Handling ramp inputs and nonlinearity in unstable systems with fractional order modified Smith predictor control

Regulating the output of unstable process is a great challenge particularly in the presence of process parameters uncertainties, nonlinearity, transportation delays and load disturbances. These processes are even more sensitive to input changes of ramp types. In this communication, a fractional order Smith predictor scheme is analytically designed to handle the unstable process undergoing above mentioned unavoidable conditions. The suitable values of the design parameters β, α and λ are determined by exploring the stability region and investigating system robustness towards process model uncertainties. The suggested control is also well implemented on a nonlinear jacketed continuous stirred tank reactor and the performance enhancement of 71.5 % is achieved under the perfectly matched condition. When the process parameters are perturbed, 73.9 % percentage improvement is observed. Performance indices such as Integral of Squared Error (ISE), Integral of Time-weighted Absolute Error (ITAE), Integral of Absolute Error (IAE), and Total Variation (TV) are also calculated.