Primary frequency control through simulated droop control with electric loads

• US 10,116,136 B2
• Filed: 03/18/2016
• Issued: 10/30/2018
• Est. Priority Date: 03/19/2015
• Status: Active Grant

• Current Assignee: Battelle Memorial Institute
• Original Assignee: Battelle Memorial Institute
• Inventors: McCullough, Jason, Rehberg, Eric, Black, Jason
• Primary Examiner(s): Kasenge, Charles R
• Application Number:
  US15/074,461
• Publication Number:
  US 20160276834A1
• Time in Patent Office: 956 Days
• CPC Class Codes: H02J 2310/12 The local stationary network supplying a household or a building
• CPC Class Codes: H02J 3/14 by switching loads on to, or off from, network, e.g. progressively balanced loading
• CPC Class Codes: Y02B 70/3225 Demand response systems, e.g. load shedding, peak shaving
• CPC Class Codes: Y04S 20/222 Demand response systems, e.g. load shedding, peak shaving

Abstract

In a frequency control system, a system controller assigns load-specific threshold frequencies to electrical loads of a fleet of electrical loads. Load controllers perform load monitoring and control operations for controlled electrical loads of the fleet including (i) comparing a measurement of the electrical frequency with the threshold frequency assigned to the controlled electrical load and (ii) operating the controlled electrical load based on the comparison. For example, each load controller may perform operation (ii) by turning the controlled electrical load on if the measurement of the electrical frequency is greater than the threshold frequency assigned to the controlled electrical load, and turning the controlled electrical load off if the measurement of the electrical frequency is less than the threshold frequency assigned to the controlled electrical load. The threshold frequencies may be assigned based on State of Charge (SOC) values for the loads.

Claims

1. A frequency control system providing frequency control for an a.c. electrical power grid operating at an electrical frequency using a fleet of electrical loads powered by the electrical power grid, the frequency control system comprising:

a system controller comprising an electronic data processing device programmed to assign load-specific threshold frequencies to electrical loads of the fleet of electrical loads, and to assign load-specific threshold frequencies to electrical loads of the fleet of electrical loads based on State of Charge (SOC) values for the electrical loads that measure energy stored in the electrical loads; and

load controllers controlling the electrical loads of the fleet of electrical loads, wherein each load controller comprises a microprocessor or microcontroller programmed to perform load monitoring and control operations for a controlled electrical load of the fleet of electrical loads including (i) comparing a measurement of the electrical frequency with the threshold frequency assigned to the controlled electrical load and (ii) operating the controlled electrical load based on the comparison.

2. The frequency control system of claim 1 wherein each load controller performs the operation (ii) by:

turning the controlled electrical load on if the measurement of the electrical frequency is greater than the threshold frequency assigned to the controlled electrical load, and

turning the controlled electrical load off if the measurement of the electrical frequency is less than the threshold frequency assigned to the controlled electrical load.

3. The frequency control system of claim 2 wherein the system controller is programmed to:

sort the electrical loads of the fleet of electrical loads by SOC value and

assign higher load-specific threshold frequencies to electrical loads with higher SOC.

4. The frequency control system of claim 2 wherein the system controller is programmed to:

designate any electrical load whose SOC value indicates zero or negative energy is stored in the electrical load as must-run; and

designate any electrical load whose SOC value is greater than a maximum SOC value as must-not-run;

wherein the load controller for any electrical load designated as must-run controls the electrical load by running the electrical load, and the load controller for any electrical load designated as must-not-run controls the electrical load by not running the electrical load.

5. The frequency control system of claim 4 wherein the system controller is programmed to:

designate any electrical load whose SOC value indicates zero or negative energy is stored in the electrical load as must-run by assigning a very low load-specific threshold frequency to the electrical load; and

designate any electrical load whose SOC value is greater than a maximum SOC value as must-not-run by assigning a very high load-specific threshold frequency to the electrical load.

6. The frequency control system of claim 2 wherein the fleet of electrical loads includes an electric water heater with a water tank, and the system controller or the load controller controlling the electric water heater is programmed to compute the SOC of the electric water heater based on a set point temperature of the electric water heater and a measured temperature of water in the water tank.

