DC Smart Grid Research Articles

Innovative Fault Current Evaluation Method for Active DC Grids

DC smart grids are a promising solution for the efficient integration of renewable energy sources and loads. Still, their widespread adoption is hindered by significant challenges related to fault response, identification, and clearance. The traditional DC fault analysis method is a useful tool for straightforwardly understanding the behaviour of fault current contributions from DC converters in LVDC networks during a fault. However, when a system with multiple converters and non-negligible fault impedance need to be considered, its accuracy is severely limited due to the assumptions included in the problem solution, thus leading to the following: (a) the dependency of the results’ reliability on fault impedance values and/or other converter fault current contributions; (b) the inaccuracy of the diode current estimation; and (c) the inaccuracy of the conductor joule integral. Thus, these results’ data may be unreliable for designing protection systems for one converter or for an entire network. In order to overcome these issues, this paper proposes an innovative, simple numerical approach to DC fault current evaluation, which can be adopted when the number of converters become significant, or the network is complex. This method arises from the primary interest in solving the circuit to extract the indicators (current peak value and time, joule integral, etc.) necessary for designing circuit protections. This approach proved to grant two main advantages over traditional methods: (a) it provides accurate results, with no need to introduce any specific assumption; (b) it can be structured to manage an arbitrary number of converters; and (c) it reduces the computational processing times and resources necessary to simulate an entire DC network in comparison to other circuit solution software.

Modular high conversion ratio soft-switching DC-DC converters with extended multi-ports structure for multi-energy storage systems interconnection

This paper focus on the advanced multi-energy storage systems interconnection by DC smart grids with high efficiency and high compactness. A non-isolated modular high conversion ratio bidirectional soft switching DC-DC converter and its extended multi-ports structure are proposed in this paper. In each power module of the converter, an auxiliary zero-current transition (ZCT) cell is integrated to achieve the zero-current turn-on and turn-off for all semiconductor devices. Therefore, the switching losses are reduced greatly and the efficiency is improved considerably. The presented converter is suitable for the small and medium power scale interconnection in smart DC grids, and can realize the flexible multi-energy storage system interaction owing to its extended multi-ports structure. Besides, various control schemes are adopted to optimize the control system of this converter, which can improve the performance on energy interaction. The operation principles and design considerations are discussed in details and a 5 kW experimental prototype is constructed to justify the validity of the theoretical analysis.

Solid-State Transformers of Smart High-Power Battery Charger for Electric Vehicles

There is no doubt that society will not turn back: most thermal vehicles will switch to electric ones, not only for cars but also for bigger vehicles. Fast chargers will become more and more essential parts of the global system, they will provide a charge control of batteries and galvanic insulation from the grid. At the present times, compact realizations are based on Solid-State Transformers (SSTs) operating at high frequencies with their well-known advantages and disadvantages, including power limits and reasonably high costs. The authors propose a medium-frequency transformer (MFT) structure using Grain Oriented Electrical Steel (GOES) wound cores and aluminum foil windings. Thanks to this solution, the cost of the device can be reduced. GOES has losses that increase with frequency but decrease with temperature; therefore, the authors propose a transformer structure allowing a hot core inside coils at usual temperatures. This idea is applied to a 400-kW compact battery charger connected to a DC smart grid.

Global Simulation Model Design of Input-Serial, Output-Parallel Solid-State Transformer for Smart Grid Applications

This paper provides an overview of an early attempt at developing a simulation model on a solid-state transformer (SST) based on input-serial and output-parallel (ISOP) topology. The proposed SST is designed as a base for a smart grid (SG). The paper provides a theoretical review of the power converters under consideration, as well as their control techniques. Further, the paper presents a simulation model of the proposed concept with a PLECS circuit simulator. The proposed simulation model examines bidirectional energy flow control between the medium-voltage AC grid and DC smart grid, while evaluating power flow efficiency and qualitative indicators of the AC grid. After the completion of design verification and electrical properties analysis by the PLECS simulation models, the synthesis offers recommendations on the optimal layout of the proposed SST topology for smart grid application.

