The application of state observers in current regulated PM synchronous drives

The application of state observer structures in digital current controllers for permanent magnet synchronous motors (PMSM) is considered. A predictive observer algorithm is developed to overcome the intrinsic sampling delay of the digital controller. The resultant control structure is shown to have larger stability margins, higher closed loop bandwidth, superior dynamic performance and better disturbance rejection capabilities than the more conventional controller. Practical results from a prototype controller are presented which illustrate these effects and quantify the possible improvements in system capability. The paper also considers the effects of parameter variations on the performance of the observer-based controller and suggests means by which such effects may be minimised