| With the rapid development of the power industry and new energy technologies,load demand is growing rapidly. Meanwhile，with a large number of DGs injectinginto the network, the operation of the system is more complex and even close to thestability limit. Distribution system as an important part of the power system, the safeand reliable operation cannot be overlooked. Load margin analysis and study ofvoltage control for distribution network has attracted more and more scholars. In thisMaster’s Thesis, I have done the following work for distribution analysis and control:The three phase model for distribution network analysis has been shown in thismaster thesis, including three phase line model, transformer model, unbalanced loadmodel, DG models and control elements model (shunt capacitor and voltage regulator:LTC&LDC).According to the bifurcation theory，the four sufficient conditions of saddle nodebifurcation (SNB) has been illustrated. Combined with the characteristics of a realdistribution network, I have verified the possibility of the four conditions. The resultsof the numerical studies of IEEE13,37bus and practical394bus cases haveconfirmed that SNB can occur due to increases in loads and/or DGs’ output.A tool of continuation power flow computation for3-phase distribution networkhas been developed. The direction vector of load and DGs are defined and the fourkey steps of continuation power flow which are parameterization, predictor, correctorand step-length control are solved. Numerical results verify the correctness of thealgorithms.The mathematic sense and physical meanings of the left eigenvectors have beendiscussed. According to the information provided by the left eigenvector and usingthe “negative ‘+’ positive ‘-’” strategy, several numerical examples confirmed theeffectiveness of using left eigenvector, i.e. the reverse direction of the left eigenvectoris the optimum direction away from the bifurcation point. |
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