Fault Analysis And Protection Characteristics Of Microgrid With High Permeability

With the application of new generation technologies,including renewable energy such as wind energy,photovoltaic energy,and efficient clean fossil fuels,inverter interfaced distributed generator has developed rapidly in recent years,and micro-grid,as its most effective utilization form,has gradually become an important research direction in the power industry.Due to the access of distributed generation,the traditional protection methods based on distribution network have been difficult to cope with the new fault characteristics of micro-grid.Exploring appropriate protection methods to ensure the safe and stable operation of micro-grid system has become one of the current research hotspots of micro-grid technology.Under the background of high permeability micro-grid,this thesis mainly studies the fault characteristics and adaptive protection methods of inverter interfaced distributed generator after it is connected to the micro-grid under constant power control and constant voltage and frequency control strategy.Firstly,this thesis introduces the control strategy of inverter interfaced distributed generator,and analyses the mathematical model and output characteristics of inverter interfaced distributed generator under different control strategies,as well as the influence of different factors on its output characteristics.Then,in order to determine the fault type and fault area,this thesis uses the wavelet transform method to decompose the voltage of grid-connected points,we train a classification model according to the voltage change eigenvalue of grid-connected points.Machine learning algorithm is used to train the classification model according to the voltage change eigenvalue of grid-connected points.The optimal algorithm for this scenario is selected from multiple classifier algorithms by cross-validation.In order to simplify the calculation,the eigenvalues are simplified by principal component analysis.By comparing the eigenvalues of different grid-connected points at the same fault location,the fault area is determined,and then the fault phase and fault type are judged by the eigenvalue ratio of different phases.Finally,in order to remove faults accurately,the whole microgrid is divided into several protection areas.On the basis of determining the fault types and fault areas,the protection areas containing fault locations are updated in real time.The calculation methods of short circuit current of different fault types and load current in normal operation are given.The simulation model of microgrid is built and various fault conditions are set up to verify the correctness of the proposed adaptive protection current scheme.