Study on the Driving Circuit for Ultrasonic Motor Using LLCC Resonant Technique

High driven voltage is required for ultrasonic motor, so the driving circuit needs transformer to boost voltage. Since the USM is a nonlinear capacitive load, a matching circuit is needed to keep the output voltage and the phase shift constant. For the switching circuit with push-pull topology, the switching loss is less under inductive load rather than capacitive load, which will increase its efficiency and reliability. A novel LLCC resonant network was proposed and its parameters were given. Theoretical analysis and simulation were presented, which demonstrated that the output voltage and phase shift of the resonant network was independent of driving conditions, such as driving frequency and load, and the load characteristics can be changed from capacitive to inductive. This novel driver is applied to the TRUM-60 type ultrasonic motor, and the experimental results are presented to verify the effectiveness of the proposed circuit.