Abstract: Aiming at the problems that the working efficiency of ultrasonic motor is too low，which limits the

working endurance of the system and affects the resonant and dynamic characteristics of the motor，a speed and

efficiency optimization bivariate control method under dynamic conditions was designed. First，the two control

variables of the motor were determined by analyzing the working characteristics of the motor drive circuit. Second，

the efficiency feedback method based on the effective value of the drive voltage was theoretically proved. And then

according to the voltage-efficiency-frequency characteristics of the motor，the maximum efficiency point tracking

（MEPT）algorithm was designed，and the frequency update step was calculated by the polynomial surface fitting

based least squares method. Finally，the proposed control method was verified and compared with the existing

efficiency optimization algorithm by simulation. The results show that this method can effectively improve the

efficiency of the motor and ensure the stability of the efficiency optimization algorithm under dynamic conditions.

      Key words: ultrasonic motor；bivariate control；efficiency optimization control；least squares method（LSM）；surface fitting