Research On Fault Detection Method And Protection Of Microgrid

Nowadays,the micro.grid of power system has been developed vigorously,and a large number of distributed generations can be effectively utilized in situ.However,with the access of various large.capacity distributed power sources,there are different fault power flow characteristics in the system from the traditional fault situations,which makes the traditional protection no longer applicable in AC micro.grid and AC.DC hybrid micro.grid.At the same time,AC.DC hybrid microgrid is different from AC microgrid,and its fault characteristics are different from AC microgrid.It will also have an impact on AC.DC hybrid microgrid protection.So this study analyzed AC microgrid protection and AC.DC microgrid protection,and proposed a protection strategy for AC microgrid and AC.DC hybrid microgrid based on pscad.The simulation results verify its effectiveness.Firstly,this paper carries out the modeling and Simulation of distributed generation.Using PSCAD modeling,the photovoltaic power generation model and its output characteristics are analyzed,the four.component combination model of wind power generation and its output characteristics are modeled,and the energy storage device model and its output characteristics are analyzed.This paves the way for the subsequent research on the impact of distributed power supply on Microgrid protection after it is connected to the microgrid.The transient characteristics of faults in AC microgrid are analyzed,and a theoretical analysis method for faults in microgrid with distributed generators is proposed.Because the control logic and current limiting device of Inverter Distributed Power Generation have great influence on its fault output characteristics,the output current of Inverter Distributed Power Generation presents obvious non.linear characteristics.Aiming at the distributed power supply with two kinds of control logic,this paper presents a transient characteristic of distributed power supply fault output satisfying control constraints by writing constraints equation,combining different fault situations(including different fault locations and different types of faults),and line fault boundary conditions under two different operation modes of grid.connected and island operation,in order to study the transient characteristics of distributed power supply fault output with inverse control constraints.The microgrid protection of the variant distributed generation provides a theoretical basis for calculation.At the same time,PSCAD simulation proves the correctness of the theoretical basis.A fault identification criterion for AC microgrid protection operation is proposed.Wavelet packet decomposition is used to extract fault transient characteristics and waveforms in characteristic frequency band.It is explained that feature frequency band extraction can effectively filter out disturbance fault waveforms.Then the definition of SOD transformation and its adaptability to microgrid protection are introduced.The SOD transformation order suitable for microgrid protection is analyzed and discussed.Finally,PSCAD simulation is used to verify the applicability of the proposed algorithm to microgrid protection under grid.connected and islanded operation,as well as different control modes of micro.power supply connected to microgrid,especially when high resistance faults occur in microgrid(high resistance faults resistance value can reach 3000Ω).The validity of the proposed algorithm is proved.A fault detection method for AC/DC hybrid microgrid commutation failure based on mathematical morphological spectrum is proposed.The commutation failure between DC and AC caused by AC microgrid faults is analyzed.The mechanism of commutation failure in AC.DC hybrid microgrid and its impact on AC side protection(i.e.AC microgrid protection)are analyzed.The definition of mathematical morphological spectrum and its application in commutation failure detection are introduced.The effectiveness of commutation failure detection based on mathematical morphological spectrum is validated by PSCAD and MATLAB simulation calculation.At the same time,this chapter uses Fast Fourier Transform to analyze the harmonics flowing from DC microgrid to AC microgrid under commutation failure,and draws a conclusion that the DC side mainly flows into the AC side of the low.order harmonics,so as to draw a conclusion that the commutation failure has no effect on the SOD high.frequency transient protection algorithm of AC microgrid proposed in Chapter 4.Finally,the SOD algorithm is validated by PSCAD simulation.The effectiveness of AC side protection in AC/DC hybrid microgrid.