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The multizonal medium voltage dc architecture of all-electric ship shipboard power systems (SPSs) includes a variety of distributed energy resources, energy storage devices, and power electronic voltage source converters. Due to the limited fuel supply and tight space, control of the converters should be aimed at increasing their efficiency and compactness. In this paper, a novel approach to voltage control in all-electric ship power systems is proposed to fulfill these goals. In contrast to the traditional SPSs that emulate the land-based electricity grid, maintaining a steady bus voltage is no longer an objective here. On the contrary, the voltage is compelled to fluctuate in order to minimize switching losses in the converters. A method for calculation of the minimum required dc voltage level is described, and results of computer simulations of an SPS with a flexible-voltage dc bus are presented. The minimum-voltage operation of the system results in a significant efficiency increase. [ABSTRACT FROM AUTHOR]

This paper proposes a new bidirectional intelligent semiconductor transformer (BIST) for the smart distribution system and smart grid. The proposed BIST consists of high-voltage high-frequency ac/dc converter, bidirectional low-voltage dc/dc converter, and hybrid-switching dc/ac inverter. It features 1) input-to-output isolation with a high-frequency transformer; 2) bidirectional power flow; 3) small size and light weight; 4) capability of compensating voltage sag and/or swell; and 5) realization of three-phase structure based on single-phase module. The operational feasibility of proposed transformer was verified not only by computer simulation with PSCAD/EMTDC software but also by a hardware prototype with rating of 1.9 kV/127 V, 2 kVA, allowing a three-phase transformer of 3.3 kV/220 V, 6 kVA with three-phase construction. [ABSTRACT FROM AUTHOR]

The uptake of variable megawatts from photovoltaics (PV) challenges distribution system operation. The primary problem is significant voltage rise in the feeder that forces existing voltage control devices such as on-load tap-changers and line voltage regulators to operate continuously. The consequence is the deterioration of the operating life of the voltage control mechanism. Also, conventional non-coordinated reactive power control can result in the operation of the line regulator at its control limit (runaway condition). This paper proposes an optimal reactive power coordination strategy based on the load and irradiance forecast. The objective is to minimize the number of tap operations so as not to reduce the operating life of the tap control mechanism and avoid runaway. The proposed objective is achieved by coordinating various reactive power control options in the distribution network while satisfying constraints such as maximum power point tracking of PV and voltage limits of the feeder. The option of voltage support from PV plant is also considered. The problem is formulated as constrained optimization and solved through the interior point technique. The effectiveness of the approach is demonstrated in a realistic distribution network model. [ABSTRACT FROM PUBLISHER]

The advantages arising from dc distribution networks are related to the possibilities of achieving higher quality supply and easier reconfigurability of the system. This paper presents the concept of introducing some dc islands interconnected with the ac distribution network. This will make it easier to connect storage systems, electrical drives, power converters, and renewable sources (i.e., photovoltaic panels). In order to realize the aforementioned goals, a methodology for designing the control strategy of different power converters connected to a dc bus without a centralized system management control unit is proposed. In this way, a plug-and-play functionality for connecting new power converter interfaced elements in the dc network able to stabilize the voltage under different working conditions is realized. In order to prove the advantages obtainable with such a network, a 100-kW dc test facility has been realized at the laboratories of RSE. Different working conditions were tested by means both of numerical and experimental results, proving the effectiveness of the proposed strategy for voltage regulation, continuity of service, and the smart use of storage devices. [ABSTRACT FROM AUTHOR]

Presents closure to the discussion on the above named paper. [ABSTRACT FROM AUTHOR]

It is difficult to estimate how much distributed generation (DG) capacity will be connected to distribution systems in the coming years; however, it is certain that increasing penetration levels require robust tools that help assess the capabilities and requirements of the networks in order to produce the best planning and control strategies. The work of this Task Force is focused on the numerous strategies and methods that have been developed in recent years to address DG integration and planning. This paper contains a critical review of the work in this field. Although there have been numerous publications in this area, widespread implementation of the methods has not taken place. The barriers to implementation of the advanced techniques are outlined, highlighting why network operators have been slow to pick up on the research to date. Furthermore, key challenges ahead which remain to be tackled are also described, many of which have come into clear focus with the current drive towards smarter distribution networks. [ABSTRACT FROM PUBLISHER]

