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 frequency response services, the method comprising:
an electrical grid with an aggregator in communication with a fleet of distributed energy resources (DERs), the DERs configured to operate according to a frequency response local control law that causes the DERs to interrupt the drawing or discharging of electrical energy from the electrical grid when a measured frequency of the electrical grid exceeds a frequency threshold;
recording a start time when each of the DERs begin drawing or discharging energy;
maintaining a timer histogram that provides a status of timer states for the fleet of DERS;
estimating a primary frequency response capability of the fleet of DERs according to the timer histogram; and
controlling operation of the DERs as a function of the frequency response capability so as to enhance grid stability and reliability.
2. The method of claim 1 , wherein the step of maintaining a timer histogram includes maintaining a histogram of normalized timer values for each of the DERs that are drawing or discharging an energy packet.
3. The method of claim 1 , further comprising estimating a stored energy level of the fleet of DERs according to the timer histogram and a history of energy consumption and discharge by the fleet of DERs.
4. The method of claim 1 , wherein the estimating a primary frequency response capability of the fleet of DERs includes calculating an equivalent damping available from the fleet of DERs.
5. The method of claim 1 , wherein the estimating a primary frequency response capability of the fleet of DERs includes calculating a real-time power deviation vs. frequency response map.
6. The method of claim 1 , wherein the DERs are configured to repeatedly draw or discharge packets of energy for predetermined energy packet time durations and determine whether to draw or discharge energy packets at predetermined communication intervals, the method further comprising:
receiving requests from the DERs to draw or discharge energy packets;
wherein controlling operation of the DERs includes accepting or denying the requests.
7. The method of claim 6 , wherein the accepting or denying the requests includes accepting or denying the requests according to a difference between a grid reference signal received from a grid operator of the electrical grid and a net energy load of the fleet of DERs.
8. The method of claim 1 , wherein the estimating a primary frequency response capability of the fleet of DERs includes estimating an available synthetic damping.
9. The method of claim 8 , further comprising providing fast or primary frequency response services forecasting and bids to a grid or market or DER operator according to the estimating.
10. The method of claim 8 , wherein estimating a primary frequency response capability of the fleet of DERs further includes determining a damping coefficient for the fleet that describes a sensitivity of a packet interruption rate of the fleet as a function of a change in frequency.
11. The method of claim 8 , wherein estimating a primary frequency response capability of the fleet of DERs further includes determining a cumulative power reduction achieved by the fleet for a given change in frequency.
12. The method of claim 1 , wherein the estimating a primary frequency response capability of the fleet of DERs includes estimating an inertia.
13. The method of claim 12 , further comprising providing frequency response services forecasting and bids to a utility according to the estimating.
14. The method of claim 12 , wherein estimating a primary frequency response capability of the fleet of DERs further includes determining a damping coefficient for the fleet that describes a sensitivity of a packet interruption rate of the fleet as a function of a change in frequency.
15. The method of claim 12 , wherein estimating a primary frequency response capability of the fleet of DERs further includes determining a cumulative power reduction achieved by the fleet for a given change in frequency.
16. The method of claim 1 , wherein the estimating a primary frequency response capability of the fleet of DERs includes estimating an available synthetic damping and an inertia.
17. The method of claim 16 , further comprising providing frequency response services forecasting and bids to a utility according to the estimating.
18. The method of claim 16 , wherein estimating a primary frequency response capability of the fleet of DERs further includes determining a damping coefficient for the fleet that describes a sensitivity of a packet interruption rate of the fleet as a function of a change in frequency.
19. The method of claim 16 , wherein estimating a primary frequency response capability of the fleet of DERs further includes determining a cumulative power reduction achieved by the fleet for a given change in frequency.
20. The method of claim 1 , further comprising providing frequency response services forecasting and bids to a grid or market or DER operator according to the estimating.