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China is the largest energy consumer worldwide, with a fast-growing rate. But the energy and environmental problems brought by its unbalanced energy structure and low energy efficiency restrict the sustainable development of China. The Distributed Energy System (DES) is one of the internationally recognized solutions to the problems. To enhance the implementation of the DES under China’s scenario, the thesis develops computational models for the Combined Cooling, Heat, and Power (CCHP) and Separated Cooling, Heat, and Power (SCHP) systems for a Micro Energy Grid in northeast China using MATLAB. The objective is to minimize the overall expenditure, energy use, and carbon emission equivalents. The results show that the CCHP system reduces 18.62% of the overall expenditure and 35.02% of the carbon emission equivalents than the SCHP system. The CCHP system has a promising prospect in China with better Greenhouse Gas emissions reduction and economic performance. / Kina är världens största energikonsument, med en snabb tillväxttakt. Men de energi- och miljöproblem som orsakas av den obalanserade energistrukturen och den låga energieffektiviteten begränsar Kinas hållbara utveckling. Distribuerade energisystem (DES) är en av de internationellt erkända lösningarna på dessa problem. För att förbättra implementeringen av DES enligt Kinas scenario utvecklar avhandlingen beräkningsmodeller för kombinerad kylning, värme och kraft (CCHP) och separerad kylning, värme och kraft (SCHP) för ett mikroenerginät i nordöstra Kina med hjälp av MATLAB. Målet är att minimera de totala kostnaderna, energianvändningen och koldioxidutsläppen. Resultaten visar att CCHP-systemet minskar de totala utgifterna med 18,62 % och koldioxidutsläppen med 35,02 % jämfört med SCHP-systemet. CCHP-systemet har lovande utsikter i Kina med bättre minskning av växthusgasutsläpp och ekonomisk prestanda.

As a promising approach for sustainable development, distributed energy systems have receive increasing attention worldwide and have become a key topic explored by researchers in the areas of building energy systems and smart grid. In line with this research trend, this dissertation presents a techno-economic analysis and optimization of distributed energy systems including combined heat and power (CHP), photovoltaics (PV), battery energy storage (BES), and thermal energy storage (TES) for commercial buildings. First, the techno-economic performance of the CHP system is analyzed and evaluated for four building types including hospital, large office, large hotel, and secondary school, located in different U.S. regions. The energy consumption of each building is obtained by EnergyPlus simulation software. The simulation models of CHP system are established for each building type. From the simulation results, the payback period (PBP) of the CHP system in different locations is calculated. The parameters that have an influence on the PBP of the CHP system are analyzed. Second, PV system and integrated PV and BES (PV-BES) system are investigated for several commercial building types, respectively. The effects of the variation in key parameters, such as PV system capacity, capital cost of PV, sell back ratio, battery capacity, and capital cost of battery, on the performance of PV and/or PV-BES system are explored. Finally, subsystems in previous chapters (CHP, PV, and BES) along with TES system are integrated together based on a proposed control strategy to meet the electric and thermal energy demand of commercial buildings (i.e., hospital and large hotel). A multi-objective particle swarm optimization (PSO) is conducted to determine the optimal size of each subsystem with the objective to minimize the payback period and maximize the reduction of carbon dioxide emissions. The results reveal how the key factors affect the performance of distributed energy system and demonstrate the proposed optimization can be effectively utilized to obtain an optimized design of distributed energy systems that can get a tradeoff between the environmental and economic impacts for different buildings.

