Research On Control Strategy Of Micro-sources Under The Unsymmetrical Fault Of Microgrid

With the wide application of microgrid technology in engineering,the research on microgrid system consisting of distributed generation units is deepening increasingly.In a microgrid system that operates independently,microgrid faults caused by many uncontrollable factors,such as environment,time or man-made,are unavoidable.In order to ensure that the micro-sources in the system are not separated and the power supply can be reliably maintained,the micro-source control is used to realize the emergency treatment of the partially recoverable faults of the micro-grid,thereby improving the reliability and system stability of the independent micro-grid.Therefore,the fault operation characteristics in the independent microgrid system and the emergency control methods have become the focus of research.In this paper,based on the fast response characteristics of the inverting micro-source,the operating characteristics of the micro-source under two kinds of asymmetric faults with high probability,single-phase grounding and two-phase-to-phase are studied,and the changes in the electrical quantity of the micro-source are analyzed in detail.Aiming at the phenomena of increasing current value,voltage drop and the waveform of the current and voltage asymmetry caused by asymmetric faults in the system,an emergency control strategy with dynamic virtual impedance during asymmetric faults is proposed.Based on the analysis of the electrical quantity correlation of dynamic virtual impedance,the quantity which has little influence on impedance value is simplified or neglected,and the calculation formula of fault virtual impedance with simpler expression and faster response is obtained.When an asymmetric fault occurs in the system,the corresponding virtual impedance is added to the micro-source inverters to improve the output side waveform of the inverters,and also to improve the working condition of the micro-source inverter.At the same time,according to the dynamic value of virtual impedance in the proposed strategy,the distance of fault occurrence points can be predicted,so that the scope of fault detection can be reduced,and the work efficiency of fault maintenance personnel can be improved.The independent microgrid simulation model composed of multi-machine micro sourse is built by MATLAB/Simulink,and the feasibility of the proposed control method is verified.The independent micro-grid experimental platform based on DSP TMS320F28335 is built to verify the control strategy of the micro source inverter under asymmetric faults.The control strategy of this paper is compared with the traditional droop control strategy.The results show that the control strategy of adding dynamic virtual impedance during the fault can improve the output voltage of the micro-source inverter and suppress the fault current.