1 Introduction
Proton exchange membrane fuel cells have been widely used in automotive, aerospace and other fields, so modeling them, and based on model performance evaluation, Control System design is particularly important. There is ADVISOR [1] internationally, which is specific to fuel cell simulation in cars. A variety of models have been proposed in the academic world, and most of these models only simulate some of the characteristics of fuel cells. In order to be able to use the fuel cell model to design the controller and evaluate the fuel cell, a control-oriented fuel cell model is needed. Jay T.pukruspan proposed a control-oriented fuel cell model in [2]. The characteristics of the fuel cell are described. This paper is a collection of this model, more in-depth modularization of various parts of the fuel cell, and based on Matlab/Simulink and Matlab's own powerful interface programming capabilities, designed a fuel cell simulator, users can fuel in the GUI interface Battery system combination, simulation, identification and design controllers.
2 Proton exchange membrane fuel cell structure and its control-oriented model
2.1 Structure of fuel cell
The fuel cell system mainly includes fuel cell reactors, compressors, flow controllers, heaters, radiators, humidifiers, etc. The composition of various fuel cell systems is different. The structure of Figure 1 is the fuel of the complex system laboratory. A structural diagram of the battery system. By modularizing the various components of the fuel cell system, the user can select the components needed to form a suitable fuel cell system.
2.2 Model of fuel cell
The model used in this simulator is based on a fuel cell model for a proton exchange membrane oriented to control [2]. The model is briefly described below. Introduced below is the model of the stack.
The current Ist is equal to the battery cell current. Current density is defined as the current per unit cell active area and is expressed as i fc = Ist / Afc . Under the assumption that all battery cells are identical, the voltage of the stack can be expressed as vst = n × v fc v fc = E . vact . vohm . vconc (1)
The open-loop voltage E is calculated from the energy balance between the reactants and the product and the Faraday constant:
The relationship between activation overvoltage and current density can be described by the Tafel equation, which is approximated by:
Then vohm is proportional to the current of the stack: vohm = i . Rohm (4)
The impedance Rohm is closely related to the humidity of the exchange membrane and the temperature of the stack. It is proportional to the thickness tm of the exchange membrane. The value of vconc can be approximated by the following equation:
Vconc =i(c2 i )c3 imax (7) where c2, c3 and imax are constants related to temperature and pressure of the reactants and can be determined empirically. It can be seen from the above series of formulas that the voltage output of the fuel cell is affected by the humidity of the membrane in the stack, the temperature of the reaction gas, and the pressure. According to this idea, the various components of the fuel cell can be designed to input these factors as the front end, and the output is also the influencing factor. For the modeling of other components, please refer to [2], [3]. 3 Simulator Design and Implementation In order to achieve the ultimate goal of the universal simulator, the simulator design must include some features that must be met for generalization, such as modular design, built-in online identification algorithm, and support component library. These characteristics.
3.1 Simulator design and structure
Modularization begins with the analysis of a complete fuel cell module, which can be divided into a hydrogen storage system, an air compression system, a humidifier [6], a temperature control system, and a stack according to our fuel cell (PEM). The models of these components are individually designed and then combined, and the coupling problem between them is complicated according to some literature [4][5], such as the influence of air flow on the humidity of the humidifier [6], temperature for The effect of the humidity saturation of the airflow through the humidifier, etc., but in order to achieve the goal of modularity, we must simplify it, and this simplification also exists in the simulator [1].
The simplified idea is to use the output of the front-end system as the input of the back-end system. Some couplings in the middle are simplified. The influence of ambient temperature, such as airflow, is transmitted in the pipeline. Due to environmental influences, the temperature is lowered, the humidity is changed, and so on. These effects ignore it. A humidifier, a compressor, etc. are used as an input and output module. From top to bottom design, the block diagram of the simulator is as follows. There are nine modules, eight of which are components of the fuel cell. The controller is a different controller designed according to the model. It can provide analog functions when the model is more accurate, providing a quick way to debug various algorithms. , safe, and economical way.
The simulator calls matlab/simulink to implement the following functions:
GUI interface; selection of fuel cell components; self-identification of imported test data (need to define the imported data format); algorithm import and interface problems
The above problems are not difficult to achieve by directly using the GUI programming function of matlab. What needs to be done is to design a unified interface and interface. In order to achieve the above functions, we can define the operation of the simulator as follows:
3.2 Implementation of the simulator
According to the design requirements, the simulator needs to include two aspects. The first one is based on Matlab's GUI simulator software, which can be used by users to select, simulate and design control algorithms. The second is a fuel cell component library that can be selected by the user to be combined into a suitable fuel cell system. In the library established in this paper, components are built for the three proton exchange membrane fuel cell systems, and the user can also add components. The second is a Matlab-based GUI simulator software that allows users to select, simulate, and design control algorithms.
The simulator software first selects the appropriate components from Matlab/Simulink, including the several modules described in the structure chapter, and then performs the simulation results. On the left side of Figure 3 is the curve after the simulation, and on the left is some parameter boxes, which can control the curve to be displayed, the parameters of the curve, and compare the simulated curve with the actual curve.
Using Matlab's toolbox can add a user-defined model mechanism. Users can build their own modules into the Toolbox library. In the future, through the above software combination, the Simulink simulation system can be automatically generated for simulation.
4 Conclusion
Fuel cells are a very active area of ​​research recently, and many theories and tools are constantly appearing. With the powerful ability of Matlab, this paper modularizes each component of a fuel cell model and successfully implements a fuel cell simulator software. According to the needs, the appropriate fuel cell system can be combined, and then through a friendly GUI interface, the user can Easy to build models, simulate and design controllers.
This paper innovates: In-depth modularization of a control-oriented model, freely combine various appropriate components, and then design a set of simulator software based on theory, providing an easy-to-use but powerful tool for engineering and scientific research. Project value: 150,000 yuan
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