Research On Symmetrical Fault Tolerant Control Of Island Microgrid Based On Adaptive Virtual Impedance

Parallel microgrid consists of distributed generations has been a hot area of research with the rapid development of the new energy and the increase of system power levels.Meanwhile the reliability of microgrid system,especially during the faults and its fault-tolerant operation should be focused seriously along with the wide application of microgrid.More differences are existed in protection strategies between the traditional large-scale power grids and the island microgrid because of its inherent characteristics.A feasible approach for microgrid characteristics and the advantage of micro-source self control to achieve fault-tolerant operation during microgrid faults should be proposed.The changes of the micro-source electric quantity and the characteristics of the power flow of the feeder under the fault condition for the inverting microgrid is researched and analyzed,the fault equivalent model is studied and established.Based on the characteristics of the fast response of the micro-source inverter,the fault contingency strategy with the fault-tolerant control of the micro-source inverter is studied to provide a guarantee for the reliable operation of the smart micro-grid.The fault characteristics of island microgrid under different control strategies are analyzed in this thesis.The fault emergency control under different control strategies based on the results of fault analysis is presented to ensure the stable operation of microgrid.Focusing on the output electrical fault characteristics of the inverter when droop control strategy is adopted,and for traditional current limiting control,the structural change greatly before and after the symmetric fault resulting in a large overshoot of fault recovery and the weak ability to support frequency and voltage during faults.Against the above deficiency,the adaptive fault virtual impedance control strategy is proposed in this thesis.According to the change of the fault current,the value of the virtual impedance of the fault is automatically adjusted,the fault micro-source is not disentangled and reliably parallel connection,the overshoot of the fault recovery is reduced,and the frequency and voltage support capability is improved during the fault.Aiming at the disadvantages of the traditional complexible fault impedance estimation algorithm,the method of estimating fault pointdistance based on the size of fault virtual impedance is proposed to improve the fault detection quickness and reduce the fault repair time.Finally,microgrid simulation model based on MATLAB/Simulink has been built to verify and analyze the proposed control strategy and microgrid experimental platform based on DSP TMS320F28335 to verify the emergency response measures proposed in this thesis for the power control and droop controlled micro-grid.The experiments of the adaptive fault virtual impedance control and the traditional current limiting control strategy proposed in this thesis are compared,the correctness of the control proposed in this thesis is verified by the simulation and experimental results.