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The urge to reduce the dependence on natural gas for heating at the residential level has led to the deployment of different fossil fuel-free alternatives. In the Netherlands, two technologies are leading the transition: heat pumps, due to their high COP, and photovoltaic–thermal systems, due to their dual electric-thermal output. However, both represent a challenge for users and grid operators, aside from their stochastic behavior. Heat pumps alone can surpass a typical Dutch house's total energy and power consumption. Photovoltaic–thermal systems, as their only electric homologs, usually have a mismatch between generation and demand, causing energy injections to the grid. From the electric perspective, storage systems are a proven solution to reduce the energy exchange with the distribution network. This paper proposes four multi-carrier energy system configurations for a Dutch household, comprising different combinations of a photovoltaic–thermal system, a battery energy storage, a heat pump, and an underground water tank thermal energy system, providing analytical models for every component (including the thermal losses from the thermal storage to the ground), and the space heating and electrical demands. We determined the components’ compatibility and evaluated the combinations considering their thermal performance, electrical performance, and equivalent CO2 emissions. The results suggest that using a heat pump combined with a photovoltaic system and a battery provides the best trade-off. The photovoltaic–thermal system alone could not supply the thermal demand required for comfortable space heating nor reach temperatures high enough to charge the thermal storage. Combining the thermal storage with the heat pump allows a certain degree of flexibility for the heat pump activation at the cost of COPs between 0.8 and 1.38 when used to charge the thermal storage, thus increasing energy consumption and equivalent emissions considerably., DC systems, Energy conversion & Storage

Batteries are one of the main tools to provide the flexibility distribution and transmission systems need due to their increasing dependence on weather conditions. However, environmental and economic factors pose a significant problem. New types of batteries that do not rely on rare earth metals and organic solvents but instead use water and more common ions could be a cost-effective and environmentally safe way to provide energy storage in the future. We studied the performance of sea-salt cells designed as a low-cost, environmentally friendly method to store electricity. We used a constant current charge/discharge test with different currents, from 50 mA to 300 mA, to identify the maximum efficiencies of the cell. Then, we introduced a new strategy to determine the cut-off voltage to discharge the battery, inspired by the maximum power point found in photovoltaics. We used a constant voltage charge to determine the cell’s energy density. However, evidence of side reactions urged us to use constant current charge/discharge tests to identify the battery’s capacity based on the efficiencies drop. Results showed a maximum energy efficiency of 74.6% at 200 mA and a maximum Coulombic efficiency of 88.7% at 300 mA. The cut-off voltage of the cell during discharge should be between 1.4 V and 1.6 V. The energy densities range from 10.1 Wh/kg(6.53 WhL) with an efficiency of 57.5% and 4.18 Wh/kg(2.7 WhL) with an efficiency of 69.8%., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., DC systems, Energy conversion & Storage

The energy transition requires electrical alternatives for domestic heating. Heat pumps are the most common alternatives to gas boilers. However, heat pumps consume a significant amount of electrical power. We simulated an 18-node low voltage network with five buildings with six apartments each to evaluate the effect of deploying heat pumps as part of multi-carrier energy systems at the residential level. We also combined heat pumps with solar collectors and thermal energy storage to quantity whether a more complex system benefits the low-voltage network. Replacing the gas boilers for heat pumps in the majority of the buildings resulted in voltage drops below the limit of the standard EN50160. The voltage drops were significantly improved when we included solar collectors and thermal energy storage in the domestic heating system., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., DC systems, Energy conversion & Storage

Energy storage is vital for a future where energy generation transitions from a fossil fuels-based one to an energy system that relies heavily on clean energy sources such as photovoltaic (PV) solar energy. To foster this transition, engineers and practitioners must have open-access models of PV systems coupled with battery storage systems (BESS). These models are fundamental to quantifying their economic and technical merits during the design phase. This paper contributes in this direction by carefully describing a model that accurately represents the power directions and energy dealings between the PV modules, the battery pack, and the loads. Moreover, the general model can be implemented using two different PV generation methods, the Gaussian model and the meteorological data-based model (MDB). We found that the MDB model is more appropriate for short-term analysis compared to the Gaussian model, while for long-term studies, the Gaussian model is closer to measured data. Moreover, the proposed model can reproduce two different energy management strategies: peak-shaving and maximizing self-consumption, allowing them to be used during PV–BESS sizing stages. Furthermore, the results obtained by the simulation are closed when compared to a real grid-tied PV–BESS, demonstrating the model’s validity., DC systems, Energy conversion & Storage

Smart MicroGrids (SMGs) can be seen as a promising option when it comes to addressing the urgent need for sustainable transition in electric systems from the current fossil fuel-based centralised system to a low-carbon, renewable-based decentralised system. Unlike previous studies that were restricted to a limited number of actors and only took a mono-disciplinary research approach, this current review adopts a multidisciplinary, socio-technical approach and addresses the factors that have been hindering the development of SMGs and considers how these barriers interact. This study contributes to the body of literature on the development of SMGs by mapping and discerning technical, regulatory, market, social and institutional barriers for different types of actors, including technology providers, consumers, Distributed Generation (DG) providers and system operators, based on information derived from laboratory reports, demonstration pilots, and academic journals. In addition, attention is paid to how these barriers interact based on real-life experimentation. A holistic picture of barriers and their interaction is presented as well as recommendations for future research., DC systems, Energy conversion & Storage, Organisation and Governance

