A method for closed loop automatic tuning of PID controllers

Abstract

A simple method for the automatic tuning of PID controllers in closed loop is proposed. A limit cycle is generated through a nonlinear feedback path from the process output to the controller reference signal. The frequency of this oscillation is above the crossover frequency and below the critical frequency of the loop transfer function. The amplitude and frequency of the oscillation are estimated and the control parameters are adjusted iteratively such that the closed loop transfer function from the controller reference to the process output attains a specified amplitude at the oscillation frequency.

Keywords

• Adaptive control
• closed-loop systems
• describing functions
• identification
• industrial control
• limit cycles
• Nyquist criterion
• PID control