A low temperature start-up method for a water-cooled fuel cell stack based on optimal energy efficiency

Abstract

The present invention provides a low-temperature start method for a water-cooled fuel cell stack based on optimal energy efficiency, which belongs to the technical field of new energy power generation. The minimum temperature required for the self-heating start of the stack, the maximum time limit, and the electronic load current density when the low-temperature start of the stack is successful are set, and the power supply of the electric heating wire is turned on and adjusted to the maximum power; the controlled variables, control variables, and constraints of the external auxiliary multi-constraint predictive controller are determined, and the power of the electric heating wire is adjusted in real time until the temperature of the stack reaches the minimum temperature required for the self-heating start, and the power is turned off; the controlled variables, control variables, and constraints of the self-heating multi-constraint predictive controller are determined, and the electronic load current density is adjusted in real time until the electronic load current density when the low-temperature start of the stack is successful is reached, and the low-temperature start is successful. The present invention controls the low-temperature start time of the stack within a safe range, is safe and reliable, and at the same time maximizes energy utilization, reduces costs, and realizes fast, stable, and energy-efficient water-cooled fuel cell low-temperature start control.

Description

Technical Field

[0001] The present invention belongs to the technical field of renewable energy power generation, and in particular relates to a low-temperature starting method for a water-cooled fuel cell stack based on optimal energy efficiency. Background Art

[0002] As a kind of clean energy, proton exchange membrane fuel cell (PEMFC) has the characteristics of high efficiency, zero pollutant emission, long endurance, low operating temperature, etc. It is one of the current research hotspots in the field of new energy. Its working principle is: hydrogen is decomposed at the anode under the action of oxidant to produce hydrogen protons and electrons. The hydrogen protons pass through the proton exchange membrane and react with oxygen and electrons transmitted by the external circuit at the cathode. The product is water, which does not pollute the environment.

[0003] With the widespread application of fuel cells in various fields, the requirements for the low-temperature start-up capability of fuel cells are getting higher and higher. The ideal operating temperature of PEMFC is 75-80℃, and the entire power generation process is an electrochemical reaction process associated with water. As water is continuously generated, water will accumulate inside the fuel cell. If the ambient temperature is below 0℃, such as in cities and plateau areas with low temperatures in winter, the generated water will freeze, blocking the mass transfer channel and affecting the reaction, which will lead to the failure of the fuel cell to start successfully. The repeated freezing and thawing process will damage the structure of the battery components and affect the durability and performance of PEMFC. More seriously, this process will cause changes in volume and stress, which will cause a sudden drop in the PEMFC voltage, stop the reaction, cause permanent damage to the proton exchange membrane, and have an irreversible effect on the material, which not only reduces the durability of the fuel cell, but also greatly increases the safety risks of the fuel cell. The low-temperature start-up problem of fuel cells is one of the main challenges hindering its development.

[0004] According to different heat sources, the existing low-temperature start-up methods of proton exchange membrane fuel cells mainly include self-starting and external auxiliary heating. The self-starting method uses the heat generated by the reaction of the stack itself to increase the temperature of the stack and achieve the purpose of low-temperature start-up of the stack. This method can avoid the use of external equipment, does not need to add redundant devices, and saves the cost of use. However, various studies have shown that when the ambient temperature is below -10°C, self-starting is very difficult, and the heat provided by self-starting is very limited, and it is difficult to achieve a fast and stable effect. External auxiliary heating technology refers to relying on the outside to provide heat for the stack, which can stably heat the stack and successfully achieve low-temperature start-up. Common heating methods include: electric heating, gas heating, and coolant heating. These methods require additional external equipment and will generate high energy consumption. In particular, electric heating and coolant heating require a lot of heat and heating time. In addition, external auxiliary heating technology is also prone to energy waste. Based on the defects of the above two methods, it is necessary to invent a device and control method for low-temperature start-up of water-cooled fuel cells that can achieve rapid low-temperature start-up, make full use of energy, and achieve maximum energy efficiency. Summary of the invention

[0005] In response to the problems existing in the above-mentioned prior art, the present invention proposes a low-temperature start-up method for a water-cooled fuel cell stack based on optimal energy efficiency, which combines external auxiliary heating technology with stack self-heating technology. Under the premise of ensuring the successful low-temperature start-up of the stack and not causing the performance degradation of the stack, the energy consumption required for low-temperature start-up is reduced, thereby achieving fast and stable high-performance output of the stack at low temperatures.