This paper discusses the design and optimization of electric vehicles’ fast-charging stations with on-site photovoltaic energy production and a battery energy storage system. Three scenarios, varying the number of chargers, distance from the main grid, and on-site photovoltaic generation potential, are investigated. Such scenarios are benchmarked in investment, operating costs, and grid connection requirements. The addition of a battery storage system is also evaluated to reduce the operating cost and, therefore, boost the system’s economic parameters, such as the net present value, and increase the grid independence.The analysis shows that the addition of the battery system can be effective in both performance metrics, the reduction of the grid connection, which can be reduced up to 80% by the addition of a large size battery, and the increase of the net present value, which can be even doubled with respect to the case when the battery storage system is not installed., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., DC systems, Energy conversion & Storage, Intelligent Electrical Power Grids

Renewable energy power plants and transport and heating electrification projects are being deployed to enable the replacement of fossil fuels as the primary energy source. This transition encourages distributed generation but makes the grid more weather-dependent, thus reducing its inertia. Simultaneously, electrical network operators face voltage, frequency, and stability challenges at the distribution level. Networks were not designed to manage the stochasticity of renewable energy sources or the congestion caused by the new transport and heating demands. Such challenges are commonly addressed through infrastructure reinforcements. This review studies how energy storage systems with different carriers can provide a collaborative solution involving prosumers as ancillary services providers at the distribution level. We focused on the European urban context; thus, we analyzed renewable energy sources, batteries, supercapacitors, hydrogen fuel cells, thermal energy storage, and electric vehicles. A thorough review of successful implementations proved that including storage in one or more carriers benefits the distribution system operators and the prosumers, from both technical and economic perspectives. We propose a correlation between individual energy storage technologies and the ancillary services they can provide based on their responses to specific grid requirements. Therefore, distribution system operators can address network issues together with the prosumers. Nevertheless, attractive regulatory frameworks and business models are required to motivate prosumers to use their assets to support the grid. Further work is recommended to describe the joint operation of multiple storage technologies as multicarrier systems, focusing on the coupling of electrical and thermal energy storage. Additionally, how ancillary services affect the energy storage system’s aging should be studied., DC systems, Energy conversion & Storage

Battery Energy Storage Systems typically procure their primary revenues from regulated energy and ancillary services markets; nonetheless, they have great potential in supporting distribution network operators and their users. This paper evaluates the potential business case of battery storage systems integrating market application and services to a photovoltaic assisted electric vehicle fast-charging station. A mathematical deterministic optimization problem is formulated using mixed-integer linear programming to combine battery storage system operation in the day-ahead and frequency regulation market and the remunerated services offered to the charging station. The technical and economic feasibility of the solution and the applicability of the proposed framework is verified through a case study reflecting an existing photovoltaic assisted charging station in the Netherlands and considering the Dutch energy market framework and prices. The study shows that such battery storage system implementation is economically and technically advantageous for the players involved. The battery storage system can stack additional revenues on top of the market revenues. The charging station benefits from a reduced peak power and a 30% tariff reduction, and the system operator would indirectly benefit from the shaved charging station profile. Furthermore, the analysis shows that providing services to the charging station from the battery storage system does not significantly impact its market-related revenues., DC systems, Energy conversion & Storage

Fifth-generation energy networks are combined networks of heat and electricity, that have the ability to generate, distribute, store and share energy between consumers. Knowledge on the dynamic behaviour of the physical phenomena related to energy generation, distribution and storage provides insight into the performance of the system as a whole. A mixed-integer linear algorithm is proposed, implementing a partitioned clustering program for subsequent classification of typical demand, grouping specific days with similar demand profiles together. From this arrangement, the optimal network configuration can be determined using an objective function, minimizing the economic and environmental impact. To validate the optimization results, a simulation of the network was built, which mimics its physical dynamic behaviour, and through which the distribution and storage capabilities of the network can be assessed. Advanced advice on fifth-generation energy networks is presented that can be applied to early-stage network design, reducing costs and emissions, along with data on the implementation of renewable energy technologies and their performance. Additionally, this research provides the foundation for numerical modelling of such energy networks which contributes to future research., DC systems, Energy conversion & Storage

Smart MicroGrids (SMGs) can be seen as a promising option when it comes to addressing the urgent need for sustainable transition in electric systems from the current fossil fuel-based centralised system to a low-carbon, renewable-based decentralised system. Unlike previous studies that were restricted to a limited number of actors and only took a mono-disciplinary research approach, this current review adopts a multidisciplinary, socio-technical approach and addresses the factors that have been hindering the development of SMGs and considers how these barriers interact. This study contributes to the body of literature on the development of SMGs by mapping and discerning technical, regulatory, market, social and institutional barriers for different types of actors, including technology providers, consumers, Distributed Generation (DG) providers and system operators, based on information derived from laboratory reports, demonstration pilots, and academic journals. In addition, attention is paid to how these barriers interact based on real-life experimentation. A holistic picture of barriers and their interaction is presented as well as recommendations for future research., DC systems, Energy conversion & Storage, Organisation & Governance

The dynamic behaviour - steady-state and transient - of the DC Microgrids during power disturbance can affect the system’s general performance. A hybrid combination of energy storage devices with slow frequency response, like a Fuel Cell, and with a fast dynamic response, like a Super-Capacitor, provides an improved dynamic response to stabilise DC bus voltage. However, control parameters should be designed based on the preferences of the system. This paper proposes a fuzzy-based controller to determine the Virtual Capacitor Droop controller to achieve the desired transient response. The proposed dynamic control method is validated through MATLAB/Simulink., Accepted author manuscript, DC systems, Energy conversion & Storage, Organisation and Governance

