System configuration, fault detection, location, isolation and restoration: a review on LVDC Microgrid protections

Low voltage direct current (LVDC) distribution has gained the significant interest of research due to the advancements in power conversion technologies. However, the use of converters has given rise to several technical issues regarding their protections and controls of such devices under faulty conditions. Post-fault behaviour of converter-fed LVDC system involves both active converter control and passive circuit transient of similar time scale, which makes the protection for LVDC distribution significantly different and more challenging than low voltage AC. These protection and operational issues have handicapped the practical applications of DC distribution. This paper presents state-of-the-art protection schemes developed for DC Microgrids. With a close look at practical limitations such as the dependency on modelling accuracy, requirement on communications and so forth, a comprehensive evaluation is carried out on those system approaches in terms of system configurations， fault detection, location, isolation and restoration

Ancillary Services in Hybrid AC/DC Low Voltage Distribution Networks

In the last decade, distribution systems are experiencing a drastic transformation with the advent of new technologies. In fact, distribution networks are no longer passive systems, considering the current integration rates of new agents such as distributed generation, electrical vehicles and energy storage, which are greatly influencing the way these systems are operated. In addition, the intrinsic DC nature of these components, interfaced to the AC system through power electronics converters, is unlocking the possibility for new distribution topologies based on AC/DC networks. This paper analyzes the evolution of AC distribution systems, the advantages of AC/DC hybrid arrangements and the active role that the new distributed agents may play in the upcoming decarbonized paradigm by providing different ancillary services.Ministerio de Economía y Competitividad ENE2017-84813-RUnión Europea (Programa Horizonte 2020) 76409

Assessing the areas of concern regarding decarbonisation of industrial microgrids based on a novel classification framework

This thesis is made for a technology company in Vaasa, Finland which has the focus on decarbonisation of microgrids through optimisation with different aspects in mind, such as, reducing emissions, decreasing fuel consumption, increasing grid reliability and asset availability, and lowering operation costs. The aim of the thesis is to investigate the fundamental areas of concern, when making an early assessment of the potential for decarbonisation through optimisation in industrial microgrids. This is done through a qualitative study based on semi-structured interviews with experts with different areas of expertise in the company. The interviews are then analysed and compared to relevant literature in the field. The outcome is a proposed classification framework grouped into three different sections: generation, network & control, and load. These sections are further divided into different sub-sections with own themes, where categories are listed. Additionally, some suggestions on further utilisation are also proposed in the work, for example, in customer conversations or as an aid for experts.Detta diplomarbete är gjort åt ett teknologiföretag beläget i Vasa, Finland, vilket fokuserar på utfasning av fossila bränslen (eng. decarbonisation) i mikronätverk genom optimering inom olika fokusområden. Exempel på dessa är minskning av utsläpp och bränsleförbrukning, ökning av nätverksstabilitet och tillgänglighet av elproduktionsanläggningar samt optimering av driftskostnader. Målet med diplomarbetet är att utreda inom vilka områden det kan uppstå utmaningar när man i ett tidigt skede kartlägger möjligheterna för utfasning av fossila bränslen genom optimering i industriella mikronätverk. Det här är gjort genom en kvalitativ studie baserad på semistrukturerade intervjuer med sakkunniga med olika expertisområden inom företaget i fråga. Intervjuerna är sedan analyserade och jämförda med relevant litteratur inom ämnet. Resultatet av studien är ett klassificeringssystem indelat i tre olika huvudområden: generering, nätverk & kontroll och last. Dessa är vidare uppdelade i underområden med egna teman i vilka olika kategorier är listade. Därtill i arbetet ges även förslag på användningsområden för detta klassificeringssystem, exempelvis i kundsamtal eller som hjälpmedel för experter

Assessing the areas of concern regarding decarbonisation of industrial microgrids based on a novel classification framework

