Control system with maximum time constant estimation
A controller includes a communications interface configured to provide a control input to and receive feedback from a plant. The feedback is representative of a response of the plant to the control input over a response period. The controller further includes a time constant estimator. The time constant estimator calculates a normalized variable based on the feedback, each value of the normalized variable representative of the response of the plant at a different time during the response period. The time constant estimator calculates a plurality of time constant estimates, based on the plurality of values of the normalized variable. The time constant estimator determines a maximum time constant from the time constant estimates. The controller further includes a control input generator that generates the control input for the plant using the maximum time constant. The control input affects a variable state or condition of the plant.
1. A controller for a plant, the controller comprising:
a communications interface configured to provide a control input to the plant and to receive feedback from the plant, the feedback representative of a response of the plant to the control input over a response period;
a time constant estimator configured to:
calculate a plurality of values of a normalized variable by normalizing a plurality of values of the feedback from the plant relative to a range of the feedback from the plant, each value of the normalized variable representative of the response of the plant at a different time during the response period;
calculate a plurality of time constant estimates, wherein each of the time constant estimates is calculated based on one of the plurality of values of the normalized variable and represents the response of the plant to the control input at one of the different times during the response period; and
select a maximum time constant for the response of the plant over the response period from the plurality of time constant estimates; and
a control input generator configured to use the maximum time constant to generate the control input for the plant, wherein the plant uses the control input to affect a variable state or condition of the plant.
2. The controller of claim 1 , wherein the time constant estimator is configured to determine that the response of the plant to the control input is non-linear in response to the plurality of time constant estimates having a plurality of different values.
3. The controller of claim 1 , wherein:
the control input generator is configured to perform a step test of the plant by providing the plant with a step change in the control input; and
the feedback from the plant is representative of a response of the plant to the step test.
4. The controller of claim 1 , further comprising a filter configured to apply a smoothing function to the feedback to remove noise from the feedback before the feedback is provided to the time constant estimator.
5. The controller of claim 1 , wherein:
the plant comprises a building HVAC system configured to use the control input to operate HVAC equipment; and
the feedback from the plant represents the variable state or condition of the HVAC system affected by operating the HVAC equipment.
6. The controller of claim 1 , wherein the controller is an extremum-seeking controller configured to implement an extremum-seeking control algorithm to generate the control input.
7. The controller of claim 1 , wherein:
the controller is a proportional-integral (PI) controller configured to implement a PI feedback control algorithm to generate the control input; and
the control input generator is configured to use the maximum time constant to generate a parameter used by the PI feedback control algorithm.
8. The controller of claim 1 , wherein the controller is configured to use the maximum time constant to set a sampling rate for a wireless sensor of the plant from which the feedback is received.
9. A method for calculating and using a time constant to control a plant, the method comprising:
providing, at a controller, a control input to a plant;
receiving, at the controller, feedback from the plant, the feedback representative of a response of the plant to the control input over a response period;
calculating, at the controller, a plurality of values of a normalized variable by normalizing a plurality of values of the feedback from the plant relative to a range of the feedback from the plant, each value of the normalized variable representative of the response of the plant at a different time during the response period;
calculating, at the controller, a plurality of time constant estimates, wherein each of the time constant estimates is calculated based on one of the plurality of values of the normalized variable, and represents the response of the plant to the control input at one of the different times during the response period;
selecting, at the controller, a maximum time constant for the response of the plant over the response period from the plurality of time constant estimates; and
using the maximum time constant to generate the control input for the plant, wherein the plant uses the control input to affect a variable state or condition of the plant.
10. The method of claim 9 , wherein the controller is configured to determine that the response of the plant to the control input is non-linear in response to the plurality of time constant estimates having a plurality of different values.
11. The method of claim 9 , wherein a control input generator is configured to perform a step test of the plant by providing the plant with a step change in the control input; and
the feedback from the plant is representative of a response of the plant to the step test.
12. The method of claim 9 , further comprising applying a smoothing function to the feedback to remove noise from the feedback before the feedback is provided to a time constant estimator.
13. The method of claim 9 , wherein the plant comprises a building HVAC system configured to use the control input to operate HVAC equipment; and
the feedback from the plant represents the variable state or condition of the HVAC system affected by operating the HVAC equipment.
14. The method of claim 9 , wherein the controller is an extremum-seeking controller configured to implement an extremum-seeking control algorithm to generate the control input.
15. The method of claim 9 , wherein:
the controller is a proportional-integral (PI) controller configured to implement a PI feedback control algorithm to generate the control input; and
a control input generator is configured to use the maximum time constant to generate a parameter used by the PI feedback control algorithm.
16. The method of claim 9 , wherein the controller is configured to use the maximum time constant to set a sampling rate for a wireless sensor of the plant from which the feedback is received.
17. An extremum-seeking controller for a plant, the controller comprising:
a communications interface configured to:
provide a control input to a plant; and
receive feedback from the plant, the feedback representative of a response of the plant to the control input over a response period;
a time constant estimator configured to:
calculate a plurality of values of a normalized variable by normalizing a plurality of values of the feedback from the plant relative to a range of the feedback from the plant, each value of the normalized variable representative of the response of the plant at a different time during the response period;
calculate a plurality of time constant estimates, wherein each of the time constant estimates is calculated based on one of the plurality of values of the normalized variable, and represents the response of the plant to the control input at one of the different times during the response period; and
select a maximum time constant for the response of the plant over the response period from the plurality of time constant estimates; and
a control input generator configured to use the maximum time constant to generate the control input for the plant, wherein the plant uses the control input to affect a variable state or condition of the plant.
18. The extremum-seeking controller of claim 17 , wherein the time constant estimator is configured to determine that the response of the plant to the control input is non-linear in response to the plurality of time constant estimates having a plurality of different values.
19. The extremum-seeking controller of claim 17 , wherein the control input generator is configured to perform a step test of the plant by providing the plant with a step change in the control input; and
the feedback from the plant is representative of a response of the plant to the step test.
20. The extremum-seeking controller of claim 17 , further comprising a filter configured to apply a smoothing function to the feedback to remove noise from the feedback before the feedback is provided to the time constant estimator.