Slop predictive control and digital pid control for a variable temperature control system

• US 7,246,753 B2
• Filed: 03/19/2004
• Issued: 07/24/2007
• Est. Priority Date: 05/05/2000
• Status: Expired due to Term

• Current Assignee: Automated Logic Corporation (Carrier Global Corporation)
• Original Assignee: Automated Logic Corporation (Carrier Global Corporation)
• Inventors: Hull, Gerry Glancy, Tom, Steven Treece, Saar, Raynold Lee
• Primary Examiner(s): Jiang; Chen Wen
• Application Number:
  US10/804,278
• Publication Number:
  US 20040256473A1
• Time in Patent Office: 1,222 Days
• Field of Search: 236/49.3, 236/78.B, 236/78.D, 165/217, 318/610, 700/276, 700/282
• US Class Current: 236/49.3
• 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 11/70 Control systems characterised by their outputs; Constructional details thereof
• CPC Class Codes: F24F 13/08 Air-flow control members, e.g. louvres, grilles, flaps or guide plates F24F7/013, F24F13/06 take precedence
• CPC Class Codes: G05D 23/1919 characterised by the type of controller
• CPC Class Codes: G05D 7/0635 by action on throttling means G05D7/0688, G05D7/0694 take precedence

Abstract

The present invention applies a slope predictive control method to a Variable Temperature Control (VTC) system, measuring the slope of the discharge temperature as a function of flow regulation device position, and using this slope to predict the position of the flow regulation device needed to achieve the desired discharge temperature. The present invention also monitors the response of the VTC over time and utilizes a self-learning algorithm to predict the response time of the system in order to determine when further control adjustments need to be taken.

Claims

1. A method for controlling a flow of a non-solid substance in a Variable Temperature Control (VTC) box in a temperature control system, wherein the VTC box comprises a heat exchange device under control of a regulation device, comprising:

receiving an indication of a temperature setpoint;

measuring a discharge air temperature of the VTC box and calculating an error between the temperature setpoint and the measured discharge air temperature; and

until a new temperature setpoint indication is received, repeating the steps comprising;

based on the error, predicting a regulation device position adjustment to actuate the regulation device to achieve the temperature setpoint, if the predicted regulation device position adjustment is less than a minimum position adjustment, not actuating the regulation device and measuring the discharge air temperature to calculate an average discharge air temperature over a period of time, if the predicted regulation device position adjustment is not less than the minimum position adjustment, measuring the discharge air temperature in the VTC box while actuating the regulation device the predicted position adjustment or until the discharge air temperature is measured to have crossed the temperature setpoint, in response to actuating the regulation device, measuring the discharge air temperature to calculate the average discharge air temperature, and based on the average discharge air temperature, recalculating the error.

2. A computer-readable medium having stored thereon computer-executable instructions for performing the method of claim 1.

3. The method of claim 1, wherein the predicted position adjustment is determined by dividing the error by a slope of a regulation device response curve.

4. The method of claim 3, further comprising:

in response to actuating the regulation device and calculating the average discharge air temperature, determining how much the regulation device was adjusted and calculating a new slope of the regulation device response curve;

in response to determining that the regulation device was adjusted less than a second minimum position adjustment, disregarding the new slope and using the previous slope to recalculate the error;

in response to determining that the regulation device was adjusted within a predetermined position adjustment range, averaging the new slope with the previous slope and using the averaged slope to recalculate the error; and

in response to determining that the regulation device was adjusted more than the predetermined position adjustment range, using the new slope to recalculate the error.

5. A computer-readable medium having stored thereon computer-executable instructions for performing the method of claim 4.

6. The method of claim 1, wherein actuating the regulation device the predicted regulation device position adjustment or until the discharge air temperature is measured to have crossed the temperature setpoint comprises:

in response to determining that the predicted regulation device position adjustment is not greater than a second minimum position adjustment, actuating the regulation device the predicted position adjustment; and

in response to determining that the predicted regulation device position adjustment is greater than the second minimum position adjustment, actuating the regulation device until the discharge air temperature is measured to have crossed the temperature setpoint.

7. The method of claim 1, further comprising, in response to receiving the temperature setpoint indication, calculating a percent change between the temperature setpoint and a previous temperature setpoint;

and in response to determining that the percent change is greater than a predetermined percent change, replacing the previous temperature setpoint with the temperature setpoint.

