Distribution Grid Optimal Power Flow Integrating Volt-Var Droop of Smart Inverters

Smart inverters (SIs) with local volt-var droop functions are effective in maintaining voltage and reactive power on the distribution feeders. Volt-var optimization (VVO) is generally carried out using distribution grid optimal power flow (DOPF)-based model that provides set point for the inverters and/or legacy grid devices. However, the existing works do not consider volt-var droop settings in the VVO framework, making the inverter dispatch solutions unsuitable at the local inverter controller level. Therefore, in this work, we propose the inclusion of SIs' local volt-var droop functions (as per the IEEE-1547) as constraints in the VVO formulation. We adopt a well-known second-order cone programming (SOCP) version of DOPF and with the inclusion of SIs' droop functions, the resulting VVO renders an efficient mixed-integer SOCP (MISOCP) problem. The efficacy of the proposed model is shown on a 33-node distribution feeder with 4 SIs having volt-var droop functions set as per the IEEE-1547.