Controller design for periodic disturbance rejection

Abstract

In this thesis, a comparative study for time-delayed unstable process control is conducted and two new controller design methods for periodic disturbance attenuation are presented. In the comparative study for seven existing control schemes, a conspectus of their control effects is provided in terms of different performance specifications. Additionally, nonlinear PID control strategy and linear time-variant control components are investigated to enhance performance of the existing methods. As measurable periodic disturbance is concerned, the modified virtual feedforward control (VFC) is presented for disturbance rejection to facilitate its application in non-minimum phase processes and simplify the overall controller structure compared with the original VFC scheme. Another method, the modified Smith predictor control, is proposed to reject unmeasurable disturbances in a feedback way, as long as the frequency of the periodic disturbance can be detected. This scheme, giving impressive setpoint responses, can be used for both stable and unstable time-delayed processes.