Unit Commitment for Isolated Microgrids Considering Frequency Control

This paper presents a mathematical model of frequency control in isolated microgrids, which is integrated into the Unit Commitment (UC) problem. In conventional UC formulations, power outputs are considered fixed between two periods, yielding a staircase pattern with respect to the energy balance of the generation and demand for a typical dispatch time horizon (e.g., 24 h). However, in practice generation units that participate in frequency control may see a change in their output within a single dispatch time interval (e.g., 5 min), depending on the changes in the demand and/or renewable generation. The proposed approach considers these changes in the generation output using a linear model, and based on that, a novel UC Mixed Integer Quadratic Programming (MIQP), with linear constraints and quadratic objective function, is developed which yields a more cost efficient solution for isolated microgrids. The proposed UC is formulated based on a day-ahead with Model Predictive Control (MPC) approach. To test and validate the proposed UC, a modified version of a CIGRE benchmark test system is used. The results demonstrate that the proposed UC would reduce the operational costs of isolated microgrids compared to conventional UC methods, at similar complexity levels and computational costs.