Cascaded control scheme for speed variable ultrasonic drives

A novel control scheme for the most advanced traveling wave ultrasonic motor fed by a resonant power converter is presented and verified by measurements on a prototype drive. Based on a detailed simulation model, the drive's characteristics are investigated. Using this model, pull-out phenomenon can be avoided by means of a tailored control unit. Thus, the motor's performance is improved by utilizing the hysteresis bandwidth. As the simulated speed-torque curves are verified by measurements, a general control scheme for traveling wave ultrasonic drives is suggested. Equipped with a flexible test set-up, the realized cascaded drive control is outlined. The proposed control scheme is predestined for speed variable ultrasonic drives ensuring optimal torque utilization and minimized losses under consideration of the inherent amplitude threshold for torque generation.