Management Techniques for Reliable Microgrid Operation

This item may be protected under Title 17 of the U.S. Copyright Law. It is made available by UMBC for non-commercial research and education. For permission to publish or reproduce, please see http://aok.lib.umbc.edu/specoll/repro.php or contact Special Collections at speccoll(at)umbc.edu
Access limited to the UMBC community. Item may possibly be obtained via Interlibrary Loan through a local library, pending author/copyright holder's permission.
Access limited to the UMBC community. Item may possibly be obtained via Interlibrary Loan thorugh a local library, pending author/copyright holder's permission.

Abstract

The rising demand for an uninterrupted power supply and the rapid growth of infrastructure have motivated the introduction of microgrids (MGs) to facilitate power management and enable scalability. An MG corresponds to distributed energy resources (DER) and loads that can be managed in an efficient manner. It can be connected to the main grid or operate in an autonomous mode. While MGs present an efficient solution for integrating DER into traditional distribution networks, protections against failures and disturbances are considered as one of the critical challenges for successful MG operation. Most of the existing protection techniques target radial distribution networks. In the presence of DER, these techniques will not be directly applicable to MGs because DER introduces dynamic behaviors that disturb the electrical components and consequently cause a serious threat to MG stability. This dissertations addresses the challenge of fault detection, isolation, and mitigation in microgrids.It is essential for the grid network to be closely monitored for detecting failures. Hence, we first present a new technique of grid topology reconfiguration when a zero-injection bus (ZIB) is incorporated in the grid, in order to provide full observability through the phase measurement unit (PMU) devices. Then we solved an optimization problem of PMU placement; a special transformation is presented to reduce the complexity of the optimization while factoring in the contribution of a ZIB to the system's observability. Second, we use the topology reconfiguration method to protect the grid from the cascaded failure caused by frequency variations; the designed protection system, named cascade failure containment (CFC), employs power flow and topology reconfiguration optimization to prevent the spreading of failure and enable the MG to sustain its operation. The optimization strives to prevent the propagation of the failure while maximizing the supported loads by the system. Then, we increase the failure resiliency of the MG based on the power flow solution through topology reconfiguration. The topology optimization minimizes the maximum line stability index. Third, we tackle the effect of short circuit current fluctuation in the presence of distributed generators (DGs); short circuit current fluctuation impacts the overcurrent relays and makes the coordination among these relays difficult. We introduce a novel adaptive protection system that pursues two phases to handle the influence of fault current variations. The first phase opts to tolerate disturbances in the MG by minimizing the active power loss of the generators; meanwhile, the second phase strives to contain the effect of intolerable disturbance within a specific area, whose boundaries are determined through the correlation between the primary/backup relay pairs. The directional overcurrent relay (DOCR) coordination optimization minimizes the operating time of the relays within the contained area. Finally, we mitigated the effects of low fault current contributions from Inverter Bases DGs (IBDGs) that consequently degrades the MG protection and makes the fault detection and isolation more complex. The increased penetration of IBDGs would lower the fault current level; such diminished fault currents induce mal-trip and fail-to-trip problems for protective relays. To handle this challenge, we propose an adaptive protection scheme that considers renewable energy resources (RES), a Battery Energy Storage System (BESS), and hybrid units in the MG. The proposed scheme applies an internal cooperation strategy between RES and BESS to ensure a reliable power output. Then, a power flow-based fault analysis is performed to determine the fault current paths. A fault current zone (FCZ) is formed out of the IBDGs that are found to be on the observed fault current paths and an optimal residual capacity is determined for the BESS units within the FCZ; the optimization maximizes the residual capacity of the involved BESS units to ensure sufficient capacity for supplementing fault current to the fault location. We validate all proposed protection techniques using a simulation and show that they outperform competing approaches.

Management Techniques for Reliable Microgrid Operation

Files

Links to Files

Permanent Link

Collections

Author/Creator

Author/Creator ORCID

Date

Type of Work

Department

Program

Citation of Original Publication

Rights

Subjects

Abstract