Research On Background Harmonic Suppression Based On Harmonic Signal Double Point Detection And Discrete Frequency Tunning

With the highly development of modern society, more and more attention is paid on sustainable development and environmental pollution. As a kind of clean energy, power energy is widely used in our daily life. The more power energy we need, the higher power quality is needed. But the use of power electronic devices and nonlinear equipments may cause background harmonic voltage which is magnified by series and parallel resonance between capacitance and inductance in the transmission line. Thus it worsens power quality. Besides, it may affect power facilities and lead to personal safety problems.Based on the uniform transmission line theory, the distributed-parameter model and the lumped-parameter model of the radial transmission line are set up in the power distribution system. According to the distributed-parameter model, the causes of the background harmonic amplification in transmission line are analysed and the harmonic suppress principles of resistive active power filter are introduced. While the lumped-parameter model is used for simulation validation of theoretical analysis.To overcome the shortcoming that installing a shunt resistive active power filter(RAPF) at the end of the transmission line can only damp out the background harmonic magnification effectively instead of attenuating the existing harmonic further and its harmonic suppress effect turns worse when the line parameters change, this paper proposes a harmonic signal double point detection and discrete frequency tunning active power filter(DPDDFT-APF) strategy. For fifth- and seventh-harmonic, the RAPF reference current is made up by the additional harmonic current of some bus and the harmonic voltage at end point. According to the strategy, the reason why it can obtain better harmonic suppress effect is clarified by theoretical analysis based on distributed-parameter model when the line parameters change or not. Compared with the traditional RAPF, the proposed strategy can not only damp out harmonic propagation, but also attenuate the existed harmonic effectively. Besides, it has better capability of harmonic damping in response to variation of equivalent resonant capacitors. Simulation and experimental results verify the effectiveness of the new strategy.According to the lumped-parameter model, an APF experiment platform with 9km radial transmission line controlled by TMS320F2812 is built to verify the feasibility of the proposed strategy. Experiment results suggest that it can suppress harmonic propagation more effectively than traditional RAPF, which demonstrates the correctness of the theoretical analysis.