  This paper presents a cold-start linear branch flow model named modified
DistFlow. In modified DistFlow, the active and reactive power are replaced by
their ratios to voltage magnitude as state variables, so that errors introduced
by conventional branch flow linearization approaches due to their complete
ignoring of the quadratic term are reduced. Based on the path-branch incidence
matrix, branch power flows and nodal voltage magnitudes can be obtained in a
non-iterative and explicit manner. Subsequently, the proposed modified DistFlow
model is applied to the problem of reactive power optimization and network
reconfiguration, transforming it into a mixed-integer quadratic programming
(MIQP). Simulations show that the proposed modified DistFlow has a better
accuracy than existing cold-start linear branch flow models for distribution
networks, and the resulting MIQP model for reactive power optimization and
network reconfiguration is much more computationally efficient than existing
benchmarks.
