Research On Ultrasonic Power Supply Based On DSP And Bridgeless PFC

Ultrasonic welding is an application of power ultrasound and has been widely used in industrial manufacturing.The ultrasonic welding power source(UWP)is the core component of the ultrasonic welding system.It rectifies the mains power to the dc bus,which,then,inverted to ac voltage to drive the transducer.Transducer converts electrical energy into mechanical energy,and uses its high-frequency vibration to weld plastic or metal materials.USW should work at the resonance point of the transducer,and a matching circuit should be designed to offset the excess reactance to improve the output efficiency.Due to temperature changes and other reasons,the resonance point drifts resulting of transducer loss increasing and the amplitude decreasing.Therefore,USW needs to track the resonance point to keep the system working efficiently.This paper takes USW as the research project,and focus on transducer characteristics,matching circuit design,power control,frequency tracking,etc.The main contents include the following points:1.The equivalent circuit model of the transducer is analyzed,and its parameter variation characteristics is verified in experiments.The admittance circle is used to distinguish the three sets of resonance points of the transducer.The traditional LC matching parameter design method requires a large matching capacitor,which reduces the electromechanical coupling coefficient,so the USW prototype chose a LCC matching scheme with a transformer.The effects of the matching circuit parameters are modeled and analyzed in Matlab.2.The USW prototype uses Power Factor Correction(PFC)circuit whose Power Factor(PF)reach 98.9% under 800 W load to reduce the harmonic injection into the power grid.The voltage and current double loops of the PFC circuit in CCM are designed.The phase shift control strategy and advantages of Phase Shifted Full Bridge(PSFB)in welding power supply are introduced,and its low harmonic content is pointed out.A more accurate digital simulation model of the main circuit was constructed and analyzed in the Plecs simulation tool.3.Prototype used TMS320F28035 to complete hardware,software resource allocation strategy and workflow of communication,PFC,and PSFB,making full use of the controller resources.The frequency tracking scheme proposed in this paper can quickly track the resistive series resonance point,and solves the problem that it is easy to mistakenly track the resistive parallel resonance point and the loss of the resonance point in the traditional scheme.HRPWM is used to improve the accuracy of frequency tracking.The research solves the problem of pulse loss due to the DSP limitation,and verifies it in the prototype.