Optimal Mode and Droop Setting of Smart Inverters

This paper proposes a two-time-scale distribution grid optimal power flow (D-OPF) framework that provides optimal settings of smart inverters' (SIs) modes and droops in coordination with existing legacy voltage control devices. On a slow time scale, the optimal SI modes and droop settings, tap position of voltage regulator/on-load tap changers (VR/OLTC), and capacitor bank status are obtained. On a fast time scale, using the optimal solutions obtained from a slow time scale model, the SIs' optimal active/reactive power dispatch is obtained in a way that ensures the active/reactive power setpoints lie on the SIs' droop. This ensures a feasible implementation at the local controller level. The proposed approach is demonstrated using the IEEE 123-node unbalanced three-phase test feeder and is compared with an existing method of SI mode and droop setting selection in the literature. The results show the feasibility of optimally selecting the SI's modes and settings. Also, compared to the method in the literature, the proposed approach achieves better voltage regulation.