| With the rapid growth in technologies of new energy, distributed generation, modern communications and the increasing demand of energy conservation, in recent years a rise of a global wave of―Smart Grid‖study went on its way. As an important part of world's energy strategy, the study of Smart Grid involves several areas, considering how to take advantages of advanced technologies to improve the power system in every aspect such as raising the energy conversion efficiency and reducing conversion loss, at the same time improving power quality and the reliability of power supply etc.As a necessary category of Smart Grid research, power quality problems have attracted lots of experts'attention for a long time. The rapid growth of modern technology has raised efficiency of generation, transmission, transformation and distribution of power energy, but on the other hand made the grid to face a more severe load. These years the negative effects become more and more obvious with the significant improvement of power semiconductor manufacturing and increase of converter loads, which have caused varies of power quality problems such as low power factor, waveform distortion of voltage and current, reactive power unbalance, surge current, voltage sag etc; meanwhile, recently more and more new energy and distributed generation are connected to power grid in wide range, which will bring about some new issues to power quality filed and need to be studied and dealt with in the future.Among all the power quality problems, harmonic pollution is one of the most serious issues. The traditional main source of harmonics in power system was transformer, while in recent years, it turns to be the increase of nonlinear loads, such as semiconductor devices and electric locomotives, and even in the future with the development of Smart Grid, new energy-based electricity generation company will become another power system harmonic key member. Harmonic will result in reducing system stability and reliability; bringing great loss to users who need higher quality of the electricity.Faced with all of these problems, this paper takes harmonic issues in power quality field as the main object of study, doing comprehensive research works and in-depth studies in every aspect of harmonic problems, such as identifying and localization of harmonic sources, harmonic component detecting and harmonic contamination. Firstly, the working principle and classification of harmonic sources are introduced, as well as their harm and affection to power system and electric device, then the two mainly methods of current localization and detection of harmonic sources in power distribution network are systematically described, with their characteristics and shortcomings analyzed and compared. Secondly, innovative research works are done to present new methods in harmonic detecting and current control algorithm, based on presently widely used harmonic contamination device—active power filter (APF), the fuzzy regulator using non-uniform quantization rule and self-tuning factor variable step algorithm are taken advantages to make optimization of the internal low-pass filter module referred in the detecting method based on instantaneous reactive power theory, so as to constantly regulate LPF's cut-off frequency, which has improved the detecting precision and dynamic response ability and made the harmonic detecting method adaptive; on the other hand, based on the analysis of the variation of hysteresis width, the purpose to achieve a limited frequency of switching is reached by using an internal fuzzy controller to dynamically adjust the loop width of hysteresis comparator unit, compared with the traditional hysteresis method, it has more excellent dynamic response and tracking precision compared to the traditional hysteresis method, taking full advantages of conduction capability of the power switches, moreover, a reduction of the maximum switching frequency ensures that the device operates safely; finally the harmonic detecting and compensating efficiency to the typical non-linear loads of the approaches presented above is further demonstrated by series of simulation and experiment results in this paper. |
PDF Full Text Request