In telecom applications, the vision for a total power conversion efficiency from the mains to the output of point-of-load (PoL) converters of 95% demands optimization of every conversion step, i.e., the power factor correction (PFC) rectifier front-end should show an outstanding efficiency in the range of 99%. For recently discussed 400-V dc distribution bus voltages, a buck-type PFC rectifier is a logical solution. In this paper, an efficiency-optimized, 98.8% efficient, 5-kW three-phase buck-type PFC rectifier with 400-V output is presented. Methods for calculating losses of all components are described and are used to optimize the converter design for efficiency at full load. Special attention is paid to semiconductor losses, which are shown to be dominant, with the parasitic device capacitance losses being a significant component. The calculation of these parasitic capacitance losses is treated in detail, and the charge-balance approach used is verified. A prototype of the proposed rectifier is constructed which verifies the accuracy of the models used for loss calculation and optimization. [ABSTRACT FROM AUTHOR]

Continuity in power supply for the consumers is a permanent concern from the utilities, pursued with the development of technological solutions in order to improve the performance of network restoration conditions. Using remotely controlled switches corresponds to one possible approach to reach such an improvement and gives some convenient remote resources, such as the fault detect, isolation, and transfer loads. This paper presents a methodology implemented in a computer programming language for allocation of these devices in electric distribution systems based on the analytic hierarchical process (AHP) method. The main contributions focus on considering the impact of installing remotely controlled switches in the reliability indices and the AHP decision-making algorithm for the switches allocation. The effectiveness of the proposed algorithm is demonstrated with case studies involving actual systems of the AES Sul utility located in Southern Brazil. [ABSTRACT FROM AUTHOR]

This paper proposes a bilevel programming approach to determine the optimal contract price of dispatchable distributed generation (DG) units in distribution systems. Two different agents are considered in the model, namely, the distribution company (DisCo) and the owner of the DG. The former seeks the minimization of the payments incurred in attending the forecasted demand, while the latter seeks the maximization of his profit. To meet the expected demand, the DisCo has the option to purchase energy from any DG unit within its network and directly from the wholesale electricity market. A traditional distribution utility model with no competition among DG units is considered. The proposed model positions the DG owner in the outer optimization level and the DisCo in the inner one. This last optimization problem is substituted by its Karush-Kuhn-Tucker optimality conditions, turning the bilevel programming problem into an equivalent single-level nonlinear programming problem which is solved using commercially available software. Tests are performed in a modified IEEE 34-bus distribution network. [ABSTRACT FROM AUTHOR]

This paper shows a new hybrid method for risk assessment regarding interruptions in sensitive processes due to faults in electric power distribution systems. This method determines indices related to long duration interruptions and short duration voltage variations (SDVV), such as voltage sags and swells in each customer supplied by the distribution network. Frequency of such occurrences and their impact on customer processes are determined for each bus and classified according to their corresponding magnitude and duration. The method is based on information regarding network configuration, system parameters and protective devices. It randomly generates a number of fault scenarios in order to assess risk areas regarding long duration interruptions and voltage sags and swells in an especially inventive way, including frequency of events according to their magnitude and duration. Based on sensitivity curves, the method determines frequency indices regarding disruption in customer processes that represent equipment malfunction and possible process interruptions due to voltage sags and swells. Such approach allows for the assessment of the annual costs associated with each one of the evaluated power quality indices. [ABSTRACT FROM AUTHOR]

