[Paper Review] An Adaptive Overcurrent Protection for Solar-based DC Microgrids Using IEC 61850

Saeed Sanati, Maher A. Azzouz+1 more|arXiv (Cornell University)|Jul 4, 2023

Islanding Detection in Power Systems4 citations

TL;DR

This paper proposes a communication-assisted, adaptive overcurrent protection scheme for solar-based DC microgrids using the IEC 61850 protocol. By dynamically selecting relay settings based on real-time grid and fault conditions via IEC 61850 data exchange, the scheme achieves fast, selective fault clearing despite challenges like high fault current rise times and DC grounding issues, validated through MATLAB and OPAL-RT simulations.

ABSTRACT

Over-Current (OC) protection is one of the pervasive protections in solar-based DC microgrids. Fast operation is a key advantage of its popularity. On the other hand, utilizing OC in DC microgrids has some challenges that are not in AC grids. Some of these challenges are related to the grounding approach of the DC microgrid, and others are related to the high rise time of the fault current in DC microgrids. Considering these challenges, an adaptive OC scheme with high selectivity and speed is presented in this paper. The proposed scheme is communication-assisted and relies on IEC 61850 protocol. In this scheme, different setting groups for each OC relay are defined, and based on the grid and fault conditions, a setting group is selected. This option is performed considering the data transferred via communication level using IEC 61850 protocol between relays. To evaluate the efficiency of the proposed scheme, simulations using MATLAB software and the experimental tests using OPAL-RT real-time simulator and Zenon software are presented.

Motivation & Objective

• To address the challenges of conventional overcurrent protection in DC microgrids, such as high fault current rise times and grounding issues.
• To improve protection selectivity and speed in solar-based DC microgrids where traditional AC protection schemes are inadequate.
• To develop a communication-assisted protection scheme leveraging IEC 61850 for real-time coordination and adaptive relay settings.
• To validate the scheme’s performance under diverse fault conditions using simulation and real-time testing.

Proposed method

• The scheme defines multiple setting groups for each overcurrent relay based on system operating conditions and fault types.
• Relay coordination is achieved through IEC 61850-based communication, enabling real-time exchange of system and fault data between relays.
• The selection of the optimal setting group is triggered by fault detection and data exchange via the IEC 61850 protocol, ensuring adaptive response.
• The system uses MATLAB for offline simulation and OPAL-RT real-time simulator with Zenon software for experimental validation.
• Fault current rise time and DC grounding configuration are explicitly modeled to reflect real microgrid dynamics.
• The scheme integrates with existing substation automation systems via standardized IEC 61850 messaging, ensuring interoperability.

Experimental results

Research questions

• RQ1 How can overcurrent protection in DC microgrids be made adaptive to varying fault and system conditions?
• RQ2 What role does IEC 61850-based communication play in enabling dynamic relay coordination for improved selectivity?
• RQ3 How does the proposed scheme handle the high fault current rise time typical in DC microgrids?
• RQ4 To what extent does the adaptive setting selection improve fault clearing speed and selectivity compared to fixed settings?

Key findings

• The adaptive scheme successfully clears faults with high selectivity by dynamically adjusting relay settings based on real-time system data.
• The use of IEC 61850 enables reliable and fast communication between relays, supporting rapid coordination during fault events.
• Simulations and real-time tests confirmed the scheme’s ability to distinguish between internal and external faults under varying operating conditions.
• The scheme demonstrated faster fault clearing times compared to conventional fixed-setting overcurrent relays, particularly in high inductance DC systems.
• The integration of multiple setting groups based on fault current rise time and system configuration significantly improved coordination accuracy.