Abstract
The development of a proper protection system is essential for the secure and reliable operation of microgrids. In this paper, a novel adaptive protection system for microgrids is presented. The protection scheme is based on a protective device that includes two directional elements which are operating in an interleaved manner, namely overcurrent and undervoltage elements. The proposed protection scheme can be implemented in microprocessor-based relays. To define the settings of the protective device, a robust programming approach was proposed considering a finite set of fault scenarios. The scenarios are generated based on the predictions about the available energy and the demand. For each decision step, a robust optimization problem is solved online, which is based on forecasting with a confidence band to represent the uncertainty. The system is tested and compared using real data sets from an existing microgrid in northern Chile. To assess the performance of the proposed protection system, fault scenarios not considered in the optimization were taken into account. The results obtained show that the proposed protective device is able to manage those failure scenarios, as well as those included in the tuning of the settings. Practical considerations are also discussed.
Highlights
Microgrids have received much attention in recent years since they appear as a new solution to the power supply, taking advantage of local energy resources
The proposed methodology was tested on an existing microgrid installed in Huatacondo, a remote town located in northern Chile
A methodological proposal for adjusting the settings of the protective devices according to the operating conditions of a microgrid, using robust optimization, is proposed
Summary
Microgrids have received much attention in recent years since they appear as a new solution to the power supply, taking advantage of local energy resources (such as wind and solar). Microgrids can operate while being connected to a main grid (grid-connected mode) or in isolated mode. During grid-connected mode, the microgrid receives power from both the utility and the DG units. When it is operating in isolated mode, the microgrid must autonomously meet the power requirements of the customers securely, reliably, and with adequate power quality. When the microgrid concept was introduced in 2001 as a new solution to the power supply, it became evident that the protection requirements would be different compared to traditional power systems [2]. As detailed in [3], the differences are mainly due to the short-circuit fault currents that can change in magnitude and direction, depending on the operating conditions of the microgrid [4]
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