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US6697767B2
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Robust process identification and auto-tuning control
Assignee: National University of Singapore
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Filing: 2001-10-18
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Granted: 2004-02-24
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Expires: 2021-10-18
Abstract
Abstract This invention provides a novel process identification and control package for high performance. For process identification, a simple yet effective and robust identification method is presented using process step responses to give a continuous transfer function with time-delay without iteration. A new relay, called cascade relay, is devised to get more accurate and reliable points on the process frequency response. For controller tuning, the internal model principle is employed to design single-loop controller PID or high-order types with best achievable control performance. The process identification and control design parts can be easily integrated into control system auto-tuning package. Further, a general control scheme for disturbance rejection is given which can significantly improve disturbance rejection performance over conventional feedback systems with time delays. Practical issues such as noises, real-time implementation and tuning guidelines are also provided. The invention covers both open-loop and closed-loop testing, and single and multivariable cases.
Inventors
- 👤 Qing-Guo Wang
- 👤 Tong-Heng Lee
- 👤 Yong Zhang
- 👤 Yu Zhang
- 👤 Xue-Ping Yang
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 06:37
CPC Classifications
G; G05; G05B; G05B11/00; G05B11/01; G05B11/36; G05B11/42; G05B13/00; G05B13/02; G05B13/04; G05B13/042
Claims Analysis
Total Claims: 33
Claim 1
Independent Claim
83 words
A method for identification of a continuous time-delay system from a process step response, said method comprising the steps of: applying an open-loop step test and recording at least one output time response; obtaining at least one linear regression equation from the at least one output time response; estimating the regression parameters by an LS method; and recovering the process model coefficients for the continuous time-delay system using an explicit relationship between the regression parameters and the regression parameters in the actual process.
Claim 2
Independent Claim
83 words
A method for identification of a continuous time-delay system from a process step response, said method comprising the steps of: applying an open-loop step test and recording at least one output time response; obtaining at least one linear regression equation from the at least one output time response; estimating the regression parameters by an LS method; and recovering the process model coefficients for the continuous time-delay system using an explicit relationship between the regression parameters and the regression parameters in the actual process.
Claim 3
Dependent Claim
23 words
The method according to claim 1 , wherein said step of estimating the regression parameters by an LS method is completed without iterations.
Claim 4
Dependent Claim
30 words
The method according to claim 1 , wherein said method includes at least one of an FOPDT model, a SOPDT model and a SOPDTZ model for approximating an industrial process.
Claim 5
Dependent Claim
30 words
The method according to claim 3 , wherein the industrial process requires a system model for analysis, prediction, filtering, optimization, management or tuning of a controller for a process system.
Claim 6
Dependent Claim
22 words
The method according to claim 4 , wherein the process system includes monotonic or oscillatory dynamics of minimum-phase or non-minimum phase processes.
Claim 7
Dependent Claim
40 words
The method according to claim 2 , wherein said continuous time-delay system has been brought into a constant steady state with a controller and said open-loop step test is replaced by a closed loop test producing a steady state response.
Claim 8
Independent Claim
75 words
A method for closed-loop identification of a continuous time-delay system, comprising the steps of: applying a closed-loop test that attains a steady state response or stationary oscillations at the end of test; recording a process input response and an output time response for the closed-loop test; using a FFT to calculate the process frequency response; using an inverse FFT to construct the process step response; applying an open-loop identification method to obtain the process model.
Claim 9
Independent Claim
75 words
A method for closed-loop identification of a continuous time-delay system, comprising the steps of: applying a closed-loop test that attains a steady state response or stationary oscillations at the end of test; recording a process input response and an output time response for the closed-loop test; using a FFT to calculate the process frequency response; using an inverse FFT to construct the process step response; applying an open-loop identification method to obtain the process model.
Claim 10
Dependent Claim
83 words
The method according to claim 7 wherein said open-loop identification method to obtain the process model includes the steps of: applying an open-loop step test and recording at least one output time response; obtaining at least one linear regression equation from the at least one output time response; estimating the regression parameters by an LS method; and recovering the process model coefficients for the continuous time-delay system using an explicit relationship between the regression parameters and the regression parameters in the actual process.
