Study On The Application Of A Modified UPQC In LVRT Of Wind Farms

With the rapid development of wind power generation, wind power makes up a more and more important part in the power system, LVRT(low voltage ride-through) is increasingly concerned and studied. Based on the broad study of the performance characteristics of sorts of wind power generators and the principal technologies about LVRT,a modified UPQC was designed. The proposed device can apply to different types of wind generator systems,without any modification on the former generation system. It should be installed at the joint of wind field and the power grid,to help the wind generators ride through the low voltage periods.In the proposed LVRT control device,a series-connected inverter and a shunt inverter were combined in this solution, which was capable to help wind-powered generators ride through the low voltage faults. During the faults, this device can keep the voltage at the wind farm output terminals at a normal level, so as to avoid the possible damages to the wind-powered generator systems caused by the faults. At the same time, the device can supply reactive power to the power system to help the power system recover from the faults. The power overflow during the faults was controlled to be dumped to the energy storing device, then the stored energy was injected to the grid after the faults, in this way, the generator speed should not fly up to heaven and the DC-link voltage won't be over-boosted. When the power system is in the normal condition, the device can improve the power quality of the wind site. Simulation based on Matlab/Simulink is carried out and experiments are implemented to validate this solution.