Improved identification for PID controllers auto-tuning

Every auto-tuning method for PID controllers has two steps: a) identification of the plant and b) tuning of the controller parameters. This paper presents a procedure for plant identification based on two points of its frequency response, namely, the ultimate and the crossover frequency. A novel technique is presented for estimating the ultimate frequency: the Amplitude Dependent Gain (ADG) feedback. This method gives better results than the well-known relay feedback method. The crossover frequency is estimated using a variation of the method proposed by Schei [1], substituting the relay block for the ADG block presented in this paper. Plant identification using two points of its frequency response is better than using only one point, so improved auto-tuning of the controller can be achieved.