Research On Fine Plasma Power Supply And Cutting Parameter Control

This paper deals with the problems of low consumable life,low cutting quality and low current control accuracy of high-power plasma cutting power supplies.It integrates high frequency inversion technology,digital signal control technology,plasma cutting technology and power electronics technology.A 20 KW class all-digital inverter fine plasma power supply with high current control precision,long service life of wearing parts,high energy density of plasma arc and low surface roughness of cutting workpiece is designed.By reading a large amount of literature and investigating the performance and quality of plasma power supplies on the market,most of the domestic plasma cutting power supplies are ordinary plasma power supplies,and most companies are developing fine plasma power supplies that are refinement,digitization and intelligence.On this basis,study the principle of plasma arc formation combined with the trend of gas discharge with electric field frequency curve.Defining the specific control value of the current and voltage of each stage of the plasma arc arcing.Based on this,the inverter frequency is set to 20 KHZ and the control flow of the arc starting control program is designed.From the output power when input is the same,key components withstand voltage stability,high-frequency transformer core utilization,etc.Analyze the advantages and disadvantages of common main circuit conversion topology,and determine the full-bridge inverter circuit with PFC power factor correction as main circuit conversion topology.Using power electronics theory combined with actual working parameters,calculate the main parameters of each hardware module of the main circuit,including three-phase EMI filter circuit,input rectifier circuit,input filter capacitor,inverter circuit and high-frequency transformer.Analyze the IGBT structure,dynamic characteristics and turn-on characteristics,explore the relationship between the charge and discharge of the inter-electrode capacitor and the turn-on and turn-off delay.Determine the dead time of the alternate turn-on of the power switch tube to 10% of the switching period.Design control circuit according to control function requirements,design AD sampling conditioning circuit to improve current sampling accuracy;Design independent arc striking plate to improve arc success rate;Hardware anti-jamming measures such as taking a metalshield and placing the arcing circuit at 5-10 cm of the sensor,that can increase the anti-electromagnetic interference capability of the components in the high-frequency conversion.On the basis of the control circuit,according to the modular programming idea,the control program software is written,and the precise closed-loop constant current output control with precision of 0.1 millisecond can be realized.Real-time adjustment of current value by rotating encoder subroutine with panel knob.Using EDA simulation software saber to verify the rationality of the design of fine plasma power supply hardware and software system.The experimental platform was set up to perform the performance test of the fine plasma cutting power supply and the experimental analysis of the cutting parameters,including the test drive waveform,the output waveform,the output external characteristic waveform and the dynamic response characteristic waveform.Cutting process experiments on ordinary carbon steel sheets with thickness of12 mm and 25 mm by changing cutting parameters.The experimental results show that the current control accuracy is above 99.5% and the power factor is above 0.9,which further verifies the excellent technical performance of the all-digital fine plasma power supply designed by this subject.