Research On Islanding Detection Of Three-phase Grid-connected Inverter Based On Intermittent Bilateral Reactive Power Variation

It is called an islanding state that the distributed power isolated from the utility would supply energy to the local load independently when the public utility is failure. Because the occurrence of islanding is generally unpredictable, the islanding must be detected quickly and corresponding measures should be taken, otherwise it will do great harm. In the thesis, islanding detection technology of three-phase grid-connected inverter was studied.The paper reviewed the existing islanding detection methods firstly. None detection zone (NDZ) of an inverter whose output exists reactive power was presented through the analyzation of OVP/UVP and OFP/UFP detection methods when the inverter is either under constant current control mode or constant power control mode. RLC loads were designed and the experiments of passive islanding detection methods unfer different output control modes were done.Then, intermittent bilateral reactive power variation (IB-RPV) method was proposed in the aspect of active islanding detection. With the consideration of eliminating NDZ and islanding detection time requirement, the variation amplitude and variation time were both designed which were verified by islanding experiments. The intermittent bilateral reactive power disturbance islanding detection method can detect islands successfully, meet the requirement of detection time and bring little affect to power quality.As the three-phase LCL grid-connected inverter is a three-order system, the controller design is difficult. The weighted current feedback control strategy was introduced into the controller design in the paper. The control strategy of three-phase grid-connected inverter was given and the experiments were taken to verify it.