DC microgrids (MGs) have been gaining a continually increasing interest over the past couple of years both in academia and industry. The advantages of dc distribution when compared to its ac counterpart are well known. The most important ones include higher reliability and efficiency, simpler control and natural interface with renewable energy sources, and electronic loads and energy storage systems. With rapid emergence of these components in modern power systems, the importance of dc in today's society is gradually being brought to a whole new level. A broad class of traditional dc distribution applications, such as traction, telecom, vehicular, and distributed power systems can be classified under dc MG framework and ongoing development, and expansion of the field is largely influenced by concepts used over there. This paper aims first to shed light on the practical design aspects of dc MG technology concerning typical power hardware topologies and their suitability for different emerging smart grid applications. Then, an overview of the state of the art in dc MG protection and grounding is provided. Owing to the fact that there is no zero-current crossing, an arc that appears upon breaking dc current cannot be extinguished naturally, making the protection of dc MGs a challenging problem. In relation with this, a comprehensive overview of protection schemes, which discusses both design of practical protective devices and their integration into overall protection systems, is provided. Closely coupled with protection, conflicting grounding objectives, e.g., minimization of stray current and common-mode voltage, are explained and several practical solutions are presented. Also, standardization efforts for dc systems are addressed. Finally, concluding remarks and important future research directions are pointed out.

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DC Microgrids—Part II: A Review of Power Architectures, Applications, and Standardization Issues

DC microgrids are gaining popularity due to high efficiency, high reliability, and easy interconnection of renewable sources as compared to the ac system. Control objectives of dc microgrid are: 1) to ensure equal load sharing (in per unit) among sources; and 2) to maintain low-voltage regulation of the system. Conventional droop controllers are not effective in achieving both the aforementioned objectives simultaneously. Reasons for this are identified to be the error in nominal voltages and load distribution. Though centralized controller achieves these objectives, it requires high-speed communication and offers less reliability due to single point of failure. To address these limitations, this paper proposes a new decentralized controller for dc microgrid. Key advantages are high reliability, low-voltage regulation, and equal load sharing, utilizing low-bandwidth communication. To evaluate the dynamic performance, mathematical model of the scheme is derived. Stability of the system is evaluated by eigenvalue analysis. The effectiveness of the scheme is verified through a detailed simulation study. To confirm the viability of the scheme, experimental studies are carried out on a laboratory prototype developed for this purpose. Controller area network protocol is utilized to achieve communication between the sources.

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Distributed Control to Ensure Proportional Load Sharing and Improve Voltage Regulation in Low-Voltage DC Microgrids

Microgrid is becoming an attractive concept to meet the increasing demands for energy and deal with air pollutions. Distributed energy sources (DERs) in Microgrid are usually interfaced with the utility grid by inverters, so the characteristics of Microgrid stability are much different from that of a traditional grid. However, the classifications, guidelines, and analysis method of Microgrid stability are well behind of the Microgrid development. In this paper, a Microgrid stability classification methodology is proposed on the basis of the of Microgrid characteristics investigation, which considers the Microgrid operation mode, types of disturbance and time frame. Then a comprehensive review of the body of research on Microgrid stability is presented in order to identify and advance the field. Finally, some challenges and suggestions of Microgrid stability for further researches are discussed.

Microgrid stability: Classification and a review

Power-line communications (PLC) have proven to be susceptible to the next-generation power transmission/distribution systems with end-to-end communication capability, considered as a revolutionary and evolutionary regime of existing power grids More importantly, with recent advancements in PLC technological regulation, standardization and certification have spurred a lot of interest in the field of advanced communication and control technologies for heterogeneous networks These advancements are expected to greatly enhance efficiency and reliability of future power systems with renewable energy resources, as well as distributed intelligence and demand response (DR) programs As various national and international organizations have started to draw PLC regulations, standards and technologies for countries, these standards intend to determine important criteria such as bandwidth, modulation types, channel coding schemes, operating frequency and electromagnetic capability limits from fixed indoor/outdoor applications to smart grid (SG) applications Depending on the worldwide PLC regulation, standardization and technological developments, security schemes built around them can become interoperable from a standard point of view, but still have incompatible configurations or different maturity levels, or include non-standardized PLC functions Moreover, the PLC based systems/solutions for renewable energy integration, are also surveyed in terms of distributed-power system (DPS) and distributed energy resources (DERs) units monitoring/controlling and management purposes Thus, a particular section is dedicated to PLC based systems/solutions utilization of renewable energy sources (RESs) in SG covering all aspects of a monotype and hybrid energy plants Finally, the survey is carried on by reviewing the most recent and comprehensive articles to highlight the importance of PLC in a logical way in the smart grid for readers

Power-line communications for smart grid: Progress, challenges, opportunities and status

Results of a literature survey done on microgrids from conception to installation is presented. The purpose is to evaluate the current status, major obstacles and existing research efforts directed toward establishing functional microgrids within utility systems. This review paper covers technical issues associated with frequency control and re-synchronization associated with typical distributed energy sources. Also evaluated are regulatory and policy issues associated with ownership, maintenance, availability, coordinated equipment control, obligation to provide adequate power quality, etc. associated with operating an islanded microgrid within a utility company's service territory. Actual microgrids in operation today are described. Benchmark test systems for steady state and dynamic simulations are also discussed.

