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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.

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.

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.

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.

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.

This paper presents a protection framework for low voltage dc grids, which segments these grids into zones and tiers according to their fault current potential and provided protection. Furthermore, the technology and applications of different protection devices are examined. It is demonstrated that the utilization of fast fault interruption and fault limiting inductors are vital for the protection of low voltage dc grids. Moreover, a design of a solid-state circuit breaker is presented, and this devices is experimentally verified. The experimental results showed that the total time for the detection and interruption of faults can be lower than $1 \mu \mathrm{s}$ with solid-state protection devices.

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.

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.

This paper presents a steady-state model and as-sociated power flow equations that can be applied to any dc grid. State-of-art power flow methods and two newly proposed methods are discussed and applied to the proposed steady-state model. A standardized IEEE test feeder is used to benchmark the power flow methods with respect to accuracy, convergence and computational efficiency. It is shown that the two new methods have a superior performance compared to the existing techniques for the steady-state analysis of most common dc grids, providing up to a 93 % increase in computational efficiency for the system that was analyzed in this paper. Therefore, it is demonstrated in this paper that these power flow techniques can be used for the operation, planning, optimization, market simulation, and security assessment of practical dc grids., © 2020 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 works.

This paper presents a breaker arrangement concept, the multiline breaker (MLB), for the protection of multiterminal high voltage dc (MTdc) networks. Based on the design of a hybrid breaker, the MLB is an economically attractive solution for the protection of multiple dc lines in nodal connection using a single main breaker path. By using commutation units, the MLB directs the fault current through the main breaker in a unidirectional way, irrespective of the fault location. Hence, this study presents the design requirements for the MLB, regarding both hardware and control, and evaluates its operation within a grid. For this reason, a four-terminal half-bridge multilevel modular converters-based MTdc grid in radial configuration was used and pole-to-ground dc fault conditions were investigated. The dc fault response of the grid with one MLB at the central node is compared to the respective response of the grid when one hybrid breaker is employed at each dc line. The simulations show that the MLB is feasible and that the overall MTdc grid fault response for the two protection systems is very similar. As a result, the design advantages of the MLB make it a promising solution for the dc fault isolation in MTdc grids.

Employing bipolar dc distribution systems introduces the possibility of imbalance in the system. To analyze these systems it is important to create novel modelling techniques. Therefore, 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. Furthermore, equivalent circuits for several network components in the symmetrical domain are derived and are shown to be independent under symmetrical conditions. Additionally, a dynamic analysis is performed in the symmetrical domain showing that the method simplifies the analysis of dc distribution systems. Finally, the symmetrical domain equivalent circuits of several fault conditions are derived.

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.

Solar-battery systems are still expensive, bulky, and space consuming. To tackle these issues, we propose a novel device that combines all the components of a solar-battery system in one device. This device might help reduce installation cost compared to the current solar-battery systems as well as provide a plug-and-play solution. However, this physical integration means higher temperatures for the components. Therefore, this paper presents a thermal analysis of the physical integration concept to evaluate its feasibility, focusing on the batteries, the most delicate components. The thermal analysis was conducted using a Finite Element Method model and validated with experimental results on a prototype. According to the model, the temperature of the components (battery and converters) reduced drastically by adding an air gap of 5–7 cm between the solar panel and the components. Even under severe conditions, maximum battery temperature never surpassed the highest temperature of operation defined by the manufacturer. Moreover, the maximum battery temperature decreases even further by applying a phase change material as a passive cooling method, reducing it by 5 °C. As a result, the battery pack operates in a safe range when combined with a 265 Wp solar panel, demonstrating the potential of this concept for future solar-battery applications.

Due to an increasing number of power generation units and load devices operating with direct current (DC) at distribution level, there is a potential benefit of leading efforts toward building a DC distribution system. However, the implementation of DC distribution systems faces important challenges, including the market inertia of AC systems and standardization. Many of the benefits that are attributed to DC can only be realized if a complete DC system is developed, and not if only a few components are replaced. This paper presents the concept of a universal DC distribution system, as envisioned by the authors. The universal DC distribution system could be implemented in various use cases, but could also completely replace AC distribution grids. The paper covers the possibilities of having DC nanogrids inside buildings, DC microgrids in neighborhoods, and the connection to AC and DC medium voltage grids. Furthermore, considerations regarding flexibility, electricity market design, control, and protection are presented.