Design and prototyping of transformerless DC-DC converter with high voltage ratio for MVDC applications

Power boost DC-DC voltage converters have become a key element for medium-voltage DC (MVDC) applications as a link between generation and distribution grids, it is possible to classify the DC-DC converters into four families, depending on their characteristics, as well, one of the actual principal needs is to reduce the number of passive and active components needed for voltage conversions. This article presents a novel transformerles DC-DC boost-resonant converter, which is destined for the interconnection of medium and high voltage DC smart grids. The proposed DC-DC converter is composed of two inductors, a capacitor, and five IGBTs interrupters, which are responsible for the interaction between resonant and boost converters, in the same way, the resonant converter is composed of one resonant inductor and one resonant capacitor while the boost converter is composed by one boost inductor. This paper also presents the operation principle of the proposed converter, as well as its control, modular connection, and simulation to probe the behavior of the converter and an experimental 100 W prototype with 9.5 gain.

A cost-efficient DC active load laboratory solution

The increased use of DC renewable energy resources and DC storage systems, combined with the necessary reduction of energy waste, is boosting the development of DC smart grids. In this scenario, DC load emulation is of great importance. From the hardware point of view, DC buses stability of smart grids and the different DC/DC converter topologies must be tested. From the software point of view, smart grid strategies and job schedulers must be tested with different power absorption profiles. Moreover, DC load emulation can be useful for many other purposes, such as battery characterization, power supply testing, photovoltaic I-V curve measurements, etc. In this work, a cost-efficient DC Active Load (AL) solution is proposed. The principle of the circuit topology is a buck-boost-derived converter. This solution can be designed and tested considering the required voltage, current, and maximum input power. Both simulation and experimental results are shown on a 400 W size prototype. Thermal and electrical results validate the simulation model and the AL feasibility.

Islanding operation scheme for DC microgrid utilizing pseudo Droop control of photovoltaic system

The penetration levels of renewable energy sources, energy storage systems, and electric vehicles are increasing with the increase in the demand to solve energy and environmental issues. These distributed generators and energy storages can be efficiently managed in a DC smart grid by coordinated control. This paper proposes novel management schemes for DC systems to improve the reliability of power supply and improve the introduction ratio of renewable energy sources (RES). The proposed DC smart grid includes multiple DC microgrids. These configurations and control systems must be designed on the assumption of islanding operation of DC systems. In the islanding power system with the high penetration of RES, not only the utilization of energy storage but also load shedding and RES control is important. Hence, an efficient control strategy by using a storage battery, fuel cell and electrolyzer units, heat pump units, and a photovoltaic (PV) system is presented for stable islanding operation of DC microgrid. As the most important concept, a pseudo Droop control is proposed that utilizes the characteristics of the PV module. The pseudo Droop control enables the PV system to suppress the output power properly by using a simple control system without the maximum power estimation. Fault ride through protection for DC system is also adapted to the DC distribution lines. The performance of the proposed DC smart grid is demonstrated through MATLAB®/Simscape ElectricalTM simulations. The simulation results show that the DC microgrid can maintain stable islanding operation under the proposed management schemes when faults occur in the DC distribution lines.

Resource and energy efficiency assessment of an industrial DC Smart Grid

Abstract In order to achieve a CO2-neutral production, which will characterize the sustainability efforts of companies in the coming years, a resource and energy efficient energy supply is essential. The DC Smart Grid enables the efficient integration of CO2-neutral, self-produced energy from, for example, PV systems or waste-operated CHPs. The central DC supply via active infeed saves resources in supply and grid filtering as well as in installation technology. The paper systematically analyses the differences between the DC Smart Grid and the AC grid from the perspective of resource and energy efficiency. These grids are then evaluated using real examples. The goal is to determine a reasonable minimum scaling as well as efficient application scenarios of industrial DC networks. The presented results are part of the DC-INDUSTRIE research project, funded by the German government.

Smart Operations Of Smart Grids Integrated With Fuel Cell With Controlling Strategies

This paper provides the management methods of AC & DC smart grids. AC smart grids square measure a convenient approach to integration distributed energy systems with utility power systems. Smart grid may be a arrangement of smart generators, fuel cell, storage systems and masses. DC micro grids will cause additional economical integration of distributed generation. The methods of smart grids measure completely by the management of converters. In solar panel maximum cost utilized in storage systems like battery. In this paper a latest method has been recommended to replace the battery with fuel cell. Stored hydrogen used as a fuel which generate electricity. In this type of hydrogen storage system efficiency is not more than 55 percentages. This paper explaining about the scheme of the management methods of converter and the management methods of smart grids in each AC & DC conditions.

