Three Phase PFC Of Arc Welding Power Supply

Power supply technology is deeply developed today.The application of lots of power electronic circuit results in many problems,,such as harmomic pollution of the power network.The power factor of the electrical equipment is also very low.Correction of the power supply's power factor has become necessary request,and the criterion is strict more and more. In the welding power supply field, this kind criterion is also going to be implemented. The power of welding power supply is very large,so the matter it caure is more attention-getting. This thesis reviews several three phase PFC circuit first and point out their characteristics,then choose the three phase half-bridge topology as the front power factor corrector of welding power supply.The three phase half-bridge topology's AC current and DC voltage is controllable. In order to analyze its work principle, we mapped three phase variable first to α-βplane then to d-q plane using PARK transformation, things is simplified accordingly. In the d-q coordinate, the main circuit's unit power factor run principle is analyzed, so does the basic mathematical relation of the input and output and the restriction of various parameters to realize unit power factor. For the six power switchs, we adopt the space vector modulation method. Different vector synthesize mode has different macroscopical harmonic and power loss, for this reason, we analyzed several representative synthesize mode, and then chose the best one. By practical analysis, we conclude that three phase PWM rectifier is a very good circuit topology for PFC, it has the ability to run in four quadrants. The rectifier can run in different state using different control. This characteristic makes three phase boost topology has many application field, its good behave in the unit power factor rectifier state is better than the others circuit topology. We got the conditons of rectifier running in unit power factor by analysis and calculation. In this state, three phase current is inphase with three phase voltage, and it is sine wave containing high frequency modulation harmonic. When the switch freuqency is very high, we can consider the input current is single sine wave. At the same time, the output voltage is a invariablenes value. Base on this, we designed the whole control system. Introducing DSP to the control system, we realize the digitalation of the control system. compared to anolog control system, it's excellence characteristic such as convenience program and debugging, flexible control function make the digitalation of power supply a develop trend.TI company's 2000 series DSP is a good choice for digital power supply. 2000 series DSP is designed for movement control originally, its inside hardware is very suitable for bridge manner switch circuit control, it include SVPWM machine, it can build space vector waveform automaticlly without software action. Put it to the PFC control of power supply, the user's work will be greatly simplification. It's reliability is very high. In addition, the ability of DSP for fast data process and inside integration equipment, can cut user's design cost to least. It's inside 10 bit AD converter is also suitable for voltage and current sampling and computating. The control system of three phase PFC is very pivotal, in order to stabilize output voltage when the input current being in phase with input voltage, this article derivate out the small signal model of the rectifier in detail, according to tellegen theorem, making use of instantaneous power balance relation, we got the from active current to output voltage transfer function without the complex non-linear relation due to the switch state. It is very suitable for the design of outer voltage control loop. We apply two loop idea in the whole control system. The inner loop is current loop, it is used to achieve that the input current is be inphase with the input voltage using steady-stage deadbeat control to achieve best dynamic performance. This kind method can correct current error in one switch period when the circuit run in steady state. This method is very suited for DSP, even in transient operration when the power system or load vary, it also has a good transient performence; The outer loop is voltage loop, whitch control the output voltage to be a constant value and offer instruction for the inner current loop. In practice, the bandwith of the outer loop should not be too large, but it should have no steady state error, we use the classic PI control method as outer loop whitch cooperate with inner loop to ensure stabilization run of the whole sysytem. The switch drive of the three phase half-bridge circuit is also a very important question, it needs six drive signals, and all switchs are in pare whitch can not be on one ground. If we isolation the power supplies, then we will need six isolation power supplies. For this reason, we choose IR2233, which is a IR company's product. It can...