Self-tunable approximated explicit MPC: Heat exchanger implementation and analysis

TL;DR

This paper introduces a self-tunable explicit MPC that autonomously adjusts control parameters based on operating conditions, demonstrated on a heat exchanger to enhance control performance without manual retuning.

Contribution

A novel self-tunable explicit MPC method that adapts control parameters automatically during operation, suitable for nonlinear systems like heat exchangers.

Findings

Improved control accuracy and reduced overshoot.

Enhanced adaptability to changing conditions.

Decreased control error and settling time.

Abstract

The tunable approximated explicit model predictive control (MPC) comes with the benefits of real-time tunability without the necessity of solving the optimization problem online. This paper provides a novel self-tunable control policy that does not require any interventions of the control engineer during operation in order to retune the controller subject to the changed working conditions. Based on the current operating conditions, the autonomous tuning parameter scales the control input using linear interpolation between the boundary optimal control actions. The adjustment of the tuning parameter depends on the current reference value, which makes this strategy suitable for reference tracking problems. Furthermore, a novel technique for scaling the tuning parameter is proposed. This extension provides to exploit different ranges of the tuning parameter assigned to specified operating conditions. The self-tunable explicit MPC was implemented on a laboratory heat exchanger with nonlinear and asymmetric behavior. The asymmetric behavior of the plant was compensated by tuning the controller's aggressiveness, as the negative or positive sign of reference change was considered in the tuning procedure. The designed self-tunable controller improved control performance by decreasing sum-of-squared control error, maximal overshoots/ undershoots, and settling time compared to the conventional control strategy based on a single (non-tunable) controller.