Study On Power Factor Correction Of Arc Welding Inverter Supply

Uncontrolled diode-rectifiers are usually adopted as the primary stage of general arc welding inverter supply, and followed by a big smoothing capacitor. These circuits are lead to distorted waveforms of input current in AC side. At the same time, there are usually variable loads when the supply is working. Variable loads will also cause currents distortion. These distorted input currents including a lot of different order harmonic currents will contaminate the supply system when they inject into the supply net. At the mean while, they will reduce the power factor of welding supply themselves, increase the demand of supply power capacity and finally result in wasting electricity power. With acknowledging the pollution of supply system and related standards being released and put into use, it is indispensable to deal with these contamination produced by these general arc welding inverter supply.These uncontrolled diode-rectifiers belong to an universal type of rectifiers-voltage rectifiers, whose common features of input harmonics currents include as following: single-phase input current contains 2n + 1 orders harmonics currents and three-phase input currents contain 6n ?1 orders harmonics currents. So when with an ideal stable load, the input harmonics currents of arc welding inverter supplies share the common features. However, the loads of arc welding inverter supplies are always dynamic, they are to have their individual features, especially with pulse welding. Additional currents distortion caused by dynamic loads will be occurred. Pulse loads are purposely introduced into welding progress. These pulse loads will engender an accessory modulation effect on input currents, and change the distribution of input harmonics currents. It occurs preferable even order harmonics currents and DC components. The filters in supply system are usually equipped to deal with certain odd order harmonics such as 3 order, 5 order, 7 order and 11 order, and standard values of harmonics current are more strict with even order harmonics currents and DC component current is not allowed. To these extends, it is worse than other diode-rectifiers that the arc welding inverter supply contaminate the supplysystem.Analyzing input harmonics currents of arc welding inverter supply is benefit to understand the distribution of the harmonics currents. When with stable loads, the approximate analytical expression of input current is obtained through analyzing input current in one supply period. One also can get every order harmonics currents through Fourier series transformation. When with pulse loads, it is difficult to get the approximate analytical expression of input current. Under a certain condition, double side band modulation (DSBM) is adopted to deduce the approximate expression of input current of arc welding inverter supply when with pulse loads. Then, every order harmonics current value can be obtained by Fourier series transformation. It is a useful try to analyze the input harmonics currents of arc welding inverter supply when with pulse load and offer a new method to analyze harmonic current.Three-phase PWM rectifier is adopted to implement power factor correction function in arc welding inverter supply. Different models of PWM rectifier are deduced when under static coordinate or rotating coordinate. An average status modeling is also obtained and based on it, a small signal modeling is deduced to offer a principle to analyze PWM rectifier. The stability and static features of PWM rectifier are also analyzed. According to instantaneous power theory and power balance relationship, one gets the essence of power factor correction control that is to make reactive current to zero.It is necessary to study switching modulation patterns of PWM rectifier because it is the most direct measurement to realize power factor correction function of arc welding inverter supply. Compared with several switching modulation patterns such as hysteresis modulation pattern and SPWM pattern, space vector modulation mode has the smallest harm...