A repetitive control scheme for distributed solar collector field

Abstract

The control of the output fluid temperature in a distributed solar collector field implies accounting for the excitement of its intrinsic resonance modes. Resonance mode frequencies are related to the residence time of the fluid which flows through the distributed solar collector. At the same time, this physical variable is related to the fluid velocity which is, in this kind of system, the control variable. Thus, the frequencies of the resonance modes continuously change when controlling the output temperature. The addition of a repetitive compensation controller into the control system has proved to be beneficial in terms of performance and resonance capabilities. However, this kind of controller usually works with a fixed frequency, which prevents the total cancellation of the system resonance dynamics. This article proposes an alternative structure of the repetitive controller which also works with a fixed frequency, but is tuned taking into account the uncertainty in the resonance mode frequencies in order to achieve fast, well-damped system responses.

Keywords:

• repetitive control
• resonance
• distributed collector solar field

Acknowledgements

The authors wish to thank the Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), and the Spanish Ministry of Education for providing CICYT-FEDER funds (projects DPI2007-66718-C04-04 and DPI2007-62582). The authors also wish to express their gratitude to Mr Agustín Pérez for operating the ACUREX plant.