Abstract Unstable processes are hard to stabilize as they contain one or more positive poles which result in unbounded dynamic behavior. The occurrence of the delay and positive zeros often creates more difficulty in controlling such unstable plants. Most control strategies meant for first-order unstable processes fail to stabilize and control the higher-order unstable processes. Hence, a new dual-loop hybrid control structure is suggested for dead-time unbounded second-order processes with positive/negative zeros. Inner-loop has a stabilizing PID controller. The PID controller parameters are derived by comparing the numerator and characteristic polynomial coefficients in the transfer function for internal-loop servo action. A fractional-order internal model controller (FOIMC) is used in the external-loop. Methods for the selection of outer-loop tuning parameter and fractional-order are also discussed. By comparing the simulation results with a contemporary single-loop scheme, the usefulness of the suggested scheme is proved. The suggested scheme is capable of minimizing the overshoot and improving the overall dynamic performance. Finally, the usefulness of the suggested scheme is also demonstrated by a case study on temperature control of a continuous stirred tank reactor (CSTR) during a first-order irrevocable exothermic reaction.

Hybrid dual-loop control method for dead-time second-order unstable inverse response plants with a case study on CSTR

Tuning of proportional integral and derivative (PID) Controllers for stable and unstable second order plus time delay systems (SOPTD), based on Model Driven Two Degree of Freedom PID (MDTDOF PID) and Internal model controller (IMC) are proposed in this paper. Due to inherent disadvantages of conventional control techniques, model based control techniques are employed. MDTDOF PID is developed to control and maintain a constant temperature environment in Thermo Electric Cooler (TEC) and IMC PID controller is designed to control unstable Jacketed Continuous Stirred Tank Reactor (CSTR). The performance of the proposed controllers is compared with the conventional Ziegler-Nichols (Z-N) method. The paper also presents the simulation results for both stable and unstable systems with transfer function models to show the effectiveness and advantages of proposed methods.

Sreedevi Edamana

Papers

Improved parameter tuning methods for second order plus time delay processes