A Difference-of-Convex Programming-Based Method for Day-Ahead and Intraday Coordinated Voltage/Var Control in Active Distribution Networks

High photovoltaic (PV) penetration can increase active power losses and cause steady-state voltage violations in distribution networks. This paper develops an integrated day-ahead and intraday voltage/var control (VVC) framework that coordinates discrete and continuously controllable devices while explicitly checking the residual of the branch-flow second-order cone relaxation (SOCR). A common 15 min time grid is adopted: on-load tap changer (OLTC) and capacitor-bank (CB) decisions are constrained to remain unchanged within each hourly block, whereas static var compensators (SVCs) and PV inverters are scheduled every 15 min. The day-ahead stage minimizes network losses subject to switching limits and determines the discrete-device schedules. The intraday stage fixes these schedules and uses the normal-boundary intersection (NBI) method to generate trade-off solutions between average voltage deviation and active power loss. A sequential difference-of-convex programming (DCP) correction is activated when the SOCR residual exceeds the prescribed tolerance. For two representative 15 min intervals of the modified balanced single-phase IEEE 123-bus feeder, the maximum residuals of all nine reported Pareto solutions are below 4.805 × 10−5, and the most demanding voltage deviation subproblem converges after 12 DCP iterations. The results demonstrate the feasibility of the proposed deterministic coordination framework; forecast-error robustness, broader method comparisons, and field validation remain subjects for further study.