Process Optimization Using Slack Variables and Simulation

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Solution Overview

Problem

Existing process control systems face challenges in optimizing industrial processes due to limitations in model predictive control (MPC) implementations, particularly when dealing with multiple input/multiple output control strategies, as they often fail to provide solutions outside predefined ranges and limits, and lack flexibility in handling constraints effectively.

Innovation Solution

A system and method that utilizes simulated process outputs from concurrent simulation to develop target values for optimization, incorporating slack variables to extend the search range beyond primary constraint variables, allowing for optimal solutions within any process condition, and employing multi-objective linear programming optimization techniques.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If model predictive control (MPC) is used for optimization, then control performance is improved, but the system fails to provide solutions outside predefined ranges and limits

Engineering Contradiction:
Improvecontrol performanceVSAvoidsolution flexibility
Core Design Contradiction:
ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent transforms the static optimization problem into a dynamic one by introducing a moving horizon approach. The optimizer continuously updates the search range based on current process conditions and measured inputs, allowing the solution space to adapt dynamically rather than being constrained by fixed predefined ranges. This enables the system to provide solutions outside traditional limits while maintaining control performance.

Inventive Principle:
Principle #15Dynamics

Solution Approach 2:

The patent changes the parameters of the optimization problem by incorporating slack variables that modify the constraint boundaries. These slack variables allow the optimizer to temporarily violate predefined ranges and limits when beneficial, then correct deviations. This parameter transformation enables flexible adaptation while preserving the core control objectives.

Inventive Principle:
Principle #35Parameter changes

2Device complexity

If conventional optimization methods are used, then computational simplicity is maintained, but flexibility in handling constraints is insufficient

Engineering Contradiction:
Improvecomputational simplicityVSAvoidconstraint handling flexibility
Core Design Contradiction:
Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent introduces slack variables as intermediary elements between the optimizer and the process constraints. These slack variables act as buffers that absorb constraint violations, allowing the optimizer to explore a broader solution space without directly violating hard constraints. This intermediary mechanism provides flexibility in handling constraints while maintaining computational tractability through standard optimization algorithms.

Inventive Principle:
Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent extends the optimization problem into an additional dimension by incorporating slack variables that represent constraint violation margins. This dimensional extension transforms the problem from a constrained optimization in n-dimensions to an unconstrained (or softly constrained) optimization in n+1 dimensions, providing greater flexibility while maintaining computational simplicity through established mathematical programming techniques.

Inventive Principle:
Principle #17Another dimension (Dimensionality change)

3Reliability

If predefined ranges and limits are strictly enforced, then safety and operational constraints are satisfied, but optimal solutions may be missed

Engineering Contradiction:
Improveconstraint satisfactionVSAvoidoptimization performance
Core Design Contradiction:
ReliabilityVSProductivity

Solution Approach 1:

The patent applies beforehand cushioning by introducing slack variables that anticipate and buffer constraint violations before they occur. These slack variables create a cushioning layer between the optimizer and hard constraints, allowing the system to explore solutions that temporarily exceed predefined ranges while ensuring that actual process constraints are never violated. This approach prevents suboptimal solutions caused by overly restrictive constraint enforcement.

Inventive Principle:
Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The patent employs partial or excessive action by allowing the optimizer to temporarily exceed predefined ranges and limits through slack variables. Rather than strictly enforcing constraints at all times, the system permits controlled excesses when beneficial for optimization, then corrects deviations. This partial relaxation of constraints enables discovery of superior solutions while maintaining overall constraint satisfaction through feedback control.

Inventive Principle:
Principle #16Partial or excessive action

Data Source

PatentUS8055358B2Multi-objective predictive process optimization with concurrent process simulation
Publication Date: 2011.11.08 FISHER ROSEMOUNT SYST INC
  • US8055358B2 patent drawing
  • US8055358B2 patent drawing
  • US8055358B2 patent drawing

AI summary

A system and method for controlling a process includes simulating the process and producing a simulated output of the process, developing a set of target values based on measured inputs from the process and based on the simulated output from the process simulator, and producing multiple control outputs configured to control the process based on the set of target values during each operational cycle of the process control system. The simulated outputs include one or more predicted future values up to the steady state of the process.