Research Of Three-phase Four-wire Shunt Active Power Filter With PI And Repetitive Control

With the rapid development of power electronics technology, more and more powerelectronic devices applied to power system. A lot of harmonics are introduced to the grid. It’sa threat to the safe and stable operation of power system. Therefore, active power filter hasbeen developed and applied. It’s a new power electronic device, used for dynamic harmonicsuppression and reactive power compensation. Depending on the compensation requirement,the structure of APF is different. In this thesis, a three-phase four-wire shunt active powerfilter is analyzed. The main works of this paper are the following.First, the mathematical model of stationary coordinate system ABC is derived. It can beseen from the mathematical model, the system is a strong coupling high order system. Thedesign of controller will be very complex. In order to simplify the design of the controller,dq0coordinate transformation is introduced. The mathematical model under dq0rotatingcoordinate system is obtained.Second, according to the discussion whether need to remove the zero-sequence currentfrom three-phase current before harmonic current detection in three-phase four-wire system.Comparative analysis of the two calculation methods in the paper.The theory and simulationresults verified the normalization of both. Conventional PLL is poor in anti-jamming. Thepaper analyzed how the phase digital phase-locked loop works, and gives the PI controllerdesign method based on zero-pole configuration.Third, considering the compensation accuracy of single PI controller is not satisfied inAPF applications. The repetitive controllers (RCs) based on internal model principles areintroduced. Detailed designing steps of RCs are given. Considering large amount ofcalculation and the complexity of the sector verify of three-dimensional vector pulse-widthmodulation (3D-SVPWM), the paper deduced theoretically that3D-SVPWM do not need tojudge sector. A simplified a-b-c coordinate duty cycle calculation formula is derived.Fourth, hardware circuit and software of the system are designed. The parameters of themain circuit and the control circuit are selected. The software design mainly introduces the working flow chart of main program and subroutine flow chart of the system.Finally, a simulation model based on SIMULINK of the system and100A experimentalprototype is built. Comparative analysis the compensation results of the system when the loadis balanced and unbalanced, the power supply voltage is distorted and normal. The results ofmutation load are analyzed, either. Experimental results show that the harmonic currentdetection method of three-phase four-wire system used in this paper is correct. Three-phasesupply voltage DPLL achieves good lock-in results. The simplified3D-SVPWM controlstrategy is effective. PI+repetitive controllers can achieve the desired compensation effectunder various conditions.