Development of DC smart grid model for voltage stability disturbance

DC smart grid and distributed generation have evolved rapidly as the integration of renewable energy. The robustness parameter of DC smart grid can be defined by the ability of the system to maintain stability under normal or perturbed conditions and provide fast restoration after faults. This research aims to design DC smart grid to simulate the voltage stability again disturbance. A model of DC smart grid was tested by key parameters in power station such as voltage stability. Voltage stability is the ability of power system to maintain steady voltage within permissible range at all buses in reasonable condition and after having been subjected a perturbation, such as an incremental change in load. The obtained duration time for a system to recovered voltage stability problem was approximately two seconds until three seconds. It was concluded that designed DC smart grid could simulate the voltage stability disturbance.

Modulated Low Fault-Energy Protection Scheme for DC Smart Grids

DC smart grids enabled by the integration of advanced power electronic converters (PECs) can ease the integration and control of distributed renewable energy resources, electric vehicles, and energy storage systems. However, these highly flexible power systems introduce many challenges when considering the design of reliable, plug-and-play protection that does not rely on dedicated communications infrastructure for device coordination. One particularly difficult challenge is the management of dc-side filter capacitor discharge during short-circuit faults where the large peak fault-current produced can permanently damage exposed semiconductor components within the converter. One solution is to ensure that the trip-time of dc protection devices is sufficiently rapid (sub-millisecond) to guarantee that fault-current is blocked prior to reaching destructive magnitudes. However, such high-speed protection devices do not offer much margin for effective selectivity with downstream devices due to the narrow time window of operation. Accordingly, this paper proposes a non-unit protection scheme for future large-scale dc smart grid applications that increases this time-window of operation to enable improved selectivity whilst retaining a lower level of energy dissipated in the fault. Reliable protection coordination is demonstrated on a dc radial network and is realized using conventional millisecond trip-time devices, and a single solid-state microsecond trip-time device.

A New Voltage Balancing Technique for a Three-Stage Modular Smart Transformer Interfacing a DC Multibus

DC smart grids represent an alternative to traditional ac power distribution systems. The power conversion stage, interfacing the ac and the dc distribution systems, is the enabling technology to manage multiple dc loads and sources. The three-stage smart transformer (ST) is a promising solution, because it includes a dc–dc power conversion stage providing a dc multibus in output. The modular ST architecture supplies several dc outputs, which allow interfacing a dc smart grid with the ac power system. In this paper, the three-stage ST is based on a cascaded H-bridge (CHB) converter for the ac–dc power conversion, whereas dual active bridge (DAB) converters are adopted for the dc–dc power conversion stage. The peculiarity is that the dc voltage balancing is performed by the dc–dc power conversion stage instead of the CHB converter. It is advantageous for dc smart grids applications where the power sharing among the dc sources and loads is often not balanced. The design of the entire control system is based on the detailed small signal model of the ac–dc and dc–dc power conversion stages of the ST. High dynamic performance of the voltage balancing is fulfilled due to the commonly high switching frequency of the DAB converters.

LED-Lamp Design for Renewable Energy-Based DC House Application

<span lang="EN-US">This paper describes the design of an LED lamp to be used in a DC house being supplied using a renewable energy source or in a DC Smart Grid. LED lamps are widely known for its low-electricity consumption. The DC house application is becoming more and more popular due to its advantage of using DC generated electricity, for example from a solar photovoltaic system, directly without having to invert it into AC voltage. However, LED needs a driver to activate and control it. Its mounting also needs certain precaution to anticipate the high heat from the LED. An appropriate heatsink is required before activating the LED. The laboratory results indicate that a 3-watt LED bulb lamp can produce an efficiency up to 93.16% with luminous efficacy 82.29 lm/W. These results prove that an LED bulb consumes less energy and can give an optimal brightness.</span>

DCCPP = Privacy by Design. Direct Current Communications & Privacy Protocol (DCCPP) Proposed for a Privacy Protective DC Smart Grid

Contemporary society is highly dependent on electricity, specifically on reliable and continuous generation of power. Sustainable generation, using wind and solar energy, is anything but a reliable source. Deployment of these sustainable sources will make our systems more durable and at the same time more vulnerable to disruption. Production and demand are no longer synchronized, and the system needs the ability to balance supply and demand. Energy Grids must become Smart Grids to accommodate for these changes, using Smart Meters that communicate directly with contracted operators and suppliers for balancing and billing purposes.Introducing more information into Energy Grids raises privacy concerns, because information about energy usage allows anyone with that information to reconstruct parts of private life. Further it raises security concerns, because third parties will be able to analyze from the usage patterns whether people are at home or away. Finally, it introduces concerns about data ownership, (un)portability and freedom of choice.We propose a design for a DC-Smart-Grid on the operating system layer. This ‘Smartest’ Grid combines the advantages of DC Grids while addressing these concerns. In the paper key characteristics of this grid are described: embedded communication technology to minimize the exchange of personal data, freedom of choice between available electricity sources, and community ownership for prosumers. We show that a DC-Smart-Grid can be designed such that the minimum information required to maintain a safe and stable grid fulfils the requirements of privacy by design.

