Analysis of fault response of inverter-interfaced distributed generators in sequence networks

Publication Type:
Conference Proceeding
2018 IEEE Industry Applications Society Annual Meeting, IAS 2018, 2018
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© 2018 IEEE Microgrids mainly rely on distributed energy resources (DER) unable to generate electricity at the expected voltage and frequency. This necessitates the usage of inverters acting as a conditioning interface between the DER and microgrid, hence the name inverter-interfaced distributed generators (IIDG). On the other hand, the fast response of the primary control of inverters causes unconventional behavior of IIDGs under fault conditions, which can severely affect all parts of relaying, that is, fault sensing and polarization and faulted phase selection. This issue becomes more pronounced when an inverter-based microgrid operates in autonomous mode. This paper analyzes the root causes of such unconventional responses that challenge the traditional protection schemes. At first, the inverter control strategies including current limiting are briefly discussed. Then, the paper is continued by analyzing the response of an IIDG feeding its local load to balanced and unbalanced faults, where MATLAB/SIMULINK is used for simulation studies. It is shown how the constraints set by the control strategy itself and current limiter affect the response of IIDGs to fault conditions and consequently, their equivalent models under fault conditions. The findings presented in the paper clearly show that protective functions face difficulties in coping with fault conditions in IIDG-based microgrids due to their different equivalent models during fault period. These studies in turn help modify existing protection schemes or devise new ones applicable to this concept.
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