Fault Characteristics Of Distributed Generators And Micro-grid Protection

As the fast development of the power industry, the disadvantages of our country's extra-large scale power industry featuring high-capacity machine units, large HV electric systems, and high voltage emerge with each passing day. Power shortage, environment pollution and chain failures occur frequently, which become unavoidable problems in electric production and system operation. Meanwhile, the distributed generation technology based on the power electronic conversion technique, has gained rapid development for its advantages like renewable energy and no pollution. As an efficient supplement to the large HV electric system and an effective application form of the distributed generation, micro power grid, integrating multiple inverter-based distributed generations and controlling them in a unified way, changes the single electric supply-mode of the traditional grid and increases the reliability of the systematic power supply and enhances the quality of the electric energy to a great extent.However, because of the output characteristics of the distributed generation, the protection of a micro-grid differs greatly from that of a traditional power system. Therefore, the key to the research of the micro grid's protection lies in the guarantee of the selectivity, rapidity, sensitivity and reliability of the protection. Hence, the failure analysis of the distributed generation and the research into the protection principle of the micro grid display an important theoretical significance and pragmatic value.This thesis first introduces the primary energy of the distributed generation and the classification of the interfacing technique and provides a detailed introduction to the control strategy of interfacing inverter of the inverter-based distributed generation, which lays a foundation for studying the failure characteristics of the inverter-based distributed generation.After that, the thesis analyzes the output failure characteristics of the inverter-based distributed generation under different control strategies and runs a simulated modeling test of the micro grid under the islanding operation condition through the application of the DIgSILENT software. On the basis of the theoretical analysis and the data from the simulated test, the study proposed a two-stage protection strategy to the micro grid, integrating the overcurrent protection and the negative sequence overcurrent protection.Lastly, the protection principle proposed above has been realized on the hardware platform of a micro relay protection device by C language. Also, the experiment has confirmed that this protection device can work correctly and cut off the failure inside the micro grid selectively.