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Summary: The new multi‐stage wireless power transfer (WPT) systems based on series–parallel–series (SPS) and inductor–capacitor–capacitor (LCC) compensations (SPS‐WPT and LCC‐WPT) are characterized by constant output current and high transmission efficiency. To obtain applicable conditions and performance differences of these two systems, their output characteristics have been studied by theoretical derivation and experimental verification. First, the equivalent models of double‐stage SPS‐WPT and LCC‐WPT systems have been built. Second, comparative analysis of two key compensation components that affect the output performance of the two systems has been completed. Third, the influence of each stage load and coupling conditions on the output performance of the two systems has been further analyzed and compared. Finally, output performance of the two systems has been tested and compared on a newly built experimental platform. Experimental results show that the output power and transmission efficiency of the SPS‐WPT system reach 180 W and 80.39% with offset of 20 mm, which is more suitable for high power applications with low and fixed coupling condition. In addition, the output power and transmission efficiency of the LCC‐WPT system reach 127 W and 85.92% with offset of 10 mm, which is more suitable for high efficiency applications at medium and variable coupling conditions. [ABSTRACT FROM AUTHOR]

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Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study presents the design of efficient wireless power distribution systems based on resonant inductive arrays. The authors show how to use multi-resonator arrays to charge and power up several electric devices in parallel, with nearly constant transmitted power, and using a single power source. Their single-source wireless power transmission clusters, for instance, are shown to provide free positioning at better power efficiency than previous solutions. They provide analysis, simulation, and measurement performance of their multi-resonator arrays, they compare them with other types of inductive arrays employed into different schemes (multi-coil inductive links, overlapping and non-overlapping links), and they show the advantage of their strategy over previous solutions. The presented wireless power distribution systems improve power transmission efficiency (PTE) in free positioning by as much as 30%. The measured results show that their multi-resonator arrays present significant advantages: (i) they allow multiple charging zones from a single power source; (ii) they provide free positioning with strictly uniform power delivered to the load; and (iii) they provide superior efficiency through a built-in power localization mechanism, which is not available in other solutions. The PTE of the multi-resonator array in single-receiver and multi-receiver configurations outperformed previous solutions by 26% and 12%, respectively. [ABSTRACT FROM AUTHOR]

Space vector (SV)-based estimation algorithms represent attractive methods for synchronized phasor, frequency, and rate of change of frequency measurements in three-phase ac power systems. Recently, a phase-locked-loop (PLL) solution for improving the demodulation of the SV signal has been proposed. In this article, the potentialities of the SV-PLL approach are investigated in order to optimize accuracy and computational load. First, the impact of the PLL update rate on achieved performance is analyzed. Then, a novel two-step SV-PLL algorithm is presented so that the accuracy of a fast PLL execution frequency can be matched with a considerably lower computational cost. The behavior in the case of fast phase angle variations has been also significantly improved. The proposed synchrophasor estimation technique has been validated through simulations; exemplary dynamic performance suggests that it is particularly suitable for grid control applications. Experimental tests carried out on a real-time implementation confirm simulation results. [ABSTRACT FROM AUTHOR]

This paper compares different methods for voltage-dip characterization. Those methods are based on earlier proposed algorithms for extracting three-phase characteristics (dip type, characteristic voltage, and so-called “PN factor”). The difference between the 12 methods being studied in this paper is in the way in which the time variation of those characteristics is treated to result in single-event characteristics. The methods are applied to 259 measured voltage dips, and the performance of the different methods is compared. It is found that small differences in the method can result in big differences in results. From the comparison, two methods are selected and recommended for inclusion in international standards. [ABSTRACT FROM PUBLISHER]

This paper presents a novel experimental chamber with uniform wireless power distribution in 3D for enabling long-term biomedical experiments with small freely moving animal subjects. The implemented power transmission chamber prototype is based on arrays of parallel resonators and multicoil inductive links, to form a novel and highly efficient wireless power transmission system. The power transmitter unit includes several identical resonators enclosed in a scalable array of overlapping square coils which are connected in parallel to provide uniform power distribution along x and y. Moreover, the proposed chamber uses two arrays of primary resonators, facing each other, and connected in parallel to achieve uniform power distribution along the z axis. Each surface includes 9 overlapped coils connected in parallel and implemented into two layers of FR4 printed circuit board. The chamber features a natural power localization mechanism, which simplifies its implementation and ease its operation by avoiding the need for active detection and control mechanisms. A single power surface based on the proposed approach can provide a power transfer efficiency (PTE) of 69% and a power delivered to the load (PDL) of 120 mW, for a separation distance of 4 cm, whereas the complete chamber prototype provides a uniform PTE of 59% and a PDL of 100 mW in 3D, everywhere inside the chamber with a size of 27\times 27\times 16 cm^3. [ABSTRACT FROM PUBLISHER]

