Technique for aggregating loads with time-varying operating cycles
Embodiments of a system, a method, and a computer-program product (e.g., software) for aggregating an energy service from a group of loads with time-varying operating cycles are described. This aggregation may be performed by an aggregator, which provides the energy service to a power-system operator. In particular, for a desired demand response, a demand-response mechanism may modify a demand response of a given load by mapping an initial operating cycle of the load before a demand-response event to a final operating cycle. In addition, the demand-response mechanism may transition the given load to a new operating cycle associated with the demand-response event using a temporal set-point trajectory. This aggregation technique may ensure that a distribution of phases of the group of loads is, on average, uncorrelated with each other, either by preserving or modifying the distribution of phases prior to the demand-response event.
1. A method for aggregating an energy service from a group of loads, comprising:
determining a final operating cycle for a load after a demand-response event, wherein the load includes one or more appliances with a time-varying operating cycle;
mapping an initial operating cycle for the load to the final operating cycle, which involves adjusting a phase for the final operating cycle so that the phase is in accordance with a desynchronized distribution of phases of the group of loads, wherein the duty cycle for the initial operating cycle matches that of the final operating cycle; and
using a set-point trajectory to transition the load from the initial operating cycle prior to the demand-response event to the final operating cycle.
2. The method of claim 1 , wherein the transition of the load is a demand response event that achieves a desired change in the energy use from the group of loads and which is associated with the demand-response event.
3. The method of claim 1 , wherein determining the final operating cycle involves generating an operating model of the load.
4. The method of claim 3 , wherein the operating model includes a thermodynamic model of temperature in an enclosure.
5. The method of claim 1 , wherein a given operating cycle includes a steady-state duty cycle and phase.
6. The method of claim 1 , wherein the initial and final operating cycles correspond to different average power-consumption levels of the energy service.
7. The method of claim 1 , wherein the mapping preserves a characteristic of the distribution of phases of the group of loads from before the demand-response event.
8. The method of claim 7 , wherein the characteristic includes, on average, uncorrelated phases in the distribution of phases.
9. The method of claim 7 , wherein the mapping changes the characteristic of the distribution of phases of the group of loads from an initial characteristic from before the demand-response event; and
wherein the characteristic includes, on average, uncorrelated phases in the distribution of phases.
10. The method of claim 1 , wherein a change in the desired average amount of the energy service occurs immediately at the demand-response event without requiring a delay in an occurrence of any subsequent demand-response event.
11. The method of claim 10 , wherein the change in the desired average amount of the energy service occurs approximately without an increase in a relative standard deviation from prior to the demand-response event.
12. The method of claim 1 , wherein the load transitions from the initial operating cycle to the final operating cycle without experiencing additional cycles from a higher power-consumption operating mode to a lower power-consumption operating mode, or from the lower power-consumption operating mode to the higher power-consumption operating mode.
13. The method of claim 1 , further comprising calculating an appropriate contribution by the load to the desired average amount of the energy service, which is associated with the demand-response event, based at least in part on a price offered for the energy service and an associated disutility of the load.
14. The method of claim 1 , wherein the set-point trajectory controls the temperature between two operating temperatures; and
wherein the transition occurs over a time interval.
15. The method of claim 1 , wherein the set-point trajectory is determined using one or more operating points after the demand-response event and a closed-form expression for the variation in the operating point as a function of time.
16. The method of claim 15 , wherein the closed-form expression includes an exponential function.
17. The method of claim 1 , wherein the set-point trajectory is determined using an initial operating point, a final operating point and a dependence of an operating point of the load corresponding to the final operating cycle.
18. The method of claim 17 , wherein the dependence of the operating point is associated with a thermodynamic model of temperature in a control volume.
19. A computer-program product for use in conjunction with a computer system, the computer-program product comprising a non-transitory computer-readable storage medium and a computer-program mechanism embedded therein to aggregate an energy service from a group of loads, the computer-program mechanism including:
instructions for determining a final operating cycle for a load after a demand-response event, wherein the load includes one or more appliances with a time-varying operating cycle;
instructions for mapping an initial operating cycle for the load to the final operating cycle, which involves adjusting a phase for the final operating cycle so that the phase is in accordance with a desynchronized distribution of phases of the group of loads, wherein the duty cycle for the initial operating cycle matches that of the final operating cycle; and
instructions for using a set-point trajectory to transition the load from the initial operating cycle prior to the demand-response event to the final operating cycle.
20. The computer-program product of claim 19 , wherein the transition of the load is a demand response event that achieves a desired change in the energy use from the group of loads and which is associated with the demand-response event.
21. A computer system, comprising:
a processor;
memory; and
a program module, wherein the program module is stored in the memory and configured to be executed by the processor, the program module to aggregate an energy service from a group of loads, the program module including:
instructions for determining a final operating cycle for a load after a demand-response event, wherein the load includes one or more appliances with a time-varying operating cycle;
instructions for mapping an initial operating cycle for the load to the final operating cycle, which involves adjusting a phase for the final operating cycle so that the phase is in accordance with a desynchronized distribution of phases of the group of loads, wherein the duty cycle for the initial operating cycle matches that of the final operating cycle; and
instructions for using a set-point trajectory to transition the load from the initial operating cycle prior to the demand-response event to the final operating cycle.
22. The computer system of claim 21 , wherein the transition of the load is a demand response event that achieves a desired change in the energy use from the group of loads and which is associated with the demand-response event.