Adaptive flow controller for use with a flow control system

• US 5,875,109 A
• Filed: 07/03/1997
• Issued: 02/23/1999
• Est. Priority Date: 05/24/1995
• Status: Expired due to Term

• Current Assignee: Johnson Controls Technology Company (Johnson Controls International plc)
• Original Assignee: Johnson Service Company
• Inventors: Federspiel, Clifford C.
• Primary Examiner(s): Elmore, Reba I.
• Assistant Examiner(s): Brown, Thomas E.
• Application Number:
  US08/887,911
• Time in Patent Office: 600 Days
• Field of Search: 364/148-152, 364/153, 364/157, 364/160, 364/161-166, 364/176, 364/177, 454/48, 454/61, 236/46 R, 165/16
• US Class Current: 700/40
• CPC Class Codes: F24F 11/30 for purposes related to the operation of the system, e.g. for safety or monitoring
• CPC Class Codes: F24F 11/62 characterised by the type of control or by internal processing, e.g. using fuzzy logic, adaptive control or estimation of values
• CPC Class Codes: F24F 11/74 for controlling air flow rate or air velocity
• CPC Class Codes: G05B 13/024 in which a parameter or coefficient is automatically adjusted to optimise the performance
• CPC Class Codes: G05D 7/0635 by action on throttling means G05D7/0688, G05D7/0694 take precedence

Abstract

An adaptive airflow control system for positioning damper systems or controlling air units utilized in an environment control system is provided. The system is based on a fixed-gain, proportional-only feedback design to provide stable operation given the nonlinear behavior of flow through a valve or damper. A time-dependent deadzone of nonlinearity is used to reject measurement noise. The deadzone of nonlinearity is adjusted by an adaptively calculated proportionality constant which is capable of switching the control system between various operating modes for adjusting the performance of the system.

Claims

1. An environment control system including an air unit for providing air flow to an environment, the air unit being operatively associated with a controller and controlling an amount of the air flow in accordance with a flow set-point signal from the controller, the controller comprising:

a flow sensor exposed to the air flow provided by the unit, the flow sensor generating a flow signal representative of an amount of the air flow provided to the environment;

a processor connected to the flow sensor, the processor configured to cyclically receive the flow signal and generate a controller output signal in response to the flow signal and the flow setpoint signal, the controller output signal being provided to the air unit to cause the air unit to provide the amount of the air flow represented by the flow setpoint signal, the processor calculating the controller output signal in accordance with a setpoint error signal, a proportionality constant, and a deadzone of nonlinearity, whereby the processor calculates the deadzone of nonlinearity in accordance with a variance of the flow signal;

the processor switching the controller between a first operating mode and a second operating mode in response to a set of conditions associated with the flow setpoint signal, said first operating mode being a default mode;

wherein the processor changes the proportionality constant stepwise from a first predetermined constant to a second predetermined constant thereby instantaneously switching the environment control system from the first operating mode to the second operating mode in response to a predetermined change in the setpoint signal for closely tracking changes in the setpoint error signal; and

wherein the processor exponentially changes the proportionality constant from the second predetermined constant to the first predetermined constant thereby gradually switching the environment control system from the second operating mode to the first operating mode in response to a predetermined change in the flow signal for normally tracking changes in the setpoint error signal.

2. The controller of claim 1 wherein the first operating mode is a conservative operating mode and the second mode is an aggressive operating mode.

3. The controller of claim 1 wherein the setpoint error signal is related to the difference between a previous flow setpoint signal and the flow signal.

4. The controller of claim 1 including a memory for storing a software-based control algorithm executed by the processor for generating the flow setpoint signal in accordance with the software-based control algorithm.

5. The controller of claim 3 including a memory for storing a software-based control algorithm and the processor cyclically generates the controller output signal in accordance with cyclical operation of the software-based control algorithm, and wherein the previous flow setpoint signal is from a most recent previous cycle of operation of the control algorithm.

6. The controller of claim 4 wherein the deadzone of nonlinearity is stored in the memory and recalculated each cycle of operation of the control algorithm.

7. The controller of claim 6 wherein the deadzone of nonlinearity is adaptively adjusted by the standard deviation of a noise signal associated with the flow signal.

8. The controller of claim 6 wherein the deadzone of nonlinearity is adaptively adjusted by the standard deviation of the absolute value of a noise signal associated with the flow signal.

10. The controller of claim 1 wherein the first operating mode is a conservative operating mode and the second operating mode is an aggressive operating mode.

13. The controller of claim 10 including memory means for storing a software-based control algorithm and the processor means cyclically generates the flow setpoint signal in accordance with cyclical operation of the software-based control algorithm, and wherein the previous cycle is from a most recent previous cycle of operation of the control algorithm.

