CN115441017A - Water-cooled fuel cell stack low-temperature starting method based on optimal energy efficiency - Google Patents

Abstract

The invention provides a water-cooled fuel cell stack low-temperature start-up method based on optimal energy efficiency, which belongs to the technical field of new energy power generation. Load current density, turn on the power supply of the electric heating wire and adjust to the maximum power; determine the controlled variable, control variable and constraint conditions of the external auxiliary multi-constraint predictive controller, and adjust the power of the electric heating wire in real time until the stack temperature reaches the requirement for self-heating start Turn off the power at the lowest temperature; determine the controlled variables, control variables and constraints of the self-heating multi-constraint predictive controller, and adjust the electronic load current density in real time until it reaches the electronic load current density when the stack starts successfully at low temperature, and the low temperature start is successful. The invention controls the low-temperature start-up time of the electric stack within a safe range, is safe and reliable, maximizes energy utilization, reduces costs, and realizes fast, stable, and energy-efficient low-temperature start-up control of the water-cooled fuel cell.

Description

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

technical field

The invention belongs to the technical field of new energy power generation, and in particular relates to a low-temperature start-up method for a water-cooled fuel cell stack based on optimal energy efficiency.

Background technique

As a kind of clean energy, proton exchange membrane fuel cell (PEMFC) has the characteristics of high efficiency, zero pollutant emission, long battery life, and low operating temperature. It is one of the research hotspots in the field of new energy. Its working principle is: under the action of oxidant, hydrogen decomposes at the anode 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 has no pollution to the environment.

With the wide application of fuel cells in various fields, the requirements for the low-temperature start-up ability of fuel cells are getting higher and higher. The ideal working temperature of PEMFC is 75-80°C, and the whole power generation process is an electrochemical reaction process accompanied by water. With the continuous generation of water, water will accumulate inside the fuel cell. If the ambient temperature is below 0°C, such as cities and plateau areas with low winter temperatures, the generated water will freeze, blocking the mass transfer channel and affecting the reaction. , which leads to the failure of the fuel cell to start successfully, and the repeated freezing and thawing process will destroy the structure of the battery components and affect the durability and performance of the PEMFC. What's more serious is that this process will cause changes in volume and stress, which will lead to a sudden drop in PEMFC voltage, stop the reaction, cause permanent damage to the proton exchange membrane, and have an irreversible impact on the material, which not only reduces the durability of the fuel cell, It also greatly increases the potential safety hazard of fuel cells. The low-temperature start-up problem of fuel cells is one of the main challenges hindering their development.

According to different heat sources, the existing low-temperature starting 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 self-reaction of the stack to increase the temperature of the stack and realize the purpose of starting the stack at low temperature. This method can avoid the use of external equipment, does not need to add redundant devices, and saves the use cost. 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. The external auxiliary heating technology refers to relying on the outside world to provide heat for the stack, which can stably heat the stack and successfully achieve low-temperature startup. Common heating methods include: electric heating, gas heating, and coolant heating, all of which require additional external equipment and will generate high energy consumption. Especially 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 low-temperature start-up device and control method for a water-cooled fuel cell that can not only realize rapid low-temperature start-up, but also make full use of energy and achieve maximum energy efficiency.

Contents of the invention

Aiming at the problems existing in the above-mentioned prior art, the present invention proposes a water-cooled fuel cell stack low-temperature start-up method based on optimal energy efficiency, which combines external auxiliary heating technology with stack self-heating technology to ensure low temperature of the stack Under the premise of successful start-up and no performance degradation of the stack, the energy consumption required for low-temperature start-up is reduced, and the fast and stable high-performance output of the stack at low temperature is realized.

Concrete technical scheme of the present invention is as follows:

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

Step 1: Set the minimum temperature required for the self-heating start of the water-cooled fuel cell stack as T _min , set the maximum time limit for the low-temperature start-up of the stack as t _max , and set the electronic load current density when the stack starts successfully at low temperature as I _suc , when the stack voltage V _stack is not lower than the minimum operating voltage V _min , and the electronic load current density I _stack reaches I _suc , it means that the stack starts successfully at low temperature;

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

Step 3: Turn on the power supply of the electric heating wire installed at the air intake end of the stack, and adjust the power P of the electric heating wire to the maximum value P _max to heat the air entering the stack, and start the stack at low temperature;

Step 4: Let the moment when the power supply of the electric heating wire is turned on be the initial time t ₀ , and record the duration t of the low-temperature startup of the stack, the stack temperature T _stack , the stack voltage V _stack and the electronic load current density I _stack in real time;

