Improved Of Multifunction Microarc-Oxidation Power-supply

Microarc oxidation(MAO) is a new technology which can direct growth of ceramic layer on the surface of the valve metal and its alloys. For oxide coating produced by using microarc oxidation technique have many virtues such as high hardness, good wear resistance, and the substrate binding ability, corrosion resistance, etc., it has important potential applications in the machinery, automotive, defense, electronics, aerospace and civil construction industries. Microarc oxidation equipment includes special high-voltage power supply, oxidation tank, cooling system and the mixing system. The microarc oxidation power supply is an important instrument for microarc oxidation research.This thesis describes the development of the microarc oxidation power-supply in two parts.The first part introduces the hardware circuit design of the multi-functional microarc oxidation power. Power hardware architecture includes two parts which are the main circuit and power supply control circuit. The main circuit of the power is major composed by isolation transformer, three phase voltage regulator, filter circuit and IGBT inverter circuit. In order to independent adjust cathode and anode voltage of the power, the anode and cathode regulator circuits are separate. Isolation transformers isolate the power supply voltage and increase voltage. Three-phase voltage regulator changes the voltage amplitude by using thyristor and the shift control circuit, and the rectifier filter circuit changes it into a DC voltage which sent to the inverter IGBT, then IGBT control power output. In addition to these function circuits the main power loop circuit still includes drive and protection circuits, such as the IGBT drive circuit, IGBT RC snubber circuit, voltage regulator protection circuits. IGBT driver circuit controls the turn-off and conduction of IGBT. The absorption circuit controls the spike voltage as the IGBT turns off and the diode resumes to prevent the IGBT from being damaged. Thyristor is used for achieving voltage regulation function by regulator, and it is also need the circuits of overcurrent and overvoltage protections.Microcontroller is the core of Control circuit, and its peripheral circuits include data acquisition circuit, voltage and current regulation feedback circuit, IGBT waveform select circuit, etc. The power-supply chooses STM32F103VBT6 which produced by STMicroelectronics company as the microcontroller. The data acquisition circuit is divided into the voltage signal sampling circuit and the current signal acquisition circuit. They respectively gather the AD acquisition signals of anode voltage, cathode voltage, anode current, cathode current, and send back the acquisition signals to the feedback circuit. Voltage and current feedback circuit can precise control the output of voltage regulation circuit through regulating negative feedback circuit, which can use both the current way and voltage way. IGBT waveform selection circuit provides drive signals for the IGBT drive circuit to control power output waveform. In addition, there is a low-power electric power supply system, for achieving isolation power supply between the different modules to ensure circuit safety.The second part introduces the software design of the multi-functional microarc oxidation power. The software of the power includes the main control system and PC applications. The main control system use C language, and the PC application software use LabVIEW graphical to programming. Main control system is to achieve automatic controlling of the power. It includes the voltage current control, pulse control, control and monitor of voltage and current values, Power Timing, LCD display and power supply control by buttons, and PC communication, virtual PC panel display and the power control by virtual control panel buttons and other functions. The program is written by using the idea of state machine. There are four states in program. Generic Timer 3 is used to outpur PWM to control voltage and current values of power supply; Generic Timer 2 and common I / O interface are used to output PWM to control power-supply output ways; real-time clock is used to achieve power supply timing; Generic Timer 4 is used to transform anode and cathode at conversion mode.Power PC application software is developed by using National Instruments LabVIEW graphical development environment. Through the interface of virtual instrument achieves targets such as automation control, data acquisition and analysis integration. Software features include: power supply parameter setting, data acquisition, serial communication, mapping and data storage.