Simulation Of Three-phase Power Factor Correction

Converter welding power is a rectifier for electric power grid. There are high harmonics in its current of inputs. High voltage/current has phase difference which result in low power factor. Correction of the power supply's power factor has become necessary request, and the criterion is strict more and more. The power of welding power supply is very large, so the matter it cared is more attention-getting.This thesis summarized the development of three-phase PFC of Arc Welding , analyzed several three-phase PFC circuit, With the merit of AC current and DC voltage is controllable, then the three phase half-bridge topology is choose as the front power factor corrector of welding power supply. We mapped three phase variable first toα-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, and the flow of the main circuit current was gained, so did the basic mathematical relation of the input and output and the restriction of various parameters to realize unit power factor, and also offered the theory of how to design the control system. For the six power switches, we adopt the space vector modulation method, at the same time we analyzed synthesize mode of the vector, and then chose the best one. The good behave of this topology in the unit power factor rectifier state is better than the others circuit topology.We got the conditions 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 frequency is very high, we can consider the input current is single sine wave. At the same time, the output voltage is an invariableness value.We use the TMS320LF2407A digital control chip made in TI Company in this paper. The digital chip included SVPMW waveform generator, and it can be used to realize the PFC. 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.We apply two-loop idea in the whole control system. The outer loop is voltage loop, which control the output voltage to be a constant value and offer instruction for the inner current loop. 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. In order to ensure stabilization run of the whole system, we use the classic PI control method as outer loop which cooperated with inner loop.By practical analysis, we got the conditions of rectifier running in unit power factor, and in this state, three-phase current is in phase with three-phase voltage, but it is sine wave containing high frequency modulation harmonic, when the switch frequency is very high, we can consider the input current is single sine wave, at the same time, the output voltage is a invariable value.In this paper, we choose IR2233, which is an IR company's product. It can drive the switches of the three phase half-bridge circuit with single power supply, The use of the IR2233 not only realized the electronic isolated but also depressed interference. It also has many protect functions. Its design is very artful. It is be proved that its cooperation with the three phase half-bridge is very well in practice.It is under the help of simulation software that we complete the whole design. Now simulation has a hold the balance station in modern power electronic design process. Simulation is one co-worker whom engineer can't deviate from. We wrote the simulation program to simulate the system. Thus, we got the characteristic of the system not only in control aspect, but also in practical circuit point of view. All of this gave us a great help. The small signal simulation result of the system is given out in the thesis, so did some important waveform. When we compare them with the measured waveform, we found that they are especially similitude.In addition, the author discussed several important questions of the system design about compiling software in this thesis. First, we choose "simple method" to calculate the vector action time in each sector, thus sector estimate and the action time calculations can be done in real-time accordingly, the method saved the time of the DSP implementation, improved the speed of the whole system, enhanced the transient performance. Second, some mistakes easy to be made were emphasized in the paper when program DSP, reader who read this paper can go little crooked road when use the SVPWM machine inside DSP. Third, we discussed the digital realization of the PI regulator and the scaled method of decimal fraction when using DSP to calculate floating-point numbers, even the over modulation and the least pulse width restrict problems are introduced. Thereby, it ensured the realization of closed loop and the stabilization of the three-phase PFC system. At last, the author build actual circuit, made the DSP control program. From waveforms we can see, three phase input current are in phase with input voltage, and they are relative standard sine wave, the power factor is 1.