Model Based Control of Refrigeration Containers

Kresten Kjær Sørensen

Lodam electronics a/s and

Aalborg University

Lodam electronics a/s · Kærvej 77 ·  DK-6400 Sønderborg · Tlf. +45 73 42 37 37 · Fax +45 73 42 37 30 · www.lodam.com

Outline• Developmental, commercial and scientific

objectives

• System overview

• Project status

• Issues that should be addressed

• Research

Lodam electronics a/s · Kærvej 77 ·  DK-6400 Sønderborg · Tlf. +45 73 42 37 37 · Fax +45 73 42 37 30 · www.lodam.com

Developmental Objectives

“A set of methods that enable optimal, adaptive, constrained control of a refrigeration container that is also applicable to other thermodynamical systems”

Lodam electronics a/s · Kærvej 77 ·  DK-6400 Sønderborg · Tlf. +45 73 42 37 37 · Fax +45 73 42 37 30 · www.lodam.com

Commercial Objectives

• Better competitiveness through:– Reduced energy consumption– Reduced mechanical wear and tear – Improved adaptiveness of the controller

Lodam electronics a/s · Kærvej 77 ·  DK-6400 Sønderborg · Tlf. +45 73 42 37 37 · Fax +45 73 42 37 30 · www.lodam.com

Scientific Objectives

• To use MPC for refrigeration by:– Finding a suitable method for modeling

nonlinear dynamics of the refrigeration system that may be used by an MPC.

– Finding a method to cope with changes in system dynamics in the event of failure.

Lodam electronics a/s · Kærvej 77 ·  DK-6400 Sønderborg · Tlf. +45 73 42 37 37 · Fax +45 73 42 37 30 · www.lodam.com

System overview

• Known refrigeration system dynamics

• Unknown cargo dynamics

• Known constraints on cargo temperature

• Economizer gives an additional degree of freedom

Lodam electronics a/s · Kærvej 77 ·  DK-6400 Sønderborg · Tlf. +45 73 42 37 37 · Fax +45 73 42 37 30 · www.lodam.com

Log(p)-h Diagram

Lodam electronics a/s · Kærvej 77 ·  DK-6400 Sønderborg · Tlf. +45 73 42 37 37 · Fax +45 73 42 37 30 · www.lodam.com

Project Status

• A library of nonlinear refrigeration component models has been developed.

• A composite simulation model has been developed.

• A framework that allows to test a controller, working within Matlab, with real hardware is ready.

Lodam electronics a/s · Kærvej 77 ·  DK-6400 Sønderborg · Tlf. +45 73 42 37 37 · Fax +45 73 42 37 30 · www.lodam.com

Simulation Model 1/2

• Nonlinear simulation model of the refrigeration system.

• Composed of smaller component models from a library.

• Simulation is done in Matlab by a set of custom functions.

Lodam electronics a/s · Kærvej 77 ·  DK-6400 Sønderborg · Tlf. +45 73 42 37 37 · Fax +45 73 42 37 30 · www.lodam.com

Simulation Model 2/2

Simulation Model.xml

Component1.xmlComponent1.m

Component4.xmlComponent4.m

Component2.xmlComponent2.m

Component3.xmlComponent3.m

• The simulation model is described by a number of files

• Each component are simulated separately for a short time step

• All outputs at the end of the simulation is propagated to the relevant inputs

• Simulation run again for another time step

• Equivalent of simulating a large, combined function with ZOH’s inserted between components

Lodam electronics a/s · Kærvej 77 ·  DK-6400 Sønderborg · Tlf. +45 73 42 37 37 · Fax +45 73 42 37 30 · www.lodam.com

Issues that must be addressed• The system is nonlinear and has a large

area of operation for both hot and cold temperatures.

• There are discrete actuators with strong influence on the dynamics that cannot be neglected.

• In case of partial system malfunction it is very important to continue cooling.

Lodam electronics a/s · Kærvej 77 ·  DK-6400 Sønderborg · Tlf. +45 73 42 37 37 · Fax +45 73 42 37 30 · www.lodam.com

Research

• Adaptive MPC for increased robustness in the event of failure.

• Auto-generation of a model usable with MPC, based on the simulation model.