Research On Power Conversion And Energy Management In Fuel Cell Generating System

In fuel cell power generating system, the DC power generated by the fuel cell is converted to AC power by power conversion technology, and then the energy is feed to the grid and local load. The fuel cell power generating system becomes one of the essential forms of the distributed power generation in 21st century. Because of the fuel cell power generation system with merits such as high power density, high efficiency, low noise, environmental protection, adaptive characteristics, the application with fuel cell has good prospects for development in the area which required in a number of high power density and high-efficiency power such as transportation, communications, computer networks, aerospace, defense, etc.The study of this dissertation is carried out in following three aspects:1. System structure and highly efficient power conversion research.2. Energy management techniques for dynamic characterize match with load transient.3. Islanding detection and protection technologies.In the first chapter, the introduction of the fuel cell's basic working principle, types, development, and some typical applications are given. A statement reviewing typical fuel cell power generation system and topology structure are made. A summary of the technology research about energy management for guaranteeing the fuel cell operation life or improving fuel efficiency are carried out.High efficiency power conversion is the key technology to improve the utilization ratio of fuel cell capacity and reducing the cost of the entire fuel cell system. In chapter 2 of this dissertation, the static and dynamic output characteristics test of the fuel cell is given first. Two typical isolated soft switching DC/DC converters, the current-fed phase shift full bridge ZCS converter with reverse-blocking IGBT and voltage-fed phase shift full bridge ZCS converter with MOSFET, are introduced as the selection of the front-ended DC/DC converter. Following the requirement, the designs of the converters are introduced. The comparisons between the two designs are carried out from the switching stress, input current ripple, loss distribution & conversion efficiency and dynamic characterize. The simulation and experiment results are given to verify the analysis. Then, the comparison results are synthesized for the selection of the front-ended DC/DC converter.The main functions of the energy management are providing the high frequency portion of the load power through the auxiliary energy storage device technique, and then the operation safety of the fuel can be ensured. In chapter 3 of this dissertation, the comparisons among different connection mode of the super capacitor in energy management unit for fuel cell power generation system are introduced. The comparisons carried out in following two aspects:the utilization ratio of super capacitor and effects of the high frequency power compensation. The criteria and parameters for the energy management design are obtained from the dynamic test of the fuel cell, and then the energy management unit is analyzed and designed for the fuel cell power system. The analyses and designs contains the modeling the control loops, the design of the controller and filter, the design and selection of the super capacitor, and the design of the energy management algorithm and program function for the realization. The simulation results and experiment results are given to verify the analysis and designs.The Non-Detection Zone (NDZ) is the criteria for describing and comparing the effectiveness of islanding detection methods. For same islanding detection method, the NDZ will be different due to the different control mode. In chapter 4 of this dissertation, the Non-Detection Zone (NDZ) with passive islanding detection methods, such as OVP/UVP, OFP/UFP, for the DG system with the constant current control scheme are analyzed. The parameters of the point of common coupling such as the voltage amplitude and frequency are studied through mathematical derivation. The NDZ boundaries description represented in the power mismatch space re drawn base on the mathematical derivation. And the analysis is verified by the simulation results. The AFD method, as the mostly acceptable active islanding detection, is analyzed in this chapter. In this chapter, the AFD function is analyzed in the time domain, the frequency response with AFD method is obtained from the analysis. Then the NDZ boundaries of this method are first described in the power mismatch space re drawn based on the mathematical derivation. Simulation results are given to verify the analysis.In chapter 5 of this dissertation, the prototype fuel cell power generation system design is introduced, including the modular system structure design, architecture design of the control, communications design, and control designs of converters. The experiment results under grid-connected mode and stand-along mode of the fuel cell power system prototype are given.