Robust design and operation of MSF water desalination process using loop-shaping control procedure

摘要

This paper presents a two-degree-of-freedom (2-DOF) robust (H-infinity) loop-shaping algorithm to control and stabilize a multi-stage flash (MSF) desalination plant under parametric uncertainties, external disturbances and measurement noises. In this paradigm, the general uncertainty model represented by coprime factor uncertainty (CFU) description is able to cover both unmodeled dynamics and physical parameter variations at all frequencies. By using 2-DOF H-infinity loop-shaping technique, the designers can shape the frequency response of the original model into the desired shape which satisfies both transient response and robustness against various uncertainties. Top brine temperature and recycle brine flow rate have been chosen to stand for MSF plant performance. The simulation results demonstrate that the achieved controller has high stability margin, excellent abilities of disturbances and noises attenuations. In fact, it can deal with approximately 60% of parameter variations, reject at least 84% of exogenous disturbances, and 80% of sensor noises. Note that most currently used controllers reported cannot cope with those high levels of plant uncertainties and disturbances. Thus, it is necessary to implement the advanced control schemes for effectively controlling MSF plants, ensuring high water quality and optimizing water monitoring system. Finally, this robust control method with reduced-order can help prevent machine faults, stabilize MSF plants, optimize energy usage, and lower water production costs, with overcoming various limitations of some conventional controllers.