System and method for characterizing a system

• US 7,505,877 B2
• Filed: 03/08/2002
• Issued: 03/17/2009
• Est. Priority Date: 03/08/2002
• Status: Expired due to Term

• Current Assignee: Johnson Controls Tyco IP Holdings LLP (Johnson Controls International plc)
• Original Assignee: Johnson Controls Technology Company (Johnson Controls International plc)
• Inventors: Salsbury, Timothy I.
• Primary Examiner(s): Rodriguez; Paul L
• Assistant Examiner(s): GUILL, RUSSELL L
• Application Number:
  US10/093,857
• Publication Number:
  US 20030171901A1
• Time in Patent Office: 2,566 Days
• Field of Search: 703/2
• US Class Current: 703/2
• CPC Class Codes: G06F 17/11 for solving equations , e.g. nonlinear equations, general mathematical optimization problems optimization specially adapted for a specific administrative, business or logistic context G06Q10/04
• CPC Class Codes: G06F 17/12 Simultaneous equations , e.g. systems of linear equations

Abstract

A method and apparatus of identifying a system is disclosed. The method comprises estimating at least one parameter in a second-order model of the system, and approximating at least one parameter in a first-order model of the system from the at least one second-order model parameter. The method may also comprise sampling an input to the system, sampling an output from the system. The apparatus comprises a device for estimating at least one parameter in a second-order model of the system, and device for approximating at least one parameter in a first-order model of the system from the at least one second-order model parameter.

Claims

1. A method of identifying a system, the method using a controller, comprising:

calculating an estimated value of at least one parameter in a second-order model of the system;

calculating at least one parameter in a first-order model of the system from at least one second-order model parameter using a transformation function based on a magnitude and phase of the second-order model at a natural frequency for the second-order model, wherein said calculating is performed using the controller;

providing the at least one first-order model parameter to a computing device; and

using the computing device and the at least one first-order model parameter to perform at least one of pre-tuning a feedback controller, configuring the feedback controller, and reconfiguring the feedback controller.

2. The method of claim 1 wherein the second-order model is a second-order continuous time model.

3. The method of claim 2 wherein the second-order model is a second-order transfer function model or a second-order continuous-time model.

4. The method of claim 1 wherein the at least one second-order model parameter comprises at least one second-order continuous-time parameter.

5. The method of claim 1 wherein the first-order model is a first-order plus time delay model.

6. The method of claim 1 wherein the at least one first-order model parameter comprises one or more of a time delay parameter, a time constant parameter and a static gain parameter.

7. The method of claim 1 wherein the at least one second-order model parameter is calculated using sampled inputs and outputs of the system.

8. The method of claim 7 wherein the at least one second-order model parameter is calculated from the sampled inputs and outputs using a recursive least squares method.

9. The method of claim 7 wherein an output of the system is a continuous signal that is discretely sampled.

10. The method of claim 1 wherein the at least one second-order model parameter is calculated using state variable filters.

11. The method of claim 1 wherein the method is automated by a controller.

12. The method of claim 1 wherein the system is a heating, ventilation, and air-conditioning system.

13. A method of analyzing a system using a controller to calculate at least one parameter in a first-order model of the system, the method comprising:

sampling an input to the system;

sampling an output from the system;

calculating an estimated value of at least one parameter in a second-order model of the system using the sampled input and output;

calculating at least one first-order model parameter from the estimated value of the at least one second-order model parameter using a transformation function, the transformation function equating a magnitude and phase of the second-order model at a natural frequency for the second-order model with a magnitude and phase of the first-order model, wherein the steps of sampling and calculating are done using said controller; and

storing the at least one first-order model parameter.

14. The method of claim 13 wherein the second-order model is a second-order continuous-time model, and the at least one second-order model parameter comprises at least one second-order continuous-time parameter.

15. The method of claim 13 wherein the at least one first-order model parameter comprises one or more of a time delay parameter, a time constant parameter and a static gain parameter.

16. The method of claim 13 wherein the at least one second-order model parameter is calculated from the sampled input and output using a recursive least squares method.

17. The method of claim 13 wherein the at least one second-order model parameter is calculated using state variable filters.

18. The method of claim 13 wherein the at least one first-order model parameter is used to perform at least one of pre-tuning a feedback controller, configuring the feedback controller, and reconfiguring the feedback controller.

19. The method of claim 13 wherein the system is a heating, ventilation, and air-conditioning system.

20. The method of claim 13 wherein the method is automated by a controller.

21. The method of claim 13, further comprising changing an input signal to the system.

22. The method of claim 21, wherein the change in the input signal is a step change made for purposes of identifying the system.

