  This report serves as a technology description of a Julia-based
re-implementation of the fixed-point current injection algorithm, available in
PowerModelsDistribution.jl [1]. This report does not describe a novel method
for solving unbalanced power flow problems. It merely provides a description of
the fixed point iteration variant of the current injection method, inspired by
the existing open-source implementation in OpenDSS1 [2]. The current injection
method is commonly conceived as a system of nonlinear equalities solved by
Newton s method [3, 4]. However, as Roger Dugan points out in the OpenDSS
documentation, the fixed point iteration variant commonly outperforms most
methods, while supporting meshed topologies from the ground up. We note that
the unbalanced power flow algorithm in turn relies on matrix solvers for sparse
systems of equations. In the context of circuits and factorizing nodal
admittance matrices, the sparsity-exploiting KLU solver [5] has proven to be
both reliable and scalable. OpenDSS uses KLU. This report documents
work-in-progress, and the authors aim to update it when learnings are obtained
or more features are added to the implementation in PowerModelsDistribution.jl.
The authors invite collaborators to contribute through pull requests on the
repository.