Step 5: 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 constraints are t≦t _max and T _stack ≦T _min ; according to the external auxiliary multi-constraint Constrain the prediction results of the predictive controller, adjust the power P of the electric heating wire in real time until the stack temperature T _stack reaches T _min , and turn off the power supply of the electric heating wire;

Step 6: For the self-heating multi-constraint predictive controller, determine that the controlled variable is the stack temperature T _stack , the control variable is the electronic load current density I _stack , and the constraints are t≦t _max and V _stack ≦V _min ; according to the self-heating According to the prediction result of the multi-constraint predictive controller, the electronic load current density I _stack is adjusted in real time until the electronic load current density I _stack reaches I _suc , and the stack starts successfully at low temperature.

Further, in step 1, T _min and I _suc are set according to the stack structure and ambient temperature.

Further, in step 3, P _max is 5-10KW.

Further, the external auxiliary multi-constraint predictive controller and the self-heating multi-constraint predictive controller are controllers with pure hysteresis objects, and the algorithm adopted is a constrained optimization algorithm based on quadratic programming.

The beneficial effects of the present invention are:

1. The present invention proposes a water-cooled fuel cell stack low-temperature start-up method based on optimal energy efficiency. First, the 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 When the temperature is high, the current density of the electronic load is adjusted by the self-heating multi-constraint predictive controller to realize the self-heating of the stack, and then complete the low-temperature startup of the stack;

2. The present invention controls the low-temperature start-up time of the stack within a safe range, avoids damage to the performance of the stack due to too long low-temperature start-up process, is safe and reliable, and at the same time maximizes energy utilization, greatly reduces costs, saves resources, and achieves fast, stable, Water-cooled fuel cell low-temperature start-up control with optimal energy efficiency;

3. The control method provided by the present invention can realize fully automatic control through programming, and the implementation process is simple and efficient, which is beneficial to combine with specific engineering applications, and is convenient for practically solving the problems of water-cooled fuel cells in engineering applications.

Description of drawings

Fig. 1 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 Embodiment 1 of the present invention;

Fig. 2 is a working schematic diagram of the fuel cell system in the external auxiliary heating process in Example 1 of the present invention;

Fig. 3 is a working schematic diagram of the fuel cell system in the stack self-heating process in Embodiment 1 of the present invention;

Fig. 4 is a schematic diagram of the fuel cell stack temperature control method in the external auxiliary heating process in Example 1 of the present invention;

5 is a schematic diagram of a fuel cell stack temperature control method in the self-heating process of the stack in Embodiment 1 of the present invention;

Fig. 6 is the control result of the external auxiliary multi-constraint predictive controller when the start-up temperature is -30°C in Example 1 of the present invention;

Fig. 7 is the control result of the self-heating multi-constraint predictive controller when the start-up temperature is -30°C in Example 1 of the present invention.

detailed description

In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in conjunction with the following specific embodiments and with reference to the accompanying drawings.

The following non-limiting examples can enable those skilled in the art to understand the present invention more fully, but do not limit the present invention in any way.

Example 1

This embodiment proposes a water-cooled fuel cell stack low-temperature start-up method based on optimal energy efficiency, which is implemented based on the fuel cell system shown in Figure 2 and Figure 3, including water-cooled fuel cell stacks, electronic loads, and A temperature sensor for measuring the stack temperature, a voltage measuring instrument for measuring the stack voltage, an electric heating wire placed at the air intake end of the stack, a power supply for the electric heating wire, an external auxiliary multi-constraint predictive controller, and self-heating Multiple Constraint Predictive Controller.

The flow chart of the method for starting the water-cooled fuel cell stack at low temperature in this embodiment is shown in Figure 1, which specifically includes the following steps:

Step 1: Set the minimum temperature required for the self-heating start of the water-cooled fuel cell stack as T _min = -10°C, set the maximum time limit for the low-temperature start-up of the stack as t _max = 90s, and set the electronic temperature when the stack starts successfully at low temperature The load current density is I _suc = 0.6A/cm ² , when the stack voltage V _stack is not lower than the minimum operating voltage V _min = 0.5V, and the electronic load current density I _stack reaches I _suc , it means that the stack starts successfully at low temperature ;

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

Step 3: Carry out the external auxiliary heating process of the fuel cell system, as shown in Figure 2, specifically:

Step 3.1: Turn on the power supply of the electric heating wire installed at the air intake end of the stack, and adjust the power P of the electric heating wire to the maximum value P _max = 5KW to heat the air entering the stack, and the low-temperature start-up process of the stack begins;

