This paper was published for PCIM-Europe, 1999.

High-performance electric motors and their associated controllers are widely used in motion control applications. Feedback devices are employed to measure position and estimate motor velocity. The control system closes position and velocity loops using these feedback devices. A number of control schemes have been employed in industrial applications including closing a velocity loop within a position loop. Here, the velocity loop is often a Type I (integrating) loop that is enclosed within a proportional position loop. In this case, proportional-integral (PI) compensation is commonly used for the velocity loop. PI control has two advantages: it is simple and it supports rapid motion. However, it also has two shortcomings: it has a tendency to overshoot and it provides low DC stiffness. This paper details a compensation algorithm called PDFF which modifies PI, allowing the user to eliminate overshoot and provide much more DC stiffness than P