This paper presents a sweep-based three-phase power flow method for solving general distribution networks that can be heavily meshed and include transformers around the meshes/loops. A load-stepping technique is proposed for solving common convergence problems of sweep-based load-flow solvers when dealing with overloaded radial sections. The proposed power-flow algorithm is based on the iterative solution of radial subsystems assembled together with the mesh equations to comply with Kirchhoff equations. The proposed method is robust and efficient for the solution of heavily loaded systems. Examples are presented for illustration. [ABSTRACT FROM AUTHOR]

In this paper an analytical method by which the transient stability of an induction machine is maintained regardless of the fault clearance times is introduced. The method can be applied in order to improve the transient stability of a large penetration of low-voltage (LV) connected microgeneration that can be directly interfaced by single-phase induction generators within domestic premises. The analysis investigates the effectiveness of using resistive-type superconducting fault current limiters (RSFCLs) as remedial measures to prevent the microgenerators from reaching their speed limits during remote faults, and hence improving their transient stability. This will prevent unnecessary disconnection of a large penetration of LV-connected microgeneration and thus avoiding the sudden appearance of hidden loads, and unbalanced voltage conditions. The minimum required value of a resistive element of RSFCL for mitigating the transient instability phenomena of LV-connected microgeneration based on the system and connected machine parameters is determined. The analytical method has been validated by conducting informative transient studies by using detailed models of a small microwind turbine with constant mechanical output interfaced directly within residential dwellings by a single-phase induction generator, a transient model of resistive superconducting fault current limiter (RSFCL), and a typical suburban distribution network with residential loads. All the models are developed in the time-domain PSCAD/EMTDC dynamic simulation. [ABSTRACT FROM AUTHOR]

Increasing connection of variable distributed generation, like wind power, to distribution networks requires new control strategies to provide greater flexibility and use of existing network assets. Active network management (ANM) will play a major role in this but there is a continuing need to demonstrate the benefit in facilitating connection of new generation without the need for traditional reinforcements. This paper proposes a multi-period AC optimal power flow (OPF)-based technique for evaluating the maximum capacity of new variable distributed generation able to be connected to a distribution network when ANM control strategies are in place. The ANM schemes embedded into the OPF include coordinated voltage control, adaptive power factor and energy curtailment. A generic U.K. medium voltage distribution network is analyzed using coincident demand and wind availability data derived from hourly time-series. Results clearly show that very high penetration levels of new variable generation capacity can be achieved by considering ANM strategies compared to the widely used passive operation (i.e., "fit and forget"). The effects on network losses are also discussed. [ABSTRACT FROM AUTHOR]

This paper presents an efficient mixed-integer linear formulation for long term maintenance schedule of overhead lines. The proposed formulation is based on risk management approach and utilizes the model of decoupled risk factors. The proposed methodology yields a significant computational saving comparing to the previously reported dynamic programming. Risk management approach enables the asset managers to consider the actual condition of electrical equipment and expected consequence of their failures. Furthermore, the decoupled risk strategy in con- junction with the mixed-integer linear programming formulation establishes a precise description of time-dependent deterioration failure rate and provides the ability to determine the most cost-effective maintenance scenario while satisfying the reliability constraints. The proposed approach is tested on the Roy Billinton Test System distribution feeders and a typical real size case study. The results presented show the accuracy and efficiency of the proposed approach. [ABSTRACT FROM AUTHOR]

Abstract-This paper proposes a methodology for placement of sectionalizing switches in distribution networks in the presence of distributed generation sources. The multiobjective considerations are handled using a fuzzy approach. The primary objective is reliability improvement with consideration of economic aspects. Thus, the objectives are defined as reliability improvement and minimization of the cost of sectionalizing switches. A fuzzy membership function is defined for each term in the objective function according to relevant conditions. Some considerations incorporated in the proposed model are relocation of existing switches and operating constraints on distribution networks and distributed generation (DG) sources during post-fault service restoration. The Ant Colony Optimization (ACO) algorithm is adopted to solve the fuzzy multiobjective problem efficiently. The performance of the proposed approach is assessed and illustrated by various case studies on a test distribution system and also a real distribution network. [ABSTRACT FROM AUTHOR]