Claim 11
Dependent Claim
24 words
The method according to claim 8 , wherein a FOPDT model, SOPDTZ model or higher order model is obtained through said open-loop identification method.
Claim 12
Dependent Claim
19 words
The method according to claim 7 , wherein the closed-loop test is a step test or a relay test.
Claim 13
Dependent Claim
77 words
A cascade relay feedback system for exciting a process at a process critical frequency ω c , said cascade relay system including: a first loop; a second loop; a master relay in the second loop, wherein said cascade relay system permits persistent excitation at 0.5 ω c and 1.5 ω c ; and a slave relay in the first loop, wherein said cascade relay system can excite said process at said process critical frequency, ω c .
Claim 14
Dependent Claim
77 words
A cascade relay feedback system for exciting a process at a process critical frequency ω c , said cascade relay system including: a first loop; a second loop; a master relay in the second loop, wherein said cascade relay system permits persistent excitation at 0.5 ω c and 1.5 ω c ; and a slave relay in the first loop, wherein said cascade relay system can excite said process at said process critical frequency, ω c .
Claim 15
Dependent Claim
42 words
A method for identification of the cascade relay feedback system of claim 11 , said method comprising the steps of: performing a cascade relay test for a process; and using a FFT algorithm to compute a process frequency response at multiple frequencies.
Claim 16
Dependent Claim
75 words
A controller design method for a single variable process using IMC principles, said method comprising the steps of: specifying an initial value for a tuning parameter according to a performance limitation of single loop control system due to non-minimum phase elements; specifying a type of controller; using an LS method for generating the controller parameters and evaluating a corresponding approximation error; completing said design method if the corresponding approximation error satisfies a specified approximation threshold.
Claim 17
Dependent Claim
75 words
A controller design method for a single variable process using IMC principles, said method comprising the steps of: specifying an initial value for a tuning parameter according to a performance limitation of single loop control system due to non-minimum phase elements; specifying a type of controller; using an LS method for generating the controller parameters and evaluating a corresponding approximation error; completing said design method if the corresponding approximation error satisfies a specified approximation threshold.
Claim 18
Dependent Claim
53 words
The controller design method according to claim 13 , wherein the corresponding approximation error does not satisfy the specified approximation threshold, said method further comprising the steps of: updating the initial value of the tuning parameter; and repeating the steps of claim 13 until said corresponding approximation error satisfies the specified approximation threshold.
Claim 19
Dependent Claim
57 words
The controller design method according to claim 13 , wherein the corresponding approximation error does not satisfy the specified approximation threshold, said method further comprising the steps of: using an LS method to find a lowest high-order controller by increasing the order of the controller gradually until satisfying the specified approximation threshold; and completing said design method.
Claim 20
Independent Claim
57 words
A method for identifying a multivariable process, said method comprising the steps of: bringing the process to a constant steady state; specifying a test type and a test mode; performing a sequential experiment and recording all the process input and output responses; calculating a process frequency response; constructing a process step response; and estimating a process model.
Claim 21
Independent Claim
57 words
A method for identifying a multivariable process, said method comprising the steps of: bringing the process to a constant steady state; specifying a test type and a test mode; performing a sequential experiment and recording all the process input and output responses; calculating a process frequency response; constructing a process step response; and estimating a process model.
Claim 22
Dependent Claim
39 words
The method according to claim 16 , wherein said test type is at least one of a relay test and a step test, and said test mode is at least one of a open-loop test and a closed-loop test.
Claim 23
Dependent Claim
115 words
The method according to claim 17 , wherein said test mode is an open-loop test, and said steps of calculating the process frequency response, constructing the process step response and estimating the process model include an open-loop identification method to obtain the process model, said open-loop identification model including the steps of: applying an open-loop step test and recording at least one output time response; obtaining at least one linear regression equation from the at least one output time response; estimating the regression parameters by an LS method; and recovering the process model coefficients for the continuous time-delay system using an explicit relationship between the regression parameters and the regression parameters in the actual process.
