Research On Operation Control And Protection Strategies Of Low-voltage Micro-grid Containing Inverter Interface

Many black-outs which have happened in recent years exposes the drawback of model oftraditional integrated power supply and super scale power system. Under pressure of shortenergy sources and environmental issues, many countries have been developing renewablesources such as solar energy and wind energy. The DG, environmental efficient and flexible,has been applied so unprecedentedly and widely. But the drawbacks of DG result in applyingin power system difficultly. In order to develop the advantage of DG and reduce the negativeinfluences on power system, the concept of micro-grid is put forward. As a new kind of gridstructure, micro-grid can make full use of the potential of DG and energy store devices, anddeal with the above problem and achieve the optimization of energy management indemanding side and energy utilization. So it is very significant to study operation control andprotection of micro-grid, which is helpful for development and application of micro-grid.First, the concept and current situation of micro-grid is introduced, especially the controland protection of micro-grid. And several different kinds of DG with inverters are alsointroduced, as well as their normal equivalent model, among which the mathematic model ofthe inverter is analyzed in detail.Second, three common control strategies of micro-source are analyzed basing on theequivalent models, and the related parameters are also designed. Then the simulation modelsof PQ control, V/f control and Droop control were built in MATLAB/Simulink. And theresults of the simulation of signal micro-sourced and micro grids are analyzed, and it provesout its effectiveness and reliability. Comparing with characteristics of these three strategies, asynchronized control project for the grid-connected is proposed.Finally, the transient of micro-grid faults is simulated and the influence on protection isanalyzed after it connecting to distributed grid. Then a complex protection project based onthe current phase-comparison principle, over-current protection, and voltage-offset protectionis put forwarded. After analyzing the setting value of protection, examples of protectionprojects are simulated, and the result of simulation proves out its effectiveness and reliability.