Abstract
Objectives: This work seeks to present a new protective relay for short circuits in AC micro-grids, under different control strategies as well as in both grid-connected and islanded modes of operation. Methods/Statistical Analysis: An index test-bed which consists of two wind turbines as micro-sources and other requisite network elements is developed. From the dynamic short circuit analysis of the test-bed, the rules which govern interaction of four parameters are framed in fuzzy form. Using the framed rules, fuzzy logic controllers are designed for micro-source and feeder sub-relays. The hardware of each sub-relay is realized in SimPowerSystems using combinational logic components. Findings: Offline and online response tests of the proposed relay show that it generates logic 1 during short circuits and logic 0 during normal operating conditions in both grid-connected and islanded modes of operation of the micro-grid. The proposed relay also provides equivalent response under both voltage and reactive power control strategies. This is consistent with response of a reliable protective relay as reported in related literature. The proposed relay also supports plug-and-play and peer-to-peer requirements of micro-grids. Similar to digital relays reported in literature, the proposed relay is a departure from classical relays wherein protection is based on threshold of short circuit current. In the proposed relay, protection is based on parameters of micro-sources and feeders. Application/Improvements: The proposed relay finds use in providing protection for personnel and system against short circuit currents. It reliably protects against single line-to-ground, line-to-line and three-phase bolted short circuits. Keywords: Fuzzy, Micro-grids, Multivariable, Relay, Short Circuits
Highlights
The primary aim of a micro-grid is to provide quality, reliable and sustainable power to a load center[1]
This is because utility generator is located at the extreme end of the utility, far away from the PCC which is closer to the feeder sub-relay
This confirms that the proposed Multivariable Fuzzy Rule-based relay (MFR) relay exhibits capability for use in the unit scheme since feeder-a sub-relay detects abnormal flow of current and power occasioned by short circuit effect at the PCC
Summary
The primary aim of a micro-grid is to provide quality, reliable and sustainable power to a load center[1]. The micro-grid is a form of Distributed Generation (DG) and a building block of smart grid which essentially operates using advanced control architecture and quality protection. A micro-grid may have energy storage system and it may run autonomously or in grid-connected mode[2,3,4]. The benefits, topology and control of micro-grids are well established[5,6,7]. A proper design of protection scheme remains challenging owing to the nature of DG micro-sources within the distribution system[8,9]. Power flow in a micro-grid could be two-way[10], such as energy storage or plug-in electric vehicles[11,12,13].
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