(756g) Receding Horizon Optimal Operation and Control of a Solar-Thermal District Heating System

Dynamic simulation results for a solar-thermal district heating system are presented in this work. The over all system includes parabolic trough solar collector (PTC) system, thermal energy storage system and a district heating loop system. Many advanced control techniques have been developed to maintain the outlet temperature of the parabolic solar collector with the energy provided by solar irradiation and inlet oil temperature [1], [2]. These techniques are generally focused on regulating the solar collector outlet temperature by adjusting the heat transfer fluid (HTF) flow rate (the manipulated variable) through the collector field. While including a two-tank-direct thermal storage system in the overall system, additional manipulated variables are created: the flow rate from the transfer heat exchanger to the storage tank and the flow rate from the storage tank to the load heat exchanger or boiler. Therefore, while the collector field outlet temperature or fluid flow rate are fixed and controlled, the power stored and delivered to the load can be controlled independently, making it possible to maximize the energy storage, to sustain constant power output during bad weather or to shift power output to better meet variable consumer demand [3].

In the present work, mathematic modelling and optimal operation strategies for the hear transfer fluid flow rate through the collector filed and the flow rates entering the transfer heat exchanger and the load heat exchanger are investigated and developed for the overall solar-thermal district heating system such that the collected power by the collector can be maximized within a certain period and the heating demand can be satisfied. In particular, since long time horizon leads to long time calculation and inaccurate optimization solutions, in the present work, receding horizon control strategy is proposed. Moreover, in the heating season, when the stored solar-thermal energy is not able to meet the load demand, a feedforward controller is designed to adjust the heat influx from the boiler to address this problem.

[1] Johansen, Tor A., and Camilla Storaa. ``Energy-based control of a distributed solar collector field." Automatica 38.7 (2002): 1191-1199.

[2] Silva, R. N., et al. ``Cascade control of a distributed collector solar field." Journal of Process control 7.2 (1997): 111-117.

[3] Powell, Kody M., and Thomas F. Edgar. ``Modeling and control of a solar thermal power plant with thermal energy storage." Chemical Engineering Science 71 (2012): 138-145.