Fractional order automatic tuning of PIλD controller for stable processes

This paper presents modified fractional order relay based automatic tuning of (PID)-D-lambda controller for stable processes with load disturbance. The modified relay comprises of PlX controller introduced with the ideal relay in series. The proportional gain of PI lambda controller is assumed as unity and the integral time constant is chosen such that, the system attains minimum 0 degrees phase margin. A of PI lambda controller helps in reducing the harmonics in the output which ultimately leads to improvement in the accuracy of the proposed scheme. The limit cycle, thus, obtained helps in extracting the critical frequency and peak amplitude which helps in controller design. The designing of (PID)-D-lambda controller is based on the measured parameters from modified relay. Subsequently, the derivative time constant is derived in the design of (PID)-D-lambda controller using phase margin criteria and Nyquist curve is used to obtain the proportional gain. The integral time constant for (PID)-D-lambda controller is same as that of PI lambda controller for auto tuning test. The auto tuning method and (PID)-D-lambda controller design, thus proposed, is validated using typical examples through simulation. (C) 2019 ISA. Published by Elsevier Ltd. All rights reserved.