Vapor Compression Control With Disturbance Estimation for Constraints
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Solution Overview
Problem
Vapor compression systems face challenges in efficiently controlling operations due to unmeasurable thermal loads and the need for accurate predictions, leading to suboptimal performance and reactive constraint management, which compromises performance and safety.
Innovation Solution
A model predictive control system with a state estimator that prioritizes output accuracy over state estimate accuracy, allowing for the estimation of thermal load influences without direct measurement, ensuring constraint enforcement and improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If model predictive control is applied to vapor compression systems, then constraint enforcement is guaranteed and performance is optimized, but accurate prediction of thermal load disturbances is required which cannot be achieved
Solution Approach 1:
The patent introduces an intermediary disturbance observer that acts as a mediator between the uncontrollable thermal load disturbances and the model predictive control system. This observer estimates the unmeasured thermal load disturbances and feeds them to the MPC controller, enabling accurate prediction without direct measurement. The intermediary transforms the unsolvable prediction problem into a solvable estimation problem.
Solution Approach 2:
The patent replaces the direct measurement approach (which would require complex and expensive sensors) with an estimation approach using a disturbance observer. This substitution uses mathematical modeling and available measurements to infer the thermal load disturbances, achieving the same goal through a different mechanism that is practical and cost-effective.
2Reliability
If feedback controllers are used to enforce constraints reactively, then system safety is maintained, but performance is sacrificed due to conservative detuning
Solution Approach 1:
The patent applies preliminary action by using the disturbance observer to predict thermal load disturbances before they cause constraint violations. The MPC controller uses these predictions to proactively adjust control inputs, preventing constraint violations before they occur. This eliminates the need for conservative detuning while maintaining safety.
Solution Approach 2:
The patent implements a sophisticated feedback mechanism where the disturbance observer continuously monitors system behavior and estimates disturbances in real-time. These estimates are fed back to the MPC controller, which adjusts control actions accordingly. This closed-loop feedback enables aggressive constraint enforcement while maintaining safety.
Data Source
AI summary
A method for controlling an operation of a vapor compression system (VCS) determines values of measured outputs of the operation of the VCS that include performance and constrained outputs. The method determines states of the VCS using an estimator model of the VCS defining a relationship between the states of the VCS, control inputs and controlled outputs, such that a difference between outputs predicted using the estimator model and the measured outputs asymptotically approaches zero. The states of the VCS include a main state representing the operation of the VCS and an auxiliary state representing the effect of unknown disturbances on each measured output of the VCS. The control inputs for controlling the operation of the VCS are determined using a prediction model, such that the constrained output satisfies the constraints, and a difference between the performance output and the value of the setpoint asymptotically approaches zero.