Research Of Grid-Connected Control And Islanding Detection For Inverter-Based Distributed Generation

With the technological progress in power industry and the earth’s resourcesworld-wide growing failure, as well as environmental pollution and the rapid demandfor electricity, there is a growing emphasis on renewable energy development.Distributed generation technology is considered as an import part of power industryby more and more countries because of its unique environmental, economic andflexibility, and has become a research hot spot in the power system. In this thesis, amore systematic and in-depth theoretical and application is researched for thegrid-connected inverter, and laid a good foundation for the grid connected invertercontrol and the technology of islanding detection utility in the distributed generation.For the grid-connected inverter control, choosing different control methods areabout to directly influence system response speed and power quality of the outputcurrent. Repetitive control has a good inhibitory effect for periodic nonlinear loadharmonics, but its tracking error is adjusted behind a power frequency cycle. And thePI control is simple for easy parameter setting and good robustness, but it has greatlimitations for harmonic compensation. So, a composite control strategy whichcombines PI control with repetitive control is presented. This method combines theadvantages of repetitive control and PI control. Simulation verifies its correctness andfeasibility, and compare with PI control and repetitive control respectively, and thesimulation results prove that the composite control strategy can effectively improvethe grid-connected current waveform and realize tracking with zero error．Also，it canguarantee the wave of grid-connected current has the same frequency and phase as theutility voltage.With the development of distributed generation grid-connected, islandphenomenon of the possibility has more and more influence to the system user.Therefore, study of the islanding detection method is particularly important. In thisthesis, it analyzes the existing islanding detection methods, a kind of active currentdisturbing is expounded in detail, as well as proposes a new combined islandingdetection method based on phase jump and the active current disturbing combinationof grid-connected system. Simulation results prove that the new combined detectionmethod gives consideration to unity of rapidity and no blind area detection. Aiming atthe shortage of the conventional active frequency drift, an improved active frequencydrift method is put forward, we discuss its basic principle, and the simulation is verified. The method preserves all the advantages of the original, and easier to realize,simultaneously catering to effect of islanding detection and power quality, has a goodengineering application value.