Research On Grid-Connected Control And Islanding Detection Of Photovoltaic System

At present, with the green and renewable energy's developing and applying on a large scale, solar energy is accepted commonly because of its particular advantages. The inverter is the important part of grid-connected photovoltaic system. Using the single-phase grid-connected system as a research object, there are three parts in this paper. The topology, grid-connect control strategy and islanding detection methods are analyzed and studied thoroughly.First, the principle and characteristics of different main circuit topologies of grid-connected photovoltaic system are analyzed and compared.Second, the current control strategies of grid-connected system pivotally affect the grid-connected current quality and stability of the system. The common structure of LC filter is applied in this paper, and the double-loop current control with utility voltage feed-forward is adopted in practical system. For keeping the frequency and phase synchronous to the grid, the phase-locked loop is adopted in the system. The results of connected-grid experiment accord with the request of related standards.Islanding detection is the very important issue in the application of the grid-connected photovoltaic system. The mechanism of islanding occurring is analyzed and studied in details. Some kinds of islanding detection method being used in common presently, including passive and active techniques, are summarized. The conception of the nondetection zones is discussed in this paper, include the evaluation used in the determining the relative effectiveness of islanding detection. Comparing the power matching criteria with the phase criteria, the map of the nondetection zones is protracted and the form of the phase criteria is concluded in this paper.Finally, according the islanding-detection methods of the active drift of the frequency and the phase, the experiment is executed. The result of the detection is concluded and compared. The influence of detection on the THD of grid-connected current is analyzed. And then, the new method of detection based the drift of the power is put in this paper, as a result of reduced the influence on the connected-grid current. The validity is proved in the experiment.