PRESSURIZED WATER TEMPERATURE CONTROL OF A FRESNEL COLLECTOR FIELD-TYPE SOLAR COOLING SYSTEM USING EXPLICIT MODEL PREDICTIVE CONTROL Kritchai Witheephanich Department of Electrical Engineering Faculty of Engineering Srinakharinwirot University Ongkharak, Nakhonnayok, Thailand email: kritchai@swu.ac.th Juan Manual Esca˜ no, Antonio J. Gallego, and Eduardo F. Camacho Departamento de Ingenier´ ıa de Sistemas y Autom´ atica Universidad de Sevilla Sevilla, Spain email: {jescano, agallego2, efcamacho}@us.es ABSTRACT This paper addresses the design of an explicit model pre- dictive controller for the outlet water temperature control of a solar cooling plant system that uses a field of Fres- nel collectors. Solving multi-parametric quadratic pro- grams (mpQP) to obtain explicit solutions to constrained model predictive control (MPC) problems enables the off- line design before the MPC controller is implemented, e.g., on a standard programmable logic controller. The simu- lation result shows the feasibility of the proposed control design for such a system. This is implementable on indus- trial application-based hardware platforms where computa- tional and memory resources are limited. KEY WORDS Constrained solar cooling plant; Model predictive control; Piecewise affine controller. 1 Introduction During the last decades solar energy has been experienced a great impulse. The driving factor is the need of reducing the environmental impact caused by the use of fossil fu- els, [1]. The experimental solar trough plant of ACUREX at the PSA of Almer´ ıa has been used as a testbench for advanced control strategies, [2, 3]. In general, the control goal in solar systems is to maintain the outlet temperature of the field at a desired set-point in spite of disturbances. Solar plants are affected by multiple disturbance sources such as solar radiation, inlet temperature, optical efficiency etc. Conventional control strategies cannot cope with the complex dynamics and multiple disturbance sources. Ad- vanced control techniques are needed to obtain a good per- formance in controlling solar systems. One of the application of solar energy is solar cool- ing systems. In recent years there has been substantial growth in the requirements of cooling systems in com- mercial and industrial buildings in order to provide greater comfort when thermal load due to the extensive use of per- sonal computers and the use of lighting is dramatically in- creased, [4]. The coincidence between peak demand and peak production (solar maximum) is a remarkable advan- tage of the solar cooling plants compared to other applica- tions of solar energy. The utilization of solar energy for cooling can be achieved by using solar collectors that pro- duce heat to medium or high temperature and power an ab- sorption machine to supply conditioning air. In low-power solar system, Fresnel solar concentra- tor systems are a new technology intending to make it in direct competition to the parabolic trough type systems. In such systems it is important to keep the inlet tempera- ture to the absorption machine at a specific value. In this work we propose to use a model predictive control (MPC) strategy for controlling the outlet temperature while taking into account the constraints on flow level. We describe an explicit MPC formulation in such a way that an explicit form of the entire control law can be computed off-line by solving a multi-parametric quadratic program (mpQP), [5], thus making the MPC controller implementable by means of evaluating the piecewise linear function within the con- trol unit. The paper is organized as follows. Section 2 is de- voted to the formal description of the dynamic model of the particular Fresnel collector field-type solar cooling system along with the outlet temperature control problem formula- tion. In Section 3, the outlet temperature control by means of the constrained explicit MPC formulation is described. Section 4 presents a simulation result that demonstrates the viability of the proposed control scheme. Finally, conclud- ing remarks and future work are presented. 2 Problem Statement The solar cooling plant described in this section is installed on the rooftop of the School of Engineering (ESI), Univer- sity of Seville. It consists of a Fresnel solar collector field, a double effect absorption chiller, an auxiliary power system, and a phase change materials (PCM) storage tank. Figure 1 shows a scheme of the plant. The solar field, the PCM stor- age tank, and the absorption chiller are briefly described as follows. • Absorption machine: It is a double effect cycle Proceedings of the IASTED International Conference Power and Energy Systems (AsiaPES 2013) April 10 - 12, 2013 Phuket, Thailand DOI: 10.2316/P.2013.800-128 473