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QFT technique application on frozen food cold-store temperature control.

Author(s) : ESNOZ A., LÓPEZ GÓMEZ A.

Summary

For several reasons, the frozen foods cold-store optimal temperature could present certain control problems, if the evaporator is flooded overfeed. For example, the normal temperature variation interval could be -19.5 to -22.5 °C (around a set point temperature of -21 °C). This interval is caused by frequent cold-store door openings because of continuous loads of new frozen foods from freezers. The traditional control systems (on-off proportional control, for example) are not efficient in absorbing these temperature perturbations. This excessive temperature variation could be negative to frozen food quality. In this paper, a new control system for these refrigeration system elements is presented and evaluated: the QFT (Quantitative Feedback Theory) based controller. The QFT technique has been used, for example, in aircraft flight control systems and other complex applications, as shown in the Proceedings of the recent 5th International Symposium on Quantitative Feedback Theory and Robust Frequency Domain Methods, held in Pamplona (Spain) in 2001. The QFT technique is a mathematical tool linked to a control system which would absorb these temperature disturbances, avoiding excessive cold-store temperature variations. In conclusion, it has been proven that with this new frozen food cold-store temperature control system, and considering the same working conditions and temperature disturbances actually observed in a frozen food factory, the temperature variation interval obtained is -21 °C plus or minus 0.5 °C. Moreover, the QFT based controller construction is no more complex than a PID controller.

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Details

  • Original title: QFT technique application on frozen food cold-store temperature control.
  • Record ID : 2005-0148
  • Languages: English
  • Source: 21st IIR International Congress of Refrigeration: Serving the Needs of Mankind.
  • Publication date: 2003/08/17

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