An Accurate Ladder-Type Ramp Rate Constraint Derived From Field Test Data for Thermal Power Unit With Deep Peak Regulation

The power system experiences a significant increase in its flexibility in recent years, along with the increase in renewable energy penetration. Implementing the flexibility retrofit of thermal power units (TPUs) is an effective way to enhance power system flexibility. However, the conventional ramp rate constraint cannot reveal the ramping characteristics of TPUs during deep peak regulation after the retrofit. In this paper, to establish a constraint that is more consistent with the engineering practice, the relationship between ramping capability and unit load of TPUs is firstly analyzed, based on the field test data of a TPU in China. Then, a ladder-type ramp rate of the TPU is proposed before a unified expression for the constraint is derived for the first time. When a specific dispatch time scale is satisfied, an equivalent expression for this constraint is also derived. Finally, the dimensionality of the binary variables in ladder-type ramp rate constraint is discussed, and the effectiveness of the ladder-type ramp rate constraint of the TPU is initially verified, with the actual 1-year operating data of two TPUs of a power plant in Dalian, Liaoning Province, China.