Fault Detection And Protection In PFC Of Arc Welding Inverter Power

Recently the inverter technology has developed rapidly , the inverter welding power with small size, low energy consumption, energy-efficient material, good control performance, fast dynamic response, easy to implement real time control of welding process advantages Received wide attention. However , when the inverter welding power is working,it would produce a large number of high harmonics, resulting in harmonic pollution, reduce the power factor. Therefore the arc welding inverter power required factor PFC techniques used to suppress the harmonic and improve power factorIn the welding power supply with power factor correction technology, it contains valuable Electronic component such as IGBT and others .And it is very improtant that the reliability of welding power source products directly affect the quality of welding. So to protect the PFC circuit and also to ensure the proper welding ,this paper presents the work of PFC inverter arc welding fault detection and protection for the subject. The experiment we choosed the Three-phase half-bridge topology for the protected circuit ,which has a good network side of the current and DC voltage controllable.The experiment used TMS320LF2407A producted by TI company as the control center. The chip is designed for high performance, high accuracy and multiple functions of the motor control system or motion control systems development.In the chip, TI company integrates high-performance DSP cores and multiple on-chip peripherals, making it function more diversification, saving the user's design cost with high cost performance.In this paper, we use the Hall element for voltage and current sampling on front-end in the power factor correction, the sampling results were sent to AD_DIG0 and AD_DIG8 pin of TMS320LF2407A chip.The experiment can detect and protect for five power failures-- overcurrent, overvoltage, undervoltage phase, and overheating . Because different failures have different time and severity.So overcurrent, overvoltage, undervoltage and phase failure fault detected by the DSP program , but the overheating is judged by the JUC-1M Temperature Relay. We select 85 degrees Celsius for the JUC-1M operating temperature . Because there is a heat sink outside the IGBT, so we can only speculate based IGBT heat sink temperature. When the temperature of heat sink reaches 85 degrees Celsius, the thermal protection circuit is disconnected, the output from the LM339 low, pull down the PDPINT pin of DSP, the output of PWM which from DSP block. The action play a role in protection. when the temperature of IGBT is lower than 105 degree , the temperature relay is automatically close.Againsting for overcurrent, overvoltage and undervoltage, and lack of phase failure, the system uses software to detect these failures. By using DSP internal DA converter module the collected signal comes to DA conversion.The system uses program to complete the conversion process, and the converted digital value using the median average filtering method to filter, this will weed out the environmental impact or other factors interfere with the signal generated, to ensure the accuracy of judgments. The resulting interference signal, to ensure the accuracy of judgments. And after filtering procedures current and voltage signals stored in the register FIFO.The experiment set 100A for standard current,if the current reach 200A this is over-current.At the same time the experiment set 220V for standard voltage value,if the velue of votage higher 20% than 220V we call it for the over-voltage, less than 20% for the under-voltage, Any voltage between two phases is 0 we it lack of phase.according to the above criteria, the system make the failure judge program.When the software detect the failure,it will automatically drop out to the implementation of conservation programs.Depending on the failure of the system of protection used in different ways, for the under-voltage and the lack of Phase , although the welding power source will stop working, but not one of the devices caused devastating losses. We use a form of off PWM output can be shutdown as soon as possible to treat the failure. Therefore, when Trouble program detected voltage and the failure of Phase, DSP is invoked DAC output procedures, through the breadboard TLV5620 chips convert digital signals to analog signals, start and stop PWM output circuit. The circuit can realize the PDPINT quickly pin down the functions of DSP. Stop PWM output circuit in the use of high-speed optocoupler 6N136, to meet the requirements of rapid action.For the over-current, over voltage that will produce in a short time break of the fault, we only use the block protection PWM output mode power factor correction is not enough, because in the event of overcurrent or overvoltage condition, the very possible breakdown IGBT, even in this case timely block PWM output, due to power is Tong's, IGBT control will result in more damage, or other devices, so in this system in the Wei overcurrent, overvoltage fault protection designed to stop PWM output circuit of the same time, turn off the power circuit is designed to be turned off and thus increase the power factor correction circuit protection. This will not only keep the fast response, with increased reliability. The experimental design of the turn-off power supply circuit, when the fault diagnosis procedure to determine the form of fault overcurrent or overvoltage, start the DA conversion, and DAD at the same time I start the DAC, DAD port connected to the power circuit off. When DAD I have voltage coming through the amplifier circuit when the optocoupler conduction, conduction optocoupler AC contactor is triggered after the action off the power to complete the purpose.In determining the breakdown, a start-DA conversion procedures, the system also sets the liquid crystal display program, the program will start ST7920 LCD module, the module has the character and graphic display can show 128×64 dot matrix of characters and graphics. When a fault occurs, the LCD screen will show the causes for the operator to detect and effective treatment based on the reasons for failure to improve work efficiency.The experiment using the CCS software development part of the program, CCS is designed specifically for DSP programming software. Software and hardware debugging the final composition of the arc welding power supply PFC fault detection and protection circuit, the experiment shows that the system can meet the needs of arc welding power supply PFC protection, protection of the shortest action only 200us, achieve a rapid response, with the traditional fuse protection or resistance-type melting-type protection has obvious advantages compared to. And because the software is written in the protection program, and therefore have a good portable, easy changes.