Impact Of Distributed Generation On Distribution Network Voltage Stability

With the development of living standard, the distribution network loads also have a rapid development, which means that the operation states of the distribution equipment is getting closer to the limit operation states and the ability to withstand load growth of distribution network is diminishing, while the access of a large number of distributed generations increases the complexity to the operation of distribution network, which endanger the entire distribution network voltage stability. Therefore, it is necessary to study and analyze the effects of the access of distributed generations to the distribution network voltage stability in order to provide theoretical basis and decision reference for the access of distributed generations to the distribution network with high penetration. Based on the improved continuation power flow, the impacts of different types of distributed generations on the distribution network voltage stability in different conditions are studied in this paper. The main points can be summarized as follows:The concept of sensitivity matrix and Thevenin equivalent impedance matrix are given and the power element models of distribution network with distributed generations are built, on this basis, the Forward/Backward Sweep algorithm based on sensitivity matrix for the power flow calculation of distribution network with distributed generation is presented, in which the PQ and PV node bidirectional conversion logic are considered.An improved continuation power flow applied for three-phase distribution network is proposed according to the structure and operation characteristics of the distribution network. In the prediction step, the Lagrange’s second-order interpolation algorithm is used to predict the next operation state of distribution network so that the forecasting speed and computational accuracy are improved. In the correction step, the Forward/Backward Sweep algorithm based on sensitivity matrix is used to correct the predicted result so as to solve the question of the sensibility to initial value and the poor convergence of the Newton-Raphson method in the distribution network and then the PV curves of each node are tracked effectively based on the local parameterization method and the static voltage stability margin of the distribution network are accurately calculated.The impact of various kinds of distributed generations with different installationpositions, different penetrations and different grid-connected modes in distribution network on static voltage stability of distribution network is analyzed by means of case calculation based on the improved continuation power flow algorithm, and the conclusions obtained from the test distribution system may be available for the distributed generation operation and planning in distribution network.Based on the analysis of impacts of different kinds of distributed generations on static voltage stability of distribution network including the installation positions and the penetrations, a bi-level optimization mathematical model of penetration capacity of distributed generations is built, in which the penetration level of distributed generators is maximized in the upper level optimization, while the constraint conditions including the static voltage stability margin, the voltage profile and branch current of distribution network are satisfied even under the worst case in the lower level optimization. The algorithm results show the effectiveness of the proposed penetration capacity calculation model.