Application of model predictive control (MPC)-based forced ramping of process input variables and process output reference trajectory design over a prediction horizon for MPC-based paper machine grade change control

Patent metadata

Field	Value
Publication number	US-10969749-B2
Application number	US-201715683693-A
Country	US
Kind code	B2
Filing date	Aug 22, 2017
Priority date	Aug 22, 2017
Publication date	Apr 6, 2021
Grant date	Apr 6, 2021

Abstract

A controller reference trajectory design technique to enable high-performing automatic grade change performed by a model predictive control (MPC). Techniques include: (1) automatic determination of appropriate process output reference trajectory delays to enable optimum coordination of process input movements; (2) providing the entire planning process output reference trajectory ramp at the start of the grade change instead of just incrementally as the grade change progresses, again enabling movement of the process inputs to drive process outputs along the planned future path instead of just towards the current target; and (3) use of the process input forced ramping to allow linear ramping of process inputs with optimal coordination of other process input movements to keep all process outputs following the desired trajectories. The technical benefits are faster and higher performing grade changes. In addition, the use of this technology allows easier setup and maintenance of the automatic grade change package.

First claim

What is claimed is:

1. A method of model predictive control of a sheet making system, which includes a processing unit, (i) a plurality of actuators that are positioned along a machine direction relative to a moving sheet of material and (ii) sensors for measuring and acquiring property data of the moving sheet of material, that comprises:
assigning a target for one or more manipulated variables (MVs) that control the plurality of actuators;
selecting delays and ramps for the one or more MVs for which targets have been assigned;
assigning a target for one or more controlled variable (CVs);
selecting delayed linear ramp or filtered ramp rates for the one or more CVs;
calculating trajectories for the one or more MVs for which targets have been assigned based on the target and the selected delays and ramps;
calculating trajectories for at least one controlled variable based on the target and on the selected delayed linear ramps or filtered ramp rates;
calculating moves for any MVs that do not have pre-assigned targets by minimizing a cost function that penalizes deviations of the CVs from the calculated trajectories and also penalizes MV movements;
determining a grade change by generating a reference trajectory by allowing a time delay and the creation of a ramp from an initial setpoint to a final setpoint at a pre-selected ramp rate, wherein the generated reference trajectory is represented as:
Y ref( k )= P yref( z −1 ) r ( k ),

where the Pyref(z 1 ) is a (nyxH,)xny matrix of transfer functions that generates the reference trajectory and r(k) is current setpoint;
implementing the grade change using the reference trajectories and the calculated MV moves that minimize the cost function so as to transition from the production of the product having a first grade to the production of a product having a second grade.

2. The method of claim 1 wherein the sheet making system comprises a papermaking system.

3. The method of claim 2 wherein CVs comprise one or more of: a dry weight of the paper sheet, moisture content of the paper sheet, and ash content of the paper sheet and MVs comprise one or more of: wet stock flow, a filler flow, a steam pressure associated with a dryer section in the paper machine, and a machine speed associated with the paper machine.

4. The method of claim 1 wherein a target for one or more of the CVs comprises a recipe for the second grade.

5. The method of claim 1 wherein use of a process input forced ramping allows linear ramping of one or more process inputs with optimal coordination of other process input movements to keep all process outputs following the desired trajectory.

6. The method of claim 1 wherein the processing unit is configured to automatically determine appropriate process output reference trajectory delays to enable optimum coordination of process input movements.

7. The method of claim 1 wherein an entire planning process output reference trajectory ramp is provided at the start of a grade change.

8. The method of claim 7 wherein movement of process inputs drive process outputs along a planned future path and not just towards a current target.

9. The method of claim 7 wherein an output reference trajectory ramp is not provided incrementally as the grade change progresses.

10. A system of controlling the production of a sheet of material in a sheet making machine, which is moving in the machine direction (MD), which system comprises:
a plurality of actuators that is positioned along the MD wherein each of the plurality of actuators is controllable to vary a property of the material;
sensors for measuring and acquiring property data of the sheet of material;
a model predictive controller (MPC) for initiating and monitoring a transition from the production of a first grade of sheet of material to a second grade of sheet of material within a preselected time period, wherein the MPC, in response to signals that are indicative of the properties of the material, provide signals to the plurality of actuators to vary properties of the material, wherein the transition is characterized by time delays and forced ramps; and
a controller that comprises:
a processing unit;
an input for providing one or more controlled variables (CV) to the processing unit from the sheet making machine; and
an output for providing one or more manipulated variables (MV) from the processing unit to the sheet making machine, wherein one or more of the MVs has a pre-specified trajectory; wherein the processing unit is configured to (i) sample one or more of the CVs and to calculate MV movements to minimize a cost function that penalizes deviations of the CVs from their designed trajectories and also penalizes MV movements using the MPC over a time horizon, wherein the MPC uses a quadratic programming (QP) algorithm and for each CV, a primary MV is assigned and a ramp rate is selected for the CV wherein the trajectory for the CV is generated using a primary MV-CV model and the ramp rate; which is a delayed ramp or a filtered ramp, and (ii) implement a move of the one or more MVs and outputting one or more of the MVs to the sheet making machine,
wherein the processing unit is further configured to:
determine a grade change by generating a reference trajectory by allowing a time delay and the creation of a ramp from an initial setpoint to a final setpoint at a pre-selected ramp rate, wherein the generated reference trajectory is represented as:
Y _ref( k )= P _yref( z −1 ) r ( k ),

where the Pyref(z 1 ) is a (nyxH,)xny matrix of transfer functions that generates the reference trajectory and r(k) is current setpoint;
implement the grade-change using the reference trajectories and the calculated MV moves that minimize the cost function so as to transition from the production of the product having a first grade to the production of a product having a second grade.

11. The system of claim 10 wherein the MPC is configured to automatically determine appropriate process output reference trajectory delays to enable optimum coordination of process input movements.

12. The system of claim 10 wherein aqueous fibrous wet stock that is formed on a moving water permeable wire of a de-watering machine that comprises a headbox having a plurality of apertures through which wet stock discharged.

13. The system of claim 10 wherein the actuators engage and shape a continuous sheet of moving material.

14. The system of claim 10 wherein the sheet material comprises a continuous sheet of material that is selected from the group consisting of paper, metal, rubber, plastic and packaging.

15. The system of claim 10 wherein use of a process input forced ramping allows linear ramping of one or more process inputs with optimal coordination of other process input movements to keep all process outputs following the desired trajectory.

16. The system of claim 10 wherein an entire planning process output reference trajectory ramp is provided at the start of a grade change.

17. The system of claim 16 wherein movement of process inputs drive process outputs along a planned future path and not just towards a current target.

18. The system of claim 16 wherein an output reference trajectory ramp is not provided incrementally as a grade change progresses.

Assignees

• Honeywell Ltd

Inventors

• Backstrom Johan
• Choi Joyce
• Nafissi Pezhman
• Forbes Michael

Classifications

• D21G9/00 Primary

  Other accessories for paper-making machines · CPC title

• D21G9/0009

  Paper-making control systems · CPC title

• D21G9/0027

  controlling the forming section · CPC title

• G05B13/042 Primary

  in which a parameter or coefficient is automatically adjusted to optimise the performance · CPC title

• G05B17/02

  electric · CPC title