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A new methodology based on the backward/forward (b/f) technique for the load flow solution in distribution systems is here proposed. The methodology takes efficiently into account the fixed voltage nodes and uses a reduced bus impedance matrix. In this way, it is possible to attain, for the unknowns at the PV nodes, the same values that are attainable solving the network with the methods adopted for transmission systems. With the same methodology it is possible to take into account also the meshes. If the network contains only meshes, the relevant model is linear and it is the one including the compensation currents. The presence of PV nodes introduces non linearity in the model and an iterative method is required to solve it. In this case, in the solution process, two cycles are present. An external main cycle connected to the b/f method and an internal cycle due to the presence of meshes and PV nodes. After the presentation of the used methods to take into account the presence of meshes and PV nodes, the new proposed method and its implementation are detailed. The results of the applications carried out show that the developed methodology presents, else than a high precision, good convergence properties and speed, qualities that are not dependent on the loading level and on the number of PV nodes.

The paper deals with the calculation of the optimal working point of a distribution system, equipped with several distributed generators, able to operate also autonomously, i.e. disconnected from the main grid. When connected to the main grid, it appears in general convenient to assign the slack bus role to the bus that represents such a connection. The problem becomes more complex when maximum power transfer constraints through the connection must be taken into account. The adequate slack bus treatment is even more important when the optimal operating condition must refer to the condition subsequent to an intentional or unintentional disconnection from the main grid. The paper presents an analysis of different approaches and their comparison with the help of the computation results relevant to a typical test distribution network. ©2007 IEEE.