Smart DC Research Articles

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.

Super Twisting Fractional Order Energy Management Control for a Smart University System Integrated DC Micro-Grid

This paper designs an intelligent energy management control for a stand alone smart DC- micro-grid using super twisting fractional order method. Based on mathematical model of the micro-grid, controllers are derived for the source side converters such as photovoltaic (PV),wind, AC grid and battery management system, and load side converters. Based on the available measured input and consumed output power, an intelligent energy management algorithm decides the appropriate mode of operation for the source and load side converters controller. All DC loads connected to the micro-grid are treated as essential loads and no load shedding can be allowed by the energy management unit. The energy management unit prioritizes the renewable energy sources (PV and wind) in order to make the micro-grid as cost effective. The performance of the proposed control scheme is compared with the integer order controller and the system is simulated in MATLAB/SIMULINK environment for different test cases.

Research on operation control of low-voltage MTDC system in a cyber-physical environment

Cyber-physical system is becoming a new feature and hot topic in the development of smart grid and DC power distribution system. Based on the standardized cyber-physical modeling and communication system — IEC 61850, this paper establishes the operation control architecture of the low-voltage multi-terminal DC (LV-MTDC) system. The coordinated operation control strategies including power electronic transformer (PET), voltage source converter (VSC) is proposed. Then a cyber-physical model of the system based on IEC 61850 is built, according to the application requirements of operation control in the LV-MTDC system. On this basis, the implementation method of system operation control based on IEC 61850 is proposed, including the software/hardware design of intelligent electronic device (IED), dispatching operation and uninterrupted power supply. The simulation environment is further built to verify the system operation control technology, and the test platform is used to carry out the actual tests. The research results show that the operation control technology for the LV-MTDC system proposed in this paper is feasible, which can guarantee the rapid and accurate information exchange of control commands and settings, and thus effectively realize the operation control of the LV-MTDC system under complex conditions.

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.

Real-Time Simulation of Smart DC Microgrid with Decentralized Control System Under Source Disturbances

Decentralized control of DC microgrid (dcµG) using hybrid renewable energy sources (RES) and battery energy storage system (BESS) which operate with and without grid-connected mode is proposed in this paper. In dcµG integrated with multiple RES and BESS, fluctuating output characteristics of the distributed generations (DGs) due to changing input conditions and the dynamic interactions of the source and load interface converters are main factors which cause stability problem of DC bus voltage. Thus, to solve this problem, the decentralized control scheme which uses bus voltage level as communication link in the control law is proposed in this paper. Accordingly, the control method realizes different operating modes based on the available generations and load demand. Maximum power and constant voltage controls schemes are applied in the DGs interfacing control to regulate the power and voltage variations due to changing input conditions. Furthermore, in the control strategy, the source and battery interfacing converters are controlled autonomously using the bus voltage level without any communication. This maintains the reliability and flexibility of the system. The proposed system model is developed with Matlab/Simulink SimPowerSystem and simulated with real-time simulation using OPAL-RT.

Smart Integration of a DC Microgrid: Enhancing the Power Quality Management of the Neighborhood Low-Voltage Distribution Network

The fast development of the residential sector regarding the additional integration of renewable distributed energy sources and the modern expansion usage of essential DC electrical equipment may cause severe power quality problems. For example, the integration of rooftop photovoltaic (PV) may cause unbalance, and voltage fluctuation, which can add constraints for further PV integrations to the network, and the deployment of DC native loads with their nonlinear behavior adds harmonics to the network. This paper demonstrates the smart integration of a DC microgrid to the neighborhood low-voltage distribution network (NLVDN). The DC microgrid is connected to the NLVDN through a three-phase voltage source inverter (VSI), in which the VSI works as a distribution static compensator (DSTATCOM). Unlike previous STATCOM work in the literature, the proposed controller of the VSI of the DC smart building allows for many functions: (a) it enables bidirectional active/reactive power flow between the DC building and the AC grid at point of common coupling (PCC); (b) it compensates for the legacy unbalance in the distribution network, providing harmonics elimination and power factor correction capability at PCC; and (c) it provides voltage support at PCC. The proposed controller was validated by Matlab/Simulink and by experimental implementation at the lab.

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.