Enhancement of Voltage Stability of DC Smart Grid During Islanded Mode by Load Shedding Scheme

Abstract This paper presents the voltage stability of a DC smart grid based on renewable energy resources during grid connected and isolated modes. During the islanded mode the load shedding, based on the state of charge of the battery and distribution line voltage, was proposed for voltage stability and reservation of critical load power. The analyzed power system comprises a wind turbine, a photovoltaic generator, storage battery as controllable load, DC loads, and power converters. A fuzzy logic control strategy was applied for power consumption control of controllable loads and the grid-connected dual active bridge series resonant converters. The proposed DC Smart Grid operation has been verified by simulation using MATLAB® and PLECS® Blockset. The obtained results show the effectiveness of the proposed method.

Fuzzy Logic Controlled Dual Active Bridge Series Resonant Converter for DC Smart Grid Application

Fuzzy Logic Controlled Dual Active Bridge Series Resonant Converter for DC Smart Grid Application

Onboard DC grid employing smart grid technology: challenges, state of the art and future prospects

Research in All Electric Ship (AES) and onboard DC grids has already been initiated and it is going to be intensified because of its promising perspectives. This study aims to present in a coherent and methodical way why onboard DC distribution systems, smart grids and AES concept can greatly improve ship efficiency. Emerging technical challenges and future prospects are presented; state of the art is summarised while directions for a complete research roadmap are proposed.

Development of Software for Analyzing of Solar Irradiance and Sizing of Stand-Alone PV Power Systems

An analyzing software was developed for studying the solar irradiance on the Universidad Militar Nueva Granada (UMNG) Campus, as well as for sizing a stand-alone photovoltaic (PV) system in terms of power generation and energy storage, which is intended to be part of an hybrid DC smart grid with several energy sources, including not only solar but additional renewable. This software has a two stage sequential structure: First, it let to calculate the total solar energy resource and define the average irradiance and its variability for several user-defined periods, i.e. daily, monthly, annual and even multiannual. Simultaneously, the software gives the user a graphical data variation, where irradiance in hours of bright sunlight (at Standard Test Conditions - STC: 1 kWh/m2) and variability are organized in a period range (hours, days or months). The sizing stage let to define the system architecture in terms of modules and batteries, i.e. estimate PV network and battery bank. Finally, after providing load, voltage level and autonomy, it proceeds to calculations, considering factors of safety.

Development of Software of Climate Analysis for Generation the Energy with Wind Turbine

This work seeks to analyze the feasibility to integrate a renewable hybrid energy resource in the DC smart grid for the campus of Universidad Militar Nueva Granada (UMNG), which is located in Cajica - Cundinamarca. Taking the wind energy as the selected renewable resource, we developed software in Matlab® in order to do the analysis of meteorological data based on the Weibull’s probabilistic distribution model and the Betz’s efficient energy use method. The software shows the wind speed and power analysis based on its data input (atmospheric pressure, temperature, wind speed and direction, etc.) of the study site. The software also allows the simultaneous and differential power analysis of different types of commercial wind turbines, which is characterized and implemented into the software, for the appropriate selection. Moreover, the user is able to upload its own meteorological files or use a data base from any weather station, such as those installed by the Regional Autonomous Corporation (CAR).

Investigation of Microelectromechanical Switches for Next Generation DC Power Distribution System

Abstract This paper investigates the application of microelectromechanical system (MEMS) switches for DC power distribution system. Traditional electromechanical switches, solid state switches and solid state switch array are studied and simulated to understand their characteristics. Performance and characteristics of MEMS switches are reviewed and identified that electrostatically actuated MEMS switches are suitable for DC power applications. Scalable total cross tied (TCT) array configuration using MEMS switches has been proposed. The proposed configuration is suitable for variable voltage/current rating. Arc-less behavior of the switch configuration is analyzed using modified Paschen’s curve. 400 V/6 A system is considered for the simulation and comparative study. The simulated result of the proposed MEMS switch array configuration is compared with the traditional switches. The comparative study shows that the proposed switch array configuration gives better performance in terms of voltage drop, leakage current, power loss, arc and size. This can be used in DC power system protection, circuit breaking, battery protection and smart grid load switching applications.