This paper investigates the power allocation problem for artificial noise (AN) secure precoding systems, and proposes closed-form solutions for maximizing the achievable secrecy rate. It is assumed that the transmitter knows the full channel information at the legitimate receiver, and knows only the statistics of the channel information at the eavesdropper. Lower bounds are derived for the secrecy rates in multiple-input single-output channels with single or multiple eavesdroppers and multiple-input multiple-output channels with multiple eavesdroppers. When the number of transmit antennas is sufficiently large, the bounds are tight, and closed-form solutions can be derived from these bounds. The analytical results suggest simple and yet informative solutions as follows: Let the numbers of receive antennas at the legitimate receiver and at the eavesdropper be Nr and Nr,e, respectively. The system should distribute Nr,e/(Nr+Nr,e) of the power to AN in the high SNR regime, and distribute zero power to AN in the low SNR regime; the rate loss due to the eavesdropper is -Nr\log(Nr/(Nr+Nr,e))-Nr,e\log(Nr,e/(Nr+Nr,e)) bits/sec/Hz in the high SNR regime and nearly negligible in the low SNR regime. The derived results also show that equal power and water-filling power allocations lead to similar solutions and rate loss. Simulation results corroborate the theoretical results. [ABSTRACT FROM PUBLISHER]

In this paper, we analyze and quantify functional value streams of energy storage under different forms (state in which energy is stored) and network location (e.g., transmission or distribution sides). First, we consider a transmission-connected thermal form of storage coupled with concentrating solar power. Using the California power grid as a case study, we show that the coupled unit is significantly less volatile in its response and, through its load following, day-ahead dispatching, and regulation capabilities, it produces significant cost savings. Another case study examines the value of the electrical form of storage in a distribution network and in coupling with photovoltaics. The energy storage is used to mitigate component overloads and to reduce the subsequent infrastructure investments, and smooth out the intermittency of renewable generation. Storage value is quantified formally and under optimal control configuration of storage charge and discharging. Finally, a case study is constructed to examine the functional value of substation-sited storage with respect to investment deferral for the substation transformer. [ABSTRACT FROM PUBLISHER]

The articles in this special issue focus on the topics of the key technologies and applications that support wireless power transmission. [ABSTRACT FROM PUBLISHER]

After the early experimental lines realized by Gaulard and Gibbs of 1881?1884 [1], the consequent theoretical investigations by Ferraris, and the improvements developed at Ganz & Co. (Budapest, Hungary) by Zipernowsky, Bl?thy, and D?ri, who in 1885 introduced the ZBD scheme (from their initials [1]), engineers soon started building on alternating currents (ac) in several countries. Early operative ac systems, which exploited the capability of transformers to step voltages up and down, soon appeared, aimed at distributing and transmitting electric power over long distances. [ABSTRACT FROM PUBLISHER]

The three-phase dual-active bridge (DAB) is a dc–dc converter, which provides galvanic isolation, inherent soft-switching capability, and small filter size. In this study, the dynamic behavior of three-phase DAB is analyzed and a dynamic control strategy is developed. Furthermore, a compensation technique is implemented to compensate unbalanced transformer phase currents. The latter is often caused by asymmetric leakage inductances. State space averaging and first harmonic approximation models, both for the steady state and transient analysis, are developed to describe the dynamic behavior of the three-phase DAB. The accuracy of the models is compared with a detailed circuit simulation and the benefits of each model are identified. When the transferred power of the DAB changes fast, the transformer currents can become unbalanced, leading to oscillations in the output current. A unique control method is presented, which allows settling of the transformer currents within one-third of the switching period. Additionally, the transformer currents stay symmetrical and oscillations are avoided. Based on this fast current control, an outer voltage controller is designed. The comparison of the control system using the fast current control and the conventional quasi-steady-state control demonstrates the potential advantages of the new approach under dynamic conditions. In practice, it is difficult to achieve completely symmetrical short-circuit impedances in a high-power medium-voltage transformer. Asymmetric leakage inductances, however, result in unbalanced phase currents and higher dc current ripple in a three-phase DAB. The new control scheme that is developed here can be extended to compensate any unbalances in the transformer. This approach enables effectively the balancing of the three-phase currents. The new control schemes are experimentally verified. [ABSTRACT FROM AUTHOR]

