Analysis Of Voltage Stability In Smart Micro-grid

Because traditional distribution network can’t allow numbers of distributed generation units to access to grid, and distributed generation may also bring some adverse influences to feeder voltage, power quality, relaying protection and so on, micro-grid has emerged. Micro-grid, as an interface between large power grid and distributed energy resource, is one of the key technologies of smart grid, and meanwhile feeder voltage is an important index of power quality, so the research of voltage stability in micro-grid is significant.Firstly, based on the concept of CERTS micro-grid in the United States, using the existing equipment in project team, a basic structure for an experimental platform of micro-grid is designed, to deepen the annotation for structure of micro-grid, and it is the basic to set up an experimental platform of micro-grid.Secondly, four typical static load models are established, and on the basis, the expressions of voltage distribution with imaginary part for the four models are derived. Aiming at three factors of DG on the distribution of feeder voltage, which are access number of DG, access position and injection capacity of DG, simulation analysis is carried out, and the conclusions are obtained that using multiple DGs and diffusing the total capacity, can make the feeder voltage smoother and steadier; the closer the access position of DG to the end of line, the greater the impact on the feeder voltage; supporting effect of DG to voltage is proportional to the injection capacity.Based on four models of voltage distribution, the definition of real part voltage sensitivity for micro-grid is proposed. The analytical expressions for four models of real part voltage sensitivity and power point are derived, and according to the physical significance of voltage sensitivity and power point, the thesis researches the restrictions of access position and injection capacity of DG, and gets the critical conditions, and the simulation analysis is carried out. An analysis method of voltage stability based on real part voltage sensitivity is proposed, and the analysis of voltage stability, using the simulation curve of voltage sensitivity is given to verify the correctness of the research.Finally, a uniform P,f(U/I) node type and a uniform load distribution model are proposed. The results derived can reflect the distribution of feeder voltage with common DGs, and provide theoretical basis for analysing voltage stability more comprehensively. The simulation analysis of effect on the real and imaginary part of feeder voltage by DGs, which absorb reactive power from grid, is carried out. The conclusion is that when DG absorbs reactive capacity from the grid, the trend of imaginary part voltage curve tends to be the opposite to the trend of real part voltage curve.