High-Gain Observers in Feedback Control: Application to Permanent Magnet Synchronous Motors

High-gain observers play an important role in the design of feedback control for nonlinear systems. This article overviews the essentials of this technique, starting with motivating examples that illustrate the main features of high-gain observers, with emphasis on the peaking phenomenon and the role of control saturation in dealing with it. The observer design for single-output and multi-output systems is presented along with the use of the observer in feedback control. A nonlinear separation principle is discussed, and the use of an extended high-gain observer as a disturbance estimator is covered. The most serious challenge in implementing high-gain observers is the effect of measurement noise, which is covered next. The article ends by presenting an experimental application of the extended high-gain observer to speed control of a permanent magnet synchronous motor (PMSM).