This paper describes the behavior of voltage weak DC distribution systems. These systems have relatively small system capacitance. The size of system capacitance, which stores energy, has a considerable effect on the value of fault currents, control complexity, and system reliability. A number of potential definitions of voltage weak DC distribution systems are proposed. These definitions address the main characteristics of voltage weak systems. A small signal model of a general voltage weak DC distribution system is developed in order to observe sufficient conditions for system stability. This is achieved by analyzing the dominant poles. The source converters are modeled as droop-controlled current sources in parallel with their respective terminal capacitors. As constant power loads have incremental negative impedances, which affect the system stability, especially, in voltage weak system, ideal constant power loads with their terminal capacitors are included in the small signal model. A three-node voltage weak DC distribution grid is analyzed, as a case study, by implementing the developed small signal model. The effects on system stability by the values of system capacitance, cable inductance, and cable resistance are investigated using dominant pole placement. Likewise, the influence of proportional-integral regulators and droop coefficients of source converters on the stability of the system is examined. Finally, the three node DC distribution grid is developed in MATLAB/Simulink in order to demonstrate the influence of small capacitance on system stability. Moreover, effect of the rate of change of constant power loads on the system stability is simulated. These results are further compared and verified on a voltage weak DC experimental test bench with a 350 VDC bus voltage.

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.

Parallel ac-dc reconfigurable link technology can find interesting applications in medium voltage power distribution. A given system can operate in different configurations while maintaining equivalent capacity during (n-1) contingencies. It is proved that within the defined operating boundaries, a parallel ac-dc configuration has higher efficiency as compared to pure ac or pure dc power delivery. Using sensitivity analysis, the variations in these efficiency boundaries with power demand, power factor, grid voltages, link lengths, conductor areas and converter efficiency is described. It is shown that parallel ac-dc system can have smaller payback time as compared to a purely dc power transmission for the same capacity due to lower investment cost in converter station and superior efficiency. As compared to a purely ac system, the payback of a refurbished parallel acdc configuration can be less than 5 years for a 10 km, 10 kV distribution link within the specified assumptions and operating conditions., Comment: \c{opyright} 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, including reprinting/republishing this material for advertising or promotional purposes, collecting new collected works for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

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.

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.

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.

Constant power loads combined with low inertia form a major challenge for future distribution grids. This paper presents a state-space representation to model dc distribution systems. Two methods are discussed to analyze the (small-signal) stability of these dc distribution systems; an algebraic method and a Brayton-Moser method. The system models and the methods for stability analysis were verified using an experimental dc microgrid set-up. Furthermore, it was found that the instability of dc distribution systems can be classified into two categories: equilibrium instability and oscillatory instability.

To tackle the challenges of future distribution systems, dc is being reconsidered. However, broad adoption of dc distribution systems requires additional research into the modeling, stability, protection and control of these systems. Previous research presents modeling methods that only consider monopolar configurations and do not take mutual couplings into account. Therefore, this paper presents a state-space method that can be applied to any dc distribution system, regardless of configuration and mutual couplings. Moreover, it shows how the state-space matrices can be derived in a programmatic manner. Furthermore, the models are validated using an experimental dc microgrid set-up. Due to the mathematical nature, the presented modeling method can be applied easily, and the stability and control can be analyzed algebraically.

Flexible dc interlinks can be used for compact and efficient active power redirection by creating a meshed structure in existing radial distribution network. It is shown that with optimal location and sizing of a back-to-back voltage sourced converter based point-to-point dc link connecting two ac buses of the test 33-bus radial distribution system, 10-15% network loss minimization can be achieved. This possibility can be advantageous in efficiently redirecting active power flows in urban and semi -urban areas because intermittent distributed grid resources (such as photovoltaics and wind farms) and energy intensive loads (such as ultra fast charging stations for electric vehicles) are resulting in local pockets of excess generation and demand. The impact of distributed generation and high powered loads on placement of dc interlink is numerically quantified to suggest that both capacity and efficiency enhancement can be achieved in the distribution grid. It is envisioned that this method of integrating dc power transmission can be the first realistic step towards realizing a multi-terminal dc medium voltage distribution evolving out of the existing infrastructure.

DC Microgrid with integrated photo-voltaics (PV) and battery storage system is a promising technology for future smart grid applications. This paper compares three battery storage technologies namely: lithium-ion (Li-ion), lead-acid, and vanadium redox flow battery (VRFB) in the residential low-voltage dc grids, to increase the penetration of PV to improve self-sufficiency and grid independence. A multi-objective optimisation method is proposed to visualise the trade-offs between four objective functions: cost of electricity, energy autonomy, peak power reduction, and lifetime capital cost. The method is applied to a near-future scenario, based on a real residential feeder. Pareto fronts of the dominant designs are used to compare different battery technologies for this PV-battery integrated dc microgrid application. Additionally, the results provide insight into the dimensioning the battery, the PV, and the front-end ac-dc converter.

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.

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.

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&rsquo, s topology and parameters in order to achieve selective protection in these grids. However, communication complicates fast fault detection and interruption, and a system&rsquo, 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.

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.