This thesis is made for a technology company in Vaasa, Finland which has the focus on decarbonisation of microgrids through optimisation with different aspects in mind, such as, reducing emissions, decreasing fuel consumption, increasing grid reliability and asset availability, and lowering operation costs. The aim of the thesis is to investigate the fundamental areas of concern, when making an early assessment of the potential for decarbonisation through optimisation in industrial microgrids. This is done through a qualitative study based on semi-structured interviews with experts with different areas of expertise in the company. The interviews are then analysed and compared to relevant literature in the field. The outcome is a proposed classification framework grouped into three different sections: generation, network & control, and load. These sections are further divided into different sub-sections with own themes, where categories are listed. Additionally, some suggestions on further utilisation are also proposed in the work, for example, in customer conversations or as an aid for experts.Detta diplomarbete är gjort åt ett teknologiföretag beläget i Vasa, Finland, vilket fokuserar på utfasning av fossila bränslen (eng. decarbonisation) i mikronätverk genom optimering inom olika fokusområden. Exempel på dessa är minskning av utsläpp och bränsleförbrukning, ökning av nätverksstabilitet och tillgänglighet av elproduktionsanläggningar samt optimering av driftskostnader. Målet med diplomarbetet är att utreda inom vilka områden det kan uppstå utmaningar när man i ett tidigt skede kartlägger möjligheterna för utfasning av fossila bränslen genom optimering i industriella mikronätverk. Det här är gjort genom en kvalitativ studie baserad på semistrukturerade intervjuer med sakkunniga med olika expertisområden inom företaget i fråga. Intervjuerna är sedan analyserade och jämförda med relevant litteratur inom ämnet. Resultatet av studien är ett klassificeringssystem indelat i tre olika huvudområden: generering, nätverk & kontroll och last. Dessa är vidare uppdelade i underområden med egna teman i vilka olika kategorier är listade. Därtill i arbetet ges även förslag på användningsområden för detta klassificeringssystem, exempelvis i kundsamtal eller som hjälpmedel för experter

Nonlinear Control of an AC-connected DC MicroGrid

New connection constraints for the power network (Grid Codes) require more flexible and reliable systems, with robust solutions to cope with uncertainties and intermittence from renewable energy sources (renewables), such as photovoltaic arrays. A solution for interconnecting such renewables to the main grid is to use storage systems and a Direct Current (DC) MicroGrid. A "Plug and Play" approach based on the "System of Systems" philosophy using distributed control methodologies is developed in the present work. This approach allows to interconnect a number of elements to a DC MicroGrid as power sources like photovoltaic arrays, storage systems in different time scales like batteries and supercapacitors, and loads like electric vehicles and the main AC grid. The proposed scheme can easily be scalable to a much larger number of elements.Comment: IEEE IECON 2016, the 42nd Annual Conference of IEEE Industrial Electronics Society, October 24-27, 201

Microgrids: Legal and Regulatory Hurdles for a More Resilient Energy Infrastructure

Natural disasters and climate change have made it apparent that energy infrastructure needs to be modernized and microgrids are one type of technology that can help the electricity grid become more resilient, reliable, and efficient. Different states have begun developing microgrid pilot projects including California, New York, Connecticut, and Pennsylvania. The City of Pittsburgh, Pennsylvania is the first city to propose implementing “energy districts” of microgrids that will serve as critical infrastructure, in the first phase, and then expand to commercial and community settings. This large project involves many shareholders including public utilities, government agencies, and private entities. Utilizing microgrids on such a large scale raises issues regarding its classification, as energy generation or energy storage, and whether it should be regulated by public utilities, private entities, or municipalities. In a state like Pennsylvania where the energy market has been deregulated, there is strong concern on what the public utilities involvement will be with microgrid projects. This Note focuses on the regulatory issues that are raised with the construction and operation of microgrids at such a large scale in Pittsburgh. It addresses the difficulties that arise when implementing microgrids in a deregulated energy market state such as Pennsylvania, where little to no statutory language exists regarding microgrids. It will give an overview of proposed Pennsylvania legislation that may impact a public utilities’ control over microgrid technology and the benefits and costs when examining the extent of the public utilities’ role regarding ownership and control of microgrids in a deregulated energy market

