Research On Interharmonics Detection Method In Islanding Mode Of Microgrid

With the application and development of microgrid technology,the types of distributed power sources and nonlinear fluctuating loads are increasing in microgrids,resulting in complex and diverse power quality problems in microgrids.Interharmonics is one of the most important standards for measuring power quality.The primary task of studying interharmonics is to accurately detect interharmonics in microgrid.This thesis takes wind-solar storage island microgrid as the object,studies the interharmonic detection method of micro-grid,and realizes the accurate detection of interharmonics.Firstly,The working principles of the main distributed power sources in the microgrid,including wind power generation systems and photovoltaic power generation systems are analyzed in this paper and a microgrid model suitable for interharmonic analysis is built,laying the foundation for microgrid interharmonic simulation analysis.Secondly,the characteristics of the intermediate harmonics of microgrid are analyzed.Due to the complexity and instability of the signal in microgrid,the Hilbert-Huang transform(HHT)algorithm is proposed to detect it.Aiming at the empirical mode decomposition(EMD)part of the HHT algorithm,the signal decomposition process with a large number of harmonic components has problems,such as excessive decomposition and end effects,and the variational mode decomposition(VMD)algorithm is proposed to use the VMD algorithm for the middle of the microgrid to decompose harmonic signal.The basic principle of the VMD algorithm is deeply studied,and aiming at the problem that the parameter combination in the algorithm is hard to set accurately,a particle swarm algorithm(PSO)is proposed to optimize its parameter combination.Using the analog signal with interharmonics in the microgrid,the accuracy of the optimized VMD algorithm in the detection of interharmonics in the microgrid could be verified through simulation.Finally,based on particle swarm optimization optimization of the VMD algorithm,a Matlab GUI-based microgrid interharmonic detection system is designed,including interharmonic signal drawing,interharmonic detection,interharmonic instantaneous,and parameter calculation which could realize the application of improved VMD algorithm.For novel working conditions,including two micro-sources containing both wind turbines and photovoltaics,only wind turbines,and only photovoltaics,the common bus current signal of the microgrid is detected and analyzed to verify that the improved algorithm used to detect the interharmonic signals of the microgrid,the detect result is more accurate.