US 5,394,322 AGranted

Self-tuning controller that extracts process model characteristics

AssigneeThe Foxboro Company

InventorPeter D. Hansen

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Abstract

An apparatus and method for process control that extracts information from a process for developing a model of the process that is used to design system control. The apparatus includes means for selecting a process model form that has two or more selectable parameters. The apparatus also includes means for deliberately disturbing a process that is in open-loop operation and that is in a substantially settled state and further includes means for measuring the process response. The apparatus selects parameters for the process model form according to a function of the measured process response. In this way a complete model of the process is identified. The apparatus self-tunes by directly calculating new control parameters according to a function of the identified open-loop process model and a preselected target behavior.

Claims24

Dependent claims

Process control apparatus for attaining a selected closed-loop response of a control system, said apparatus comprising

an outer-control loop having
monitoring means, coupled to a controlled variable signal representative of a first characteristic of a process having an open-loop response, and to an operation control signal representative of a preselected value for said first characteristic of said process, said monitoring means for generating a difference signal representative of the difference between a signal characteristic of said controlled variable signal and said operation control signal, and
an outer-control element coupled to said monitoring means and having means for storing at least one control parameter being representative of a control parameter of said process control apparatus, and having means for generating an outer control signal as a function of said control parameter and of said difference signal, for manipulating said first characteristic of said process toward said preselected value,
an inner-control loop having
an inner-control element coupled to said controlled variable signal and having means for storing one or more control parameters representative of control parameters of said process control apparatus and having means for generating an inner control signal as a function of a said control parameter and of said controlled variable signal, for manipulating said first characteristic of said process toward said preselected value, and
summation means, coupled to said outer-control element and to said inner control element, for summing said inner-control signal and said outer-control signal to generate a manipulated variable signal for manipulating said first characteristic of said process toward said preselected value, and
automatic tuning means for modifying said control parameters, said tuning means having means for storing at least one preselected closed-loop transfer function of said outer-control loop, and having means for storing at least one preselected closed-loop transfer function for said inner-control loop, and having means for storing at least one process model representative of a said open-loop process response, and having means for generating said control parameters as a function of said process model, and said preselected transfer functions, for tuning said inner-control loop and said outer-control to achieve substantially said selected closed-loop response.

4 more elements

Process control apparatus for attaining a selected closed-loop response of a control system, said apparatus comprising

process control means having means for monitoring a controlled variable signal being representative of a first characteristic of a process having an open-loop response,
means for monitoring an operation control signal of said control system, said operation control signal being representative of a preselected value for said first characteristic of said process,
means for storing at least one parameter, said parameter being representative of a control parameter of said control system,
means for generating a manipulated variable signal as a function of at least said one control parameter, of said controlled variable signal and of said operation control signal, for manipulating said first characteristic toward said preselected value, and,
automatic tuning means for generating one or more control parameters, said tuning means includes
identification means for identifying a process model being representative of the open-loop process response, said process model having at least one variable parameter, said identification means having means for storing at least one process model, having means for selecting one of said stored process models and having means for selecting said at least one model parameter,
means for determining at least one weighting coefficient of a corresponding frequency component of said open-loop process response, said at least one weighting coefficient being determined according to a known function of said at least one model parameter,
means for storing at least one preselected closed loop system response, and,
means for generating said one or more control parameters as a function of said weighting coefficients, wherein said function is determined by a selected one of said stored system responses.

6 more elements

Process control apparatus for attaining a selected closed-loop response of a control system, said apparatus comprising

process control means for monitoring a controlled variable signal representative of a first characteristic of a process having an open-loop response,
means for monitoring an operation control signal of said control system, said operation control signal representative of a preselected value for said first characteristic of said process,
means for storing at least one control parameter representative of a control parameter of said process control apparatus,
means for generating a manipulated variable signal as a function of said control parameter, of said controlled variable signal and of said operation control signal, for manipulating said first characteristic toward said preselected value,
identification means for identifying a process model having at least one variable process parameter and being representative of said open-loop process response, including means for storing a first characteristic and a second characteristic of said process model, said first and said second characteristics being representative of a process type and being determined according to a ratio of said control parameters,
measurement means for measuring amplitude values of said controlled variable signal to characterize at least two pattern features representative of a first characteristic of the closed loop system,
means for generating said variable process parameters of said process model according to a known function of said first and said second process type characteristics and said first characteristic of said closed-loop system,
means for determining at least one weighting coefficient of a corresponding frequency component of said open-loop process response, said weighting coefficient being determined according to a known function of said model parameter,
means for storing at least one preselected closed loop system response, and,
automatic tuning means for generating said control parameters as a function of said weighting coefficients, wherein said function is determined according to a selected one of said stored closed loop system responses.

7 more elements

Dependencies are inferred from the claim text.