Voltage and current THD in microgrid with different DG unit and load configurations

After microgrid transition from the normal operation to the islanded operation the system impedance changes considerably and it affects on the harmonic voltages of the microgrid. In this paper the voltage and current THD before and after islanding are studied with different microgrid configurations. Simulations are also made by applying negative sequence filtering in control system of converters to reduce the voltage and current THD inmicrogrid during unsymmetrical load. Based on the studies recommendations for technical solutions which ensure high power quality in islanded microgrid are given.fi=vertaisarvioimaton|en=nonPeerReviewed

Sensitivity analysis of frequency and voltage stability in islanded microgrid

This paper studies the voltage and frequency stability of an islanded microgrid and the sensitivity of these quantities to certain changes in system configuration. In conventional power systems the system frequency is coupled with the rotor speed of the directly grid connected large synchronous generators and power unbalance can be seen as changed system frequency. But in an islanded microgrid it is possible that all generation units are connected to grid via converters and there is no inertia of rotating masses to affect the frequency. In that case the frequency has to be created by a power electronic device and the frequency is more of less fixed and power unbalance cannot be detected in the classical way. The studied urban low voltage (LV) network based microgrid consists of three converters and one synchronous generator based distributed generation (DG) units. The studies are made with PSCAD simulation software.fi=vertaisarvioimaton|en=nonPeerReviewed

Fault type and location detection in islanded microgrid with different control methods based converters

In this paper the fault type and location detection in an islanded low voltage (LV) distribution network based microgrid with converters applying different control methods is studied. In the future most of the distributed generation (DG) units in microgrids will be connected to network through power electronic interfaces (e.g. converters) which usually have limited capability to feed fault current due to power devices protection reasons.Also converter control methods affect to the converter fault behavior. This means that during the faults the converter cannot feed larger current than the nominal current of it or it tries to keep active power fed to grid on the reference value, so that the current of converter increases to a certain limit. Simulations show that protection of islandedmicrogrid with converters could be based on changes in phase voltages and voltage RMS values at the connection points of DG units. But, due to different control methods of converters, the fault location estimation is not that simple in every case.The simulation studies are made with PSCAD simulation software package.fi=vertaisarvioimaton|en=nonPeerReviewed

An Adaptive Protection for Radial AC Microgrid Using IEC 61850 Communication Standard : Algorithm Proposal Using Offline Simulations

The IEC 61850 communication standard is getting popular for application in electric power substation automation. This paper focuses on the potential application of the IEC 61850 generic object-oriented substation event (GOOSE) protocol in the AC microgrid for adaptive protection. The focus of the paper is to utilize the existing low-voltage ride through characteristic of distributed generators (DGs) with a reactive power supply during faults and communication between intelligent electronic devices (IEDs) at different locations for adaptive overcurrent protection. The adaptive overcurrent IEDs detect the faults with two different preplanned settings groups: lower settings for the islanded mode and higher settings for the grid-connected mode considering limited fault contributions from the converter-based DGs. Setting groups are changed to lower values quickly using the circuit breaker status signal (XCBR) after loss-of-mains, loss-of-DG or islanding is detected. The methods of fault detection and isolation for two different kinds of communication-based IEDs (adaptive/nonadaptive) are explained for three-phase faults at two different locations. The communication-based IEDs take decisions in a decentralized manner, using information about the circuit breaker status, fault detection and current magnitude comparison signals obtained from other IEDs. However, the developed algorithm can also be implemented with the centralized system. An adaptive overcurrent protection algorithm was evaluated with PSCAD (Power Systems Computer Aided Design) simulations, and results were found to be effective for the considered fault cases.© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).fi=vertaisarvioitu|en=peerReviewed

Real-Time Hardware-In-the-Loop Testing of IEC 61850 GOOSE based Logically Selective Adaptive Protection of AC Microgrid

The real-time (RT) hardware-in-the-loop (HIL) simulation-based testing is getting popular for power systems and power electronics applications. The HIL testing provides the interactive environment between the actual power system components like control and protection devices and simulated power system networks including different communication protocols. Therefore, the results of the RT simulation and HIL testing before the actual implementation in the field are generally more acceptable than offline simulations. This paper reviews the HIL testing methods and applications in the recent literature and presents a step-by-step documentation of a new HIL testing setup for a specific case study. The case study evaluates improved version of previously proposed communication-dependent logically selective adaptive protection algorithm of AC microgrids using the real-time HIL testing of IEC 61850 generic object-oriented substation event (GOOSE) protocol. The RT model of AC microgrid including the converter-based distributed energy resources and battery storage along with IEC 61850 GOOSE protocol implementation is created in MATLAB/Simulink and RT-LAB software using OPAL-RT simulator platform. The Ethernet switch acts as IEC 61850 station bus for exchanging GOOSE Boolean signals between the RT target and the actual digital relay. The evaluation of the round-trip delay using the RT simulation has been performed. It is found that the whole process of fault detection, isolation and adaptive setting using Ethernet communication is possible within the standard low voltage ride through curve maintaining the seamless transition to the islanded mode. The signal monitoring inside the relay is suggested to avoid false tripping of the relay.©2021 Institute of Electrical and Electronics Engineers. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/This work was mainly carried out in the SolarX research project funded by the Business Finland under Grant No. 6844/31/2018. Some part of this work was carried out during the VINPOWER research project funded by the European Regional Development Fund (ERDF), Project No. A73094. The financial support provided through these projects is greatly acknowledged.fi=vertaisarvioitu|en=peerReviewed