Viable residential DC microgrids combined with household smart AC and DC loads for underserved communities

The availability of fossil fuels in the future and the environmental effects such as the carbon footprint of the existing methodologies to produce electricity is an increasing area of concern. In rural areas of under-developed parts of the world, the problem is lack of access to electrification. DC microgrids have become a proven solution to electrification in these areas with demonstrated exceptional quality of power, high reliability, efficiency, and simplified integration between renewable energy sources (principally solar PV) and energy storage. In the United States, a different problem occurs that can be addressed with the same DC microgrid approach that is finding success internationally. In disinvested, underserved communities of with high unemployment and low wages, households contribute a significant portion of their income toward the fixed cost of their electrical utility connection, which by law must be supplied to every household. This paper analyzes a residential DC microgrid in an urban, underserved area that enables the sharing of renewable and stored energy resources between dwellings. The goal of the residential DC microgrid is to drive down to fixed costs of utility-provided electricity to all participants, such that the percentage of utility cost to total household income comes can be made comparable to that of more advantaged communities. A group of renovated dwellings constitute the community which the DC microgrid would serve. The distributed installation of solar panels and battery storage among dwelling locations are optimized based upon varying consumption patterns. Also, consumption patterns during different seasons of the year are considered. Electrical distribution architectures within the dwellings are based upon conventional AC. Each dwelling has a DC interface to the residential microgrid and progressive insertion of DC loads, with associated household DC distribution, is considered.

A Real-Life Application of a Smart User Network

Smart Community microgrids could help to improve overall energy efficiency reducing transmission and distribution losses and allowing the implementation of optimal load control and resource dispatching. In this context, the authors have proposed the realization of DC smart microgrids. They are considered as a future prospective according to the increase of DC loads and DC output type distribution energy sources such as Photovoltaic and energy storage systems. In this paper, a DC smart microgrid, called Smart User Network, realized in a real-life application as a part of pilot site under the national research project PON04_00146 Smart cities and Communities and Social innovation named “Reti, Edifici, Strade Nuovi Obiettivi Virtuosi per l’Ambiente e l’Energia” (RES NOVAE), is illustrated. The Smart User Network, is managed by a distributed and decentralized control logic, the DC Bus Signaling, which allows the converters to operate independently of each other according to a decentralized logic. It guarantees the reliability, the continuity and the quality of supply, optimizing the use of energy produced by renewable energy sources, also in stand-alone configuration. The most significant experimental results obtained both in grid-connected and stand-alone configuration are presented and discussed.

Modeling Electronic Power Converters in Smart DC Microgrids—An Overview

Electronic power converters (EPCs) are the key elements of the smart dc microgrid architectures. In order to enhance the controllability of the system, most of the elements are envisioned to be connected to the different buses through EPCs. Therefore, power flow, stability, and dynamic response in the microgrid are function of the behavior of the EPCs and their control loops. Besides, dc microgrids constitute a new paradigm in power distribution systems due to the high variability of their operating conditions, owing to the intermittent behavior of the renewable sources and customer energy consumption. Furthermore, in order to deal with this variability, the power converters can modify their operation mode, adding complexity to the dynamic and stability analysis of the system. This paper gives an overview of the various analytical and blackbox modeling strategies applied to smart dc micro/nanogrids. Different linear and nonlinear modeling techniques are reviewed describing their capabilities, but also their limitations. Finally, differences among blackbox models will be highlighted by means of illustrative examples.

Protection of Smart DC Microgrid With Ring Configuration Using Parameter Estimation Approach

In a smart dc microgrid, power electronic devices limit the current during fault and therefore, an overcurrent-based relaying scheme cannot provide required sensitivity and selectivity for such a system. For a dc microgrid with ring configuration having bidirectional power flow, the protection design is further complicated. For reliable supply to customers and to avoid unwanted disconnection of renewable resources, selectivity of a protection scheme is important. In this paper, using local voltage and current data, a least square-based technique estimates the parameter of the fault path, from which the direction of the fault is inferred. Using the direction of fault information of both ends of a line segment in a ring system, internal and external faults are discriminated for network protection. Using PSCAD/EMTDC simulations for a ring system, proposed method is tested for various fault situations including high resistance fault, close-in fault, signals with noise, and considering different modes of distributed generation operations. The proposed algorithm is also validated on a scaled-down hardware setup in the laboratory. The method is found to be more accurate compared to available technique.

Optimization of Distributed Generation Based Hybrid Renewable Energy System for a DC Micro-Grid Using Particle Swarm Optimization

This research work aims to design and optimize a multi-objectivefunction modeled on the variables concerning distributed generatorsbased on photovoltaic, wind and biogas based IC engine hybrid systemfor community smart DC Micro-grid using particle swarm optimization(PSO). The objectives of the research are to maximize the availabilityof power and reduction of the cost, which in turn will reduce the sizeof system with premier achievable availability. The output power ofphotovoltaic, wind and biogas based IC engine generators would havethe highest priority for feeding the direct current bus as per the meth -odology proposed. It was found that proposed method especially par -ticle swarm optimization had shown the effective cost and availabilityof photovoltaic, wind and biogas based IC engine generators in termsof accuracy to the practical values and a faster rate of convergence.When compared with other algorithms, particle swarm optimizationperforms well in reducing the cost of the photovoltaic, wind and biogasbased IC engine generators. In addition, it was noted that availabilityof photovoltaic, wind and biogas based IC engine generators would beeasily obtained using PSO algorithm. Future work would pertain to thedesigning of a similar hybrid Renewable energy system considering Up-time and Ramp rate constraints of biogas based IC engine generators forcommunity smart direct current micro-grid and optimize it using MultiObjective Genetic Algorithm and compare its results with PSO.

