Ultrasonic Driving Power Based on Resonance Frequency Tracking Method with Variable Step Size

In the ultrasonic driving power system for ultrasonic cleaning, the natural resonance frequency will drift as the depth in water variation of the piezoelectric transducer. Then, the efficiency of the power supply will decrease because of the detuning state. To solve this detuning problem, a resonance frequency tracking method with variable step size is adopted in this paper. By measuring the output current from full bridge inverter and DC source, and adjusting the output frequency of the power supply with variable step size, the current ratio between them is minimized, which makes the power return to resonant state and improves its efficiency. Finally, the series resonant frequency tracking experiments are carried out against different depths in water of piezoelectric transducer by a prototype setup. The test results show that the power can track the series resonant frequency effectively with different depths in water by the proposed method. Moreover, the efficiency of the overall power increases up to 14.06%.