Algorithm Design And Implementation Of Automatical Frequency Tracking Of Ultrasonic Transducer Based On Fuzzy-PID Control

Ultrasonic transducers have wide application in ultrasonic area,such as ultrasonic cutting,ultrasonic welding,ultrasonic cleaning,and so on.In ultrasonic transducer system,to achieve high efficiency,it requires the whole system working in resonant state,which means high consistency between the driving frequency of power and the resonant frequency of the ultrasonic transducer.However,change of temperature and load abrasion leads to the drifting of inherent frequency of the ultrasonic transducer.Meanwhile,excessive overshoot current,long response time and long hardware design period remain the urgent issue.Therefore,how to quickly and precisely realize the automatic frequency tracking and how to shorten the hardware design period is the key point to the high efficiency of the ultrasonic transducer.In this paper,from the perspective of automatic frequency tracking,the author proposes the Fuzzy-PID algorithm on automatic frequency tracking of the ultrasonic transducer system based on the STM32 microcontroller and the Field Programmable Gate Array(FPGA)development board of Alter company.The research contents of this paper mainly include:1.This paper analyzes the impedance characteristics around the parallel resonant frequency and determines feedback signal of ultrasonic system close-loop control.Moreover,a new software structure of automatic frequency tracking is proposed based on the analysis of existing frequency tracking principle of the ultrasonic system.2.This paper designs the Fuzzy-PID algorithm on automatic frequency tracking,a fuzzy controller with double inputs,single output and incremental PID are used to realize both quick and accurate frequency tracking from the view of software.3.MATLAB is used to design the required fuzzy controller with double inputs and single output,feedback current and feedback current change rate is targeted chosen as the input variables to lower the overshoot current,to prevent the ultrasonic system from serious damage for the long-term excessive overshoot current.4.This paper design a PWM wave produce circuit based on FPGA,taking full advantage of field programmable gate array,this module strengthens the hardware expandability and shortens the design or modification period.5.An experimental platform of the automatic frequency tracking system is set up,meanwhile,debugging and testing work is carried out to verify the superiority of Fuzzy-PID algorithm and the validity of the FPGA circuit.The result shows that the technique can reduce overshoot current of the ultrasonic transducer and shorten the time for achieving stabilization of the system.Moreover,FPGA improves the expandability of the hardware,and greatly shorten the design period and modified period of the hardware.