Abstract-The rapid increase in installed distributed generation (DG) has led to concerns about the impact on the proper operation of the protection system. In particular, the limited fault current capability of inverter interfaced distributed generation (IIDG) could lead to malfunctioning of the distribution network protection system which largely relies on overcurrent based protection techniques. The absence of tried and tested models and methods to calculate the inverter fault current contribution has been a significant challenge to the introduction of IIDG. This paper shows that with a few subtle changes, conventional analytical network analysis techniques can be used to analyse the fault response of inverter dominated distribution networks. The theoretical results are validated by PSCAD simulations and experimental results.

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Abstract-This paper investigates the fault behaviour of inverter-interfaced distributed generators in stand-alone networks. It is shown that the rapid transient response of the inverter control system allows its fault behaviour to be characterised by quasi steady-state equivalent fault models. The choice of inverter control strategy, control reference frame and the method of active current limiting dominate the fault response, especially in case of unbalanced faults. The proposed fault models can be directly incorporated in conventional fault analysis methods of which an example is given for a faulty islanded microgrid. Model validation is carried out by comparing experimental measurements with results of analytical fault analysis using the developed fault models and PSCAD time domain simulations.