Comprehensive mixed‐integer linear programming model for distribution system reconfiguration considering DGs (original) (raw)

2018, Iet Generation Transmission & Distribution

Distribution system reconfiguration (DSR) is a critical process that improves the power transfer efficiency and reduces the overall operational cost. There have been various methods for addressing the DSR problems. Recently, DSR problems formulated in mixed-integer linear programming (MILP) has gained popularity as they generally can be solved by the state-ofthe-art commercially accessible linear programming solvers, and is able to solve the system with thousands of unknown variables within a reasonable time. However, in some MILP formulations, the distribution line losses are omitted in the nodal power injections for the sake of simplicity. This compromises the accuracy of the linearised model and contributes to the disparity between the MILP and the true non-linear model. Hence, in this study, new formulations are introduced for embedding the expressions of line losses inside load flow equations so that the deviations between the modelled and exact losses notably reduce. Moreover, other novel formulations have also been presented for simultaneously optimising distributed generation (DG) locations and sizes, while at the same time considering various DG's modes of connection to the distribution grid. The validity and effectiveness of the proposed MILP model is tested on standard IEEE systems and actual distribution network. Nomenclature Indices i/ j, N node (bus), number of nodes (buses) k, D i , D s node (bus), set of downstream nodes connected to node i, set of feeder (substation) nodes s, S segment, set of segments l, L PV , L PQ DG index, set of PV type DGs, set of PQ type DGs Parameters R j, i , X j, i resistance and reactance of branch connecting nodes i and j PD i , QD j active and reactive power demands at node i SB j, i MAX line capacities SG l MIN , SG l MAX DG size limits PS j, i s , QS j, i s parameters known prior to optimisation for determining the maximum active and reactive power flows of the sth segment mp j, i s , mq j, i s slopes of the sth segment for real and reactive power flows pl MAX maximum allowable DG penetration level n g maximum number of DGs that can be connected to any bus V i MIN , V i MAX upper and lower boundaries of voltage magnitude V i SP specified voltage magnitude for PV bus pf l power factor of the lth DG Variables PB j, i , QB j, i active and reactive power flows from bus i to bus j PL j, i , QL j, i active and reactive losses of a branch from node j to node i PG l, i , QG l, i active and reactive power outputs of the lth DG located at ith bus V i voltage magnitude of the bus i V i s square of voltage magnitude of the bus i SW j, i branch status (OPEN/CLOSED) of the line connecting node j to node i XW j, i binary variable which is equal to 1 if i is an upstream (parent) node connected to j LC l binary variable that takes a value of 1 if the lth DG is connected to the ith bus