| Arc welding inverters have many good qualities, such as small volume,lightness, high efficiency and rapid dynamic response and are recognized as the most prospective welding power supply in the welding field . With the improvement of power electronics technology, especially the emergence of the power element IGBT and the consummation in its consummation, in its performance, the arc welding inverter's future will be more beautiful. In order to decrease volume of Arc welding power supply, we can fulfill it through increasing frequency of it. And the further improvement in arc welding power supply's inverter frequency can bring more good qualities, But in conventional PWM control arc welding power supply, switching elements are forced to be on or off, so there exit many problems, such as great loss, inductive switch-off, capacitive switch-on and diode's reverse current. The switch loss increases with the improvement of inverter's frequency, so it is hard to improve inverter frequency further. Soft switching PWM technique can resolve this problem existing in conventional PWM technique, so it becomes one focus of welding field more and more. Conventional input current of Arc-welding is rectified by diodes, and smoothed by big capacitors. So this causes the differences between input voltage and input current to be very large, and the distortion of the current is large too .The results of which are as follows: first, power factor is low; second, harmonic current of input current is so high; at last it pollutes electrified wire netting. Now people begin to realize this point, and start to make some rules to limit the harmonic current of the equipment connected to electrified wire netting .In order to restrain harmonic current and enhance power factor, power factor correction is introduced. At the same time, in order to lighten volume, active power factor correction is the first choice. Most of three phase active power correction utilizes "boost" converter to be its main circuit, and its output voltage is 760-800V, sometimes even to 1000V, which requires the rear switch to have high endure voltage, the result of which is the costing of the equipment becomes so high .In three-level converter, endure voltage of the switch is half of input voltage, so it fits to be the rear circuit of the three phase power factor correction. And in order to lighten switching loss, soft switching is introduced to thee level converter. So a novel soft-switching PWM converter emerges. Soft switching PWM three level converters can be classified as ZVS three level converter and ZVZCS three level converter. ZVS three level converter has following drawbacks:â‘ forelegs can fulfill its ZVS very easy by the energy in the filter and leakage inductor , but the lag legs can only fulfill its ZVS by the energy in the leakage inductor , when the load current is not enough ,the energy is too small to fulfill ZVS of lag legs , if we make the leakage inductor too large , big loss of duty cycle will emerge . â‘¡When it is at the state of zero , primary don't conduct energy to load , but there exits loop current ,which cause conduct loss in switch and primary of transformer , so limits the efficiency. For this reason, I choose ZVZCS-PWM three level converter to be Arc-welding' main circuit. This paper analyze the principle of ZVZCS-PWM three level converters in detail, gives out the condition of soft switching and solution to design the parameter. Before designing circuit, I simulate it by use of software Pspice9.2, and demonstrate the feasibility in theory. At the same time, this paper uses control theory to analyze the system and gets the system transfer function model. To reduce the influence of voltage and current disturbance on the output, the regulator and corrector are reasonably selected, By selecting suitable parameters, a control system with high stability, good dynamic characteristic and high static accuracy is got. Following this, this paper simulates the control system by use of MATLAB, and demonstrates the correctness of the de...
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