Research On Micro-grid Fault Transient Characteristics And Integrated Protection

Nowadays, the research on distributed generation seems to be efficient and dependable. The micro-grid is one of method which based on distributed generation. However, there seem to have new challenges in the operation of the grid since the introduction of distributed generation.This paper does an in-depth analysis and discussion about the fault transient characteristics of Micro-grid which focuses of the fault response of the Inverter-based distributed generators(IBDG).IBDG are integrated into distribution network through power electronic devices. In the process of parallel operation, when the power system disturbances occur, IBDG will adjust themselves through a series of operation to return to the original state or transit to a new stable state. Adjustment process between two stable states is called fault transient process. IBDG is controlled by its own controller in the transient process. In order to study the impact of the control strategy on the fault transient characteristics, a concrete model was set up including the inverter control strategy. Based on this model, the thorough analysis on the impact of the control parameters on the fault transient characteristics of IBDG was carried on. Then in-depth analysis on the fault transient characteristics of IBDG was carried on respectively in the cases of symmetry and asymmetry fault.A new integrated protection scheme based on transient polarity comparison is proposed for the multi-distributed generators distribution system. Transient polarity comparison theory is to extract the information of fault transient high frequency signal using wavelet transform, by comparing the polarity of which to judge the fault position quickly. In the new scheme, the transient polarity comparison protection is applied to the integrated protection, in which the integrated relay unit is built based on the busbars. The integrated relay unit compares the polarity of the lines out of the busbar to judge the busbar fault, and makes the judgement of line fault by comparing the polarity of the both ends of the line in use of the fault information and the information from the adjacent to busbar protection unit. Meanwhile integrated network protection unit extracts more information and makes a comprehensive comparison between the transient signal polarity to the whole area, to realize the fault isolation, rapid positioning and to provide backup protection for local protection.