Key Technology Research And Design Of Digital Ultrasonic Power Supply

Ultrasonic transducer(hereinafter referred to as transducer)is an essential component for artificial ultrasonic,it can convert electrical energy into ultrasonic.Ultrasonic power supply can provide the high frequency alternating current which the transducer requires to work,the frequency of alternating current is in line with series resonance frequency of the transducer.Traditional analog ultrasonic power supply,who's tracking precision of frequency is low,tracking speed is slow and frequency adjustment range is restricted,these defects influence the performance of the ultrasonic power supply.So in this paper,the digital ultrasonic power was studied,the main functions of this power supply are implemented by digital method the main contents are as follows:Firstly in this article impedance characteristic analysis is done to the equivalent circuit of transducer,when the transducer working frequency changes,the impedance will change: impedance module is minimum in the near series resonant frequency,is maximum near the parallel resonant frequency;when working frequency differs a lot from resonance frequency the absolute value of impedance Angle is very big and hardly changes over frequency,when close to the series resonance frequency,the impedance angle radical changes in a very small frequency interval.In this paper,after comparing different matching circuit,the inductor and capacitor circuit is adopted as a transducer matching circuit,in order to better realize the impedance transformation and power factor adjustment and filtering function.Secondly hardware circuit of the digital ultrasonic power supply is designed: DDS chip AD9850 is used in digital signal generator,its output signal frequency can be adjusted quickly by tracking program,which is always consistent with the transducer resonant frequency;Inverter circuit adopts a half bridge inverter circuit,driven by the output signal of AD9850,inverting dc into high frequency alternating current;In order to achieve the stability and adjust output power,a half bridge DC/DC conversion circuit is used to convert the voltage of direct current(DC)obtained by rectifying,in order to get stable direct current,and by changing the DC voltage to adjust output power of ultrasonic power supply,the circuit is controlled by dsPIC30F2020 specific chip for the power controlling.Finally a kind of tracking strategy combined with digital phase discriminator and maximum current tracking is brought forward,considering the characteristics of the impedance of the transducer,on the basis of analyzing the advantages and disadvantages of existing tracking method,aiming at the phenomenon that transducer resonant frequency will change as its parameters such as temperature and load changes,causing the working frequency offset resonance frequency,leading to output power and power factor reducing: fast frequency sweep program is run to search the maximum current frequency when Ultrasonic power starts,and then phase tracking program is run using the frequency as initial frequency to adjust output frequency with PI controller.MATLAB simulation shows that the speed of tacking is faster and precision of tracking is higher by using this method.