Claim 24
Dependent Claim
69 words
A controller design method for a multivariable process using multivariable decoupling and IMC-principles, said method comprising the steps of: specifying an objective closed-loop transfer function matrix with each diagonal element taking into account time delay and non-minimum phase zeros; using an LS method to find a PID controller and evaluating a corresponding approximation error; and completing said design method if the corresponding approximation error satisfies a specified approximation threshold.
Claim 25
Dependent Claim
69 words
A controller design method for a multivariable process using multivariable decoupling and IMC-principles, said method comprising the steps of: specifying an objective closed-loop transfer function matrix with each diagonal element taking into account time delay and non-minimum phase zeros; using an LS method to find a PID controller and evaluating a corresponding approximation error; and completing said design method if the corresponding approximation error satisfies a specified approximation threshold.
Claim 26
Dependent Claim
86 words
The controller design method according to claim 19 , wherein the corresponding approximation error does not satisfy the specified approximation accuracy, said method further comprising the steps of: updating a tuning parameter in said closed loop; specifying the objective closed-loop transfer function matrix with each diagonal element taking into account time delay and non-minimum phase zeros; using the LS method to find another PID controller and evaluating a corresponding approximation error; and completing said design method if the corresponding approximation error satisfies the specified approximation threshold.
Claim 27
Dependent Claim
58 words
The controller design method according to claim 19 , wherein the corresponding approximation error does not satisfy the specified approximation threshold, said method further comprising the steps of using LS method for each element of the controller matrix to find the simplest high-order controller by increasing the order of each element gradually until satisfying the specified approximation threshold.
Claim 28
Independent Claim
67 words
A method for high performance conversion between a continuous-time system and a discrete-time system, said method comprising the steps of: specifying an initial weighting function and an initial model; conducting a RLS approximation to give a rational transfer function; updating the weighting function according to the last RLS approximation; and repeating said conducting step and said updating step until a corresponding approximation satisfies a specified approximation threshold.
Claim 29
Independent Claim
67 words
A method for high performance conversion between a continuous-time system and a discrete-time system, said method comprising the steps of: specifying an initial weighting function and an initial model; conducting a RLS approximation to give a rational transfer function; updating the weighting function according to the last RLS approximation; and repeating said conducting step and said updating step until a corresponding approximation satisfies a specified approximation threshold.
Claim 30
Independent Claim
111 words
A method for disturbance compensation for a time-delay process using a disturbance observer, said method comprising the steps of: estimating a process model; determining if a delay free part of the model is of minimum-phase, and factorizing the delay free part of the model into a minimum-phase part and non-minimum-phase part if said delay free part of the model is not in minimum phase; specifying a filter to make an inversed minimum-phase part of the model proper; and approximating a pure predictor by choosing parameters according to a suggested guideline for rejecting general disturbance or specifying the time-delay in the disturbance observer according to a suggested guideline for rejecting periodic disturbance.
Claim 31
Independent Claim
111 words
A method for disturbance compensation for a time-delay process using a disturbance observer, said method comprising the steps of: estimating a process model; determining if a delay free part of the model is of minimum-phase, and factorizing the delay free part of the model into a minimum-phase part and non-minimum-phase part if said delay free part of the model is not in minimum phase; specifying a filter to make an inversed minimum-phase part of the model proper; and approximating a pure predictor by choosing parameters according to a suggested guideline for rejecting general disturbance or specifying the time-delay in the disturbance observer according to a suggested guideline for rejecting periodic disturbance.
Claim 32
Dependent Claim
43 words
A processor-readable article of manufacture having embodied thereon software comprising a plurality of code segments that implements the method of claim 1 , in order to enable an operator to identify, control and manage a continuous time-delay system from a process step response.
Claim 33
Dependent Claim
37 words
A single loop control system for a single variable process, said single loop control system having a system input, a system output, and a controller having the controller parameters generated by the method of claim 13 .
References Cited (Backward Citations)
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