Abstract-In this paper, we present the greedy reconfiguration algorithm (GRA) and the fast greedy reconfiguration algorithm (FGRA)-two reconfiguration algorithms that minimize the energy not supplied (ENS) of medium-voltage (MV)-distribution network (DNs). The algorithms are derived from a graph-theoretic model for the MV-DNs and an iterative formulation for the ENS. Given a DN composed of n loads, GRA yields an initial radial topology with minimal ENS after executing n - 1 iterations of a multistage decision process. Next, GRA executes a verification algorithm to evaluate all of those candidate topologies randomly discarded during the decision process. After the second stage, GRA announces the optimal topology as well as the minimum ENS of the system. The second algorithm proposed is called FGRA and is obtained when heuristic graph compression is performed throughout the execution of GRA. The aforementioned graph compression reduces the dimension of the problem, thereby producing substantial savings in computing time at the expense of possibly achieving a suboptimal solution. [ABSTRACT FROM AUTHOR]

Large-scale distributed measurement systems are the° object of several applications and research. The goal of this paper is to develop, by employing Global Positioning System (GPS) receivers, measurement techniques that are suited to the continuous monitoring of the electrical quantities in distribution networks in terms of synchronized phasors. The proposed measurement procedures, differently from commercially available phasor measurement units, are based on general-purpose acquisition hardware and processing software, thus guaranteeing the possibility of being easily reconfigured and reprogrammed according to the specific requirements of different possible fields of application and to their future developments. [ABSTRACT FROM AUTHOR]

In the last decade, distributed generation, with its various technologies, has increased its presence in the energy mix presenting distribution networks with challenges in terms of evaluating the technical impacts that require a wide range of network operational effects to be qualified and quantified. The inherent time-varying behavior of demand and distributed generation (particularly when renewable sources are used), need to be taken into account since considering critical scenarios of loading and generation may mask the impacts. One means of dealing with such complexity is through the use of indices that indicate the benefit or otherwise of connections at a given location and for a given horizon. This paper presents a multiobjective performance index for distribution networks with time-varying distributed generation which consider a number of technical issues. The approach has been applied to a medium voltage distribution network considering hourly demand and wind speeds. Results show that this proposal has a better response to the natural behavior of loads and generation than solely considering a single operation scenario. [ABSTRACT FROM AUTHOR]

The paper describes genetic-algorithm (GA)-based optimization software for reconfiguration of a distribution net- work in order to minimize financial losses due to voltage sags. The developed methodology starts with a selected number of switches which generate various topologies. Load flows are then performed to evaluate the feasibility of topologies. For each feasible topology, fault analysis is performed to first calculate voltage sags at different buses in the network and then to calculate financial losses incurred by voltage sags at buses with sensitive industrial processes. The result of the optimization is the topology which yields the lowest voltage sag cost to customers. The main features of the GA include double-point crossover and adaptive mutation. The developed software tool is applied to the 295-bus generic distribution system. [ABSTRACT FROM AUTHOR]

Increasing numbers of very small generators are being connected to electricity distribution systems around the world. Examples include photovoltaics (PV) and gas-fired domestic-scale combined heat and power (micro-CHP) systems, with electrical outputs in the region of 1 to 2 kW. These generators are normally installed within consumers' premises and connected to the domestic electricity supply network (230 V single-phase in Europe, 120 V in North America). There is a growing need to understand and quantify the technical impact that high penetrations of such generators may have on the operation of distribution systems. This paper presents an approach to analyzing this impact together with results indicating that considerable penetrations of micro-generation can be accommodated in a typical distribution system. [ABSTRACT FROM AUTHOR]

