| In recent years, with the intensification of energy crisis and the enhancement ofpeople’s environmental awareness, microgrid gradually becomes a focus for its energyefficiency, environment friendliness, and flexibility. The randomness andintermittence of new energy power generation in microgrid impact on quality ofpower seriously, and power system has set down strict criteria for grid-connectedpower generation of microgrid. Then, it is a pivotal issue to improve the powerquality of microgrid in order to make microgrid work more effectively. This thesisanalyzes voltage sags in microgrid and proposes a new compensation method.Microgrid is a kind of low-voltage active network. Low-voltage line parametersof microgrid determine the fact that the amplitude of voltage can be affected by activepower largely, and microgrid should be different from traditional power systems interms of analyzing voltage sags. Besides, microgrid can not only absorb power frompower system, but also input power to power system though it connects with theterminal of distribution network like other loads. All these items determine theparticularity of voltage sags compensation in microgrid.To compensate microgrid voltage sags, this thesis proposes a new method bycombining energy-storage-based active power filter (APF) and virtual inductance.Energy-storage-based APF has two kinds of operation mode: when microgrid operatesnormally, it works in harmonic reduction mode to suppress harmonics, and whenmicrogrid suffers from voltage sags, it works in voltage compensation mode tocompensate voltage sags. As voltage sags in microgrid are caused by different factors,they should be compensated in different ways: if voltage sags are caused by microgriditself and there is a small decline in voltage, energy-storage-based APF will be used,and if voltage sags are caused by distribution system, the new method by combingenergy-storage-based APF and virtual inductance will be used.The validity and effectiveness of the new method has been verified by simulationof practical algorithm cases. The new method proposed in this thesis operates veryflexibly in supplying effective compensation for voltage sags caused by differentfactors, and works effectively in limiting fault current between microgrid anddistribution system in the presence of voltage sags caused by distribution system. |