This paper proposes an evolutionary computing strategy to solve the problem of fault indicator (FI) placement in primary distribution feeders. More specifically, a genetic algorithm (GA) is employed to search for an efficient configuration of FIs, located at the best positions on the main feeder of a real-life distribution system. Thus, the problem is modeled as one of optimization, aimed at improving the distribution reliability indices, while, at the same time, finding the least expensive solution. Based on actual data, the results confirm the efficiency of the GA approach to the FI placement problem. [ABSTRACT FROM PUBLISHER]

Estimating technical losses is fundamental to the planning and economics of electric power networks. This paper surveys the evolution of the ideas behind energy loss estimation and focuses on the development of the concepts of the loss factor and equivalent hours. The paper next identifies difficulties in using maximum demands and the loss factor to estimate energy losses. Based on this analysis, this study proposes an alternative loss estimation approach that relies on the “loss coefficient” as the fundamental parameter for describing load variations in loss estimation. A large load-curve data bank from Brazilian utilities is used to characterize load-curve parameters and provide perspective on the old and new concepts. Practical applications put the proposed ideas into perspective, showing how the use of average demands and loss coefficient can help to make better cable choices, increase accuracy in loss estimation for distribution transformers, and enhance the quality of information in loss estimation analysis. [ABSTRACT FROM PUBLISHER]

The first commercial high-voltage dc (hvdc) electric transmission link was installed to power the Swedish island of Gotland from shore by means of a 96-km, 100-kV subsea cable in 1954. Since this first 20-MW transmission system, more than 100 HVdc systems have been installed worldwide. Some of the major technical breakthroughs have included the introduction of thyristor-based valves in the 1970s, the first large multiterminal schemes in the early 1990s, insulated gate bipolar transistor (IGBT)-based converters in the late 1990s, and ultrahigh-voltage (UHV) dc transmission system operation at 800 kV with transmission capacities above 6 GW in operation since 2010. [ABSTRACT FROM PUBLISHER]

Renewable energy sources, such as solar energy and fuel cells, are desirable due to their pollution-free properties. In order to utilize the present infrastructure of the utility grid for power transmission and distribution, grid-connected inverters are required for distributed generation systems, which should have high reliability. However, a shoot-through problem, which is a major deterrent to the reliability of the inverters, exists in the conventional bridge-type voltage-source inverters. In order to solve the aforementioned problem, this paper proposes a two-switch dual-buck grid-connected inverter. The freewheeling current flows through the independent diodes instead of the body diodes of the switches, so reverse-recovery loss of the diodes can be reduced. Half of the power devices operate in high frequency; the others switch at grid period with zero-current switching. Moreover, unipolar modulation is used. The operating principle, design guidelines and example, and stability analysis are provided. The proposed inverter can be simplified to a current amplifier with hysteresis current control, so it is globally stable. Simulation and experimental results verify the theoretical analysis and satisfy IEEE Std. 929-2000. A comparison of a full-bridge inverter and the proposed inverter shows that the proposed inverter is more attractive in high-reliability applications. [ABSTRACT FROM AUTHOR]

This paper analyzes the strategies for injecting power-line communications (PLC) metering signals in secondary substations with multiple distribution transformers. The study is based on real measurements of PLC connectivity across the low-voltage sections of transformers in a representative set of secondary substations. The results show that there is not a general rule indicating the quality of the PLC channel among secondary windings of distribution transformers in a secondary substation and, consequently, there is no general solution based in pre-existing information. Following this conclusion, a strategy is defined to maximize the performance of the PLC system, based on the PRIME PLC specification. This strategy is based in the use of a base node connected to one of the low-voltage panels, together with auxiliary nodes connected to the remaining low-voltage panels, and interconnecting all of the elements (base node and auxiliary devices) by means of non-PLC technologies. [ABSTRACT FROM AUTHOR]

