A Two-Timescale Voltage Control Framework for Distribution Networks under Weather-Driven PV Variability

With the growing penetration of distributed photovoltaics (PV), voltage regulation in active distribution networks becomes more challenging due to weather-driven variability of PV output. Rapid changes in solar irradiance can induce significant intra-hour fluctuations that are difficult to handle by conventional slow-response devices. To address this issue, this paper proposes a two-timescale weather-driven voltage control framework. In the slow timescale, weather evolution is explicitly modeled to construct PV output intervals, and a robust optimal power flow model is formulated to coordinate on-load tap changers (OLTCs) and capacitor banks (CBs). In the fast timescale, a multi-agent soft actor-critic (MASAC) algorithm is employed to provide real-time reactive power support from PV inverters, compensating for intra-hour PV fluctuations. Simulation results on a modified IEEE 33-bus system demonstrate that the proposed method effectively improves voltage profiles under various weather scenarios. In particular, under highly unstable conditions, the average voltage deviation is reduced by over 50%, highlighting the effectiveness of the proposed framework in handling fast PV variability.