  The reduced level of system inertia in low-carbon power grids increases the
need for alternative frequency services. However, simultaneously optimising the
provision of these services in the scheduling process, subject to significant
uncertainty, is a complex task given the challenge of linking the steady-state
optimisation with frequency dynamics. This paper proposes a novel
frequency-constrained Stochastic Unit Commitment (SUC) model which, for the
first time, co-optimises energy production along with the provision of
synchronised and synthetic inertia, Enhanced Frequency Response (EFR), Primary
Frequency Response (PFR) and a dynamically-reduced largest power infeed. The
contribution of load damping is modelled through a linear inner approximation.
The effectiveness of the proposed model is demonstrated through several case
studies for Great Britain's 2030 power system, which highlight the synergies
and conflicts among alternative frequency services, as well as the significant
economic savings and carbon reduction achieved by simultaneously optimising all
these services.