This paper studies the effectiveness of reactive power compensation using a multilevel, hexagram-converter-based STATic COMpensator (STATCOM) with one-cycle control (OCC) for a wind farm with fixed-speed turbines, and the interaction with the power system network. Comparison is made with several common types of multilevel voltage source converters used for STATCOM applications. A new voltage control method based on OCC principles for hexagram-based STATCOMs is proposed and proven by a wind farm power system simulation showing the improvement of voltage variations caused by wind speed changes. The experimental results from tests of a small-scale hexagram converter prototype have verified the proposed converter and control method. [ABSTRACT FROM AUTHOR]

The local DC power distribution system of More Electric Aircraft is one of the cores of the electric power transmission. Because the mechanical source (turbine engine) is unidirectional, the system is not totally reversible. Some storage and dissipation systems are necessary to store or/and dissipate the returned energy to maintain the dc bus voltage. Different power-management strategies are proposed and compared. The development of experimental test benches is necessary to validate these strategies. In this paper, we present a 3-kW test bench, emulating a unidirectional source that supplies a bidirectional load with the help of a hybrid system using supercapacitors and a dissipation system. The experimental validation of the power-management strategies is presented in this paper, too. [ABSTRACT FROM PUBLISHER]

All over the world there is a growing need for current limiting devices in electrical networks with steadily increasing power demands and fault currents. Production of YBCO coated conductors (CCs) paves the way for the economic viability of superconducting fault current limiters (FCLs) both in power distribution and transmission networks. In a cooperation between AMSC and Siemens the limiting capability of YBCO CCs has been investigated and was demonstrated in a successful laboratory test of a 2.2 MVA medium voltage FCL. This device is based on bifilar coils as switching elements and corresponds to one phase of a 3-phase FCL designed for the 13kV-class distribution voltage level. In more than 40 switching tests at voltages up to 7.7 kV the device showed excellent limiting performance. Presently this cooperation has entered a new DOE funded joint project that encompasses the design, construction and test of a 115 kV FCL for power transmission within a time frame of 4-5 years and additional partners. AMSC as the project leader is responsible for wire manufacturing, system integration and cryogenics. Siemens' main task is switching modules development, Nexans contributes the high voltage terminations and Los Alamos National Lab investigates AC losses. Installation and testing are planned for a Southern California Edison substation. A project overview and progress under the first phase will be reported. [ABSTRACT FROM AUTHOR]

Abstract-Electrical power system robustness is defined as the intrinsic capacity of an electrical power system to maintain assigned disturbance levels when external conditions change. This paper compares two methods for estimating voltage dip severity: the critical distance method and the fault position method. Their differences are not linked to the type of network but to the type of results which we are searching for. This paper proposes a graphical color visualization of the during fault voltage matrices that immediately correlates dip severity with colors defined by a proper scale. New robustness indices are also proposed to synthesize bus performance in terms of affected and exposed areas. Numerical applications refer to real transmission and real distribution systems. [ABSTRACT FROM AUTHOR]

The benefit of shifting load from the peak to the off-peak period is well known from the viewpoints of demand response and deferral of capacity upgrade. However, the impact of load leveling on reducing transmission and distribution (T&D) losses is often ignored or lightly mentioned in the literature. A detailed analysis of T&D loss reduction is very specific to the considered power system and cannot be readily generalized. Therefore, the objective of this paper is to identify the key parameters and quantify the saved T&D losses as a function of the size or power of the energy storage in a set of normalized charts to help assess the benefits of energy storage as a means to level a utility load. This is a benefit of utility-scale energy storage that is not fully recognized. [ABSTRACT FROM AUTHOR]

Recently, the interest in offshore wind farms has been increased significantly. Besides the huge amount of space available, they have the advantage of an increased and more constant wind speed, leading to a higher and more constant production of power. Although, a lot of mechanical problems for constructing these farms have been solved during the past decade, the electrification is still a major issue in research. For large wind farms situated more than 60 km from the shore, an HVdc connection is favorable. Consequently, a pure dc system could be an interesting and cost-effective solution for offshore wind farms. In this paper, a control structure for such a dc grid is presented and analyzed. Furthermore, different configurations are compared and the developed simulation models are presented. [ABSTRACT FROM AUTHOR]