[0006] The specific technical solutions of the present invention are as follows:

[0007] A low temperature start-up method for a water-cooled fuel cell stack based on optimal energy efficiency, characterized in that it comprises the following steps:

[0008] Step 1: Set the minimum temperature required for the water-cooled fuel cell stack to start automatically as T min , set the maximum time limit for low temperature startup of the stack to t max , set the electronic load current density when the stack is successfully started at low temperature to I suc , when the stack voltage V stack Not less than the minimum operating voltage V min , and the electronic load current density I stack Reach I suc When , it means that the stack low temperature start-up is successful;

[0009] Step 2: Open the air intake valve and adjust the intake pressure to a fixed value;

[0010] Step 3: Turn on the power of the electric heating wire set at the air inlet end of the fuel cell stack, and adjust the power P of the electric heating wire to the maximum value Pmax , heat the air entering the fuel cell stack, and start the fuel cell stack at low temperature;

[0011] Step 4: Let the moment when the power of the electric heating wire is turned on be the initial moment t 0 , real-time record of the duration t of the low-temperature start-up of the stack and the stack temperature T stack , Stack voltage V stack and the electronic load current density I stack ;

[0012] Step 5: For the external multi-constraint predictive controller, determine the controlled variable as the stack temperature T stack , the control variable is the electric heating wire power P, and the constraint condition is t≦t max And T stack ≦T min According to the prediction results of the external multi-constraint prediction controller, the electric heating wire power P is adjusted in real time until the stack temperature T stack Reach T min , turn off the power supply of the electric heating wire;

[0013] Step 6: For the self-heating multi-constraint predictive controller, determine the controlled variable as the stack temperature T stack , the control variable is the electronic load current density I stack , the constraint is t≦t max And V stack ≦V min ; According to the prediction results of the self-heating multi-constraint predictive controller, the electronic load current density I is adjusted in real time stack , until the electronic load current density I stack Reach I suc , the fuel cell stack was successfully started at low temperature.

[0014] Furthermore, in step 1, T is set according to the stack structure and ambient temperature. min and I suc .

[0015] Furthermore, in step 3, P max 5~10KW.

[0016] Furthermore, the external auxiliary multi-constraint predictive controller and the self-heating multi-constraint predictive controller are controllers with pure lag objects, and the algorithms used are constrained optimization algorithms based on quadratic programming.

[0017] The beneficial effects of the present invention are:

[0018] 1. The present invention proposes a low-temperature start-up method for a water-cooled fuel cell stack based on optimal energy efficiency. First, an external auxiliary multi-constraint predictive controller is used to adjust the power of the electric heating wire to preheat the stack. When the stack reaches a certain temperature, the self-heating multi-constraint predictive controller is used to adjust the current density of the electronic load to achieve self-heating of the stack, thereby completing the low-temperature start-up of the stack.

