Study On The Microgrid Modeling And Harmonic Analysis Methods

A microgrid is a new power grid structure system consisted by distributed generator (DG), energy storage units, loads and control device. The microgrid technology played the advantages of DGs, and coordinated the conflicts between DGs and the power grid. With the depth study of the microgrid, it’s power quality problems have been taken more and more attentions, harmonic is one of the key criterions of the power quality measurement. The priority task of researching harmonic problem of microgrid is the detection and analysis of the harmonics.The harmonic of the microgrid is randomness and non-stationary, traditional harmonic detection methods have limitations when analyzing the harmonics of the microgrid. The Hilbert-Huang transform is very suitable for analyzing nonlinear and non-stationary signals, it can overcome the defects of traditional methods, however it also exists envelope fitting and modal aliasing problems.This paper studied and modeled the photovoltaic systems and wind power systems; By using the Matlab Simulink simulation software a microgrid model was built, which supplied the simulation basis for analyzing the harmonics of the microgrid.An improved envelope fitting idea was provided in this paper to ameliorate the envelope fitting problem. And a digital high-pass filter was designed to filter the fundamental component of the harmonic signal to inhibit the modal aliasing phenomenon when using HHT method. By combine the two ideas, an improved HHT method was provided in this paper. The simulation results show that the improved HHT method can achieve good results in harmonic detection; By using Matlab GUI, a harmonic detection platform was designed, which contain the functions as the draw of the waveform, harmonic analysis and the calculation of the instantaneous parameters of each harmonic. The harmonic detection platform improved the practicability of the method.This paper used the improved HHT method to analysis the grid current of photovoltaic systems and wind power systems, the simulation result verified the accuracy of the improved method; then the improved method was used to analyze the current signals of the point of common coupling of the microgrid in different situation. The simulation results show that the improved HHT method can accurately detect each harmonic component, and can reflect the mutation point of the non-stationary signal.