Battery Energy Storage Systems (BESSs) are a new asset for Primary Frequency Regulation (PFR), an ancillary service for improving the grid stability. The system operators determine the implementation and remuneration of PFR. However, assessing the revenue stream is not enough to define the business case, as also the components’ lifetime has to be estimated. Previous studies of lifetime estimation for BESSs performing PFR considered only the electrochemical storage, disregarding the power electronics (PE). Nonetheless, researchers have shown the importance of estimating PE wear due to the operation when applied in renewable energy generation and microgrids. This paper presents a lifetime analysis of BESSs providing PFR considering IGBT modules, electrolytic capacitors and electrochemical storage degradation. The lifetime information is used to estimate BESS's Net-Present-Value (NPV), evaluating the benefits of deploying PE-based BESS in the European grid. A comparison between different countries, Germany, the Netherlands, and the U.K., is performed, considering the PFR implementation and remuneration differences. The analysis shows that the BESS management strategy can extend its lifetime and that the component that exhibits the shortest lifetime is the electrochemical storage. The PE components are subject to low wear due to the low power utilization and, therefore, small thermal swings while performing PFR. In conclusion, the provision of PFR by means of BESS has been found to be profitable in all three countries. However, in the Netherlands, the potential NPV has been estimated to be 47% and 76% higher than in Germany and the U.K., respectively., DC systems, Energy conversion & Storage, Intelligent Electrical Power Grids

The dynamic behaviour - steady-state and transient - of the DC Microgrids during power disturbance can affect the system’s general performance. A hybrid combination of energy storage devices with slow frequency response, like a Fuel Cell, and with a fast dynamic response, like a Super-Capacitor, provides an improved dynamic response to stabilise DC bus voltage. However, control parameters should be designed based on the preferences of the system. This paper proposes a fuzzy-based controller to determine the Virtual Capacitor Droop controller to achieve the desired transient response. The proposed dynamic control method is validated through MATLAB/Simulink., Accepted author manuscript, DC systems, Energy conversion & Storage, Organisation & Governance

Battery Energy Storage Systems (BESSs) are a new asset for Primary Frequency Regulation (PFR), an ancillary service for improving the grid stability. The system operators determine the implementation and remuneration of PFR. However, assessing the revenue stream is not enough to define the business case, as also the components’ lifetime has to be estimated. Previous studies of lifetime estimation for BESSs performing PFR considered only the electrochemical storage, disregarding the power electronics (PE). Nonetheless, researchers have shown the importance of estimating PE wear due to the operation when applied in renewable energy generation and microgrids. This paper presents a lifetime analysis of BESSs providing PFR considering IGBT modules, electrolytic capacitors and electrochemical storage degradation. The lifetime information is used to estimate BESS's Net-Present-Value (NPV), evaluating the benefits of deploying PE-based BESS in the European grid. A comparison between different countries, Germany, the Netherlands, and the U.K., is performed, considering the PFR implementation and remuneration differences. The analysis shows that the BESS management strategy can extend its lifetime and that the component that exhibits the shortest lifetime is the electrochemical storage. The PE components are subject to low wear due to the low power utilization and, therefore, small thermal swings while performing PFR. In conclusion, the provision of PFR by means of BESS has been found to be profitable in all three countries. However, in the Netherlands, the potential NPV has been estimated to be 47% and 76% higher than in Germany and the U.K., respectively., DC systems, Energy conversion & Storage, Intelligent Electrical Power Grids

Hybrid ac–dc reconfigurable link technology can find interesting applications in medium-voltage power distribution. These are networks having dc links operating in parallel alongside ac links with post-fault reconfiguration capability. A given system can operate in different configurations while maintaining equivalent capacity during (n−1) contingencies using reconfigurability. This paper provides a method for the ideal selection of the link configuration by defining the efficiency and economic viability boundaries with varying operating power demand and power factor. A sensitivity analysis with parameters such as grid voltage, link length, conductor area, and converter efficiency as well as economic factors such as converter cost and link conductor installation cost is discussed. The study identifies the operating zones wherein the refurbished parallel ac–dc reconfigurable distribution links can be an efficient and economically preferred option of delivering power as compared to a system with only ac or dc links., DC systems, Energy conversion & Storage

Hybrid ac-dc distribution systems with multiple parallel operating ac and dc links are being developed to maximize system capacity during (n-1) contingencies. This paper shows that offline reconfigurability between such ac and dc links post-fault clearance allows an additional design flexibility of reducing the required substation converter rating to maintain the same required capacity by maximizing the utilization of healthy infrastructure. The associated variation of system capacity with power rating and number of substation converters is determined for different types of component faults. It is discussed that while converter downsizing is possible, as a consequence the parallel ac-dc link system is forced to operate at a sub-optimal efficiency during normal conditions. Using case studies, the economics of this trade-off is quantified for determining the optimal de-rating factor for varying grid voltage, link length, and conductor area., DC systems, Energy conversion & Storage

Energy Storage Systems (ESSs) are promising solutions for mitigating the technical problems created by high penetration of Distributed Generation (DG) in distribution grids. This paper presents a methodology for the ESS sizing and placement within the distribution networks. Those are found through an optimization routine that considers the impact of the use of storage on voltage regulation and system losses. Several scenarios, varying the load and PV panels power, are investigated. In addition, the impact on the energy storage requirements of a basic residential self-consumption scheme is evaluated. The proposed method has demonstrated to be effective in determining the ESS size in the studied scenarios. Furthermore, the results show that the location that requires the lowest ESS rating does not necessarily offer satisfactory performances in terms of losses reduction and voltage control. Also, the paper shows that by encouraging residential users to self-consume the energy produced by the PV panels installed in their house, the grids ESS requirements can be significantly reduced., Accepted author manuscript, DC systems, Energy conversion & Storage

