| This thesis was supported by Natural Science Foundation of Chongqing(CSTC 2009BB6190) and independent research project of State Key Laboratory of Power Transmission Equipment & System Security and New Technology(2007DA1051270 9208).Microgrid can effectively solve the effects of distributed generation accessing network on the voltage, current, and reliability of distribution networks and play positive role of distributed generation, so it has become the hot spot in the current researches. SOFC has the advantages of simple structure, low noise, high load capacity, less pollution, long life and high comprehensive utilization efficient, etc, so SOFC has been played more and more attention as distributed power. The model of solid oxide fuel cell operated in constant fuel flow as well as in constant fuel utilization have been developed and the steady-state (V-I and P-I) characteristics and dynamic characteristics of SOFC model have been analyzed. The control strategies of the SOFC generation system have been analyzed in detail in which increased the current limit protection and synchronization loop for ensuring smooth and safe transition from the island mode to grid-connected mode. The main contents are as follows:The background and significance has been introduced. The article researched on the research status of microgrid and fuel cell technology, as well as the problems of fuel cell as a distributed power in power system. By comparing the four kinds of fuel cell major applied in present, solid oxide fuel cell has the better advantages of no leakage of pollution, high cogeneration comprehensive utilization efficiency and power and long life than other fuel cell.According to the work principles of solid oxide fuel cell and the formula of gas pressure and output voltage, solid oxide fuel cell models operated in constant fuel flow as well as in constant fuel utilization have been developed. Based on the SOFC model, steady-state characteristic curve operated in two different modes have been analyzed and compared. Meanwhile, the dynamic characteristics of hydrogen flow, gas pressure, the output voltage and power have been studied.An overall model and control of a SOFC generation system have been analyzed. DC/AC inverter adopts V/f droop control strategy which includes inner current and outer voltage control, and external power control loops for controlling real and reactive power. Current limit protection in order to effectively limit the fault current and protect the power electronic devices and fuel cell and synchronization loop for ensuring smooth and safe transition from the island mode to grid-connected mode have been set. In order to improve the dynamic response speed, BESS is in parallel with DC bus through buck-boost converter which adopts hysteretic control strategy.The model of Microgrid containing SOFC has been established in the PSCAD/EMTDC simulation platform, and then the proposed control strategies are verified. SOFC operates in constant fuel utilization for linking fuel flow and load. The dynamic characteristics of load change in grid-connected mode and the island mode, the microgrid transition between the island mode and grid-connected mode, and single-phase ground fault happened in the island mode have been analyzed. |
PDF Full Text Request