A new method for closed-loop identification based on enforced oscillations

In this paper, a new method for the closed-loop identification is proposed. The method is a generalization of the Ziegler-Nichols's method, although it does not require to enforce a system to the boundary of the stability. The application of the method does not require any additional equipment which is not already included in a control loop. The plant may even be unstable, and the order of the plant need not to be known in advance. This paper shows the application of the method to obtain points on the Nyquist curve of an unknown plant, and for the parametric identification of a plant with a known transport delay.