[0019] 2. The present invention controls the low-temperature start-up time of the fuel cell stack within a safe range, avoiding damage to the performance of the fuel cell stack due to a long low-temperature start-up process. It is safe and reliable, while maximizing energy utilization, greatly reducing costs, saving resources, and achieving fast, stable, and energy-efficient low-temperature start-up control of water-cooled fuel cells;

[0020] 3. The control method provided by the present invention can realize full-automatic control through programming. The implementation process is simple and efficient, which is conducive to combining with specific engineering applications and is convenient for actually solving the problems of water-cooled fuel cells in engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of a low-temperature start-up method for a water-cooled fuel cell stack based on optimal energy efficiency proposed in Example 1 of the present invention;

[0022] Figure 2 This is a schematic diagram of the operation of the fuel cell system in the external auxiliary heating process in Example 1 of the present invention;

[0023] Figure 3 This is a schematic diagram of the operation of the fuel cell system during the stack self-heating process in Example 1 of the present invention;

[0024] Figure 4 This is a schematic diagram of a fuel cell stack temperature control method in an external auxiliary heating process in Example 1 of the present invention;

[0025] Figure 5 This is a schematic diagram of a fuel cell stack temperature control method during a stack self-heating process in Example 1 of the present invention;

[0026] Figure 6 The control result of the external auxiliary multi-constraint predictive controller when the starting temperature is -30°C in Example 1 of the present invention;

[0027] Figure 7 This is the control result of the self-heating multi-constraint predictive controller when the starting temperature is -30°C in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in conjunction with the following specific embodiments and with reference to the accompanying drawings.

[0029] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0030] Example 1

[0031] This embodiment proposes a low-temperature start-up method for a water-cooled fuel cell stack based on optimal energy efficiency. Figure 2 and Figure 3 The fuel cell system shown in the figure includes a water-cooled fuel cell stack, an electronic load, a temperature sensor for measuring the temperature of the stack, a voltage measuring instrument for measuring the voltage of the stack, an electric heating wire placed at the air intake end of the stack, a power supply for powering the electric heating wire, an external multi-constraint predictive controller, and a self-heating multi-constraint predictive controller.

[0032] The process of the low temperature start-up method of the water-cooled fuel cell stack described in this embodiment is as follows: Figure 1 As shown, the specific steps include:

[0033] Step 1: Set the minimum temperature required for the water-cooled fuel cell stack to start automatically as T min = -10℃, set the maximum time limit of low temperature start of the stack to t max = 90s, set the electronic load current density when the stack is successfully started at low temperature to I suc =0.6A / cm 2 , when the stack voltage V stack Not less than the minimum operating voltage V min =0.5V, and the electronic load current density I stack Reach I suc When , it means that the stack low temperature start-up is successful;

[0034] Step 2: Open the air intake valve and adjust the intake pressure to a fixed value of 20KPa;

[0035] Step 3: Perform external auxiliary heating process of the fuel cell system, such as Figure 2 As shown, specifically:

[0036] Step 3.1: Turn on the power of the electric heating wire installed at the air inlet end of the fuel cell stack, and adjust the power P of the electric heating wire to the maximum value P max =5KW, the air entering the fuel cell stack is heated, and the low-temperature startup process of the fuel cell stack begins;

[0037] Step 3.2: Let the moment when the power of the electric heating wire is turned on be the initial moment t 0 = 0, real-time recording of the duration t of the low-temperature start-up of the stack and the stack temperature T stack , Stack voltage V stack and the electronic load current density I stack ;

[0038] Step 3.3: If Figure 4 As shown, for the external auxiliary multi-constraint predictive controller, the controlled variable is determined to be the stack temperature T stack , the control variable is the electric heating wire power P, and the constraint condition is t≦t max And T stack ≦T min ;

[0039] The last moment t, the stack temperature T stack The electric heating wire power P is used as the input of the external auxiliary multi-constraint predictive controller to predict the temperature of the battery stack and the electric heating wire power at the next time t+1, and then the electric heating wire power P is adjusted in real time according to the prediction result of the external auxiliary multi-constraint predictive controller;

[0040] Select the data of a certain experiment for explanation: When the stack temperature T stack is -20℃, and the electric heating wire power P is 4.02KW. Then the stack temperature T stack The power P of the electric heating wire is used as the input of the external auxiliary multi-constraint predictive controller. The external auxiliary multi-constraint predictive controller calculates that the power of the heating wire at the next moment should be 3.84KW.