This paper decomposes the effects of the transition from an average cost distribution tariff to a cost causation-based distribution tariff, in terms of time and location, that uses nodal prices to recover losses and an "extent-of-use" method to recover fixed network costs based on use at coincident peak. Our decomposition is designed so that the effects of using coincident peak and location for fixed network charges, as well as using marginal losses under constraints recovering the exact amount of losses, and recovering exactly the cost of network service in total can be isolated and analyzed separately. We apply our tariff transition and decomposition method to an example network with data from Uruguay to isolate the various effects with and without a distributed generation (DG) resource. We show moving to coincident peak charges and to fully charging for marginal losses while rebating the merchandising surplus through the fixed charges have the greatest effects on changes in distribution tariff charges. DG provides countervailing cost changes to distribution tariffs for loads through loss reductions and the implicit "creation" of new network capacity for which it is paid. The interaction of all these effects may lead to outcomes that are counter-intuitive, which further supports the need to decompose the tariff changes to fully understand the reasons for the direction and magnitude of changes in tariff charges in the transition to tariffs based more on cost causation. [ABSTRACT FROM AUTHOR]

This paper describes a method for calculating energy losses in any system element assuming that the transmitted energy across it is known. The method identifies two components of losses: load variance and load mean. The load variance component can be neglected for large loads, but it is significant for small loads, which are dominant in low voltage networks. Needed parameters for loss calculation are determined by two load duration curves (LDC5) per load type. The formulae for loss calculation in transformers and distribution lines of various phase systems are given, including the formulae for energy losses and average current in the neutral conductor. A new algorithm for voltage calculation at network nodes is proposed and shown to provide high accuracy of calculated losses. The method enables loss calculation for compounded (nonhomogeneous) loads and gives the exact relationship between traditional Loss factor and the load factor. [ABSTRACT FROM AUTHOR]

Evaluating the technical impacts associated with connecting distributed generation to distribution networks is a complex activity requiring a wide range of network operational and security effects to be qualified and quantified. One means of dealing with such complexity is through the use of indices that indicate the benefit or otherwise of connections at a given location and which could be used to shape the nature of the contract between the utility and distributed generator. This paper presents a multiobjective performance index for distribution networks with distributed generation which considers a wide range of technical issues. Distributed generation is extensively located and sized within the IEEE-34 test feeder, wherein the multiobjective performance index is computed for each configuration. The results are presented and discussed. [ABSTRACT FROM AUTHOR]

In this paper, we propose a method for the allocation of fixed (capital and nonvariable operation and maintenance) costs at the medium voltage (MV) distribution level. The method is derived from the philosophy behind the widely used MW-mile methodology for transmission networks that bases fixed cost allocations on the ‘extent of use’ that is derived from load flows. We calculate the ‘extent of use’ by multiplying the total consumption or generation at a busbar by the marginal current variations, or power to current distribution factors (PIDFs) that an increment of active and reactive power consumed, or generated in the case of distributed generation, at each busbar, produces in each circuit. These PIDFs are analogous to power transfer distribution factors (PTDFs). Unlike traditional tariff designs that average fixed costs on a per kWh basis across all customers, the proposed method provides more cost-reflective price signals and helps eliminate possible cross-subsidies that deter profitable (in the case of competition) or. cost-effective (in the case of a fully regulated industry) deployment of DG by directly accounting for use and location in the allocation of fixed costs. An application of this method for a rural radial distribution network is presented. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of the accuracy of several approaches to modeling the annual number of supply interruptions and their duration in an MV municipal cable distribution network when estimating the costs of penalty payments to be paid by the given distribution company to individual consumers as a result of breaching the guaranteed standards of supply continuity. [ABSTRACT FROM AUTHOR]

In Part I of this two-paper set, the inference of the operative configuration (OC) in real lime has been analyzed. This Part II presents an approach to infer the OC in extended real time, by proposing a mathematical model based on fuzzy relation equations and fuzzy abductive inference. This model sets a methodological framework to integrate the realtime data from SCADA, the qualitative data supplied by expert operators, and the extended real-time data (customer trouble calls) from CIS. In this way, all the knowledge available is used, and the results are dynamically improved as more data are received. At every stage, all the plausible alternatives of solution are calculated, and a complete outlook of possible options is obtained. The results from testing the methodology on a real distribution feeder are presented and discussed. [ABSTRACT FROM AUTHOR]

