Linear Power Flow Method for Radial Distribution Systems Including Voltage Control Devices

In large distribution systems the solution of nonlinear power flow (PF) equations requires high computational burden. To reduce complexity, various approximate linear PF methods have been proposed in literature. However, existing linear PF methods require a revision to account for new smart controllable components, introduced to increase the flexibility of distribution systems. Recently, an accurate and efficient constrained Jacobian-based method has been presented which incorporates the presence of distributed energy resources. In this paper, this method is extended to consider the presence in the network of voltage control devices (VCDs). Firstly, a new model of the supplying system is proposed to consider variations in the operating conditions of the higher voltage network, and to incorporate the presence of a VCD in the substation. Then, the most common types of direct and indirect VCDs are included into the new generalized branch model of the network. Finally, a new solving algorithm is presented which accounts for the discrete variables that are present in some VCD models, avoiding the use of any iterative procedure. The validity of the proposed method is verified by performing PF analysis on the IEEE 123-bus test feeder with VCDs and photovoltaic systems. The accuracy and the computing time of the proposed approach are analyzed by comparing them with both the exact PF and the approximated LinDistFlow solutions, accounting for several operating conditions of the network. The presented results give evidence of the good performance of the proposed linear method, that combines computational efficiency with adequate accuracy.