Short-term scheduling of electric power systems under minimum load conditions

Thermal unit operating constraints, hydro spill conditions, must-take resou rces and inflexible demand can all contribute to an electric power system's minimum load, or "backdown" problem's severity. We present two approaches to addressing minimum load constraints in the unit commitment problem. The first, traditional approach is to perform a unit commitment without conside ring the minimum load constraints, and then make the solution feasible by a pplying a predetermined "non-economic" backdown order to curtail must-take resources. The second approach considers minimum load constraints as system constraints similar to operating capacity constraints, and characterizes r esources to be backed as having bath a decremental cost and an incremental value to the system where these are not necessarily equal and so impact the decision to make economy sales or pump with pumped-storage resources.