Protection of the Future Harbor Area AC Microgrids Containing Renewable Energy Sources and Batteries

A significant share of global carbon emissions is related to marine vessels running solely on fossil fuels. The hybrid or fully electrified marine vessels using battery energy storage systems (BESS) both for onboard propulsion system and for cold-ironing during docking at harbor areas will significantly reduce marine related carbon emissions. However, the transformation of marine vessels’ operations from diesel engines to BESS will necessarily require charging stations and other electric power infrastructure at harbor areas. The sustainable and cheap energy of renewable energy sources like wind turbine generators (WTGs), photovoltaic (PV) systems and related BESS could be used at harbor areas for charging depleted vessel-BESS and supplying power to cold-ironing loads. For this purpose, two new harbor area smart grid or AC microgrid models have been developed by our research group. This paper presents a comprehensive analysis of three-phase short-circuit faults for one of the proposed AC microgrid models using PSCAD/EMTDC simulations. The fault study of harbor area AC microgrid-1 is done for both grid-connected and islanded modes. The main purpose of the fault study is to check if grid-connected mode overcurrent settings of intelligent electronic devices (IEDs) will also be valid for different islanded mode fault cases with different fault current contributions from converter-based distributed energy resources (DERs) including WTG, PV and BESS. The extent of fault current contribution from DERs and BESS to avoid adaptive protection settings and to ensure definite-time protection coordination and fast fuse operations during different islanded modes is investigated.©2023 Authors. Published by IEEE. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/fi=vertaisarvioitu|en=peerReviewed

Protection system for future LV microgrids

Traditional protection of low voltage (LV) network will not be applicable for future LV microgrids and new adaptive protection system must be developed. In this paper adaptive protection system for LV microgrid during normal and island operation will be presented. Adaptivity means that protection system will e.g. change settings of LV feeder protective devices (PDs) according to the operation state of the LV microgrid, i.e. normal or island operation, and in the settings of LV feeder PDs also the number and type of DG units connected to the corresponding LV feeder and also their fault current feeding capabilities will be taken into account. Fast and selective operation between different PDs is achieved by intelligent utilization of high-speed communication.fi=vertaisarvioimaton|en=nonPeerReviewed

Active network management scheme for reactive power control

In the future new options to provide needed technical ancillary services locally and system-wide by distributed energy resources (DER) are needed. One ancillary service which DER could provide is the reactive power management when microgrid is operated in utility grid-connected mode. In this paper different requirements for reactive power flow between distribution and transmission grids were considered in Sundom Smart Grid (SSG) and the measured data from SSG was used for developing a concept for reactive power management. Based on these different requirements “Future Reactive Power Window” was formulated for SSG which was the basis for control scheme formulation. The simulations showed that coordinated reactive power management scheme across different voltage levels by utilizing control of distributed generation could be very beneficial to the voltage support ancillary service.fi=vertaisarvioitu|en=peerReviewed

Monitoring and Protection of Power Distribution Networks with IEC 61850-9-2 Standard

In the modern power grid, communication plays a vital role in making the system more reliable and secure. The communications network transfers data between different units to a control center or to Intelligent Electric Devices (IEDs) in order to accurately control or protect the modern power system. The paper discussed possible ways to monitor the measured values for protecting the power system according to IEC 61850-9-2 (sample value). The sequence of the process consists of streaming the sample value packet, decoding it, and phasor extraction and filtering, which are discussed here. To validate the research, Sundom Smart Grid was used as a pilot to measure the values converted to digital form (IEC 61850-9-2) and to stream it to the system through a highly secure communications network. To decode the SV packet, two scenarios are presented in the case study, based on processing useful features of the IEC 61850-9-2 standard-based raw data streamed from the SSG, including μPMU in a range of embedded instruments and a real-time simulator. The main result of this paper is an algorithm for analyzing SV packets and determining whether the network is operating normally.©2020 IET. This paper is a postprint of a paper submitted to and accepted for publication in 15th International Conference on Developments in Power System Protection (DPSP 2020) and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at the IET Digital Library.fi=vertaisarvioitu|en=peerReviewed

Non-Directional Earth Fault Passage Indication in Isolated Neutral Distribution Networks

In this paper, two new methods for locating single-phase to ground faults in isolated neutral distribution networks are proposed. The methods are based on the analysis of symmetrical sequence currents. They are solely based on currents, not requiring voltage measurement. The first method employs only the zero sequence current and the second one utilizes the negative sequence current in combination with the zero sequence current. It is revealed why using only zero sequence current with a simple threshold is insufficient and may lead to false results. Using the proposed methods, earth faults with high resistances can be located in isolated neutral distribution networks with overhead lines or cables.© Writers. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license, http://creativecommons.org/licenses/by/4.0/fi=vertaisarvioitu|en=peerReviewed