Since the voltages and currents in dc grids do not have a natural zero-crossing, the protection of these grids is more challenging than the protection of conventional ac grids. Literature presents several unit and non-unit protection schemes that rely on communication, or knowledge about the system's topology and parameters in order to achieve selective protection in these grids. However, communication complicates fast fault detection and interruption, and a system's parameters are subject to uncertainty and change. This paper demonstrates that, in low voltage dc grids, faults propagate fast through the grid and interrupted inductive currents commutate to non-faulted sections of the grid, which both can cause circuit breakers in non-faulted sections to trip. A decentralized plug-and-play protection scheme is proposed that ensures selectivity via an augmented solid-state circuit breaker topology and by utilizing the proposed time-current characteristic. It is experimentally shown that the proposed scheme provides secure and selective fault interruption for radial and meshed low voltage dc grids under various conditions., DC systems, Energy conversion & Storage, Algorithmics

This paper discusses a qualitative comparison between Two and Three-Level Voltage Source Converter (VSC) topologies for battery energy storage applications. Three-Level Neutral Point Clamped (NPC) and T-Type circuit topologies are benchmarked versus the state-of-art Two-Level VSC in terms of efficiency and power density considering a 100 kW system. Analytical equations for determining the power losses in the semiconductor modules are given, and the procedure for designing the output LCL filter and the DC-link capacitors is described. The analysis, based on off-the-shelf circuit components, shows that the Three-Level topologies perform better than the Two-Level one in both considered metrics, mainly due to their lower switching losses that allow operating at higher switching frequency without significantly degrading the system efficiency, and, at the same time, increasing the system power density. Additionally, it is found that the T-Type topology shows better performances than the NPC topology at full and high partial loads, being then more suitable for applications that require most of the operation at maximum power., Virtual/online event due to COVID-19 Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., DC systems, Energy conversion & Storage, Intelligent Electrical Power Grids

LCL filters are commonly adopted to attenuate the current harmonics produced by Pulse Width Modulation (PWM) Voltage Source Converters (VSC). Due to the nature of LCL filters, several combinations of L and C can deliver the attenuation required by the standards. The optimal configuration is generally evaluated, considering power density, costs, and filter efficiency. This paper shows that semiconductor efficiency should also be considered as an important design variable. It is shown that the AC ripple across the converter side inductor can reduce, to a certain extent, the overall semiconductor losses, when commercial IGBTs and the respective anti-parallel diodes are used. Reduced losses have benefits in terms of semiconductor module lifetime, chip area and cost reduction, and simplification of cooling requirements. Higher AC ripple, however, negatively affect the filter losses. Nonetheless, inductive components are typically much less critical in terms of losses dissipation and lifetime than semiconductors., "Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.", DC systems, Energy conversion & Storage, Intelligent Electrical Power Grids

Recent developments in the electricity sector encourage a high penetration of Renewable Energy Sources (RES). In addition, European policies are pushing for mass deployment of Electric Vehicles (EVs). Due to their non-controllable characteristics, these loads have brought new challenges in distribution networks, resulting in increased difficulty for Distribution System Operators (DSOs) to guarantee a safe and reliable operation of the grid. Battery Energy Storage Systems (BESSs) are promising solutions for mitigating the impact of the new loads and RES. In this paper, different aspects of the BESS's integration in distribution grids are reviewed. At first, the physical layer will be considered, focusing on the main battery technologies commercially available and on the power electronics converter. Secondly, the different functionalities that a grid-connected BESS can provide will be investigated, and then its sizing, location and control in distribution network will be discussed. In addition, an overview of actual BESSs installations is given. All in all, this paper aims at providing a comprehensive view of BESSs integration in distribution grids, highlighting the main focus, challenges, and research gaps for each one of these aspects., DC systems, Energy conversion & Storage, Intelligent Electrical Power Grids

Due to the distributed nature of future electrical power systems, decentralized control is essential for these grids. This paper shows that converters that have identical voltage thresholds switch off simultaneously even if some could have remained operational. Therefore, inadequate system and energy utilization can occur when decentralized demand or supply response is utilized. The Grid Sense Multiple Acces (GSMA) algorithm proposed in this paper ensures that, after a change occurs in the system, a subset of the converters remains connected to the grid, without the need of utilizing any form of communication. This is achieved by introducing an exponential backoff time between failed connection attempts. Furthermore, several simulations and experiments are conducted to illustrate and validate the behavior of the GSMA algorithm, showing that it can be applied to dc grids in order to improve system and energy utilization., DC systems, Energy conversion & Storage, Algorithmics

Energy Storage Systems (ESSs) are promising solutions for mitigating the technical problems created by high penetration of Distributed Generation (DG) in distribution grids. This paper presents a methodology for the ESS sizing and placement within the distribution networks. Those are found through an optimization routine that considers the impact of the use of storage on voltage regulation and system losses. Several scenarios, varying the load and PV panels power, are investigated. In addition, the impact on the energy storage requirements of a basic residential self-consumption scheme is evaluated. The proposed method has demonstrated to be effective in determining the ESS size in the studied scenarios. Furthermore, the results show that the location that requires the lowest ESS rating does not necessarily offer satisfactory performances in terms of losses reduction and voltage control. Also, the paper shows that by encouraging residential users to self-consume the energy produced by the PV panels installed in their house, the grids ESS requirements can be significantly reduced., Accepted author manuscript, DC systems, Energy conversion & Storage

