Reach and hold flexibility characterization and trade-off analysis for aggregations of thermostatically controlled loads

Thermostatically controlled loads (TCLs) have the potential to be flexible and responsive loads to be used in demand response (DR) schemes. With increasing renewable penetration, DR is playing an increasingly important role in enhancing power grid reliability. The aggregate demand of a population of TCLs can be modulated by changing their temperature setpoint. When and/or what proportion of the population sees the setpoint change determines the change in aggregate demand. However, since the TCL population is finite, not all changes in aggregate demand can be maintained for arbitrarily long periods of time. In this paper, the dynamic behavior of a TCL fleet is modeled and used to characterize the set possible changes in aggregate demand that can be reached and the corresponding time for which the demand change can be held, for a given change in setpoint. This set is referred to, in this paper, as the reach and hold set of a TCL fleet. Furthermore, the effect of the setpoint change and ambient temperature on the reach and hold are analyzed. The characterized set is then validated through simulation using both the population TCL models and individual TCL micro-models.