Fractional order automatic tuning of [formula omitted] controller for stable processes

Abstract

This paper presents modified fractional order relay based automatic tuning of PIλD controller for stable processes with load disturbance. The modified relay comprises of PIλcontroller introduced with the ideal relay in series. The proportional gain of PIλ controller is assumed as unity and the integral time constant is chosen such that, the system attains minimum 0° phase margin. λ of PIλ 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 PIλD controller is based on the measured parameters from modified relay. Subsequently, the derivative time constant is derived in the design of PIλD controller using phase margin criteria and Nyquist curve is used to obtain the proportional gain. The integral time constant for PIλD controller is same as that of PIλ controller for auto tuning test. The auto tuning method and PIλD controller design, thus proposed, is validated using typical examples through simulation.