Abstract
The deployment of distributed generators (DGs) gives rise to several challenges for a microgrid or conventional distribution feeder, regarding control and protection issues. The major ones are: bi-directional flow of power, changes in fault current magnitude, and continuous changes in operational configuration due to both the plug-and-play of DGs and loads, and the intermittency of the renewable DGs. This issue is exacerbated when the microgrid contains several converter-interfaced DGs and operates in the islanded mode of operation. Hence, conventional protection strategies and relaying techniques will no longer be sufficient to protect islanded microgrids against network faults and disturbance conditions. This paper proposes a fast and reliable communication-supported protection strategy for ensuring the safe operation of converter-interfaced islanded microgrids. The strategy is implementable using commercially accessible microprocessor based digital relays, and is applicable for the protection of low voltage islanded microgrids. It provides backup protection to handle communication failures and malfunctions of protective devices. The paper also presents the detailed structural layout of the digital relay, which executes the proposed protection strategy. A number of improvements are proposed to find an alternative method for conventional overcurrent relays to reliably detect small-magnitude fault currents and high impedance faults, commonly encountered in converter-interfaced islanded microgrids. A simple and economical bus protection method is also proposed. Several simulations are conducted on a comprehensive model of a realistic operational industrial microgrid (Goldwind Smart Microgrid System) using PSCAD/EMTDC software environment—for different case studies and fault scenarios—to verify the effectiveness of the present strategy and its digital relay.
Highlights
Hybrid energy systems containing distributed generators (DGs), powered by micro-sources such as photovoltaic power systems, microturbines, wind power systems, mini-hydros, and fuel cells have been gaining acceptance among power industries and utilities because of their easy accessibility, reduced-emissions, simplicity, enhanced operational efficiency, and higher reliability
Due to the special features of microgrids, traditional power system protection and control strategies which rely on large fault current and unidirectional power flow assumptions of radial network structure are not sufficient for operating microgrids [5,6]
This paper proposes a rapid and reliable protection strategy for low voltage microgrids operating in the islanded mode of operation or physically isolated from the main utility grid
Summary
Hybrid energy systems containing distributed generators (DGs), powered by micro-sources such as photovoltaic power systems, microturbines, wind power systems, mini-hydros, and fuel cells have been gaining acceptance among power industries and utilities because of their easy accessibility (the renewables: especially wind and solar), reduced-emissions (environmental friendly clean energy), simplicity (less complex structure), enhanced operational efficiency, and higher reliability. Lai et al [21] and Kexing et al [22] have proposed a comprehensive protection strategy for microgrids operating in the islanded mode by employing microprocessor based intelligent relays These strategies provide solutions to microgrid protection problems resulting from HIFs and unnecessary outage of important DGs and loads. They employ adaptive overcurrent (50/51) relays to detect solid fault occurrences in the microgrid. This paper proposes a rapid and reliable protection strategy for low voltage microgrids operating in the islanded mode of operation or physically isolated from the main utility grid Several simulations are conducted on a comprehensive model of a realistic operational industrial microgrid (Goldwind Smart Microgrid System) using PSCAD/EMTDC software environment, for different case studies and fault scenarios, to verify the effectiveness of the presented strategy and its digital relay
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