A generalised fault protection structure for unigrounded low-voltage AC microgrids

This paper introduces uni-grounded low-voltage (LV) AC microgrid configurations. A generalised fault protection structure is proposed for all different uni-grounded LVAC microgrids. This protection structure consists of six individual protection zones in a uni-grounded LVAC microgrid. They are protection zones of distributed generators (DGs) and energy storage devices (ESSs), transformers, power converters, source branches, load branches, AC trunk lines and common buses. A variety of available fault protection methods are considered for each above protection zone of the uni-grounded AC microgrid. Primary and secondary protection schemes of each different protection zone are designed to ensure stable-reliable-adaptable-scalable operation of a uni-grounded LVAC MG. As a result, main contributions of the paper are: (i) definition of different uni-grounded LVAC microgrids; (ii) concept of a unified fault protection structure for uni-grounded MGs; and (iii) appropriate fault protection methods proposed for primary and secondary protection of uni-grounded MGs.