Model reference adaptive control of a direct-drive DC motor

An adaptive time-optimal position controller for a direct-drive DC motor with a design based on the model reference adaptive approach is presented. The high-acceleration torque of DC motors with permanent magnets permits direct coupling of the load to the motor axis, avoiding the use of a transmission with its inherent disadvantages (such as backlash and friction). However, direct coupling induces a large sensitivity to load variations, so the desired response and the reference model in the adaptive controller are adjusted to the motor capabilities. This is achieved by estimating the load inertia by means of a least-squares method and adjusting the reference model accordingly. The controller is tested on a direct-drive motor, and the results are compared with those obtained with a fixed proportional-integral-derivative controller.<>