Study On Islanding Detection Method Of Negative Sequence Current Disturbance Based On Wavelet Transform

Islanding effect should be prevented in grid-connected photovoltaic system for harmfulness on the Power Grid Operation, power system overhaul and the Electrical Equipment Security. Negative sequence current perturbation method of Current perturbation often used at present has its virtue of non-detection zone and low voltage distortion. This paper researches into inverter islanding detection method in three-phase Voltage Unbalance situation by analyzing the Principle of Single-phase current disturbance.For detecting Algorithm of three-phase Negative sequence current perturbation method is insensitive to load variation, and components extraction algorithm cannot effectively identify and filter out the occurrence of High-frequency transient overvoltage components in Point of Common Coupling’s voltage, the following research has been conducted:Firstly, do park transformer to the positive and negative sequence voltage to ensure the accuracy of current detection method when the three-phase grid voltage is unbalanced. Utilize PLL synchronization method based space vector transformation to effectively reduce Phase-locked loop phase angle delays time when inverter collected to grid.Secondly, improve the algorithm of negative sequence wave extractor current extraction, filter out the high frequency component of mutations to improve the quality of the extracted current, reducing the time of detection and the amount of calculation of positive and negative sequence component.Thirdly, application of Daubechies wavelet to quantify the PCC voltage signal analysis and to improve the islanding detection threshold calculation, the robustness of the algorithm and obtain the accurate detection threshold to solve the problem that island threshold judgment error caused by the load disturbance in negative sequence current perturbation method in the practical application.Fourthly, establish three-phase grid-connected system islanding detection model in MATLAB/Simulink, utilize TMS320F28335 DSP control chip to Design the hardware and software of 10 KW three-phase grid-connected inverter island detection system.Fifthly, prove and analyze the effectiveness of improved negative sequence current perturbation method by Load disturbance experiment in the power match between the inverter output and the load consumption of power, and the setup of load power factor is 2.5.The simulation and experimental results show that through the PCC voltage amplitude of discrete wavelet decomposition and the corresponding real-time control strategy, the occurrence of an island can be judged in the 2-3 power cycle with rapid and non-blind characteristics when the system is broken symmetry.