Analysis And Simulation Verification Of Signal Variation Law Of Main Circuit Of Inverter Resistance Welding Machine

Resistance spot welding is widely used in automotive,home appliances and other manufacturing industries for its low cost,high efficiency,reliable welding strength,and the advantages of automated production,In this thesis,the welding circuit of inverter power supply is used as the research object,and the change law of electric signal is studied,and the calculator program of electrical signal is compiled by LabVIEW.Based on the establishment of the current and voltage mathematical model,the transient and steady state of the current are analyzed,and the time of steady state being setup is determined by the calculation program.The voltage distribution at each point in the circuit is calculated which reflects the effect of the diode drop in the circuit,and the reverse voltage when it is turned off.Using the LabVIEW program to study the influence of frequency and duty cycle on the current waveform,it is found that the duty cycle only affects the size and fluctuation of the current,but has nothing to do with the steady state establishment time,and the frequency affects the establishment time and fluctuation.In the welding circuit,the total power and the effective power is not equal,due to the presence of inductance which is an energy storage with charge and discharge process.Due to the existence of conduction voltage drop of diodes in rectifier,the output power will reduce.In this paper,the analysis of the electrical signal in time domain will reflect the effective value of the electrical signal,the average value,and the components of power.the power factor is changed by the duty cycle,independent of the inverter frequency,and the existence of the diode cause the power efficiency is always less than 100%.Resistance spot welding monitoring is an important means to ensure the quality of welding,monitoring the general need to collect the welding process of electrical signals,and calculate the dynamic resistance.In this paper,the frequency domain of the electrical signal is analyzed,and the spectral distribution of the current and voltage is obtained,which provides the basis for the filter frequency selection.The welding current is measured by Hall current sensor,the signal is collected by single chip microcomputer,and the resistance calculation is carried out by using the collected current voltage signal.In the traditional method of resistance calculation,we use the rms method and the mean method respectively.In this paper,two new methods of equal current method and iterative method are proposed,which are verified by the program.Finally,in order to verify the correctness of the analysis results,the electrical signals of the actual welding process are monitored,and the current change trend is the same as the analysis results.By using the equal current method to calculate the resistance,the dynamic resistance curve obtained is the same as the typical dynamic resistance curve variation law.