8. A Variable Temperature Control (VTC) temperature control system comprising:

a VTC box including a heat exchange device and a discharge air temperature sensor for measuring the discharge air temperature;

a flow regulation device for controlling a volume of non-solid substance delivered to the heat exchange device; and

a micro-controller configured for executing computer-executable instructions for;

receiving a discharge temperature setpoint, receiving a discharge air temperature measurement from the temperature sensor and calculating an error between the discharge temperature setpoint and the discharge air temperature measurement, and until a new discharge temperature setpoint is received, repeating the steps comprising;

based on the error, predicting a flow regulation device position adjustment to actuate the flow regulation device in the VTC box to achieve the temperature setpoint, if the predicted flow regulation device position adjustment is less than a minimum position adjustment, not generating a signal for actuating the flow regulation device and receiving discharge air temperature measurements from the discharge air temperature sensor to calculate an average temperature over a period of time, if the predicted flow regulation device position adjustment is not less than the minimum position adjustment, receiving discharge air temperature measurements from the discharge air temperature sensor while generating the signal for actuating the flow regulation device the predicted flow regulation device position adjustment or until one of the temperature measurements is determined to have crossed the temperature setpoint, in response to actuation of the flow regulation device, receiving discharge air temperature measurements from the discharge air temperature sensor to calculate the average temperature, and based on the average discharge air temperature, recalculating the error.

9. The system of claim 8, wherein the predicted flow regulation device position adjustment is determined by dividing the error by a slope of a flow regulation device response curve.

10. The system of claim 9, wherein the micro-controller further executes computer-executable instructions comprising:

in response to actuation of the flow regulation device and calculation of the average discharge air temperature, determining how much the flow regulation device was actuated and calculating a new slope of the flow regulation device response curve;

in response to determining that the flow regulation device was actuated less than a second minimum position adjustment, disregarding the new slope and using the previous slope to recalculate the error;

in response to determining that the flow regulation device was actuated within a predetermined position adjustment range, averaging the new slope with the previous slope and using the averaged slope to recalculate the error; and

in response to determining that the flow regulation device was actuated more than the predetermined position adjustment range, using the new slope to recalculate the error.

11. The system of claim 8, wherein generating the signal for actuating the flow regulation device the predicted flow regulation device position adjustment or until the discharge air temperature is measured to have crossed the temperature setpoint comprises:

in response to determining that the predicted flow regulation device position adjustment is not greater than a second minimum position adjustment, generating the signal for actuating the flow regulation device the predicted position adjustment; and

in response to determining that the predicted flow regulation device position adjustment is greater than the second minimum position adjustment, generating the signal for actuating the flow regulation device until the airflow is measured to have crossed the airflow setpoint.

12. The system of claim 8, wherein the micro-controller further executes computer-executable instructions comprising:

in response to calculating the temperature setpoint, calculating a percent change between the temperature setpoint and a previous temperature setpoint; and

in response to determining that the percent change is greater than a predetermined percent change, replacing the previous temperature setpoint with the temperature setpoint.

13. A method for controlling a Variable Temperature Control (VTC) box in a temperature control system, wherein the VTC box comprises a heat exchange device under control of a regulation device, comprising:

receiving an indication of a temperature setpoint;

measuring a discharge air temperature of the VTC box and calculating an error between the temperature setpoint and the measured discharge air temperature; and

until a new temperature setpoint indication is received, repeating the steps comprising;

based on the error, predicting a regulation device setting to which the regulation device is actuated to achieve the temperature setpoint, if the predicted regulation device setting requires less than a minimum setting change, not actuating the regulation device and measuring the discharge air temperature to calculate an average discharge air temperature over a period of time, if the predicted regulation device setting does not require less than the minimum setting change, measuring the discharge air temperature in the VTC box while actuating the regulation device to the predicted regulation device setting or until the discharge air temperature is measured to have crossed the temperature setpoint, in response to actuating the regulation device, measuring the discharge air temperature to calculate the average discharge air temperature, and based on the average discharge air temperature, recalculating the error.

14. A computer-readable medium having stored thereon computer-executable instructions for performing the method of claim 13.