Enhanced fractional-order PI^λD^μ control for a forced circulation evaporator system via advanced disturbance observer

Strong disturbances, time delays, and coupling effects complicate the control of evaporator systems. In this paper, to overcome these difficulties a three-stage controller design is given and as a first step a disturbance observer (DOB) is designed. Then, fractional order PI^λD^μ controllers (PI^λD^μ FOC) with inverted decoupling structure are realized. Finally, PI^λD^μ FOC is enhanced via DOB and applied to control of a considered forced circulation evaporator system. Controlling the evaporator system with the DOB-enhanced PI^λD^μ FOC is showed more accurate and precise control results when compared with the optimally tuned PID and fuzzy logic controller (FLC). The DOB-enhanced PI^λD^μ FOC method has remarkable superiority in disturbance rejection and the proposed control method is improved the tracking ability of the system for reference changes.