Assessing the adjustment flexibility of hydropower plant precisely and optimizing its load distribution considering the constraint of flexible margin

In response to the issues that the conventional calculation method of load reserve capacity from the plant level ignores the forbidden zones, resulting in rough calculation results and likely overestimating the capability to absorb the uncertain loads, this paper carries out a calculation method from the unit level to assess the adjustment flexibility of hydropower plant precisely considering the unit forbidden zones, and then incorporates the constraint of adjustment flexibility into the general load distribution model to develop the optimization distribution model considering the constraint of flexible margin. The case study of Dongfeng hydropower plant in Wujiang River Basin shows that the unit forbidden zones make the feasible output zone of the plant exhibit discontinuous characteristics and the load reserve capacity calculated by the conventional method is significantly larger than the true load reserve capacity when the number of operating units is low. In addition, the optimal load distribution strategy demonstrates superior performance compared with the historical strategy, with sufficient adjustment flexibility to absorb the uncertain loads and a reduction in the number of start-up and shut-down operations of nearly 30 %. The study provides a valuable technical approach for enhancing the integration of intermittent wind and photovoltaic power through strategic utilization of hydropower plant flexibility.