Microgrids — A review of modeling, control, protection, simulation and future potential

This paper presents an electric line study of microgrid. To optimize the management of electric sources, generally a proposed solution is the load shedding. To achieve it, the power line communication (PLC) is often used to communicate when it is not possible to add cables. Such technologies use the power line network as a propagation and communication medium. The network quality depends mainly on the power grid topology, but also on the connected household electrical appliances that have a large impact on the PLC systems due to their impedances and noise. In this paper, we propose a new simulation program with integrated circuit emphasis (SPICE) approach for modeling both the electromagnetic (EM) disturbances generated by a printer and the power network. First, the high-frequency power cable characteristics are extracted from S parameter measurements. Then, the model of EM noise generated by a printer is deduced from time-domain measurement and integrated to the SPICE simulator by means of its Laplace transform. Simulation and modeling results of a simple power grid are given in terms of insertion loss evaluation (S21 parameter). A validation of the EM noise model is performed by means of a comparison between simulation and measurement results in frequency domain at several points of a simple power network. The present approach allows the prediction of EM interference generated by all household devices at any access points of a power line network without carrying out a systematic measurement.

Modeling of Electromagnetic Interference and PLC Transmission for Loads Shedding in a Microgrid

Broadband Power Line Communication (PLC) technologies represent a main factor of the development of the digital convergence voice-data-video in the home environment. Such technologies use the power line network as a propagation and a communication medium whose quality depends mainly on the power grid topology, but also on the connected household electrical appliances which impedance and noise levels have a great impact on the PLC systems. In this paper, we propose a new approach for modeling temporal variations of noise and channel in indoor power line. Three-conductor power cable (phase, neutral and ground) is modeled by a RLCG circuit. RLCG parameters are deduced from the impedance measurement seen by the generator in open circuit and in short circuit. Cable model is validated in both time and frequency domains. Then, the temporal variation of periodic noise is investigated. The global model combining the channel model and the noise variations is validated by comparing simulated results with measurements.

Channel modeling and periodic impulsive noise analysis in indoor Power Line

Broadband Power Line Communication (PLC) technologies represent a main factor of the development of the digital convergence voice-data-video in the home environment. Such technologies use the power line network as a propagation and a communication medium. The performance and the quality of the PLC link depend on the power grid topology and on the connected household electrical appliances according to their impedances and noise levels. In this paper, we propose a new SPICE approach for modelling power cable based on the extraction of high frequency power cable characteristics from S parameters measurements. The variation of each parameter as a function of frequency is expressed in a polynomial form using a least squares method. Then, we propose to integrate the obtained polynomials into a SPICE model by means of controlled SPICE sources and modeling of power cable using the so-called theory of transmission line. Simulation results of a power cable and simple PLC transmission link are given in terms of insertion loss evaluation (S21 parameter) with a specific appliance connected to the power line network. A validation of this SPICE model is performed by means of a comparison between simulation and measurements results of the insertion loss parameter.

SPICE model for the PLC propagation channel in the high frequency range

Broadband power-line communication (PLC) technologies are one of the main parameters of digital convergence voice-data-video in the home environment. These technologies use the power-line network as a propagation and a communication medium. Its transmission quality depends on the frequency behavior of the propagation medium and the connected household electrical appliances. The impedance of those devices and noise levels has a great impact on the PLC systems. In this paper, a simulator for indoor power-line channels is presented. In this paper, a new approach is presented for modeling temporal variations of noise and channel on indoor power lines. A three-conductor power cable (phase, neutral, and ground) is modeled by a circuit of four elements (resistor R, inductor L, capacitance C, conductance G). The RLCG parameters are deduced from the impedance measurement in open circuit and in short circuit. The cable model is validated in time and frequency domains. Then, the temporal variation of periodic noise is modeled by a stochastic approach. The global model, combining both channel and noise variations, is validated by comparing SPICE simulation and measurement results.

Modeling and Simulation of Temporal Variation of Channel and Noise in Indoor Power-Line Network

Broadband power line communication (PLC) technologies represent a main factor of the development of the digital convergence voice-data-video in the home environment Such technologies use the power line network as a propagation and a communication medium which quality depends mainly on the power grid topology, but also on the connected household electrical appliances which impedances have a great impact on the PLC systems In this paper, we propose a new approach for modeling the impact of such appliances on the PLC transmission link, based on a measurement of their impedance The protocol of the impedance measurement is described first Then, we propose to integrate this impedance measurement into a SPICE model of the PLC transmission link, using the so-called theory of transmission line Simulation and modeling results of a simple PLC transmission link (1 path) are given in terms of insertion loss evaluation (S21 parameter) with a specific appliance connected to the power line network A validation of this SPICE model is performed by means of a comparison between simulation and measurements results of the insertion loss parameter in the appliance free case

D. Guezgouz

Papers

Modeling of Electromagnetic Interference and PLC Transmission for Loads Shedding in a Microgrid

Channel modeling and periodic impulsive noise analysis in indoor Power Line

SPICE model for the PLC propagation channel in the high frequency range

Modeling and Simulation of Temporal Variation of Channel and Noise in Indoor Power-Line Network

Electromagnetic compatibility between power line communication and powers converters