Research And Design Of Three-Phase Four-Wire Shunt Active Power Filter

With various kinds of nonlinear power electronic devices being widely used, the current pollution problems such as harmonic and reactive current are becoming serious day by day. As a new power electronic device to restrain the harmonic and compensate the reactive power dynamically, Active Power Filter (APF) is sure to be widely used in the industrial field. Currently researches are mainly on three-phase three-wire APF, but with the harmonic and load unbalance becoming more and more notable in the three-phase four-wire system, research on the three-phase four-wire APF has also become a focus. Therefore, two key techniques of APF in three-phase four-wire power system are deeply researched in this thesis: the current detection and current track techniques, and the software and hardware on the APF control system are also designed.(1) In the current detection aspect, two three-phase four-wire harmonic detection techniques are proposed in the thesis on the basis of the study of the three phase three wire harmonic detection algorithm. In addition the thesis summarizes the application steps, and the harmonic detection system is designed. The simulation results show that:in the case that the three-phase voltage is balanced, the above two methods can detect the harmonic, reactive current and unbalanced current component accurately. Meanwhile, in view of the existing detection error when the three-phase voltage is asymmetry, the thesis proposes a fundamental positive sequence voltage detector based on directional rotating coordinate to solve the problem.(2) In the current track aspect, the space vector control method which has a high utilization rate in DC voltage side, little ripple, and is suitable for digital realization is studied in this thesis. And based on four-leg inverter, the thesis makes deduction and induction on3D space vector control method and application steps which are suitable for three-phase four-wire APF. In addition, with the four-leg APF system modeling in the αβ0coordinate, the thesis simplifies the computation steps and realizes the direct control of inverter with instruction current to apply3D space vector control method in the three-phase four-wire APF system. Simulation results show that:the four-leg APF system has a good compensation performance on the harmonic, reactive and unbalanced three-phase current, whether separately or at the same time.(3) Based on the above research, software and hardware on the control system are designed in the thesis. And mainly with DSP control and operation module, the main and interrupt program flow charts are showed, and the transformer modules, signal conditioning modules, A/D sampling module and driver module are introduced in the thesis. In addition, the above current detection techniques on the energy and3D space vector control method are completed in C language based on DSP according to the application steps the thesis summarized. And the experimental results show that they are of practical value.