The Indian power sector has grown to a large size in the last 60 years after the country's independence in 1947, and it has opened up with unbundling into distinctive entities of generation, transmission, and distribution. With both public and private participation, reliable load forecasting, planning, and system operation ensuring security to meet the demand at each instant have become the utmost necessities in the context of having electricity for all by the end of current five- year plan (March 2012). In this context adequacy as well as reliability of existing transmission systems have assumed a great significance in the entire power sector. Beyond this period, with continued growth in the economy, projection in power demand and commensurate addition in generation capacity also call for large network expansion for the Indian National Grid as a whole. Enhancement of voltage level of transmission, both with HVAC as well as HVDC, for hauling power from surplus to deficit regions poses challenges that need to be overcome through adoption of technologies. [ABSTRACT FROM PUBLISHER]

A novel formulation for service restoration algorithm for unbalanced three phase distribution systems is described. This problem is a constrained multiobjective optimization formulated as a mixed integer non-linear programming problem. A comparison of the solutions with and without switch pairs has been made. The formulation was first validated using already developed three-phase unbalanced power flow software. The three-phase unbalanced power flow equations were embedded in the formulation, and hence separate calculations were not needed. Simulation results are presented for modified IEEE 13-node and IEEE 37-node test cases. [ABSTRACT FROM AUTHOR]

Outsourcing of maintenance activities from the core distribution operator business prompted the reorganization of the operations sequence of activities and affects, to some extent, the reliability of the distribution network. Repair times, a major component in the reliability calculations, arrive to a new understanding from operations point of view and the adequacy of established probabilistic representations has to be assessed. This paper proposes a mechanism to identify the layout of the sequence of activities for distribution component repair, resulting from reorganization, and revises the adequate representation of the times associated with various stages of the derived repair process. Statistical-based techniques employing estimates of distribution parameters and hypothesis testing serve to determine probabilistic distributions. The validity of the independence assumption for the random variables associated with individual times which compose the repair time is checked via statistical methods in order to confirm applicability of probabilistic-based calculations. By means of such a mechanism, an objective analysis of the time components of the repair time can be conducted, such as areas of improvement, and can be outlined. The results obtained for a large real power distribution system are presented. [ABSTRACT FROM AUTHOR]

There are advantages of installing distributed generation (DG) in distribution systems: for example, improving reliability, mitigating voltage sags, unloading subtransmission and transmission system, and sometimes utilizing renewables. All of these factors have resulted in an increase in the use of DGs. However, the increase of fault currents in power systems is a consequence of the appearance of new generation sources. Some operating and planning limitations may be imposed by the resulting fault currents. This paper discusses a model of inverter based DGs which can be used to analyze the dynamic performance of power systems in the presence of DGs. In a style similar to protective relaying analysis, three-dimensional plots are used to depict the behavior of system reactance (X) and resistance (R) versus time. These plots depict operating parameters in relation to zones of protection, and this information is useful for the coordination of protection systems in the presence of DG. [ABSTRACT FROM AUTHOR]

This paper discusses the aging US electricity infrastructure, including generation, transmission and distribution. From the analysis in this article, there is no doubt that the U.S. electricity infrastructure is aging. Aging infrastructure has higher cost to operate and maintain and, more importantly, lower reliability. The lower reliability of aging infrastructure makes the physical system less reliable and the electricity market more risky. The healthy operation of an electricity market should take into consideration the reliability of individual infrastructure components, and one way to do that is to make the reliability a cost driver [ABSTRACT FROM PUBLISHER]

This paper discusses asset management for transmission and distribution companies. It first presents the goals and objectives of asset management, a corporate framework, and the competencies required to make it all work. It also discusses some of the pressing issues facing transmission and distribution companies today and the ability of asset management to help address these issues in an effective manner. [ABSTRACT FROM PUBLISHER]

This paper provides a brief historical review of the rapid revolutionary technological progress in power systems in Japan during the later part of the 1800s. A century ago, many Japanese engineers visited the United States and Europe to survey power systems and power equipment in pursuit of the most advanced systems of light and power. With expert foreign assistance, it was possible to build just such an advanced power system. Japan also imported necessary products from major manufacturing companies in the West and also made great strides in developing and manufacturing them. For instance, a 100-MW hydroelectric turbine and generator developed in Japan in 1939 had, at that time, the largest capacity in the world. [ABSTRACT FROM PUBLISHER]

