| Abstract:With the obvious prominence of the contradiction caused by energy and environment problem, solar energy regarded as a sort of green energy in future is more and more important, and the ratio of electrical power produced by PV generation system in the whole power system keeps increasing continuously too. So there is great value in researching power quality in PV distributed generation system. The passage adopts harmonic suppression technology in photovoltaic grid-connected inverter with LCL filter as researching object, analyzes photovoltaic inverter’s mathematic model and the causees of harmonic current, discusses the mechanism of harmonic suppression of photovoltaic inverter, proposes two harmonic suppression strategies with high performance and verifies the two methods’ effectiveness by simulation.Firstly, the passage analyzes two frequently-used grid-connected control strategy by building the mathematical model of photovoltaic grid-connected inverter with LCL filter to find out the two control strategies can’t suppress the harmonic current caused by voltage and current, then analyzes SPWM modulation means in math and simulation to draw a conclusion of different modulation ratio of magnitude and frequency’s influence on frequency spectrum of output harmonics, then analyzes the filtering performance of LCL output filter to find out LCL output filter can highly weaken the higher harmonics and can’t efficiently work on low-order harmonics.At end, proposes the theoretical mechanism of harmonic suppression in this thesis to provide theoretical basis for harmonic suppression.Secondly, by analyzing and comparing three existed sorts of current-detecting means of harmonic, The author choose LMS self-adaption method in intelligent harmonic detection algorithms, and take advantage of LMS self-adaption detecting method with variable step to overcome the contradiction between rate of convergence and detection precision of traditional LMS self-adaption detecting method. Introduce PI controller into harmonic detection module to reduce the amount of calculation and save controller resource in the process of designing harmonic detection controller, to compress the amount of calculation and improve system performance propose harmonic suppression controller without harmonic detection, that is, directly apply PR controller on harmonic suppression.Finally, to verify effectiveness of the two harmonic suppression methods, Author construct the two simulation model separately in Matlab/Simulink and do some preliminary experiments with the500kW PV grid-connected inverter made by a solar inverter company. The simulation and experiment results indicate that both of the two harmonic suppression methods can restrain appointed-order harmonic effectively, and can’t cause changes of other harmonics’ content,can be applied in engineering practice directly. |
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