A simple method of tuning parallel cascade controllers for unstable FOPTD systems

Area of Science:

• Control Engineering
• Process Control
• Automation Systems

Background:

• Designing controllers for open-loop unstable processes is challenging.
• Parallel cascade control configurations are effective but complex to design.
• Existing methods for P/PI controller design have limitations in performance and robustness.

Purpose of the Study:

• To propose a simple and effective method for designing parallel cascade controllers for open-loop unstable processes.
• To evaluate the performance and robustness of the proposed P/PI control configuration.
• To compare the proposed method with existing controller design techniques.

Main Methods:

• A proportional (P) controller for the secondary loop and a proportional integral (PI) controller for the primary loop (P/PI control configuration).
• Matching coefficients of the Laplace variable (s) in the numerator and denominator of the closed-loop transfer function for servo problems.
• Simulation case studies involving stable/unstable primary and secondary processes, and a nonlinear bioreactor model.

Main Results:

• The proposed P/PI control configuration method demonstrates superior performance compared to improved simultaneous relay autotuning, synthesis, and ISE criterion methods.
• Robust stability analysis using the complementary sensitivity function confirms the enhanced robustness of the proposed method.
• The method effectively handles both stable and unstable processes, including complex nonlinear systems.

Conclusions:

• The proposed simple method for designing parallel cascade controllers (P/PI configuration) is effective for open-loop unstable processes.
• The P/PI control configuration offers improved performance and robust stability.
• This method provides a valuable alternative for industrial process control applications.