  This paper presents a method for the optimal siting and sizing of energy
storage systems (ESSs) in active distribution networks (ADNs) to achieve their
dispatchability. The problem formulation accounts for the uncertainty inherent
to the stochastic nature of distributed energy sources and loads. Thanks to the
operation of ESSs, the main optimization objective is to minimize the dispatch
error, which accounts for the mismatch between the realization and prediction
of the power profile at the ADN connecting point to the upper layer grid, while
respecting the grid voltages and ampacity constraints. The proposed formulation
relies on the so-called Augmented Relaxed Optimal Power Flow (AR-OPF) method:
it expresses a convex full AC optimal power flow, which is proven to provide a
global optimal and exact solution in the case of radial power grids. The AR-OPF
is coupled with the proposed dispatching control resulting in a two-level
optimization problem. In the first block, the site and size of the ESSs are
decided along with the level of dispatchability that the ADN can achieve. Then,
in the second block, the adequacy of the ESS allocations and the feasibility of
the grid operating points are verified over operating scenarios using the
Benders decomposition technique. Consequently, the optimal size and site of the
ESSs are adjusted. To validate the proposed method, simulations are conducted
on a real Swiss ADN hosting a large amount of stochastic Photovoltaic (PV)
generation.
