Non-Pilot Protection of the Inverter- Dominated Microgrid

Houman Lahiji,Firouz Badrkhani Ajaei,Ryan E Boudreau

doi:10.1109/access.2019.2944137

Houman Lahiji, Firouz Badrkhani Ajaei + Show 1 more

Open Access

https://doi.org/10.1109/access.2019.2944137

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Abstract

Without utilizing costly communication systems, the existing protection strategies fail to reliably detect the occurrence and direction of faults in the inverter-dominated microgrid. To address this issue, this paper introduces a selective and reliable non-pilot protection strategy for the inverter-dominated microgrid. The proposed protection strategy (i) does not require communication signals, (ii) incorporates phase- and sequence-domain protective elements for reliable detection of symmetrical and asymmetrical faults, (iii) improves the existing sequence-domain directional elements and effectively utilizes them for accurate determination of the fault direction in the presence of inverter-interfaced distributed energy resources, (iv) selectively protects the inverter-dominated microgrid against internal and external faults, (v) is robust against the grid-connection mode of the microgrid, and (vi) enables fuse protection of laterals and non-critical circuits. The acceptable performance of the proposed protection strategy is verified through comprehensive fault studies conducted on a realistic study system simulated in the PSCAD/EMTDC software environment. This paper also demonstrates that the proposed protection strategy can be implemented using an off-the-shelf digital relay.

Highlights

The proliferation of the alternating current (AC) microgrid has been constrained by the lack of a cost-effective, selective, and reliable strategy for its protection against faults [1]–[4]
The results indicate that the proposed protection strategy operates reliably and selectively in an inverter-dominated microgrid, under both grid-connected and islanded operation modes
The study results indicate that the proposed protection strategy selectively and reliably protects the microgrid under the grid-connected and islanded modes and various fault conditions

Summary

INTRODUCTION

The proliferation of the alternating current (AC) microgrid has been constrained by the lack of a cost-effective, selective, and reliable strategy for its protection against faults [1]–[4]. The protection strategy of [6], which utilizes phase OC and negative-sequence OC elements, reliably detects asymmetrical faults but has low sensitivity to symmetrical faults in the islanded inverter-dominated microgrid. This paper introduces a non-pilot protection strategy that effectively addresses the aforementioned issues related to fault detection, fault direction identification, and protection coordination, in the inverter-dominated microgrid. The proposed protection strategy incorporates (i) phase- and sequence-domain protective elements for reliable detection of symmetrical and asymmetrical faults, (ii) improved positive and negative sequence-domain directional elements for reliable detection of the fault direction, and (iii) a protection coordination strategy inspired by the definite-time grading technique of [6], [7], [18], for selective protection under both grid-connected and islanded operation modes. VOLUME 7, 2019 protection strategy is verified by implementing it in an off-the-shelf digital relay and demonstrating its desirable operation using an industrial relay testing platform

DIRECTIONAL PROTECTION ELEMENTS

SYMMETRICAL FAULTS

REVISITING THE NSDE

STUDY RESULTS

CONCLUSION