23. The method of claim 22 wherein the change in the input signal is made during normal operation of the system.

24. The method of claim 13, further comprising:

providing a step change input from a test signal generator to the system based on the at least one first-order model parameter.

25. A method of analyzing a non-first order system having inputs and outputs, the method comprising:

using a controller to perform the steps of;

providing a first change to the system;

sampling the inputs;

sampling the outputs;

calculating an estimated value of at least one parameter for a second-order model of the system based on the sampled inputs and outputs;

calculating an estimated value of at least one parameter for a first-order model of the system from the estimated value of at least one parameter for a second-order model using a transformation function, the transformation function equating a magnitude and phase of the second-order model at a natural frequency for the second-order model with a magnitude and phase of the first-order model;

determining whether the estimated value of at least one parameter for a first-order model of the system is within a predetermined range;

providing a second change to the system when the estimated value of at least one parameter for a first-order model of the system is outside the predetermined range; and

storing the estimated value of at least one parameter for a first-order model of the system.

26. The method of claim 25 wherein the first-order model is a first-order plus time delay model.

27. The method of claim 25 wherein the estimated value of at least one parameter for a first-order model of the system comprises one or more of a time delay parameter, a time constant parameter and a static gain parameter.

28. The method of claim 25, wherein determining whether the estimated value of at least one parameter for a first-order model of the system is within the predetermined range comprises applying a convergence test to the estimated value of at least one parameter for a first-order model of the system.

29. The method of claim 25 wherein the second-order model is a second-order transfer function model and the estimated value of at least one parameter thereof is calculated using state variable filters.

30. The method of claim 25 wherein the sampled outputs of the system are discrete measurements of a continuous output signal of the system.

31. The method of claim 30, further comprising passing the sampled outputs through a filter.

32. The method of claim 31 wherein the filter is a high-pass filter that focuses the estimated value of at least one parameter for a first-order model of the system on a frequency range of interest.

33. The method of claim 25 further comprising passing the estimated value of at least one parameter for a first-order model of the system through a filter.

34. The method of claim 33 wherein the filter is a low-pass filter that checks the viability of the first-order model.

35. The method of claim 25 wherein the step of calculating the estimated value of at least one parameter for a first-order model of the system is implemented in a digital controller.

36. The method of claim 25 wherein the system is a heating, ventilation, and air-conditioning system.

37. An apparatus for identifying a system, the apparatus comprising:

a controller, the controller configured to;

calculate at least one parameter in a second-order model of the system and calculate at least one parameter in a first-order model of the system from the at least one parameter in a second-order model using a transformation function based on a magnitude and phase of the second-order model at a natural frequency for the second-order model;

determine whether the at least one parameter in a first-order model of the system is within a predetermined range;

provide a step change to the system when the at least one parameter in a first-order model of the system is outside the predetermined range; and

store the at least one parameter in a first-order model of the system.

38. The apparatus of claim 37 wherein the second-order model is a second-order continuous-time model.

39. The apparatus of claim 37 wherein the at least one parameter in a second-order model comprises at least one second-order continuous-time parameter.

40. The apparatus of claim 37 wherein the first-order model is a first-order plus time delay model.

41. The apparatus of claim 37 wherein the at least one parameter in a first-order model of the system comprises one or more of a time delay parameter, a time constant parameter and a static gain parameter.

42. The apparatus of claim 37 wherein the second-order model is a second-order transfer function model.

43. The apparatus of claim 37, the controller further configured to sample inputs and outputs of the system, and wherein the at least one parameter in a second-order model of the system is calculated using the sampled inputs and outputs.

44. The apparatus of claim 43 wherein the at least one parameter in a second-order model of the system is calculated from the sampled inputs and outputs using a recursive least squares method.

45. The apparatus of claim 43 wherein an output of the system is a continuous signal that is discretely sampled.

46. The apparatus of claim 37 wherein the at least one parameter in a second-order model of the system is calculated using state variable filters.

47. The apparatus of claim 37 wherein the at least one parameter in a first-order model of the system is used for at least one of pre-tuning a feedback controller, configuring the feedback controller, and reconfiguring the feedback controller.

48. The apparatus of claim 37, wherein the controller runs a program configured to calculate the at least one parameter in a second-order model of the system and calculate the at least one parameter in a first-order model of the system from the at least one parameter in a second-order model using the transformation function.

49. The apparatus of claim 37 wherein the system is a heating, ventilation, and air-conditioning system.