Research On Three-phase Four-leg APF Based On Improved PR Control

In this paper, the main object of study is a three-phase four-wire shunt active power filter. And three key techniques of APF in three-phase four-wire power system are deeply researched in this thesis: the current detection techniques, the 3D-SVPWM techniques and the current track techniques. In the final, the software and hardware on the APF control system are also designed.Firstly, in current detection techniques aspect, with reference to the recent literature, the three harmonic current detection algorithms used in three-phase four-wire system such as ip-iq-0 harmonics detection, dq0 harmonics detection and abc harmonics detection are explicitly summarized. Moreover, an improved three-phase four-wire system harmonic current detection algorithm based on instantaneous reactive power theory is derived. And the final simulation of switch strategy in MATLAB validated the consistency with theory analysis.Secondly, in current tracking technique aspect, the comparative analysis of PI controller and PR controller in steady error elimination and anti-grid voltage disturbance ability is conducted respectively. And the result shows that PR controller is superior to PI controller in no static error tracking ability. In order to widen the bandwidth of PR controller and improve its capability of anti-frequency offset, an improved PR control strategy is proposed in the paper. What is more, how the parameters influence the PR controller is studied thoroughly. In modulation algorithm aspect, a further optimization in 3D-SVPWM on coordinate vector is made, and the choice of space vector and the calculation of duty cycle are analysed detailedly. The final Matlab/Simulink results prove PR controller functions perfectly in steady-state performance and no static error tracking ability.Finally, the software and hardware on control system based on the above research are designed in this thesis. The software design includes: the main flow charts, the 3-D SVPWM in a-b-c coordinate, the improved harmonic current detection algorithm flow charts. The hardware design includes: the transformer modules, signal conditioning modules, A/D sampling module and driver modules and so on. The results showed that the improved PR control algorithm used in three-phase four-wire APF system works well and is consistent with the previous simulation results.