Operating-State-Aware Hydropower Dynamic Support Index and Hierarchical Coordinated Voltage Control for Renewable-Rich Active Distribution Networks

With increasing renewable penetration, heterogeneous hydropower resources in active distribution networks exhibit distinct dynamic voltage support characteristics, which makes capacity-based or fixed-weight indices insufficient for state-dependent assessment. This paper proposes an operating-state-aware hydropower dynamic support index (HDSI) and an HDSI-guided hierarchical voltage-control strategy. Conventional synchronous hydropower, variable-speed hydropower, and pumped storage units in synchronous condenser mode are uniformly characterized by a dynamic reactive power margin, response capability, and spatial support efficiency. State-dependent weights are continuously blended according to critical bus voltage deficits and their evolution, and the resulting HDSI is embedded into supervisory reactive power coordination. On a modified IEEE 33-bus system, the proposed HDSI achieves a Spearman correlation of 0.680 with actual dynamic support contribution, compared with 0.655 for the fixed-weight HDSI, with a statistically significant improvement. Under the representative main fault, the proposed control reduces voltage recovery time from 0.344 to 0.172 s and decreases hydropower saturation exposure by 12.9% relative to the fixed-weight method while maintaining comparable voltage recovery. Across 48 structured and 60 randomized scenarios, the control success rate reaches 100%, with a maximum online QP solution time of 12.440 ms. These results demonstrate effective state-aware support assessment and coordinated resource utilization.