MIMO controller for reefer system


Companies / Organizations


South Jutland

Reefer containers are used for transport of goods and other commodities all over the world. Lodam delivers the electronic control system for the Star Cool reefer unit, and the complete Star Cool reefer container is produced by Maersk Container Industry. The refrigeration system in a reefer container operates in harsh environments, mainly at sea. However, sometimes it also operates in areas very far from the coastline. It operates in a very broad temperature range, from loading of fruits in very hot areas, to unloading in very cold areas, where the cargo destination might be. The refrigeration system should be able to keep the specified box temperature at all times. The Star Cool reefer utilizes a frequency inverter controlled two-stage compressor in order to increase both cooling capacity and energy efficiency. 

In order to optimize the energy efficiency of the system, the evaporator should be filled to an appropriate level, corresponding to a so-called superheat of x degrees, because a too low superheat causes damage to the compressor, and a too high superheat leads to lower cooling capacity and thus lower energy efficiency. The superheat is controlled by the evaporator expansion valve, but is influenced by all the surrounding factors, such as compressor speed, fan speed, sub-cooling of the refrigerant etc. Today, the box temperature is controlled by the expansion valve, based on temperature and pressure measurements.

Project description
The projects aim is to develop a multiple-input multiple-output controller, which as a minimum includes control of the compressor speed and the expansion valve in order to optimize the cooling capacity, while preventing damage to the compressor, due to low superheat. A working simulation model of the refrigeration system is readily available in MATLAB, however, small adjustments and tweaks are needed in order to use it for this type of controller design.

Furthermore, test facilities are available at Lodam electronics, and we deem it important that you come to Sønderborg and see our facilities.

Further information
Please contact Kresten K. Sørensen either by e-mail: or by phone: +45 73 42 37 37.

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Technical University of Denmark

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