The Research On The Algorithm Of Automatic Tracking Resonant Frequency For Ultrasonic Transducer

The ultrasonic transducer matching impedance and automatic tracking resonantfrequency are two key problems of the ultrasonic transducer. The transducer itself hasan inherent resonant frequency, and it owns high stable and efficient quality onlyapplying with the inherent resonant frequency. Thus the resonant frequency of theultrasonic transducer is a vital parameter. However the resonant frequency of ultrasonictransducer will be shifted by the change of temperature, environment, aging ofcomponents and other factors. The resonant frequency shift will lead to reduce theefficiency of the ultrasonic transducer. It is very necessary to seek one way of automatictracking the resonant frequency. It has important practical significance that theultrasonic transducer runs with the highly efficient and stable quality.Tracking technology is based on hardware and software development. The PIcontrol has been widely used in industrial closed-loop system, but rarely be found in theautomatic resonant frequency application. The common working frequency of ultrasonictransducer ranges from15kHz to30kHz, which brings more complex degree for thedesign of control and sample circuit. With the development of DSP, FPGA, and otherhigh-performance chip, digital and intelligent control for the ultrasonic transducer hasbecome a reality. It laid the foundation for the digital control system for automatictracking resonant frequency of ultrasonic transducer based on the PI strategy proposedin this paper.The impedance characteristics of ultrasonic transducer were analyzed according tothe equivalent circuit of transducer. How the matching network with different patternsand parameter conditions affects the mechanical-electrical coupling coefficient wasdiscussed by utilizing the Matlab simulation platform. A reasonable matching networkand parameter setting were selected, and provide a basis for the ultrasonic transducerresonant frequency automatic tracking. Second, the simulation model of tracking theresonant frequency of ultrasonic transducer has been built in the Matlab platform, theintroduction of the PI Simulink model of the closed-loop system resonant frequencyautomatic tracking. By tuning the PI parameters, the research on both cases of start-upand parameter perturbations, and simulation results demonstrate the resonant frequencybased on PI control algorithm to automatically track the effectiveness of the strategy. Study Inverter main circuit based on a combination of high performanceTMS320F28335and FPGA platform,AC voltage transforms into DC voltage by rectifier bridge, then inverter28KHz ofthe AC voltage by PWM control of full-bridge, and to provide high-frequency voltagetransducer. Using high-frequency transformers and high frequency current transformersfor voltage and current waveforms, the use of the FFT algorithm analysis phase ofcurrent and voltage, and the introduction of the PI algorithm constitutes a closed-loopcontrol system, in order to build the digital control automatically track the resonantfrequency of the ultrasonic transducer systems.The transducer used for experiment was supplied by the cooperative enterprise.This paper investigated the phase change between the current and voltage of transducerby adjusting the working frequency manually. After that, the PI control strategy wasapplied in the control loop to track the resonant frequency from a appointed frequency.The experiment results proved that the PI control algorithm and hardware designproposed in this paper can track the resonant frequency of ultrasonic transducer.The research results can provide some references for automatic tracking theresonant frequency.