  With increasing penetration of solar PV, some distribution feeders are
experiencing highly variable net-load flows and even reverse flows. To optimize
distribution systems under such conditions, the scheduling of mechanical
devices, such as OLTCs and capacitor banks, needs to take into account
forecasted solar PV and actual grid conditions. However, these legacy switching
assets are operated on a daily or hourly timescale, due to the wear and tear
associated with mechanical switching, which makes them unsuitable for real-time
control. Therefore, there is a natural timescale-separation between these
slower mechanical assets and the responsive nature of inverter-based resources.
In this paper, we present a network admissible convex formulation for
holistically scheduling controllable grid assets to position voltage optimally
against solarPV. An optimal hourly schedule is presented that utilizes
mechanical resources to position the predicted voltages close to nominal
values, while minimizing the use of inverter-based resources (i.e.,
DERs),making them available for control at a faster time-scale (after the
uncertainty reveals itself). A convex, inner approximation of the OPF problem
is adapted to a mixed-integer linear program that minimizes voltage deviations
from nominal (i.e., maximizes voltage margins). The resulting OPF solution
respects all the network constraints and is, hence, robust against modeling
simplifications. Simulation based analysis on IEEE distribution feeders
validates the approach.
