功率超声技术在诸如切割、焊接、清洗、医疗等多个生产领域得到了广泛应用。在负载剧烈变化且加工精度要求高的应用场景中，稳定且精确的振幅输出是决定加工效果和效率的关键，因此对功率超声输出控制的研究具有重要意义。振幅控制的前提是换能器处于谐振状态，目前基于并联谐振的功率超声振幅控制方案存在输出精度不足、线性度较差、结构复杂等问题。本文通过研究功率超声控制方式并对相应软硬件进行设计，旨在实现超声波电源的恒振幅输出控制。本文的主要研究内容如下：

首先，对常见的换能器的等效模型进行分析，通过导纳圆曲线得出其阻抗特性。在此基础上，对换能器机电耦合模型进行分析，通过模型的等效转换，推导换能器输入电能与输出振幅关系。对变负载情况下换能器阻抗特性进行分析，并搭建超声电源主电路仿真模型，以此确立频率与振幅控制策略。

其次，设计并实现了超声波电源控制系统。在满足控制精度与响应速度的前提下，设计可适用于不同谐振频率换能器的控制系统硬件电路。为提高控制系统数字化程度，基于FPGA设计针对高频电压电流的数字信号处理模块，如IIR滤波器、数字鉴相器、有效值计算等。根据变负载情况下换能器阻抗特性，采用以电压电流相位差为被控量，以扫频所得谐振频率为起始频率的变步长频率跟踪算法；采用以换能器并联谐振模型中动态电阻端电压为被控量的PID振幅控制算法。控制系统输出两路频率移相角可调的高精度PWM波驱动逆变电路，实现换能器的频率振幅双闭环控制。

最后，通过实验对振幅控制策略进行验证。在负载变化情况下，记录并观测换能器输入电气参数与输出振幅间关系。实验结果表明，换能器振幅与并联等效模型中动态电阻端电压保持了良好的线性关系。

在频率振幅双闭环控制模式下运行超声波电源，负载剧烈变化时，频率输出能跟踪至并联谐振频率，使换能器保持在谐振状态；功率输出能自适应调节，使换能器振幅保持稳定。设计成功运用于实际功率超声切割中，为功率超声波电源的恒振幅控制提供了一种可行性方案。

Power ultrasonic technology has been widely used in many production fields such as cutting, welding, cleaning, medical treatment, etc. In application scenarios with drastic load changes and high processing accuracy requirements, stable and accurate amplitude output is the key to determining the processing effect and efficiency. Therefore, the research on power ultrasonic output control is of great significance. The premise of amplitude control is that the transducer is in a resonant state. The current power ultrasonic amplitude control scheme based on parallel resonance has problems such as insufficient output accuracy, poor linearity, and complex structure. This article aims to realize constant amplitude output control of ultrasonic power supply by studying the power ultrasonic control method and designing the corresponding software and hardware. The main research contents of this article are as follows:

First, the equivalent model of a common transducer is analyzed, and its impedance characteristics are obtained through the admittance circle curve. On this basis, the electromechanical coupling model of the transducer is analyzed, and through the equivalent conversion of the model, the relationship between the input electric energy and the output amplitude of the transducer is deduced. Analyze the impedance characteristics of the transducer under variable load conditions, and build a simulation model of the main circuit of the ultrasonic power supply to establish the frequency and amplitude control strategy.

Secondly, the ultrasonic power control system is designed and implemented. On the premise of satisfying the control accuracy and response speed, design the control system hardware circuit applicable to transducers with different resonant frequencies. In order to improve the digitalization of the control system, digital signal processing modules for high-frequency voltage and current are designed based on FPGA, such as IIR filters, digital phase detectors, effective value calculations, etc. According to the impedance characteristics of the transducer under variable load conditions, a variable step frequency tracking algorithm is adopted that uses the voltage and current phase difference as the controlled quantity and the resonant frequency obtained by frequency sweep as the starting frequency; the dynamic in the parallel resonance model of the transducer is used The voltage at the resistor terminal is the PID amplitude control algorithm of the controlled quantity. The control system outputs two high-precision PWM waves with adjustable frequency and phase shift angles to drive the inverter circuit to realize double closed-loop control of the frequency and amplitude of the transducer.

Finally, the amplitude control strategy is verified through experiments. Under load changes, record and observe the relationship between the input electrical parameters of the transducer and the output amplitude. Experimental results show that the transducer amplitude maintains a good linear relationship with the dynamic resistor terminal voltage in the parallel equivalent model.

When the ultrasonic power supply is operated in the frequency-amplitude double closed-loop control mode, when the load changes drastically, the frequency output can track to the parallel resonant frequency to keep the transducer in the resonant state; the power output can be adaptively adjusted to keep the transducer amplitude stable. The design has been successfully used in actual power ultrasonic cutting, providing a feasible solution for constant amplitude control of power ultrasonic power supply.

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