The prevalent engineering practice (PEP) for maximum demand estimation in low voltage (LV) electricity networks is based on an After Diversity Maximum Demand (ADMD) modified by a diversity factor. This method predicts the maximum likely voltage drop accounting for consumer diversity. However, this approach does not take into account the stochastic nature of the demand and is inconsistent with international power quality standards. We present a Monte Carlo simulation model of consumer demand taking into account the statistical spread of demand in each half hour using data sampled from a gamma distribution. The parameters of the gamma distribution are based on data metered at a number of residential properties fed by one transformer. The simulated demand is corrected for temperature and total consumption. The simulated profiles at the residential properties are aggregated and the simulated maximum demand is compared with actual maximum demand at a given transformer and an entire distribution network showing good agreement in both cases. [ABSTRACT FROM AUTHOR]

In this paper, the problem of voltage regulation and power losses minimization for automated distribution systems is dealt with. The classical formulation of the problem of optimal control of shunt capacitor banks and Under Load Tap Changers located at HV/MV substations has been coupled with the optimal control of tie-switches and capacitor banks on the feeders of a large radially operated meshed distribution system with the aim of attaining minimum power losses and the flattening of the voltage profile. The considered formulation requires the optimization of two different objectives; therefore the use of adequate multiobjective heuristic optimization methods is needed. The heuristic strategy used for the optimization is based on fuzzy sets theory. After a brief description of the general problem of optimal control of voltage and power losses in automated distribution networks, the most recent papers on the topic are reported and commented. Then the problem formulation and the solution algorithm are described in detail. Finally, numerical results on a large distribution system demonstrate that the proposed formulation and approach are effective and feasible for finding an optimal generalized dispatching schedule. [ABSTRACT FROM AUTHOR]

This paper describes the first "polyphase" (more than one phase) system developed for the distribution of alternating current (AC) power. This two-phase system was subsequently rendered obsolete, however, by the superior three-phase system that is now universally used throughout the world. Today, the large-scale generation, transmission, and distribution of electric power is by means of the three-phase AC system; that is, three individual single-phase voltages and currents having a 120° phase relationship to each other and intermingled on three wires. The three-phase system has been adopted because it provides for a constant rather than pulsating power flow to motors, and because it is an efficient system as far as the amount of copper required per kilowatt transmitted. The theoretical complexity of the three-phase system, however, delayed its complete acceptance in the early days of electric power system development. [ABSTRACT FROM PUBLISHER]

This paper presents a new method for optimal reconfiguration of radial distribution systems (RDS). Optimal reconfiguration involves selection of the best set of branches to be opened, one each from each loop, such that the, resulting RDS has the desired performance. Amongst the several performance criteria considered for optimal network reconfiguration, maximizing loadability is an important one. Owing to the discrete nature of the solution space, a fuzzy adaptation of the evolutionary programming algorithm for optimal reconfiguration of RDS to maximize loadability is proposed in this paper. This method maximizes a fuzzy index developed using a maximum loadability index. A 33-bus RDS is optimally reconfigured by the proposed method and the results are presented. [ABSTRACT FROM AUTHOR]

The voltage waveform on the electric power distribution system is distorted by harmonic-producing loads. Regardless of the terminal voltage waveform with or without harmonics, the conventional current waveform of the pulse width-modulated converter systems connected to the power distribution system is always controlled to be sinusoidal. For harmonic suppression of the voltage and current on the distribution system, the authors propose the distorted current waveform whose harmonic components are in phase with the terminal voltage harmonics. The effectiveness of the proposed current waveform has been verified by experiments. [ABSTRACT FROM AUTHOR]

Voltage sag distributions caused by faults at different voltage levels and experienced by low-voltage customers were established for four different power system areas. The shares of different fault types at each voltage level and the sag propagation throughout the power system were taken into account. The results show that the origin of sags in urban and rural areas tends to be different. These data are needed when, for example, planning measures for sag mitigation in different parts of the power system. [ABSTRACT FROM AUTHOR]

In this paper, the authors present an overview of the European Union internal electricity market directive, which establishes common standards for the generation, transmission and distribution of electricity [ABSTRACT FROM PUBLISHER]