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>

Decentralized Cooperative Control for Smart DC Home With DC Fault Handling Capability

This paper presents a decentralized cooperative control (DCC) method along with a fault segment identification (FSI) scheme to achieve the control and protection objectives for a smart dc home by using only local measurements. The dc home is interfaced with the utility grid via a new modular multilevel converter configuration. Distributed generators are also integrated into the dc home via power converters to guarantee sufficient energy capacity and to support ac and dc loads consumption in the off-grid mode. The proposed DCC method ensures accurate current sharing, dc bus voltage regulation, and fast restoration after the fault clearance. On the other hand, the main objective of the proposed FSI scheme is to quickly identify and isolate the faulty segment to protect the sensitive power electronic components in the dc home from the high fault current. The FSI technique identifies the faulty segment by using only the information extracted from the local current sensor. Time-domain simulation studies using detailed nonlinear models confirm the effectiveness of the proposed control and protection schemes under various normal and faulted operating scenarios. Hardware-in-the-loop studies demonstrate the feasibility of hardware implementation and verify the proposed system performance.

A Laboratory-Scale Prototype of a Smart User Network with DBS Control

The paper presents the experimental results of a research project focus on the development of smart DC microgrids for residential applications. A single-phase laboratory-scale prototype of a DC microgrid, named by the authors Smart User Network, is illustrated in details. It is realized in the Laboratory of Electrical Energy Systems and Renewable Energy of University of Calabria. It can represent several type of users, such as consumers, producers and so-called prosumers (producer and consumer at the same time). For highly efficient integration, several type of micro sources, storage systems and loads are connected to the same DC bus and interfaced to LV grid via appropriate power converters. The power management of the Smart User Network is based on the DC bus signaling control logic to guarantee safe operation both in grid-connected that in stand-alone mode, as proposed by the authors in a previous paper. A technical description of the laboratory-scale prototype components and of the control concepts are reported. Experimental results from the operation of the laboratory-scale prototype demonstrates the validity of the DBS as decentralized control for DC microgrid highlighting all the necessary steps to shift the technology from laboratory-scale to real industry.

Smart Sensing of Loads in an Extra Low Voltage DC Pico-Grid Using Machine Learning Techniques

Aiming at the rising number of dc appliances and the growing interest in their monitoring systems, this paper describes the injection of intelligence into dc pico-grids that are made up of “dumb” appliances and loads. Due to reality of economic, dc appliances and loads are usually low in cost and lack intelligence and communication features for effective monitoring and management. This paper proposes a smart sensor design for dc pico-grid with the use of a single sensor multiple loads and states detection in monitoring the “dumb” appliances. This eliminates the need to have intelligence and communication features for every appliance. With the smart sensor, several such smart dc pico-grids can be bundled into bigger scale of smart nano-grid or micro-grid. In addition to knowing how much energy or power the pico-grid is using, the smart sensor also provides load disaggregation and state-change detection. The states of the loads can be learned and detected via the signatures and features obtained from the transient state or the steady state of the entire grid’s current waveform. Computational intelligence techniques, $k$ -nearest neighbors, $K$ -means clustering, and other algorithms are used in the system for loads classification and state-change detection. Working together with the software in the smart sensor is hardware implementation of low cost operational amplifiers and logic gates; these hardware help to share the burden on the controller and release resources for the controller to perform more advanced processes. Experimental results are presented to demonstrate the operation of the smart sensor in dc pico-grid.

Domestic Electrical Load Management Using Smart Grid

Demand side load management is one of the basic features in smart grid, which enable end users to know major characteristics about their energy consumption during peak and off peak hours and encourage the utility to maintain load demand in extreme conditions. This results in more reliable system with overall improvement of efficiency and low CO2 emission in smart grid. Most of the previous techniques used in demand side load management are specific to traditional energy management strategies with limited number of load controlling technologies. In this paper, we focus on operating the system with more efficiency and reliability. Integration of solar PV distributed generation, smart DC storage and smart load is expected to add valuable operations in the smart grid. Direct load control (DLC) and load shifting techniques for overkill load offers various outcomes during extreme conditions.