Modeling of Unit Commitment With AC Power Flow Constraints Through Semi-Continuous Variables

Unit commitment is fundamental to power system operations, and the problem model is more precise with the consideration of AC power flow constraints. However, unit commitment with AC power flow constraints (ACUC) is intractable, and new formulations and methods that can improve the solution efficiency are still desired. In this paper, we propose a new optimization formulation for ACUC that is based on the inherent semi-continuous variables. Instead of using auxiliary binary variables that indicate the on/off states of generating units, we directly utilize the semi-continuous variables to describe the operation levels of units, and the overall problem is reformulated without changing the original logical relation except for few and close approximations. Therefore, it reduces the number of variables and simplifies the search space compared with the commonly used binary paradigm. As an important result, the proposed formulation can leverage commercial solvers to obtain a solution more effectively. The numerical experiments on the IEEE 39- and 118-bus test systems and a large-scale 739-bus system demonstrate the effectiveness of our model and method.