The assets and working philosophy of individual utilities will in large measure be reflected by the modernization of their power systems in the next 2 decades. The power system of the future should enable utilities to: be more competitive with their overall strategies; provide better service; better manage their assets; extend equipment life; improve diagnostics; and develop reliability-centered maintenance. In looking ahead at the next 2 decades, we consider various options that are available, point out the less likely, and highlight those that have the potential of achieving major improvements. Although the next 20 years is a little soon for dispersed generation to have a significant impact, some of the implications of dispersed generation are considered. The following topics are covered in this paper: transmission and distribution developments; comparison of overhead and underground power delivery; the pros and cons of underground delivery; superconducting power transmission including cables; and cryoresistive delivery including conventional cryoresistive delivery, hyperconductivity and metal-plated graphite fibres [ABSTRACT FROM PUBLISHER]

This paper proposes the algorithm to control the current ratio of the transmitting (Tx) coils for proper power distribution to the two receiving (Rx) coils in wireless power transfer (WPT) system. The proposed algorithm assumes that each Rx coil appears at different times to consider the situation where multiple users request power transmission as practically as possible. That is, suppose the second Rx coil enters the charging space later than the first Rx coil. When each coil enters the charging space, only the Tx coil is used to obtain the value required for calculation. Using the obtained result, the optimized Tx coil current is calculated by the proposed algorithm and proper power distribution to both Rx coils is achieved. Three Tx coils and two Rx coils are constructed using the ANSYS MAXWELL simulation tool. As a result of applying the proposed algorithm, it was confirmed that a similar level of power was transmitted between 40∼60%, respectively. The sum of the power transmitted to the two Rx coils also appeared as more than 75%. [ABSTRACT FROM AUTHOR]

This paper presents a literature review on the coordination between transmission and distribution grid operators in power systems, with particular emphasis on the provision of balancing and congestion management services. Firstly, a brief historical background is presented in order to highlight the ongoing changes current power systems are experiencing and that call for greater coordination between transmission system operators (TSO) and distribution system operators (DSO). These include the growth in distributed energy resources (DER), new roles to be adopted by both system operators (SO), and the integration of new agents such as independent aggregators. Next, the paper places its focus on a particular topic which, based on the review presented, is presumably considered as the most relevant issue requiring tighter cooperation mechanisms, that is, the procurement of balancing services from DER by TSOs whilst DSOs procures the same DER flexibility to manage local congestions. Four key elements are identified for this coordination to take place, namely (a) DER flexibility integration, (b) coordination schemes, (c) transmission‐distribution optimization, and (d) data exchange. For each one of them, the paper presents a literature review and identifies the main existing technical, economic, and regulatory barriers. These barriers include, among others, the limitation for small DER flexibility to participate in grid service markets, the challenges for independent aggregators, the technical barriers for optimizing a transmission‐distribution grid, and the lack of maturity in coordination schemes and TSO‐DSO data exchange models.This article is categorized under: Energy Systems Analysis > Systems and Infrastructure Energy Systems Economics > Economics and Policy [ABSTRACT FROM AUTHOR]

The strict operational condition of driving motors for vehicles propels the development of more complicated configurations in pure electric vehicles (PEVs). Multi-power-source powertrain configurations are one of the efficient technologies to reduce the manufacturing difficulty of driving motors. However, most of the existing studies are predominantly focused on optimal designs of powertrains and power distribution between the engine and motor of hybrid electric vehicles, which are not appropriate for PEVs. This paper proposes a novel dual-motor coupling-propulsion powertrain system that improves the dynamic and economic performance of the powertrain system in PEVs. The proposed powertrain system can realize both the single-motor driving mode and dual-motor coupling driving mode. The driving modes are divided and a power distribution strategy for the different driving modes based on an optimal system efficiency rule is employed, which enhances the performance of the proposed system. Further, a mode-switching strategy that ensures driving comfort by preventing jerk during mode switching is incorporated into the system. The results of comparative evaluations that were conducted using a dual-motor electric vehicle model implemented in MATLAB/Simulink, indicate that the mileage and dynamic performance of the proposed powertrain system are significantly better than those of the traditional single-motor powertrain system. [ABSTRACT FROM AUTHOR]

This spring I published an article in MIT's Technology Review magazine, Edison's Revenge: The Rise of DC Power, predicting that dc might once again flow through the power distribution grids that deliver electricity to power consumers. It is an improbable scenario in the view of many power engineers, so I half expected some blowback. The most colorful response I received, however, was a note from a Canadian engineer who had reason to question the seemingly unimpeachable presumption that dc had long since disappeared from the distribution scene. [ABSTRACT FROM PUBLISHER]