Electrical energy storage system with variable state-of-charge frequency response optimization
A frequency response optimization system includes a battery configured to store and discharge electric power, a power inverter configured to control an amount of the electric power stored or discharged from the battery at each of a plurality of time steps during a frequency response period, and a frequency response controller. The frequency response controller is configured to receive a regulation signal from an incentive provider, determine statistics of the regulation signal, use the statistics of the regulation signal to generate an optimal frequency response midpoint that achieves a desired change in a state-of-charge (SOC) of the battery while participating in a frequency response program, and use the midpoints to determine optimal battery power setpoints for the power inverter. The power inverter is configured to use the optimal battery power setpoints to control the amount of the electric power stored or discharged from the battery.
1. A frequency response optimization system comprising:
a battery configured to store and discharge electric power;
a power inverter configured to control an amount of the electric power stored or discharged from the battery at each of a plurality of time steps during a frequency response period; and
a frequency response controller configured to:
receive a regulation signal from an incentive provider,
determine statistics of the regulation signal,
use the statistics of the regulation signal to generate an optimal frequency response midpoint for participating in a frequency response program that simultaneously achieves a predefined change in a state-of-charge (SOC) of the battery, and
use the optimal frequency response midpoint to determine optimal battery power setpoints for the power inverter;
wherein the power inverter is configured to use the optimal battery power setpoints to control the amount of the electric power stored or discharged from the battery.
2. The frequency response optimization system of claim 1 , wherein the frequency response controller comprises:
a high level controller configured to determine the optimal frequency response midpoint at the beginning of the frequency response period; and
a low level controller configured to determine the optimal battery power setpoints at each of a plurality of time steps during the frequency response period.
3. The frequency response optimization system of claim 1 , wherein the frequency response controller comprises a battery power loss estimator configured to estimate an amount of power lost in the battery based on the statistics of the regulation signal.
4. The frequency response optimization system of claim 1 , wherein the frequency response controller comprises:
a high level controller configured to generate filter parameters based on the optimal frequency response midpoint; and
a low level controller configured to use the filter parameters to filter the regulation signal and determine the optimal battery power setpoints using the filtered regulation signal.
5. The frequency response optimization system of claim 1 , wherein the frequency response controller is configured to generate an objective function comprising:
an estimated amount of frequency response revenue that will result from the optimal frequency response midpoint; and
an estimated cost of battery degradation that will result from the optimal frequency response midpoint.
6. The frequency response optimization system of claim 5 , wherein the frequency response controller is configured to implement constraints on the objective function, the constraints comprising at least one of:
a first constraint constraining the state-of-charge of the battery between a minimum state-of-charge and a maximum state-of-charge; or
a second constraint constraining the optimal frequency response midpoint such that a sum of the midpoint and a campus power usage does not exceed a maximum power rating of the power inverter.
7. The frequency response optimization system of claim 1 , wherein the frequency response controller is configured to generate an objective function comprising:
an estimated amount of frequency response revenue that will result from the optimal battery power setpoints; and
an estimated cost of battery degradation that will result from the optimal battery power setpoints.
8. The frequency response optimization system of claim 1 , wherein the frequency response controller is configured to use a battery life model to determine an estimated cost of battery degradation, the battery life model comprising a plurality of variables that depend on the optimal battery power setpoints, the variables comprising at least one of:
a temperature of the battery;
the state-of-charge of the battery;
a depth of discharge of the battery;
a power ratio of the battery; or
an effort ratio of the battery.
9. The frequency response optimization system of claim 1 , further comprising a campus having a campus power usage and a point of intersection at which the campus power usage combines with the electric power discharged from the battery;
wherein the frequency response controller is configured to determine the optimal setpoints based on both the campus power usage and the regulation signal.
10. A method for optimizing frequency response, the method comprising:
receiving a regulation signal from an incentive provider;
determining statistics of the regulation signal;
using the statistics of the regulation signal to generate an optimal frequency response midpoint for participating in a frequency response program that simultaneously achieves a predefined change in a state-of-charge (SOC) of a battery;
using the optimal frequency response midpoint to determine optimal battery power setpoints; and
using the optimal battery power setpoints to control an amount of electric power stored or discharged from the battery.
11. The method of claim 10 , further comprising:
determining the optimal frequency response midpoint at the beginning of the frequency response period; and
determining the optimal battery power setpoints at each of a plurality of time steps during the frequency response period.
12. The method of claim 10 , further comprising estimating an amount of power lost in the battery based on the statistics of the regulation signal.
13. The method of claim 10 , further comprising:
generating filter parameters based on the optimal frequency response midpoint;
using the filter parameters to filter the regulation signal; and
determining the optimal battery power setpoints using the filtered regulation signal.
14. The method of claim 10 , further comprising generating an objective function comprising:
an estimated amount of frequency response revenue that will result from the optimal frequency response midpoint; and
an estimated cost of battery degradation that will result from the midpoint.
15. The method of claim 14 , further comprising implementing constraints on the objective function, the constraints comprising at least one of:
a first constraint constraining the state-of-charge of the battery between a minimum state-of-charge and a maximum state-of-charge; or
a second constraint constraining the midpoint such that a sum of the midpoint and a campus power usage does not exceed a maximum power rating of a battery power inverter.
16. The method of claim 10 , further comprising generating an objective function comprising:
an estimated amount of frequency response revenue that will result from the optimal battery power setpoints; and
an estimated cost of battery degradation that will result from the optimal battery power setpoints.
17. The method of claim 10 , further comprising using a battery life model to determine an estimated cost of battery degradation, the battery life model comprising a plurality of variables that depend on the optimal battery power setpoints, the variables comprising at least one of:
a temperature of the battery;
the state-of-charge of the battery;
a depth of discharge of the battery;
a power ratio of the battery; or
an effort ratio of the battery.
18. The method of claim 10 , further comprising determining the optimal setpoints based on both a campus power usage and the regulation signal, wherein the campus power usage combines with the electric power discharged from the battery at a point of interconnection.
19. A frequency response controller comprising:
a processing circuit configured to:
receive a regulation signal from an incentive provider;
determine statistics of the regulation signal;
use the statistics of the regulation signal to generate an optimal frequency response midpoint for participating in a frequency response program that simultaneously achieves a predefined change in a state-of-charge (SOC) of a battery;
use the optimal frequency response midpoint to determine optimal battery power setpoints; and
use the optimal battery power setpoints to control an amount of electric power stored or discharged from the battery.
20. The controller of claim 19 , wherein the processing circuit comprises:
a high level controller configured to determine the optimal frequency response midpoint at the beginning of the frequency response period; and
a low level controller configured to determine the optimal battery power setpoints at each of a plurality of time steps during the frequency response period.