Inclusion of frequency stability constraints in unit commitment using separable programming*

In this paper we address the problem of frequency stability in the unit commitment (UC) optimisation process. We include a set of appropriately defined frequency stability constraints in the UC problem formulation for operational planning scenarios in advance of real-time operation. Consequently, we cover the system against the loss of the largest infeed under the N - 1 security criterion.The main contribution of our work consists of using the method of separable programming to incorporate a linearised Frequency Nadir constraint into the UC problem. In our work, the UC problem is formulated as a mixed-integer linear program (MILP). This renders a fast convergence in the solution for a system such as the the three area IEEE RTS-96 system. Meanwhile, we have included the possibility of synthetic inertia provision from the wind farms, which helps to increase the available inertia in the system before a generation outage. The simulations are run using an extended version of MATPOWER tailored for solving UC problems (MOST) which is run in MATLAB.