Collaborative PI Controller For Digital Speed Servomechanism

In order to secure satisfactory performance of modern digital servomechanisms, it is essential to design an appropriate control system. Use of simple and interpretable controllers such as PI controller is motivated by many practical applications. These controllers, when tuned properly, can provide good performance and certain level of robustness against modelling errors and external disturbances. However, when the magnitude of uncertainties in the system cannot be neglected, it is desirable to introduce some sort of adaptability. Adaptive controllers tend to adjust controller’s parameters using some optimization criteria. But, in some cases, mechanism of adaptation can cause overfitting the parameters, leading to poor control quality. To overcome these problems, in this paper we propose collaborative controller that combines two PI controllers – one with fixed and one with adaptive parameters. Combination of the two controllers is done in convex fashion, with mixing factor being adapted in real-time by gradient descent procedure. Brief discussion on stability properties is given. Also, results of computer simulations that justify use of such a control system is provided.