Hybrid ac-dc distribution systems with multiple parallel operating ac and dc links are being developed to maximize system capacity during (n-1) contingencies. This paper shows that offline reconfigurability between such ac and dc links post-fault clearance allows an additional design flexibility of reducing the required substation converter rating to maintain the same required capacity by maximizing the utilization of healthy infrastructure. The associated variation of system capacity with power rating and number of substation converters is determined for different types of component faults. It is discussed that while converter downsizing is possible, as a consequence the parallel ac-dc link system is forced to operate at a sub-optimal efficiency during normal conditions. Using case studies, the economics of this trade-off is quantified for determining the optimal de-rating factor for varying grid voltage, link length, and conductor area., DC systems, Energy conversion & Storage

Hybrid ac–dc reconfigurable link technology can find interesting applications in medium-voltage power distribution. These are networks having dc links operating in parallel alongside ac links with post-fault reconfiguration capability. A given system can operate in different configurations while maintaining equivalent capacity during (n−1) contingencies using reconfigurability. This paper provides a method for the ideal selection of the link configuration by defining the efficiency and economic viability boundaries with varying operating power demand and power factor. A sensitivity analysis with parameters such as grid voltage, link length, conductor area, and converter efficiency as well as economic factors such as converter cost and link conductor installation cost is discussed. The study identifies the operating zones wherein the refurbished parallel ac–dc reconfigurable distribution links can be an efficient and economically preferred option of delivering power as compared to a system with only ac or dc links., DC systems, Energy conversion & Storage

Recent developments in the electricity sector encourage a high penetration of Renewable Energy Sources (RES). In addition, European policies are pushing for mass deployment of Electric Vehicles (EVs). Due to their non-controllable characteristics, these loads have brought new challenges in distribution networks, resulting in increased difficulty for Distribution System Operators (DSOs) to guarantee a safe and reliable operation of the grid. Battery Energy Storage Systems (BESSs) are promising solutions for mitigating the impact of the new loads and RES. In this paper, different aspects of the BESS's integration in distribution grids are reviewed. At first, the physical layer will be considered, focusing on the main battery technologies commercially available and on the power electronics converter. Secondly, the different functionalities that a grid-connected BESS can provide will be investigated, and then its sizing, location and control in distribution network will be discussed. In addition, an overview of actual BESSs installations is given. All in all, this paper aims at providing a comprehensive view of BESSs integration in distribution grids, highlighting the main focus, challenges, and research gaps for each one of these aspects., DC systems, Energy conversion & Storage, Intelligent Electrical Power Grids

Since the voltages and currents in dc grids do not have a natural zero-crossing, the protection of these grids is more challenging than the protection of conventional ac grids. Literature presents several unit and non-unit protection schemes that rely on communication, or knowledge about the system's topology and parameters in order to achieve selective protection in these grids. However, communication complicates fast fault detection and interruption, and a system's parameters are subject to uncertainty and change. This paper demonstrates that, in low voltage dc grids, faults propagate fast through the grid and interrupted inductive currents commutate to non-faulted sections of the grid, which both can cause circuit breakers in non-faulted sections to trip. A decentralized plug-and-play protection scheme is proposed that ensures selectivity via an augmented solid-state circuit breaker topology and by utilizing the proposed time-current characteristic. It is experimentally shown that the proposed scheme provides secure and selective fault interruption for radial and meshed low voltage dc grids under various conditions., DC systems, Energy conversion & Storage, Algorithmics

This paper discusses a qualitative comparison between Two and Three-Level Voltage Source Converter (VSC) topologies for battery energy storage applications. Three-Level Neutral Point Clamped (NPC) and T-Type circuit topologies are benchmarked versus the state-of-art Two-Level VSC in terms of efficiency and power density considering a 100 kW system. Analytical equations for determining the power losses in the semiconductor modules are given, and the procedure for designing the output LCL filter and the DC-link capacitors is described. The analysis, based on off-the-shelf circuit components, shows that the Three-Level topologies perform better than the Two-Level one in both considered metrics, mainly due to their lower switching losses that allow operating at higher switching frequency without significantly degrading the system efficiency, and, at the same time, increasing the system power density. Additionally, it is found that the T-Type topology shows better performances than the NPC topology at full and high partial loads, being then more suitable for applications that require most of the operation at maximum power., Virtual/online event due to COVID-19 Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., DC systems, Energy conversion & Storage, Intelligent Electrical Power Grids

LCL filters are commonly adopted to attenuate the current harmonics produced by Pulse Width Modulation (PWM) Voltage Source Converters (VSC). Due to the nature of LCL filters, several combinations of L and C can deliver the attenuation required by the standards. The optimal configuration is generally evaluated, considering power density, costs, and filter efficiency. This paper shows that semiconductor efficiency should also be considered as an important design variable. It is shown that the AC ripple across the converter side inductor can reduce, to a certain extent, the overall semiconductor losses, when commercial IGBTs and the respective anti-parallel diodes are used. Reduced losses have benefits in terms of semiconductor module lifetime, chip area and cost reduction, and simplification of cooling requirements. Higher AC ripple, however, negatively affect the filter losses. Nonetheless, inductive components are typically much less critical in terms of losses dissipation and lifetime than semiconductors., "Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.", DC systems, Energy conversion & Storage, Intelligent Electrical Power Grids

