  In this letter, we describe and develop edge-based and node-based
formulations for combined-cycle units (CCUs) with different levels of accuracy
in respecting physical restrictions of each turbine, from no restriction
requirement of each turbine, to include min-up/-down time restrictions of each
turbine, to finally include most restrictions such as min-up/-down time,
capacity, and ramping restrictions of each turbine. We develop corresponding
models for Independent System Operators (ISOs) and Vertically Integrated
Utilities (VIUs), respectively. These models demonstrate the complexity in
terms of the size of decision variables and show the tradeoff between accuracy
and computational complexity. In general, to the best of our knowledge, this
letter provides one of the first models that can capture both
configuration-based model needs and all physical restrictions for each turbine
within CCUs.
