| When we work in the project construction of high-speed railway, natural gas and power from west to east in China, we need to carry out welding work in wild field, Generally, this field always remote locations.Therefore, there is no available electric network power in these places or though there has electric network power of direct use power in the nearby place, also take several hours to pull lines, it is not only waste of time but also inconvenient. Therefore, the permanent magnet passive intermediate frequency (IF) welding machine of light weight and small size replace active welding machine, It has been widely used in these welding situations. But the generator in permanent magnet IF welding machine only output output AC of 500-600Hz. Its frequency and amplitude are different from the commercial power. Therefore, many other devices that need commercial power to supply power in construction site, such as slurry pump, welding quality tester, electric angle grinder and so on, they can not work by welding power. This takes inconvenient to construction of the entire welding operation. In this case, the project was commissioned by the welding machine manufacturer, under premise of project's technical requirements and conditions which had been proposed by welding machine manufacturer. We have developed for their much-needed permanent magnet IF welding machine passive inverter which had been urgently needed. Technical requirements are following:Output square-wave voltage of frequency 50Hz, Voltage RMS is around 230V, with function of strong anti-interference, against harsh environment, against start over current, simple operation and so on.According to the project's technical requirements and conditions, in complete process, innovation are following:First, Proposed PWM method, using 3525 internal error amplifier and compared complete directly the function of system inverter and stabilize voltage; effective solve the problem that stabilize Output voltage at 230V±5% V, when input phase voltage change between 96-130V;Second,replace capacitor filter methods with Inductive energy storage filter methods, Effective solve problem of output sampling feedback link isn't sensitive to change PWM pulse width,under output square-wave voltage; Third, use welding winding supply power for control circuit of inverter, and using the voltage fluctuation amplitude as the action threshold inverter lock, this ideal excellent solve problem that interlock between welding winding and auxiliary power winding and greatly improving work reliability of two supply system in welding machine.Preface of this paper describes international Current Situation of the project, technical requirements, and the main work of this project. On the basis of this, it also discusses the theory related to the completion of this project, such as Development of power electronics technology, square-wave voltage inverter; stabilize voltage mode selection of power frequency square-wave output voltage and key circuit design. Focus on implementation of project and technical requirements of project, Inverter main circuit and driver circuit topology design, circuit theory; power switching device parameter calculation, the choice of power switching devices, protection for power device has been described detailed in main part. In the control circuit, briefly discusses principle of PWM pulse generation circuit, PWM pulse control circuit and the key circuit chip. Finally, this article introduces site debugging process of the entire inverter, give measured waveform, and the measured waveforms are analyzed and discussed. Through the measured waveform, the project achieved the objectives and requirements and proved the correctness of circuit design, and welding machine manufacturers are ready to mass production. |
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