DeepOPF-V, a deep neural network (DNN)-based voltage-constrained approach for solving an alternating-current optimal power flow (AC-OPF) problem, is used to determine an operating point of an AC electrical power system. DeepOPE-V advantageously uses two DNNs to separately determine voltage magnitudes and voltage phase angles of buses in the system without cross-over operations between the two DNNs. A computation complexity is reduced when compared to using a single DNN for generating both the magnitudes and phase angles, allowing high computation efficiency achieved by DeepOPE-V. Remaining variables of the system are computed based on the determined magnitudes and phase angles. A solution for the operating condition is predicted. A fast post-processing (PP) method is developed to improve the feasibility of the predicted solution. The PP method uses linear adjustment to adjust the predicted solution to improve the solution feasibility while enabling fast execution of the PP method.