Mixed-integer-linear-programming-based energy management system for hybrid PV-wind-battery microgrids: Modeling, design, and experimental verification

© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksMicrogrids are energy systems that aggregate distributed energy resources, loads, and power electronics devices in a stable and balanced way. They rely on energy management systems to schedule optimally the distributed energy resources. Conventionally, many scheduling problems have been solved by using complex algorithms that, even so, do not consider the operation of the distributed energy resources. This paper presents the modeling and design of a modular energy management system and its integration to a grid-connected battery-based microgrid. The scheduling model is a power generation-side strategy, defined as a general mixed-integer linear programming by taking into account two stages for proper charging of the storage units. This model is considered as a deterministic problem that aims to minimize operating costs and promote self-consumption based on 24-hour ahead forecast data. The operation of the microgrid is complemented with a supervisory control stage that compensates any mismatch between the offline scheduling process and the real time microgrid operation. The proposal has been tested experimentally in a hybrid microgrid at the Microgrid Research Laboratory, Aalborg University.Peer ReviewedPostprint (author's final draft

Various approaches for power balancing in grid-connected and islanded microgrids

One of the promising solutions to reduce power imbalance, an undesired impact of intermittent renewable energy sources, is to supply the loads by means of local distributed energy resources in the form of a microgrid. Microgrids offer several benefits such as reduction of line losses, increased system reliability, and maximum utilisation of local energy resources. A microgrid, during its islanded operation, is more susceptible to the frequency and voltage fluctuation caused by a sudden dispatch either from the generation or load. Therefore, additional control is required to manage either the output power from the generation side or the demand from the end-user side. Thus, appropriate and efficient control and monitoring systems need to be installed. However, the cost of such a system will reduce the rate of investment return on microgrid projects. This research has focused on developing various techniques to maintain the voltage and frequency within acceptable limits in microgrids, taking into account various influencing factors. This study proposes an additional active power management technique through the use of inverters, that can maintain the microgrid’s frequency when the generated power in the microgrid is much higher than its demand. Also, to facilitate the microgrid’s transition from grid-connected to islanded mode, the inverters can be controlled with a soft starting ramp. Moreover, a control function employing a droop control method is proposed in order to reduce the output power of the renewable sources when the microgrid frequency is much higher than the nominal frequency. On the other hand, when the demand is higher than the generated power, managing the demand under a demand response program is proposed as a means of maintaining the microgrid stability. This is an inexpensive solution which will not reduce the rate of investment return on the microgrid project. However, this requires the installation of appropriate enabling technologies at the utility and end-user sides. Moreover, the participation from demand response participants is influenced by the profit earned from engaging in the program. Therefore, in this research, the technical and economic benefits of demand response deployment are analysed in detail. The execution of the demand response program through load-shifting, reducing the appliances’ consumed power, and load-shedding causes customer discomfort. To minimise this discomfort, in this thesis, suitable strategies are suggested for various groups of loads. Furthermore, each load profile contains information on its capacity, flexibility, and operating time. The proposed approach ensures that the loads with a larger capacity and flexibility are the most preferred ones to be controlled during demand response events so that customer discomfort and the number of affected loads can be minimised. Also, this study examines the load’s economic value, power losses, emission factor, and cost of energy production to maximise the microgrid operator’s profit as a result of deploying the demand response program. Meanwhile, to encourage end-users’ engagement in demand response programs, the microgrid operator should offer incentives to the customer as compensation for any incurred costs and discomfort felt. The given incentives should be such that both the microgrid operator and the end-user gain the maximum profit. Therefore, this study proposes an approach for calculating the level of incentives that should be given to the participants by comparing the differences between ongoing revenue and the cost of energy with and without demand response