Design And Implementation Of Ultrasonic Power Supply Amplitude Control System Based On FPGA

The application of power ultrasound plays an important role in national economic production.In some highly demanding processes,precise amplitude control determines the processing efficiency and effect.Traditional power ultrasonic control methods have problems such as nonlinearity,poor flexibility,and complicated structure.This paper aims to realize a constant amplitude control scheme by real-time calculation and closed-loop control of the dynamic branch current that can reflect the amplitude through the design of power ultrasonic control mode and feedback circuit.The main research contents of this paper include:1.According to the relevant application background and technical development of the power ultrasonic power supply,the working frequency of the anti-resonance point and the frequency tracking scheme of the phase method are established.On this basis,the physical model of the piezoelectric transducer is analyzed,and the amplitude control scheme with the dynamic branch current as the closed-loop control object is obtained.This solution simplifies the design of the matching circuit and the amplitude measuring device.2.Design and simulate the hardware circuit of the power drive and detection loop.The drive circuit includes an inverter circuit,a filter circuit and a transformer circuit to generate a power signal suitable for driving the piezoelectric transducer.In the detection loop,the amplitude of the transducer voltage and current is fed back through the two-way AD sampling,and the phase of the transducer voltage is fed back through the phase discrimination circuit.3.FPGA-based phase-detection signal and high-precision interface logic for generating PWM waves are designed.The phase-detection interface logic converts the phase-detection signal fed back in level form into time data for embodying the phase difference.The PWM generation logic is responsible for converting the control word into two high-precision symmetric PWM waves for controlling the inverter circuit.The conversion accuracy of the two directly determines the upper limit of the control accuracy of the power supply.4.FPGA-based dual closed-loop control logic for frequency and duty cycle is designed.In terms of frequency closed loop,according to the phase discrimination result of current and voltage,the P frequency is used to close the operating frequency.In terms of amplitude closed loop,the high-speed sampling result of the current voltage amplitude is calculated,and the dynamic current of the transducer capable of reflecting the amplitude is calculated in real time,and the duty ratio is closed by the P control.Through the experiment,the working performance of the power supply was tested.The experimental results show that the power frequency tracking performance is good,and it can track to the anti-resonant frequency under different working conditions.Under no-load conditions,the transducer amplitude maintains a good linear relationship with the dynamic branch current.The power supply can stably output amplitude under load changes.After the instrument is measured,the maximum amplitude control error after loading is 6.2%.The research results provide a solution for the constant amplitude design of power ultrasonic power supplies.