Research On Coordination Control Srategy Of Fuel Cells-photovoltaic-battery Hybird Gneration

With the depletion of the traditional energy sources and the increasingly serious environmental pollution, the world show more emphasis on renewable energy. As solar energy has the lagest amout among the energy and hydrogen is the most abundant element on earth, the large amount makes them become the focus of research. But both of them have their own shortness: the output of solar power is variably related to environmental factors; although the output of the hydrogen fuel cell is stable, the response of fuel cell is slowly because of the complexity of power systems. Co-generation system can integrated the advantages and disadvantages of various energy sources. So as to improve the security, stability and economy of the system, generations need to work coordinately. Therefore, this paper designed a coordinated control strategy for a co-generation system with photovoltaic, fuel cell and lead-acid batterry.First, this paper introduces the background and significance. Then an overview of the current exploitation status of hydrogen energy and solar energy and research achivement of co-generation system design is given. Based on the existing research results, the main works of this paper is introduced.Secondly, the hydrogen fuel cells, photovoltaic cells, batteries and power converters involved in co-generation system have been studied seperataly. In the basis of the principle of fuel cells, photovoltaic cells and batteries, their mathematical models are described and simulated in Matlab environment. In consideration of the output characteristics of generation, through comparative analysis, a full-bridge LLC interleaved cascade combination type DC/DC topology is selected by comparison, then the state-space model is given. Finally, the single-phase off-grid inverse transformer topology and state-space model is analyzed.Thirdly the co-generation system is separated into blocks. DC/DC controller involved in the generation systems is designed firstly. Then the architecture and controller of the fuel cell subsystem and photovoltaic subsystem is designed. The controller make the system works steadily in different working state. In order to improve energy efficiency, the application of variable step perturbation method is used for controlling photovoltaic and fuel cells tracks the maximum power point. In the end of the chapter, a DC/AC controller is designed.On the basis of the stable output of subsystem, a coordinated control strategy for co-generation system based on hierarchical control is designed. The underlying controller is response to load changes and make the power generation track the maximum power point; the upper controller decide the output amount of photovoltaic cell and the fuel cell in consideration of the state of the battery and control the state transition according to the strategy designed.Finally, rooted in a ‘long-life AC backup power fuel cell stack and system’ project, the coordinated control strategy designed in this paper is verificated by simulation and experiment. The result show that the application of coordinated control strategies not only make co-generation system works steady in various conditions, the corresponding parameters of the system meet the national standard and demand of the project, but also help save operating costs.