| With the development of power technology, especially the development of the welding power source technology, an increasing number of applications of power electronic devices has led to the harmonic pollution in power system with low power factor of electrical problem in itself. Using power factor correction within the power has become an inevitable requirement in the worldwide production of electrical equipment and the standards have become more sophisticated. In the field of welding power source, such a request is bound to be realized. Because of the higher capacity factor of welding power supply, it raises even more sensitivities.This article reviews the harmonic pollution in the preferred and commonly used method of controlling the development of digital technology, particularly in the field of welding power supply applications, as well as the principles of welding inverter power source and digital development, and ultimately selected half-bridge circuit topology for three-phase welding power source as its pre-stage power factor corrector. Three-phase half-bridge circuit topology has a good control of current of the network side and voltage of DC side.Research at this stage of digital power supply is basically in order to achieve the digital PID control. The more popular way is the use of voltage and current two-way closed-loop feedback control. Use the digital signal processors to deal with voltage and current signals taken from the welding scene, by controlling the PWM pulse duty cycle and institutions to regulate the output of welding power source and control wire feed . PFC in the welding power source is also improved for the rectifier so that it does not produce as much harmonic current as possible and makes voltage with the phase of current.In the inverter welding power supply with power factor correction, there are many electronic components and complex circuits, including the IGBT devices and other valuables. When inverter power source is working, it is bound to be some unusual circumstances, such as the lack of phase, short circuit, as well as staff of the error operation. That could cause damage to the inverter power source, if damage is common device, we can replace, but if the damage is a valuable device, it would cause serious economic losses, which is we do not want to see. Research and articles of fault determination and protection in the PFC of the welding power source are few. This paper shows innovative research mainly in the fault diagnosis and code display in the PFC of the welding power source.The design choose TMS320LF2407A Texas Instruments TI series chips. This chip is designed for controlling applications and the field of motion control, with a small size, low power consumption, high reliability, high performance and so on. The using of fast computing power of DSP2407 for real-time monitoring to the pre-correction circuit, and when the abnormal situation in the inverter power source occurs the system will immediately display the fault code which shows the correct way to determine the type of fault as soon as possible so that we can discover problem in order to restore the normal operation of inverter power supply and the protection of welding work quality. The whole system is divided into main control panels and control panel. Main control board is to realize the initialization of chip, register allocation, to function of ADC module features, data filtering, and the Fault determination and code display. Control panel is the keyboard to start the system and display the code, and can be expanded in the follow-up study.The system is based on the 10-bit A / D conversion module. The chip has a total of 16 analog input channels, and the system only expand two channels, respectively, is the first 0 channel and 8th channel, with internal sample-and-hold circuit, and the completion of an A / D conversion time is approximately 6.6us. The A / D input signal range that DSP can withstand is 0-3.3V. In this system there is no single reference source but used directly the 3.3V of the system as A / D converter the reference signal. In the design of system, the signal used in A / D conversion is measured by the straight-type Hall current sensor CSK3-500A and Hall voltage sensor KV20AP collection, and has designed the corresponding conditioning circuit for them. Actually due to the use of the hardware simulator in supporting the introduction, it has the basic equivalent to the effect with the actual signal acquisition, then the DSP chip used D / A output signal as the A / D input signal. In the system A / D conversion is started by software trigging.The system used the average median filtering method, that is, procedures for collecting the input signal 18 times to determine the concentration of sampling the signal maximum and minimum values. Then remove the maximum and minimum values and sum the remaining 16 signals to get the number of arithmetic the average sample value. This algorithm can effectively suppress random interference, but the measurement is slow, so the number should not be excessive.In the design of the keyboard system, we use an independent key-based mechanical electric shock-type non-coding keyboard. That the keyboard uses the pull-up resistor is in order to ensure all I / O identified high level when the button is disconnected. In the non-coding keyboard system, the information acquisition of the key closing, search and other key tasks are all completed by the software. The system keyboard sampling is to notify the system to deal with the A/D conversion, so it takes the scanning method to work.The digital display in the Control Panel uses the Seven-Segment LED digital tube, and it is often shown in decimal or hexadecimal number, so we have to test it by the use of the binary number for decoding, converting them into a decimal number or hexadecimal number. In hardware it uses the chip of EPM240 to drive Seven-Segment LED digital tube. This experiment uses a type of Yin-class digital pipe connection, which high level is effective.After completing the hardware design the procedure is written for the various modules and then got them to a overall integration process. It gets the expected results through the use of CCS software, and real-time performance of fault detection is also very high. It could meet the determination that the system displays the fault code when the Fault happens in almost the same time, and lays the foundation for the equipment protection in the future. |
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