Development Of The New Micro-arc Oxidation Power Supply Based On PLC Control

Micro-arc oxidation technology is non-ferrous metal surface treatment technology, thistechnology has been the film excellent performance. Affecting the micro-arc oxidation offactors are electrolyte formula and power parameters. Where in the power supply parameterincludes voltage, current amplitude, the power output mode and so on. Development ofmicro-arc oxidation power must be based on characteristics of the load requirements. Thedevelopment of modern power electronics technology to promote the development ofmulti-function power supply. Better performance of the metal film through bidirectionalasymmetric pulse power according to the load requirements. Asymmetric bidirectionalasymmetric pulse power can be output pulse, and voltage amplitude, pulse frequency, dutycycle continuously adjustable.Development of bidirectional asymmetric pulse power is consists of two parts that are themain circuit and control circuit. Main circuit includes transformer buck-boost, thyristorrectifier filter circuit and inverter circuit. The control circuit includes hardware and software ofcontrol systems.380V grad voltage after be step-down through transformer into two differentvoltage amplitude, the output of the rectifier filter circuit DC voltage ripple smaller. Theinverter circuit converts DV voltage output to pulse. Control thyristor firing angle to changethe pulse amplitude and control the inverter circuit device breaking time to change pulsefrequency and duty cycle. The core of power control system is S7-200PLC. The mainachievement is to preset and sampling of voltage and current, controlling the powerparameters, driving the IGBT. The HIM of power is formed by Kunlun-state touch screen.Touch screen can show power parameters, real-time and process of control. Micro-arcoxidation process load is changing slowly, needed to maintain output voltage and currentstable. PI regulator with fast and steady-state or error-free feature, so digital PID can meet thecontrol requirements. The methods of controlling are constant voltage and constant current,but the constant current is simple and easy controlled. Constant current and pressure limitingthe voltage dual closed-loop control is more accurate to the result. When the sampled voltagevalue is greater than given to call the dual-loop PID, when the sampled voltage value issmaller than given to maintain the maximum output. This approach can avoids ablationphenomenon occurred while voltage excessive. The PLC as the core of micro-arc oxidation power control system, with real-time datadisplayed, data processed function, adjustable resistance, perfectly meet the technologicalrequirements. Designed of micro-arc oxidation power after several on-site commissioning toachieve the desired output waveform, the output voltage stability, good process performanceprogrammable, simple man-machine interface. Development of technology for micro-arcoxidation power programmable is foundation of widely range of industrial application.