In recent years, several demonstration projects using dc microgrids have been implemented across the world due to some distinct advantages of dc over ac systems. The purpose of such initiatives is to validate the theoretically predicted benefits of dc distribution in practical scenarios. This chapter presents a noncomprehensive overview of existing demonstrations and pilot projects for a wide range of applications such as off-grid microgrids, transportation electrification, datacenters, residential and industrial purposes. For each application, key aspects such as architecture, components, control, protection and socioeconomic impacts are highlighted. A short discussion is offered on trends in voltage levels, capacity and topology, progressing toward possible standardization approaches based on recognized best practice.

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.

The fluctuating nature of solar power generation Makes the coupling of energy storage and solar energy inevitable. This paper explores the integration of all the typical components of a PV-battery system in one single module, introducing a prototype of the so-called PV-Battery Integrated Module (PBIM). The electrical and thermal performance of the prototype were studied in order to analyse its behaviour under severe testing conditions. The prototype exhibited an appropriate charging efficiency of 95.7% on average, while the battery pack operated safely (at less than $45^\circ\mathrm {C}$). When compared to a conventional system (battery and charge controller in a separated manner), the mean solar panel temperature of the prototype was 9.34% higher. However, in terms of power, the thermal losses in the PBIM resulted in an average increase of just 1.3 W (4.6%) in comparison to a conventional system. The testing validated the applicability of the integrated concept in harsh conditions, providing valuable information for future design improvements.

The coupling of solar panels and energy storage is inevitable and especially pertinent in places with no access to the electricity grid. This combination must be modular, providing the opportunity to scale up the system if energy demand increases, but also easy to install and user-friendly. These requirements validate the PV-Battery Integrated Module (PBIM) as a potential solution for stand-alone applications. In this paper, we assess the performance of directly integrating a battery system at the back of a PV panel in comparison to a typical solar home system (SHS) with all the components in a separated manner. The study is carried out using data from a community in the countryside of Stung Treng (Cambodia). First, the optimum battery size and PV panel rating were determined using the loss of load probability metric. Second, the extra PV power losses in the case of (PBIM) were calculated, finding that it is 2.16% less efficient than a normal SHS due to the poorer heat dissipation induced by integrating the converter and batteries at the back of the PV panel. Third, the battery capacity faded by 1% after a year of simulation. Although when compared to a typical SHS PBIM results in slightly higher system losses, the losses are moderated and their impact is minimum when considering the expected benefits derived from using PBIM in SHS. Therefore in this paper, we validate the feasibility of PBIM as a solution for standalone systems in developing countries.

Autonomous operation of the dc grids with converter interfaced renewable energy sources and energy storage with droop based control can lead to instability. This paper analyzes the stability of droop based closed loop controllers in a dc nanogrid. Linear state space modeling approach is used to model the small signal model of the droop controlled dc-dc converters. The dominant eigenvalues are analyzed, and the effect of closed-loop gains of the converters are investigated. Detailed parametric sensitivity analysis and participation factor of the system parasitics and the controller gains are also presented. Based on that, a segmented droop strategy is proposed to divide the operating ranges into segments with adaptive controller gains to ensure system stability in all of them. A particle swarm optimization algorithm is used to optimize for the converter gains of individual segments.

In meshed low voltage DC distribution grids, one of the main challenges is achieving controllability of the power flow. The most common approach to achieve the full control over the power flow in the meshed DC grid is to deploy DC-DC converters rated for the full power rating of the grid. The drawbacks of this solution are costs and losses of such DC-DC converters. To reduce the costs and the losses from the system standpoint, we introduce a partially rated power flow control converter. This paper presents the control modes of the partially rated power flow control converter and experimentally demonstrates its functionality. The proposed power flow control converter consists of two cascaded converters. On one side the converter is rated for the maximum grid voltage but only a fraction of the grid current, and on the other side, it is rated for the maximum grid current but only a fraction of the grid voltage. The proposed converter can operate in three modes and demonstrates the power flow control capability.

Traditional optimization and control techniques are no longer suitable to account for the interactions introduced by new technologies like combined heat and power units (CHP) and renewable sources. In this paper a general optimization framework and a hierarchical control architecture are presented for systems with multiple energy carriers, i.e. electricity, heat, gas, etc. The proposed framework is based on the energy hub approach and is an extension of previous research done in this field. Two-level architectures can be adjusted to fulfill the needs of future power systems, where there will be a higher participation of decentralized generation. Nevertheless, the papers generally focus exclusively on electricity flows, even when they include cogeneration units like fuel cells. For this reason the contribution of this paper is to propose a two-level control strategy that can be applied in systems with multiple energy carriers and to provide an illustrative example in which the results of using the strategy can be observed. The complete framework presented in this paper consists of an optimization algorithm and a real-time control algorithm. The optimization algorithm indicates when to turn on and turn off a generation unit and how much power it should deliver at a certain time period. The optimization is done for a forecasted period of 24 h and the real-time control strategy runs continuously to compensate for the mismatches between the scheduled load and the real load by means of control actions.

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.

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.

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). 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.