Decentralized frequency control with packet-based energy management
Demand response methodologies for primary frequency response (PFR) for under or over frequency events. Aspects of the present disclosure include methods for controlling a fleet of distributed energy resources equipped for PFR and quantifying in real time an amount of primary frequency control capacity available in the fleet. In some examples, the DERs may be configured to consume and discharge electrical energy in discrete energy packets and be equipped with a frequency response local control law that causes each DER to independently and instantaneously interrupt an energy packet in response to local frequency measurements indicating a grid disturbance event has occurred.
1. A method of providing a frequency response to an electrical grid with a distributed energy resource (DER), the method comprising:
transitioning to an active state and drawing energy from or discharging energy to the electrical grid;
maintaining a timer that indicates an amount of time since the DER transitioned to the active state or a remaining amount of time before the DER will cease drawing or discharging energy and transition from the active state to an inactive state;
calculating a timer interruption threshold according to a measured frequency of the electrical grid;
comparing the timer to the timer interruption threshold; and
interrupting the active state in response to the timer exceeding the timer interruption threshold.
2. The method of claim 1 , wherein the step of drawing or discharging energy includes drawing energy from the electrical grid and the step of interrupting an energy packet includes reducing or eliminating the drawing of energy.
3. The method of claim 2 , further comprising, after the interrupting step, immediately discharging energy to the electrical grid.
4. The method of claim 1 , wherein the step of drawing or discharging energy includes discharging energy to the electrical grid and the step of interrupting includes reducing or eliminating the discharging of energy.
5. The method of claim 4 , further comprising, after the interrupting step, immediately drawing energy from the electrical grid.
6. The method of claim 1 , wherein the timer interruption threshold varies as a function of the measured frequency.
7. The method of claim 1 , wherein the timer interruption threshold varies as a function of the measured frequency and a locally sensed value that indicates the DER's need for energy.
8. The method of claim 7 , wherein the locally sensed value is at least one of a state of charge of the DER and a temperature of a temperature-controlled space controlled by the DER.
9. The method of claim 1 , wherein the step of calculating includes:
calculating a frequency deviation, Δf, wherein Δf is an absolute value of a deviation of the magnitude or rate of change of the measured frequency from a frequency setpoint; and
comparing Δf to a frequency threshold parameter.
10. The method of claim 9 , wherein the frequency threshold parameter includes a frequency dead band and a maximum frequency deviation.
11. The method of claim 10 , wherein the timer interruption threshold decreases when Δf exceeds the frequency dead band and is a constant value when Δf is equal to or greater than the maximum frequency deviation.
12. The method of claim 1 , wherein the measured frequency is a frequency measurement of electrical power on the electrical grid obtained from a frequency sensor proximate the DER.
13. The method of claim 1 , further comprising communicating with an aggregator when transitioning to the active state for grid frequency response monitoring and forecasting by the aggregator.
14. The method of claim 1 , wherein the step of transitioning to an active state includes drawing energy from or discharging energy to the electrical grid in discrete energy packets drawn or discharged during a predetermined energy packet time duration, wherein the timer indicates an amount of time since the energy packet began or a remaining amount of time before the completion of an energy packet.
15. The method of claim 14 , wherein the step of drawing or discharging energy includes:
determining, at predetermined communication intervals, whether to make a request to draw or discharge an energy packet; and
making a request to an aggregator to draw or discharge an energy packet in response to determining to make a request.
16. The method of claim 15 , wherein the determining step includes stochastically determining to make a request according to a probability calculation.
17. The method of claim 1 , wherein the step of transitioning to an active state includes drawing or discharging energy according to a duty cycle that includes on and off periods, wherein the timer indicates an amount of time since the DER transitioned to an active state or a remaining amount of time before the completion of an on period of the duty cycle.