A Variable Frequency Ultrasonic Power Supply With Adjustable Impedance Matching

With the development of industrial automation,ultrasonic technology has been widely used in the fields of welding,cleaning,cutting and medical.As one of the key technologies of ultrasonic technology,the development of ultrasonic power supply has changed greatly with the development of power electronics technology and digital control technology.However,most of the ultrasonic power supply on the market is a special one,it means that one ultrasonic power supply can only be matched with a fixed transducer,which means the ultrasonic power supply exists the problems of wide-band phase locking and automatic tracking.In this paper,we design a wide-band ultrasonic power supply based on the point of frequency tracking and impedance matching,which can realize the dynamic impedance matching within wide-band frequency by the way of frequency tracking,and also design the prototype system on ZYNQ platform.The main contents of this paper are as follows:(1)The impedance matching and frequency searching method are confirmed after the analysis of transducer's characteristics: using frequency tracking method to achieve dynamic impedance matching and using variable step strategy to achieve fast and accurate frequency seeking.(2)The main circuit of ultrasonic power supply is divided into several sub-modules for principle analysis and hardware circuit design.The Buck chopper circuit exports variable DC voltage to achieve the purpose of power adjustment;The inverter circuit with full-bridge topology converts the DC voltage into AC signal with variable frequency;The matching network circuit is designed to match the inverter circuit and transducer;The voltage signal and current signal are sent to the control system after the processing of feedback system,which are also the basis for the frequency seeking frequency tracking.In addition,a drive circuit for the inverter circuit is designed to ensure the inverter circuit system's safety and reliability.(3)The overall control system is designed on the ZYNQ platform according the design index,including the hardware circuit design of frequency seeking module,frequency tracking module and power adjustment module,the drive signal for Buck chopper and full-bridge inverter circuit.(4)The prototype with hardware circuit test and software program debugging is designed on the basis of theoretical analysis,and during the test,the hardware and software parameters are modified after the theoretical analysis to solve the problem in order to meet the design requirements.The experimental results show that the wide-band ultrasonic power supply designed in this paper can automatically seek the resonance frequency in the frequency band,and it can also meets the transducer's frequency drift by the way of indirectly changes the impedance matching with frequency tracking and locking the overall system in the resonant state.