15. The controller of claim 13 wherein the deadzone of nonlinearity is related to a previous deadzone of nonlinearity calculated in a previous cycle.

9. A controller for use in an environment control system including an air duct including a damper operatively associated with an actuator, the actuator positioning the damper so that the damper provides a rate of air flow to an environment in response to an actuator control signal, the actuator being operatively coupled to the controller, the controller comprising:

sensor means for generating an actual flow signal representative of the rate of the air flow provided across the damper; and

processor means connected the sensor means for cyclically receiving the actual flow signal from the sensor means, and for cyclically generating the actuator control signal in response to the actual flow signal, wherein the actuator control signal is related to a desired rate for the rate of the air flow provided across the damper, the processor means calculating the actuator control signal in accordance with a setpoint error signal and a deadzone of nonlinearity, wherein the deadzone of nonlinearity is calculated in accordance with an estimate of the standard deviation of a noise signal associated with the actual flow signal;

the processor means switching the controller between a first operating mode and a second operating mode in response to a set of conditions associated with the flow setpoint signal;

wherein the processor means changes the proportionality constant stepwise from a first predetermined constant to a second predetermined constant thereby instantaneously switching the controller from the first operating mode to the second operating mode in response to a predetermined change in the setpoint signal for closely tracking changes in the setpoint error signal; and

wherein the processor means exponentially changes the proportionality constant from the second predetermined constant to the first predetermined constant thereby gradually switching the controller from the second operating mode to the first operating mode in response to a predetermined change in the flow signal for normally tracking changes in the setpoint error signal.

11. The controller of claim 9 wherein the setpoint error signal is related to a difference between a flow setpoint signal generated in a previous cycle of operation of the processing means and the actual flow signal received in a current cycle of operation of the processing means.

12. The controller of claim 9 including memory means for storing a software-based control algorithm and wherein the processor means generates the actuator output signal in accordance with the software-based control algorithm.

14. The controller of claim 9 including memory means for storing a software-based control algorithm and the processor means cyclically generates the flow setpoint signal in accordance with cyclical operation of the software-based control algorithm, and wherein the deadzone of nonlinearity is stored in the memory means and recalculated each cycle of operation of the control algorithm.

16. The controller of claim 14 wherein the deadzone of nonlinearity is adaptively related to the variance.

17. In a control system including a unit for providing a flow of a fluid, a controller for providing a controller output signal, and a flow sensor for providing an actual flow signal, the unit being operatively associated with a controller and controlling an amount of the flow in accordance with a controller output signal from the controller, the flow sensor being exposed to the flow provided by the unit, the flow sensor generating the actual flow signal representative of the amount of flow provided, a method of controlling the amount of the flow provided by the unit comprising steps of:

receiving the actual flow signal from the flow sensor;

determining a setpoint error signal based on a flow setpoint signal and the actual flow signal;

calculating a proportionality constant for switching the control system between a first operating mode and a second operating mode in response to a set of conditions associated with the flow setpoint signal;

calculating a deadzone of nonlinearity in accordance with a variance of the flow signal due to noise, and in accordance with the proportionality constant;

applying the deadzone of nonlinearity to the setpoint error signal to develop the controller output signal; and

providing the controller output signal to the unit.

18. The method of claim 17 wherein the first operating mode is a conservative operating mode and the second operating mode is an aggressive operating mode.

19. The method of claim 17 wherein the controller changes the proportionality constant stepwise from a first predetermined constant to a second predetermined constant thereby instantaneously switching the control system from the first operating mode to the second operating mode in response to a predetermined change in the setpoint signal for closely tracking changes in the setpoint error signal.

20. The method of claim 17 wherein the controller exponentially changes the proportionality constant from a second predetermined constant to a first predetermined constant thereby gradually switching the control system from the second operating mode to the first operating mode in response to a predetermined change in the flow signal for normally tracking changes in the setpoint error signal.

21. The method of claim 17 wherein the step of calculating the deadzone of nonlinearity includes calculating the standard deviation of the absolute value of a noise signal associated with the flow signal.

22. The method of claim 17 including the step of high pass filtering the flow signal for rejecting ramping attributes associated with the actual flow signal.

23. The method of claim 17 wherein the controller includes a memory and a processor, the memory including a software-based control algorithm and the processor generating the actuator output signal in accordance with the software-based control algorithm.

24. The method of claim 17 wherein the deadzone of nonlinearity is adaptively calculated, whereby the deadzone of nonlinearity is related to previous values of the deadzone of nonlinearity.