Efficiency optimization of rotary ultrasonic motors using extremum seeking control with current feedback

摘要

Despite their great features, ultrasonic motors' (USM) driving schemes still suffer from suboptimum driving efficiencies and limited operating range. The driving efficiency and operation range are mainly functions of the vibration amplitude and the preload. Vibration amplitude is generally controlled by means of adjusting the driving frequency. Unfortunately, there exists a narrow frequency band where efficiency is maximized resulting in a limited output power range. Due to temperature rise, this frequency is continuously shifting which necessitates dynamic tracking of the optimum state. Fortunately, maximum driving efficiency was experimentally confirmed to have good correspondence with minimum current. Current feedback was thus utilized within an Extremum Seeking Control (ESC) loop to track maximum efficiency. Besides driving frequency control, voltage amplitude and preload can be controlled to realize the desired output power while maintaining maximum efficiency. Using ESC technique, the maximum efficiency was successfully located and tracked under different voltage amplitudes and preloads. The output power under optimum condition was found to have a wider control range with preload control than with voltage amplitude control. (C) 2019 Elsevier B.V. All rights reserved.