Due to the distributed nature of future electrical power systems, decentralized control is essential for these grids. This paper shows that converters that have identical voltage thresholds switch off simultaneously even if some could have remained operational. Therefore, inadequate system and energy utilization can occur when decentralized demand or supply response is utilized. The Grid Sense Multiple Acces (GSMA) algorithm proposed in this paper ensures that, after a change occurs in the system, a subset of the converters remains connected to the grid, without the need of utilizing any form of communication. This is achieved by introducing an exponential backoff time between failed connection attempts. Furthermore, several simulations and experiments are conducted to illustrate and validate the behavior of the GSMA algorithm, showing that it can be applied to dc grids in order to improve system and energy utilization., DC systems, Energy conversion & Storage, Algorithmics

Microgrid with integrated photo-voltaics (PV) and battery storage system (BSS) is a promising technology for future residential applications. Optimally sizing the PV system and BSS can maximise self-sufficiency, grid relief, and at the same time can be cost-effective by exploiting tariff incentives. To that end, this paper presents a comprehensive optimisation model for the sizing of PV, battery, and grid converter for a microgrid system considering multiple objectives like energy autonomy, power autonomy, payback period, and capital costs. The proposed approach involves developing a holistic techno-economic microgrid model based on variables like PV system power, azimuth angle, battery size, converter ratings, capital investment and electricity tariffs. The proposed method is applied to determine the optimum capacity of a PV system and BSS for two case residential load profiles in the Netherlands and Texas, US to investigate the effect of meteorological conditions on the relative size of PV and battery. Based on the optimisation results, thumb rules for optimal system sizing are derived to facilitate microgrid design engineers during the initial design phase., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., DC systems, Energy conversion & Storage

During the operation of a three line ac link in parallel with a ac-dc-ac link system that employs Back-to-Back (B2B)Medium Voltage Modular Multilevel Converters (MMC), a path for the low frequency zero sequence currents is shown to exist. Apart from causing additional losses, these currents can result in limitations on power capacity. A detailed analysis on the influence of cell capacitance, arm inductance and link conductor length on the circulating zero sequence currents and the means to mitigate them through a simulated control strategy is investigated. The simulations show that the dc link employing B2B-MMC can successfully operate in parallel with ac link without transformer isolation by controlling the zero sequence currents., DC systems, Energy conversion & Storage

The use of batteries is indispensable in stand-alone photovoltaic (PV) systems, and the physical integration of a battery pack and a PV panel in one device enables this concept while easing the installation and system scaling. However, the influence of high temperatures is one of the main challenges of placing a solar panel close to a battery pack. Therefore, this paper aims to select a suitable battery technology considering the temperature of operation and the expected current profiles. The methodology for battery selection is composed of a literature review, an integrated model, the design of an application-based testing, and the execution of the aging test. The integrated model was employed to choose among the battery technologies, and to design a testing procedure that simulated the operational conditions of the PV-battery Integrated Module (PBIM). Two Li-ion pouch cells were tested at two representative temperatures while applying various charging/discharging profiles. After the testing, the LiFePO4 (LFP) cells showed better performance when compared to LiCoO2 batteries (LCO), where for instance, the LCO cells capacity tested at 45∘C, faded 2,45% more than the LFP cells at the same testing conditions. Therefore, LFP cells are selected as a suitable option to be part of the PBIM., DC systems, Energy conversion & Storage

Microgrid with integrated photo-voltaics (PV) and battery storage system (BSS) is a promising technology for future residential applications. Optimally sizing the PV system and BSS can maximise self-sufficiency, grid relief, and at the same time can be cost-effective by exploiting tariff incentives. To that end, this paper presents a comprehensive optimisation model for the sizing of PV, battery, and grid converter for a microgrid system considering multiple objectives like energy autonomy, power autonomy, payback period, and capital costs. The proposed approach involves developing a holistic techno-economic microgrid model based on variables like PV system power, azimuth angle, battery size, converter ratings, capital investment and electricity tariffs. The proposed method is applied to determine the optimum capacity of a PV system and BSS for two case residential load profiles in the Netherlands and Texas, US to investigate the effect of meteorological conditions on the relative size of PV and battery. Based on the optimisation results, thumb rules for optimal system sizing are derived to facilitate microgrid design engineers during the initial design phase., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., DC systems, Energy conversion & Storage

During the operation of a three line ac link in parallel with a ac-dc-ac link system that employs Back-to-Back (B2B)Medium Voltage Modular Multilevel Converters (MMC), a path for the low frequency zero sequence currents is shown to exist. Apart from causing additional losses, these currents can result in limitations on power capacity. A detailed analysis on the influence of cell capacitance, arm inductance and link conductor length on the circulating zero sequence currents and the means to mitigate them through a simulated control strategy is investigated. The simulations show that the dc link employing B2B-MMC can successfully operate in parallel with ac link without transformer isolation by controlling the zero sequence currents., DC systems, Energy conversion & Storage

