Design Of Digital Ultrasonic Power Supply Control System Based On FPGA

Power ultrasonic technology has been widely used in all walks of life.The common applications are cleaning,atomization,welding,traditional Chinese medicine extraction and so on.As the core of power ultrasound,ultrasonic power supply has always been the focus of research,such as power adaptive adjustment,fast frequency tracking,high stability and high digitization.At present,the ultrasonic power supply adopts a large number of analog circuit designs,carries out signal processing through cumbersome hardware circuits,and the output frequency accuracy is low,resulting in poor stability.To solve the above problems,this paper designs a digital ultrasonic power supply control system based on FPGA.Firstly,the impedance characteristics of the transducer are analyzed according to the equivalent model of the transducer.The equivalent impedance of the transducer changes with the working frequency.There is a minimum impedance in series resonance and a maximum impedance in parallel resonance.After the transducer is loaded,the impedance near the series resonance point increases with the increase of the load,and the impedance near the parallel resonance point decreases with the increase of the load,that is,when the input voltage remains unchanged,the output power of the transducer working at the parallel resonance point increases with the increase of the load.Therefore,this paper selects the parallel resonant frequency as the working frequency of the transducer to solve the problem of power adaptive regulation.Secondly,the software and hardware of the ultrasonic power supply control system are designed.The existing control system hardware circuit is optimized,and the functions of hardware circuits such as RMS measurement and phase detector are realized by algorithm in FPGA to improve the digitization degree of the system.When the transducer works at the parallel resonance point,the current signal is seriously distorted.The current signal is processd by the combination of analog filtering and digital filtering to extract the effective signal in the current signal.In order to solve the problem of frequency drift,a compound frequency tracking algorithm is designed.According to the characteristics of the minimum current when the transducer resonates in parallel,the resonant frequency of the transducer is scanned to obtain the parallel resonant frequency of the transducer.On this basis,the variable step frequency tracking algorithm is used for fast frequency tracking.Direct frequency synthesis(DDS)technology is used to output digital sine wave,and high-precision PWM wave output is realized through hardware circuits such as DA conversion and voltage comparator.Finally,build a test platform for experiments.The results show that the control system greatly simplifies the hardware circuit,and the RMS measurement module and digital phase detector module have high measurement accuracy;When the load changes suddenly,the control system can quickly track the frequency,and the output power increases with the increase of the load,which meets the requirements of this subject and has certain practical value in the field of power ultrasound.