7. The frequency control system of claim 1 wherein the system controller is programmed to assign different load-specific threshold frequencies to different electrical loads of the fleet of electrical loads such that the load controllers controlling the electrical loads of the fleet of electrical loads generates a total power draw of the fleet of electrical loads that increases with increasing electrical frequency over an operational range of the frequency control system.

8. The frequency control system of claim 1 wherein the system controller is programmed to assign different load-specific threshold frequencies to different electrical loads of the fleet of electrical loads such that the load controllers controlling the electrical loads of the fleet of electrical loads generates a total power draw of the fleet of electrical loads in accordance with an inverse droop control curve over an operational range of the inverse droop control curve.

9. The frequency control system of claim 1 wherein each load controller includes a frequency meter configured to measure electrical frequency at the controlled electrical load and output the measurement of the electrical frequency used in the operation (i).

10. A frequency control method providing frequency control for an a.c. electrical power grid operating at an electrical frequency using a fleet of electrical loads powered by the electrical power grid, the frequency control method comprising:

estimating a State of Charge (SOC) value for each electrical load of the fleet which measures energy stored in the electrical load;

assigning load-specific threshold frequencies to electrical loads of the fleet based on the estimated SOC values; and

operating electric loads of the fleet whose load-specific threshold frequencies are below the electrical frequency of the grid while not operating electric loads of the fleet whose load-specific threshold frequencies are above the electrical frequency of the grid.

11. The frequency control method of claim 10 wherein the estimating comprises:

estimating the SOC value for an electrical load of the fleet comprising an electric water heater based on a set point temperature of the electric water heater and a measured water temperature of the electric water heater.

12. The frequency control method of claim 10 wherein the assigning comprises:

assigning load-specific threshold frequencies to the electrical loads such that the assigned load-specific threshold frequency increases with increasing SOC value.

13. The frequency control method of claim 10 wherein the assigning comprises:

assigning load-specific threshold frequencies to the electrical loads such that the operating causes the fleet of electrical loads to draw power from the electrical power grid in accordance with an inverse droop control curve.

14. The frequency control method of claim 10 wherein the operating further comprises:

operating any electric load of the fleet whose SOC value indicates a must-run state; and

not operating any electric load of the fleet whose SOC value indicates a must-not-run state.

15. A load controller for controlling an electrical load, the load controller comprising:

a frequency meter configured to measure electrical frequency at the controlled electrical load; and

a microprocessor or microcontroller programmed to perform load monitoring and control operations for the controlled electrical load including (i) comparing the electrical frequency at the controlled electrical load measured by the frequency meter with a threshold frequency assigned to the controlled electrical load and (ii) operating the controlled electrical load based on the comparison, wherein the load-specific threshold frequencies is assigned to the controlled electrical load of a fleet of electrical loads based on State of Charge (SOC) values for the electrical load that measure energy stored in the electrical load, and wherein the load controller performs the operation (ii) by;

turning the controlled electrical load on if the measurement of the electrical frequency is greater than the threshold frequency assigned to the controlled electrical load; and

turning the controlled electrical load off if the measurement of the electrical frequency is less than the threshold frequency assigned to the controlled electrical load.

16. A frequency control system providing frequency control for an a.c. electrical power grid operating at an electrical frequency using a fleet of electrical loads powered by the electrical power grid, the frequency control system comprising:

a system controller comprising an electronic data processing device programmed to assign load-specific threshold frequencies to electrical loads of the fleet of electrical loads based on State of Charge (SOC) values for the electrical loads that measure energy stored in the electrical loads, wherein the system controller is programmed to assign load-specific threshold frequencies to electrical loads of the fleet of electrical loads by operations including;

sorting the electrical loads of the fleet of electrical loads by SOC value; and

assigning higher load-specific threshold frequencies to electrical loads with higher SOC.

17. A frequency control system providing frequency control for an a.c. electrical power grid operating at an electrical frequency using a fleet of electrical loads powered by the electrical power grid, the frequency control system comprising:

a system controller comprising an electronic data processing device programmed to assign load-specific threshold frequencies to electrical loads of the fleet of electrical loads based on State of Charge (SOC) values for the electrical loads that measure energy stored in the electrical loads, wherein the system controller is programmed to assign different load-specific threshold frequencies to different electrical loads of the fleet of electrical loads such that the load controllers controlling the electrical loads of the fleet of electrical loads generates a total power draw of the fleet of electrical loads that increases with increasing electrical frequency over an operational range of the frequency control system.