The use of batteries is indispensable in stand-alone photovoltaic (PV) systems, and the physical integration of a battery pack and a PV panel in one device enables this concept while easing the installation and system scaling. However, the influence of high temperatures is one of the main challenges of placing a solar panel close to a battery pack. Therefore, this paper aims to select a suitable battery technology considering the temperature of operation and the expected current profiles. The methodology for battery selection is composed of a literature review, an integrated model, the design of an application-based testing, and the execution of the aging test. The integrated model was employed to choose among the battery technologies, and to design a testing procedure that simulated the operational conditions of the PV-battery Integrated Module (PBIM). Two Li-ion pouch cells were tested at two representative temperatures while applying various charging/discharging profiles. After the testing, the LiFePO4 (LFP) cells showed better performance when compared to LiCoO2 batteries (LCO), where for instance, the LCO cells capacity tested at 45∘C, faded 2,45% more than the LFP cells at the same testing conditions. Therefore, LFP cells are selected as a suitable option to be part of the PBIM., DC systems, Energy conversion & Storage

Inductive power transfer (IPT) is gaining popularity across a wide range of battery charging applications like biomedical, consumer electronics and electric vehicle (EV) charging. One of the major challenges in designing IPT charge pads is determining the optimal physical sizes of the magnetic couplers resulting in efficient power transfer and low cost of materials. In EV applications, it is especially difficult due to the variation in nominal air gap, required power levels associated with different vehicle classes, and charging locations that may be encountered. This paper aims to determine the relationship between optimal coupler sizes and the nominal air gap of an IPT system. Finite element analysis (FEA) is used to model the electromagnetic behavior of the magnetic couplers. A multi-objective optimization framework is built to reveal the Pareto fronts which show the trade-offs between the power transfer efficiencies and the coupler power densities at different air gaps. This method is applied on polarized double-D (DD) couplers for a 5 kW IPT system at different air gaps. Analyzing the power densities of the Pareto Optimal designs an approximate relation between optimal pad sizes and the air gap is derived. Results show that there is an exponential relationship between the optimal coupler sizes and the nominal air gap., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., DC systems, Energy conversion & Storage

In [1], the name of one co-author, Germán Morales-Espana, was rendered incorrectly as Germán Morales-Espana Mouli. The correct byline is shown above. We sincerely regret the error., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., DC systems, Energy conversion & Storage, Algorithmics

An important step in Voltage-Source Modular Multilevel Converter (MMC) design is the selection of adequate semiconductor blocking voltage class. This paper highlights that particularly for grid connected medium voltage applications, the choice of suitable switch blocking voltage class is not so straightforward. The market available switch voltage ratings results in a discrete integer relationship for the number of submodules (N) with a fixed dc link voltage. This is shown to introduce interesting design trade-offs in consideration to investment costs, required capacitance for reasonable ripple voltage, submodule redundancy requirements, conduction switching losses. Using the example of a 10 MVA half bridge MMC connected to a 10 kV grid, it is shown that 1.7 kV and 3.3 kV insulated gate bipolar transitors (IGBTs) can be possible choices as compared to 1.2 kV, 4.5 kV and 6.5 kV blocking voltage., DC systems, Energy conversion & Storage

Back-to-back Modular multilevel converters (MMC) for medium voltage dc (MVDC) distribution link applications offer exciting opportunities due to its superior harmonic performance and high efficiency. Based on the steady state equations, it is shown that under specific active and reactive power operation, an increase in dc link voltage can be achieved without necessarily increasing the voltage seen by the MMC submodule components. Using steady state loss model, it is proved that the converter operating efficiency can be improved if this concept is applied., DC systems, Energy conversion & Storage

A practical issue faced by today's ac grid is the rapidly growing power demand on its aging infrastructure. One possibility to maximize the capacity of the existing infrastructure is to refurbish the ac links to operate under dc conditions using modular multilevel converters. In this paper, the idea is applied to restructure an actual medium voltage distribution system. Further, a systematic reconfiguration strategy is proposed to maintain high power delivery capacity even during (n-1) contingency. Contingency analysis is carried out for faults in different system components of the distribution grid. Towards this goal, novel concepts such as reconfigurable switch, dc link converter bypass and flexible dc to ac operational transition are proposed., DC systems, Energy conversion & Storage

The role of MVDC links for distribution network expansion is important. The distribution network operators (DNOs) can maximize the power transfer capacity of existing grid infrastructure during (n-1] contingencies using reconfigurable parallel ac-dc architecture. In addition this concept involves a range of efficiency, reliability and economic trade-offs. The object of this paper is to present a discussion on the emerging choices involved in adopting a parallel ac-dc reconfigurable link architecture in designing future and flexible power grids., DC systems, Energy conversion & Storage

The thermal behavior of medium voltage dc cables can find useful applications for efficient and capacity enhanced operation in cities as well as compact power transmission on all electric ships. Concepts such as dynamic current and voltage rating, difference in thermal proximity in ac and dc operation, pulsed load application and thermal degradation with enhanced dc voltage; all are interlaced with the crucial temperature profile of insulated conductors. This paper develops a theoretical thermal model to highlight the possibility of dynamic current rating with pulsed loads. Further, a novel idea of imposing a thermal profile on cables for dc partial discharge testing is discussed. For this purpose a heat transfer model for a segmented cable is developed and experimentally validated., DC systems, Energy conversion & Storage

Low voltage dc distribution grids face issues associated with arc faults, aggravated by the absence of current zero crossing. The focus of this paper is to comprehensively develop a method of series arc fault detection at the load side power electronics, based on the electrode dependent initial voltage drop occurring at the arc initiation. The proposed arc detection algorithm is described along with the structure and time constants of the designed bandpass filter. The operational boundaries of the arc detection algorithm are defined for copper electrodes depending on the set threshold voltage and the system parameters, like grid inductance, resistance, and the load capacitance. Further, the detection time and the zone of guaranteed positive detection are depicted. These are validated through test simulations on the state space model of the system. Finally, experimental validation of the proposed scheme is carried out, wherein, a series arc is generated in the dc circuit and the programmed micro-controller provides a real time signal upon detecting the arcing event. The results on variation in detection time with set threshold voltage are also presented experimentally., Accepted Author Manuscript, DC systems, Energy conversion & Storage

