Disturbance observer control for AC speed servo with improved noise attenuation

Abstract

The paper deals with a noise attenuation design of a modification of the disturbance observer (DO) based PI control for an AC servo drive with the dominant first-order dynamics. The achieved results are compared with the traditional PI control. The DO based filtered PI (DO-FPI) controller consists of the P control with adjustable filter. It is augmented with an integral action based on load reconstruction using equally filtered plant dynamics inversion. The availability of broadly scalable filters requires a simple one-parameter based tuning. In looking for a possibly good noise attenuation, it allows changing the filter order and time constants by keeping nearly the same speed of disturbance responses as in the PI control. An application to the speed servo control with an incremental position sensor brings to light interesting properties of the compared solutions. The DO FPI and PI control give nearly equally robust solutions. However, in case of PI control it is at the expense of significantly increased torque ripple.