Klimatförändring ställer idag krav på högre energieffektivitet vilket lett till utbyggnaden av ett distribuerat energisystem. Samtidigt introduceras framväxande teknologier som digitala tvillingar till det nya energisystemet i hopp om att ytterligare effektivisera systemet. För att främja samarbete mellan industrin och akademin, och således stödja utvecklingen och implementeringen av digitala tvillingar, bör aktörernas syner sammanföras. Syftet med arbetet är därav att undersöka ifall det finns några likheter och skillnader mellan industri och akademi i hur de uppfattar användningsområdena och utmaningarna med digitala tvillingar av distribuerade energisystem. För att besvara forskningsfrågan utfördes inledningsvis en systematisk litteraturstudie. Studien utgör arbetets underlag för akademins uppfattning om digitala tvillingars användningsområden och utmaningar. Vidare utfördes fem intervjuer med olika industriaktörer med insikt i digitala tvillingar och distribuerade energisystem för att avgöra deras uppfattning om teknologin. Insikterna från litteraturstudien och intervjuerna ställdes sedan mot varandra för att identifiera eventuella likheter och skillnader. De användningsområden som identifierades av akademin och industrin var simulering, felidentifiering och prediktivt underhåll, visualisering och styrning, cybersäkerhet, optimering av kraftnätet samt prognostisering och estimering. Utmaningarna som identifierades av akademin var standardiserade ramverk för modellering och för datahantering, brist på passande sensorer, datalagringsmöjligheter, datorers beräkningskapacitet och cyberattacker. Industrin identifierade motstånd till ny teknologi, kompetensbrist, silotänk, teknologins värdeskapande, datahantering och cyberattacker som huvudutmaningarna med digitala tvillingar. Utifrån analysen har industrin och akademin en liknande uppfattning om digitala tvillingars användningsområden inom distribuerade energisystem men uppfattningen om utmaningarna med digitala tvillingar var, inom akademin, mer teknikbaserad medan den inom industrin var främst icketeknisk. / Today, the increasing threat of climate change has created a greater need for higher energy efficiency, which has led to the development of a distributed energy system. At the same time, emerging technologies such as digital twins are being introduced into the new energy system in the hope of further improving the efficiency of the system. To promote cooperation between industry and academia, and thus support the development and implementation of digital twins, the views of the actors should be brought together. The purpose of this work is therefore to investigate whether there are any similarities and differences between industry and academia in how they perceive the applications and challenges of digital twins of distributed energy systems.  To answer the research question, a systematic literature study was initially conducted. The study constitutes the basis for the academia's perception of the use cases and challenges of digital twins. Furthermore, five interviews were conducted with different industrial actors with insight into digital twins and distributed energy systems to determine their perception of the technology. The insights from the literature study and interviews were then compared to identify any similarities and differences.  The application areas identified by academia and industry were simulation, fault identification and predictive maintenance, visualization and control, cyber security, grid optimization, and forecasting and estimation.  The challenges identified by academia were standardized modelling and data management frameworks, lack of suitable sensors, data storage capabilities, computational capacity of computers and cyber-attacks. Industry identified resistance to new technologies, skills shortages, silo thinking, technology value creation, data management and cyber-attacks as the main challenges of digital twins. Based on the analysis, industry and academia have a similar perception of the use cases of digital twins of distributed energy systems but the perception of the challenges of digital twins was, in academia, more technology-based while in industry it was mainly non-technical.

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Integrating energy across different sectors is an efficient solution for improving energy systems to meet energy demands with low CO2 emissions. Such integration includes combining the supply and demand of heating, cooling, and electricity by implementing appropriate equipment, as well as combining the energy systems of civic and industrial sectors. This thesis develops various optimization approaches to identify the optimal design and operation of distributed energy systems and the integration of energy systems across commercial, industrial, and transportation sectors, which minimize CO2 emissions and costs of the systems. Available equipment of the energy systems includes combined cooling, heating, and power system, absorption chiller, solar thermal collector, photovoltaic, boiler, electric chiller, battery, ground source heat pump, and air source heat pump. This thesis provides the following contributions to this area. (1) Identify optimal structures of distributed energy systems under different electric grid CO2 footprints. The work implements representative periods when formulating the energy system, which reduces computation time. (2) Differentiate heating demands of entities in the integrated system at different temperature levels to ensure feasible heat transfer. It removes the simplified assumptions in existing studies on the integrated energy system that assume all heating demands are at a uniform temperature. (3) Optimize production rates of plants instead of assuming steady industrial production rates. The switchable production rates lead to a further reduction in CO2 emissions of the integrated system. (4) Identify the environmental and economic benefits of the integrated operation under different electric grid CO2 footprints. It presents that integrated operation reduces more CO2 emissions when the electric grid has higher CO2 footprints. (5) Identify the optimal relative sizes of entities in the integrated system that maximize the CO2 emissions reduction benefits brought by the integrated system. (6) Prove the integrated system has lower CO2 emissions than individual energy systems both under deterministic and stochastic scenarios. Overall, the work in this thesis contributes to developing energy systems and integrated energy systems with the lowest possible CO2 emissions under various scenarios. / Thesis / Doctor of Philosophy (PhD) / As the total population continues to increase worldwide, it is necessary to improve community energy systems to reduce CO2 emissions when meeting energy demands. An efficient solution is integrating energy systems across different sectors. This work explores novel structures of energy systems – integrated energy systems that combine the supply and demand of heating, cooling, and electricity in residential, commercial, industrial, and transportation sectors. The optimal energy system configurations, sizes of subsystems, production rates of plants, heat transfer and electricity transfer, as well as capacity and operation of the equipment, have been identified by developing optimization approaches that minimize CO2 emissions and costs of the integrated system. The optimal design and operation are found under both deterministic and stochastic scenarios and different grid electricity generation scenarios, which provide references for developing community energy systems with the lowest possible CO2 emissions under various scenarios.

