Research On Harmonic Detection And Control Strategy Of Active Power Filter

Power electronic equipment is more and more widely used in the modern society. It improves the quality of people’s life but generates harmonics, which heavily influences the power quality. Active power filter is used in reactive power compensation and dynamic harmonic suppression. Compared with conventional passive filter, active power filter can eliminate harmonics better.This thesis studies three-phase shunt active power filter. Based on the analysis in its topological structure and working principle, the author focuses on two key technologies that influence active power filter’s performance: the technologies of harmonic current detection and harmonic current tracking control.For harmonic current detection, this paper introduces the adaptive theory and constructs an adaptive filter to replace the low-pass filter to make up for the shortcomings of widely-used ip-iq harmonic detection method, which is based on instantaneous reactive power theory but with the disadvantages of low filtering precision and long time delay.As with harmonic current tracking control, by constructing the model of three-phase three-wire active power filter in abc coordinate system and dq coordinate system, it can be learned that in the dq coordinate system, active power filter is a nonlinear system with dq shaft coupling component and requires decoupling and linearization in the control process,increasing the difficulty of control. Therefore, this thesis adopts αβ static coordinate system,designing sliding mode controller through independent subsystems to improve the control accuracy of harmonic currents. Then the control law of saturation function is adopted instead of that of symbol function to weaken chattering.In the Matlab simulation software, the author builds the whole simulation model of active power filter to discuss the different forms of current under different grid modes. The results demonstrate the effectiveness of the improved algorithm in harmonic compensation.With the existing experimental system, using DSP as the control core of active power filter and designing hardware and software of the experiment system, the final result verifies the correctness of active power filter harmonic detection and tracking control theory.