[0041] And so on, until the stack temperature T stack Reach T min , and get Figure 6 The control result (i.e., control trajectory) of the external auxiliary multi-constraint predictive controller shown turns off the power supply of the electric heating wire;

[0042] Step 4: Perform the fuel cell system stack self-heating process, such as Figure 3 As shown, specifically:

[0043] like Figure 5 As shown, for the self-heating multi-constraint predictive controller, the controlled variable is determined to be the stack temperature T stack , the control variable is the electronic load current density I stack , the constraint is t≦t max And V stack ≦V min ;

[0044] The last moment t, the stack voltage V stack and the electronic load current density I stack As the input of the self-heating multi-constraint predictive controller, the stack temperature and the electronic load current density at the next time t+1 are predicted. Then, according to the prediction results of the self-heating multi-constraint predictive controller, the electronic load current density I is adjusted in real time. stack ;

[0045] Select the data of a certain experiment for explanation: When the load current density is 0.24A / cm 2 At this time, the stack voltage V stack is 0.857V, which is less than V min The load current density and stack voltage at this time are used as the input of the self-heating multi-constraint predictive controller. The self-heating multi-constraint predictive controller calculates that the load current density at the next moment should be 0.31A / cm 2 ;

[0046] And so on, until the electronic load current density I stack Reach I suc , and get Figure 7 The control results of the self-heating multi-constraint predictive controller are shown, and the low-temperature start-up of the fuel cell stack is successful.

[0047] Finally, it should be noted that the above embodiments 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 the embodiments, a person 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 purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A low-temperature start-up method for a water-cooled fuel cell stack based on optimal energy efficiency, characterized in that: The following steps are involved: Step 1: Set the minimum temperature required for the stack to start self-heating to T min The maximum time limit for low temperature startup of the stack is t max , and the electronic load current density when the stack is successfully started at low temperature is I suc ; When the stack voltage V stack Not less than the minimum operating voltage V min , and the electronic load current density I stack Reach I suc When , it means that the stack low temperature start-up is successful; Step 2: Open the air intake valve and adjust the intake pressure to a fixed value; Step 3: Turn on the power of the electric heating wire set at the air inlet end of the fuel cell stack, and adjust the power P of the electric heating wire to the maximum value P max , the stack starts at low temperature; Step 4: Let the moment when the power of the electric heating wire is turned on be the initial moment t0, and record the duration t of the low-temperature start-up of the battery stack and the temperature T of the battery stack in real time stack 、V stack and I stack ; Step 5: For the external multi-constraint predictive controller, determine the controlled variable as T stack , the control variable is P, and the constraint condition is t≦t max And T stack ≦T min ; According to the prediction results of the external auxiliary multi-constraint predictive controller, adjust P in real time until T stack Reach T min , turn off the power supply of the electric heating wire; Step 6: For the self-heating multi-constraint predictive controller, determine the controlled variable as T stack , the control variable is I stack , the constraint is t≦t max And V stack ≦V min ; According to the prediction results of the self-heating multi-constraint predictive controller, adjust I in real time stack , until I stack Reach I suc , the fuel cell stack was successfully started at low temperature.

2. The low temperature start-up method for a water-cooled fuel cell stack based on optimal energy efficiency according to claim 1, characterized in that: In step 1, set T according to the stack structure and ambient temperature. min and I suc .

3. The low temperature start-up method for a water-cooled fuel cell stack based on optimal energy efficiency according to claim 2, characterized in that: Step 3 max 5~10KW.

4. The low temperature start-up method of a water-cooled fuel cell stack based on optimal energy efficiency according to claim 1, characterized in that: The algorithms adopted by the external auxiliary multi-constraint predictive controller and the self-heating multi-constraint predictive controller are constraint optimization algorithms based on quadratic programming.

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