Step 3.2: Let the moment of turning on the power supply of the electric heating wire be the initial moment t ₀ =0, and record the duration t of the low-temperature start-up of the stack, the stack temperature T _stack , the stack voltage V _stack and the electronic load current density I _stack in real time;

Step 3.3: As shown in Figure 4, for the external auxiliary multi-constraint predictive controller, the controlled variable is determined to be the stack temperature T _stack , the controlled variable is the electric heating wire power P, and the constraint conditions are t≦t _max and T _stack ≦T _min ;

Taking the last time t, the stack temperature T _stack and the electric heating wire power P as the input of the external auxiliary multi-constraint predictive controller, predict the next time t+1 stack temperature and electric heating wire power, and then according to the external auxiliary multi-constraint Constrain the prediction results of the predictive controller, and adjust the electric heating wire power P in real time;

Select the data of a certain experiment for explanation: when the stack temperature T _stack is -20°C, the electric heating wire power P at this time is 4.02KW, then the electric stack temperature T _stack and the electric heating wire power P at this time are taken 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;

By analogy, until the stack temperature T _stack reaches T _min , the control result (that is, the control trajectory) of the external auxiliary multi-constraint predictive controller shown in Figure 6 is obtained, and the power supply of the electric heating wire is turned off;

Step 4: Carry out the stack self-heating process of the fuel cell system, as shown in Figure 3, specifically:

As shown in Figure 5, 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 , and the constraints are t≦t _max and V _stack ≦V _min ;

Taking the last time 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, predict the stack temperature and the electronic load current density at the next time t+1, and then according to the self-heating The prediction result of the multi-constraint predictive controller adjusts the electronic load current density I _stack in real time;

The data of an experiment is selected for explanation: when the load current density is 0.24A/cm ² , the stack voltage V _stack at this time is 0.857V, which meets the requirement of being less than V _min . The stack voltage is taken as the input of the self-heating multi-constraint predictive controller, and the self-heating multi-constraint predictive controller calculates that the load current density at the next moment should be 0.31A/cm ² ;

By analogy, until the electronic load current density I _stack reaches I _suc , the control result of the self-heating multi-constraint predictive controller shown in Figure 7 is obtained, and the stack starts successfully at low temperature.

Finally, it is noted that the above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or Equivalent replacements without departing from the spirit and scope of the technical solution shall be covered by the scope of the claims of the present invention.

Claims (4)

1. A water-cooled fuel cell stack low-temperature starting method based on energy efficiency optimization, is characterized in that, comprises the following steps: Step 1: Set the minimum temperature required for the self-heating start of the stack as T _min , the maximum time limit for the low-temperature start-up of the stack as t _max , and the electronic load current density when the stack starts successfully at low temperature as I _suc ; when the stack voltage When V _stack is not lower than the minimum operating voltage V _min , and the electronic load current density I _stack reaches I _suc , it means that the stack starts successfully at low temperature; Step 2: Open the air intake valve and adjust the intake pressure to a fixed value; Step 3: Turn on the power supply of the electric heating wire installed at the air inlet end of the electric stack, adjust the power P of the electric heating wire to the maximum value P _max , and start the electric stack at low temperature; Step 4: Let the moment of turning on the power supply of the electric heating wire be the initial moment t ₀ , record the duration t of the low-temperature start-up of the stack, the stack temperature T _stack , V _stack and I _stack in real time; Step 5: For the external auxiliary multi-constraint predictive controller, determine the controlled variable as T _stack , the control variable as P, and the constraints as 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 reaches T _min , then 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 as I _stack , and the constraints as t≦t _max and V _stack ≦V _min ; according to the prediction of the self-heating multi-constraint predictive controller As a result, the I _stack is adjusted in real time until the I _stack reaches I _suc , and the stack starts successfully at low temperature. 2. The low-temperature start-up method for water-cooled fuel cell stacks based on optimal energy efficiency according to claim 1, characterized in that in step 1, T _min and I _suc are set according to the stack structure and ambient temperature. 3. The low-temperature start-up method for water-cooled fuel cell stacks based on optimal energy efficiency according to claim 2, characterized in that in step 3, P _max is 5-10KW. 4. The low-temperature start-up method for water-cooled fuel cell stacks based on optimal energy efficiency according to claim 1, wherein the algorithm adopted by the external auxiliary multi-constraint predictive controller and the self-heating multi-constraint predictive controller is based on two A constrained optimization algorithm for subprogramming.

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