Distribution Grid Optimal Power Flow in Unbalanced Multiphase Networks With Volt-VAr and Volt-Watt Droop Settings of Smart Inverters

High penetration of photovoltaic (PV) generators in active distribution networks (ADNs) cause overvoltage due to reverse power flow. Smart inverter (SI) functionalities can be configured to provide efficient voltage regulation and reactive power support in ADNs. Moreover, the mismatch between peak PV generation and peak demand make battery energy storage systems (BESSs) increasingly important assets in power grids, capable of enabling higher penetration of renewable energy resources by mitigating the system-wide effects of PV intermittency. In this work, we propose the inclusion of local piecewise Volt-VAr and Volt-Watt droop functions of PV (as per the IEEE-1547) as constraints in a multiperiod distribution grid optimal power flow (DOPF) formulation. This approach is an efficient voltage control method for unbalanced multiphase networks, making the inverter dispatch solutions abide by the IEEE-1547 standard and therefore suitable at the local inverter controller level. We adopt a well-known LinDist3Flow version of DOPF, and the resulting multiperiod DOPF becomes a mixed-integer linear programming problem. Simulations on the IEEE 123-node feeder with 15 utility-scale PV and BESS inverters validate the efficacy of the proposed formulation in performing effective voltage regulation and control that abide by the IEEE-1547 standard. The case studies show that SI droop-integrated DOPF can ensure reduced variation in bus voltages, reducing the risk of voltage violations, and net load smoothing can be achieved with BESS, reducing the disparity between inexpensive midday and expensive evening energy price.