Interconnection of DERs into the transmission lines is starting to take a substantial share of the total power capacity. Although the largest share of power generation attributes to coal and gas power plants, renewable energy is gradually increasing. However, in the past, the size of DERs was relatively smaller, and rooftop PV was the dominant renewable energy source. As a result, the studies for interconnection focused on those rooftop PVs on the distribution side. Since the scenario is slowly changing as more utilities increase the share of clean energy by building large-scale solar farms and wind farms, it is necessary to study the effect of those DERs in the transmission system. Among the various issues, this work focuses on the impact on a transmission system's voltage stability. When the voltage stability at a point in the system is compromised, it can affect the entire power system's overall security, quality, and reliability. Therefore, this work aims to assess the system's stress due to increased loading conditions and increased growth of DERs integration. A steady-state voltage stability index is used to generate a heat-map that identifies the areas where the system can go unstable in events like the loss of the renewable generation under a bus. The steady-state simulation is performed on the IEEE 14 bus system in Distributed Engineering Workstation (DEW) to find the system's weak links using the stability heat-map. DERs are added to the corresponding weak buses, and the improvement in the stability margin for various penetration levels are studied. The results obtained from the steady-state analysis are also verified using the dynamic simulation of the model using OpenModelica. / Master of Science / Transmission networks are going through some of the fundamental changes in how they are planned and operated as more and more renewable energy sources are connected to the grid. Unlike the traditional setup where the transmission line transfers bulk power from a large generator to the load center at a different location, the advent of renewable energy resources enables the power to be generated in distributed form. It allows electrical power to be generated closer to the demand. In the long run, the transmission system's stress reduces as a significant portion of demand is supplied locally. Thus, the distributed energy resources (DERs) in the power grid have the potential for substantial economic and environmental benefits. However, it can also bring about a range of challenges to the power system. Among the various issues, this work focuses on the effects on a transmission system's voltage stability. When the voltage stability at a point in the system is compromised, it can affect the entire power system. Therefore, this work aims to assess the stress on the system due to increased loading conditions and increased growth of DERs integration, utilizing a voltage stability index to identify the areas where the system can go unstable in events like the loss of renewable generation under a bus. The steady-state simulation is performed on the IEEE 14 bus system to find the weak links in the system where DERs can improve the system's stability. The results obtained from the steady-state analysis are verified using the dynamic simulation of the model.

Residential solar Photovoltaic (PV) installations are increasing at a very high pace in the United States. In 2017 there are approximately one million residential solar PV installations in the US. A significant share of these installations are downstream of distribution transformers and thus connected to the secondary. To precisely analyze voltage variations induced by PV systems into distribution systems, accurate models of load and PV systems connected to the secondary side of distribution transformers are required. In the work here we consider two secondary circuit modeling approaches, simple secondary and detailed secondary models. In simple secondary models all loads and all PV generators below a distribution transformer are modeled as an aggregate load and an aggregate PV generator. In the detailed secondary models all loads and PV systems below the distribution transformers are modeled individually and secondary conductors and service drops are also modeled. Using a cloud motion simulator, it is observed that employing the simple secondary models can lead to inaccurate and conservative results. Moreover, the locations with the greatest voltage changes are different in the two modeling approaches. This paper highlights the importance of utilizing detailed secondary models over simple secondary models in analyzing PV generation. / Master of Science

Yes / Hybrid AC-DC microgrid (HMG) allows direct integration of both AC distributed generators (DGs) and DC DGs, AC and DC loads into the grid. The AC and DC sources, loads are separate out and are connected to respective subgrid mainly to reduce the power conversion, thus the overall efficiency of the system increases. This paper aims to introduce a novel hybrid AC-DC microgrid planning and design model within a microgrid market environment to maximize net social welfare (NSW). NSW is defined as present value of total demand payment minus present value of total planning cost including investment cost of distributed energy sources (DERs) and converters, operation cost of DERs and the cost of energy exchange with the utility grid subject to network constraints. Scenario Tree approach is used to model the uncertainties related to load demand, wind speed and solar irradiation. The effectiveness of the proposed model is validated through the simulation studies on a 28-bus real hybrid AC-DC microgrid.

Power systems constitute a pillar of the critical infrastructure and, as a result, their cybersecurity is paramount. Traditional power system architectures are moving from their original centralized nature to a distributed paradigm. This transition has been propelled by the rapid penetration of distributed energy resources (DERs) such as rooftop solar panels, battery storage, etc. However, with the introduction of new DER devices, technologies, and operation models, the threat surface of power systems is inadvertently expanding. This dissertation provides a comprehensive overview of the cybersecurity landscape of DER-enabled power systems outlining potential attack entry points, system vulnerabilities, and the corresponding cyberattack impacts. Cyber-physical energy systems (CPES) testbeds are crucial tools to study power systems and perform vulnerability analyses, test security defenses, and evaluate the impact of cyberattacks in a controlled manner without impacting the actual electric grid. This work also attempts to provide bottom-up security solutions to secure power systems from their lowest abstraction layer, i.e., hardware. Specifically, custom-built hardware performance counters (HPCs) are proposed for the detection of malicious firmware, e.g., malware, within DER inverter controllers. The experimental results prove that HPCs are an effective host-based defense and can accurately identify malicious firmware with minimum performance overheads. Also, methodologies to secure communication protocols and ensure the nominal operation of DER devices using physics-informed schemes are presented. First, DERauth, a battery-based secure authentication primitive that can be used to enhance the security of DER communication, is proposed and evaluated in a CPES testbed. Then, a physics-based attack detection scheme that leverages system measurements to construct models of autonomous DER agents is presented. These measurement-based models are then used to discern between nominal and malicious DER behavior. The dissertation concludes by discussing how the proposed defense mechanisms can be used synergistically in an automated framework for grid islanding to improve power system security and resilience, before it provides prospective directions for future research.