality:

[0050]

[0051] The switching of the system is included in the linear inequality, so the system state variables at the next moment that are uniquely determined by the system state at the current moment can be obtained by solving the linear mixed inequality.

[0052] In Matlab / Simulink, using the hybrid toolbox and HYSDEL modeling language for programming, we can get the hybrid logic dynamic model of the integrated fuel cell thermal management system, on this basis, we further design the hybrid model predictive controller. The finite level optimal control problem mentioned above can be transformed into a mixed integer linear programming optimal problem at each time step, thereby realizing the solution of the hybrid model predictive control controller.

[0053] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art may make several improvements and modifications without departing from the concept of the present invention. These improvements and modifications should also be regarded as within the protection scope of the present invention.

Claims

1. A control method for an integrated fuel cell thermal management system based on hybrid theory, characterized in that: The integrated fuel cell thermal management system includes a fuel cell coolant cycle, an electric drive coolant cycle, and an electric drive waste heat heating fuel cell coolant cycle; wherein: The fuel cell coolant small cycle includes a fuel cell (101), a thermostat (102) and a first water pump (103); The fuel cell coolant large cycle includes a fuel cell (101), a thermostat (102), a first water pump (103), a first radiator (104) and a fan (301); The electric drive coolant circulation includes a second water pump (201), an inverter (202), a motor (203), a second radiator (205) and a fan (301); The electric drive waste heat heating fuel cell coolant circulation comprises a fuel cell (101), a thermostat (102), a first switch valve (105), a plate heat exchanger (106), a second water pump (201), an inverter (202), a motor (203), and a second switch valve (204); The fan provides the required air flow for heat exchange between the radiator coolant and the air; The control method of the integrated fuel cell thermal management system based on hybrid theory adopts a hybrid logic dynamic model to model the mode switching process of the integrated fuel cell thermal management system. The main modeling process is: S1. Establish a linear state space model for each stage of mode switching; S2. The division basis of each stage of mode switching is expressed as propositional logic, and auxiliary logic variables are introduced to express the switching process, and the logical relationship is converted into a linear integer inequality; S3. By combining the logical variables that express the current stage of the system and the continuous auxiliary variables that express the state change of the system in the current stage, the continuous state change of the system and the discrete stage switching are described in a unified framework; The specific form of the hybrid dynamic model of the integrated fuel cell thermal management system established based on the hybrid logic dynamic modeling method is: Where k is the discrete step length; x(k) is the system state variable, including the coolant temperature at the fuel cell outlet, the coolant temperature at the first radiator outlet, the coolant temperature at the motor outlet, and the coolant temperature at the second radiator outlet; u(k) is the input variable of the system, including the on-off state of the first switch valve, the second switch valve, the on-off state of the thermostat, and the on-off state of the fan; y(k) is the system output variable, including the coolant temperature at the first radiator outlet and the coolant temperature at the second radiator outlet; δ(k) and z(k) are the auxiliary discrete variables and auxiliary continuous variables introduced by the system in the hybrid logic modeling; A m is the system state matrix, which describes the influence of the linear continuous dynamic part of the system on the current state; B mu is the input matrix, describing the influence of the control input of the linear part of the system on the state change; B maux is the auxiliary variable matrix, which describes the influence of the auxiliary variables in the linear part of the system on the state change; B maff is the offset vector, which represents the fixed offset or constant term in the state equation; C m is the output matrix, defining the influence of system state on output; D mu D is the input matrix of the output, defining the direct impact of the control input on the output; maux is the auxiliary variable matrix of the output, defining the influence of the auxiliary variables on the output; D maff is the offset vector of the output equation, indicating the fixed offset term in the output; E mux is the state constraint matrix, defining the influence of the state in the constraint conditions; E mu is the input constraint matrix, defining the influence of the control input on the constraint conditions; E maux is the auxiliary variable constraint matrix, defining the influence of auxiliary variables in the constraint conditions; E maff is the offset vector in the constraint condition, representing the invariant part of the constraint; The objective function of the hybrid model predictive control developed based on the hybrid logic dynamic mode switching model consists of the state quantity objective function and the control quantity objective function, where the state quantity-related objective function can be expressed as: The objective function related to the control quantity Δu can be expressed as: By optimizing certain performance indicators at each time step, the mode switching coordinated control is transformed into a finite level optimal control problem, and then the following finite level optimal control problem is solved at each time step: Where J is the control objective function value, N is the prediction time domain, and J x (k+i|k) is the system prediction output objective function, Q is the weight system matrix of the output value, J Δu (k+i|k) is the difference objective function of the control quantity at the two sampling moments before and after, and R is the corresponding weight coefficient matrix of the control quantity; only the first control quantity will be applied to the system at time k, and a new round of prediction and optimization will be carried out at time k+1; The hybrid controller design based on the integrated fuel cell thermal management system can be transformed into a mixed integer linear programming optimal problem, and the auxiliary variable ε is introduced to express the upper and lower limits of the objective function, which is expressed as the following inequality group:

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