Due to the variable nature of the photovoltaic generation, energy storage is imperative, and the combination of both in one device is appealing for more efficient and easy‐to‐use devices. Among the myriads of proposed approaches, there are multiple challenges to overcome to make these solutions realistic alternatives to current systems. This paper classifies and identifies previous efforts to achieve integrated photovoltaic storage devices. Moreover, the gaps and future perspectives are analysed to give an overview of the field, paying attention to low‐power devices (<10 W) as well as high‐power devices (>10 W). We focus on devices that combine solar cells with supercapacitors or batteries, providing information about the structure, materials used, and performance. On the one hand, small power devices must concentrate on including power electronics to increase the efficiency of the system as well as ensuring a safe operation; likewise, more attention should be drawn to validate the feasibility of novel concepts by carrying out more realistic and standardised tests, including long‐term testing. On the other hand, high‐power devices must be researched thoroughly to evaluate the impact of high temperatures on energy storage and solar module ageing; furthermore, optimum system sizing is a relevant topic that deserves attention and its relation to modular solutions. This critical literature review serves as a guide to understand the characteristics of the approaches followed to integrate photovoltaic devices and storage in one device, shedding light on the improvements required to develop more robust products for a sustainable future., DC systems, Energy conversion & Storage

Changes in distribution grids pose significant challenges with respect to the control and management of these grids. Stability and decentralized control are vital to ensure the availability and accessibility of plug-and-play dc distribution grids that are (temporarily) without communication. Therefore, this paper presents guidelines for these grids that ensure global stability and a decentralized control strategy that implements these stability guidelines. The stability guidelines are derived using a Brayton-Moser representation of the system to arrive at a Lyapunov candidate function. Furthermore, the decentralized control strategy implements these stability guidelines and ensures that the voltages in the system remain within a specified range. Additionally, several simulations are performed to illustrate the stability of the system and the behavior of the control strategy under different scenarios., DC systems, Energy conversion & Storage, Algorithmics

Given the complementary nature of photovoltaic (PV) generation and energy storage, the combination of a solar panel and a battery pack in one single device is proposed. To realize this concept, the PV Battery-Integrated Module (PBIM), it is fundamental to analyze the system architecture and energy management. This paper focuses on selecting a suitable architecture among the different options, while also indicating the control strategy that the converters must follow to ensure appropriate performance. Also, several modes of operation for the complete system are introduced to implement energy management. For the selected DC architecture, two case studies, viz. off-grid and peak-shaving for a grid-tied system, were employed to characterize the response of the model demonstrating its utility to perform maximum power-point tracking, excess solar power curtailment, and battery charging and discharging. The proposed control and system architecture prove to be feasible for a PV battery-integrated device such as PBIM., DC systems, Energy conversion & Storage

The emergence of distributed energy resources can lead to congestion in distribution grids. DC distribution grids are becoming more relevant as more sources and loads connected to the low voltage grid use dc. Bipolar dc distribution grids with asymmetric loading can experience partial congestion resulting in a nodal price difference between the two polarities if a respective market model is applied. In order to take into account this price difference, this paper presents an optimal power flow (OPF) model formulated in terms of voltage and current. In the case of bipolar dc distribution grids, the single line approximation is no longer valid because current can flow in the neutral conductors as well. Moreover, loads and sources can be connected between any two nodes in the network. The proposed exact OPF formulation includes bilinear equations. The locational marginal prices (LMP) are derived by linearizing the problem at the optimal solution. Example cases show the various phenomena that can appear under asymmetric loading, such as pole-to-pole connections combined with pole-to-neutral connections, parallel sources, meshed grids and their effect on the LMP., DC systems, Energy conversion & Storage

Many modelling methods for the analysis of dc distribution grids only consider monopolar configurations and do not allow for mutual couplings to be taken into account. The modelling method presented in this paper aims to deal with both of these issues. A state-space approach was chosen for its flexibility and computational speed. The derived approach can be applied to any dc distribution system regardless of its configuration and takes into account mutual couplings between phase conductors. Moreover, the state-space matrices can be derived in a programmatic manner. The derived model was verified empirically and by a reference model created in Simulink using PowerLib blocks. Subsequently, an illustrative system was analyzed, which showed the utility of the presented method in analyzing the dynamics of dc distribution systems. The presented method could especially be useful for the analysis, design and optimization of, for example, the stability and control systems of dc distribution systems., Accepted Author Manuscript, DC systems, Energy conversion & Storage, Algorithmics

Employing bipolar dc distribution systems introduces the possibility of imbalance in the system. To analyze these systems it is crucial to create novel modelling techniques. This paper presents a method to decompose dc distribution systems into symmetrical components. The presented method simplifies the analysis of balanced, unbalanced, and fault conditions of bipolar dc distribution systems. Equivalent circuits for several network components in the symmetrical domain are derived and are shown to be independent under symmetrical conditions. Furthermore, a dynamic analysis is performed in the symmetrical domain showing that the method simplifies the analysis of dc distribution systems. Additionally, the symmetrical domain equivalent circuits of several fault conditions are derived., Accepted Author Manuscript, DC systems, Energy conversion & Storage, Algorithmics