Research On Closed-loop Control Strategy Of Harmonic Current Of Apf

The existence of a large number of non-linear load, made the problem of harmonic much more serious, so that power quality was seriously affected. Traditional LC passive filters, because of their technical limitations, unable to meet the requirements of high performance filter. While the appearance of active filter technology, made it possible to solution the problem of power quality.The focus of this article is about closed-loop control strategy of APF based on power grids current detection. In this paper, two types of closed-loop control strategies and ideas have been proposed. The first closed-loop control strategy is from the improving of open-loop control. While, the second one is proposed based on the predictive current control. There is simulation and analysis about the two strategies, and Besides, the experiments of the first strategy is carried out to draw relevant conclusions.Simulation and analysis of the first closed-loop control strategy, show that this program is feasible. In the simulation, both PI control and repetitive control are used. And from the results of simulation, it is known that the effect of PI control & repetitive control is much better than PI control alone in harmonic current compensation. When using PI control alone, the THD of the source current is reduced from 28.5% to 14%, while using PI control & repetitive control, the THD of the source current is reduced from 28.5% to 3%, it is obvious that the repetitive control is very important. And the experiment of the strategy is also made to support some perspective above. The results of experiment conform with the results of simulation well. And the effect of PI control & repetitive control is also better than which of PI control. Of course, it is inevitable that there is some gap between theory and practice. When using PI control, the THD is reduced from 28.5% to 14% in simulation, compared with 28.5% to 19% in experiment; while using PI control & repetitive control, the THD is reduced from 28.5%to 3% in simulation, compared with 28.5% to 10% in experiment. Though the effect of experiment is not very well, it can still prove the correctness of the closed-loop control strategy.The second program use the closed-loop control strategy of APF based on the predictive current control. In this control strategy there is on need to detect the output current of APF, it means that, in this control system, just three types of variable are necessary to detect, including the signal of the source voltage, the signal of the source current and the DC voltage of APF. Obviously, this control strategy is more straightforward and simple than the first one. And also, the PI control and repetitive control are both used in this control strategy, the final THD of the compensated current is about 4%, of course in simulation.