In this first part of a two-paper set, the operative configuration (OC) is defined as the state (closed/open) of the protective and switching devices installed on the medium voltage distribution network. OC identification is fundamental for the outage management and state estimation of these networks, particularly for those with a low level of real-time supervision and control. In these networks, however, it is difficult to obtain the OC with conventional analytical techniques because of the scarcity or unavailability of monitored devices and measuring points. To overcome this, a novel methodology of inference is presented here. Part I develops a real-time approach based on power flow analysis, fuzzy fault currents calculation and rule-based Type-2 Fuzzy Logic Systems. Part II proposes an extended real-time approach based on fuzzy relation equations and fuzzy abductive inference. The performance of the methodology is evaluated on a real distribution feeder, and results are shown and discussed. [ABSTRACT FROM AUTHOR]

In the restructured electricity industry, the engineering aspects of planning need to be reformulated even though the goal to attain remains substantially the same, requiring various objectives to be simultaneously accomplished to achieve the optimality of the power system development and operation. In many cases, these objectives contradict each other and cannot be handled by conventional single optimization techniques. In this paper, a multiobjective formulation for the siting and sizing of DG resources into existing distribution networks is proposed. The methodology adopted permits the planner to decide the best compromise between cost of network upgrading, cost of power losses, cost of energy not supplied, and cost of energy required by the served customers. The implemented technique is based on a genetic algorithm and an ϵ-constrained method that allows obtaining a set of noninferior solutions. Application examples are presented to demonstrate the effectiveness of the proposed procedure. [ABSTRACT FROM AUTHOR]

This paper is devoted to efficiently modeling the connectivity of distribution networks, which are structurally meshed but radially operated. A new approach, based on the "path-to-node" concept, is presented, allowing both topological and electrical constraints to be algebraically formulated before the actual radial configuration is determined. In order to illustrate the possibilities of the proposed framework, the problem of network reconfiguration for power loss reduction is considered. Two different optimization algorithms--one resorting to a genetic algorithm and the other solving a conventional mixed-integer linear problem--are fully developed. The validity and effectiveness of the path-based distribution network modeling are demonstrated on different test systems. [ABSTRACT FROM AUTHOR]

The load unbalance and the nonlinear loads result in a significant neutral current in the three-phase four-wire distribution power system. The Zig-Zag transformer has been proposed to attenuate the neutral current of the three-phase four-wire distribution power system. In this paper, an analysis is carried out and computer simulation is used to evaluate the performance of the Zig-Zag transformer under ideal and nonideal power conditions. The simulation results show that (a) the Zig-Zag transformer can effectively attenuate the neutral current and zero-sequence harmonic currents on the utility side under the balanced utility voltage, (b) the utility side neutral current becomes larger under the unbalanced utility voltage or the distorted utility voltage with zero sequence harmonic components after applying the Zig-Zag transformer, (c) the insertion of an inductor in the utility side of the neutral conductor can alleviate overloading of the neutral current caused by the unbalanced utility voltages and the distorted utility voltages with zero sequence harmonic components. [ABSTRACT FROM PUBLISHER]

Ignoring mutual coupling in three-phase load-flow computations saves a lot of computational effort but provides inaccurate results for many applications. In this paper, the effect of mutual coupling is taken into account through equivalent branch voltage sources or bus current injections. This simple idea allows accurate enough solutions to be obtained, while much of the computational saving associated with decoupled load flows is retained. Experiments on several unbalanced networks are reported showing the performance of the proposed idea when applied to distribution load flows based on the forward/backward tree sweeps. [ABSTRACT FROM AUTHOR]

This paper presents how the application of the minimal loss reconfiguration in distribution networks can help to evaluate online reconfiguration benefits, considering the time varying nature of loads, using daily load profiles in each node of the system. The emphasis in this evaluation is hourly reconfiguration in distribution systems, compared to fixed topologies, considering maximum and average demand of the system. The results of applications to two real systems show unexpectedly that hourly reconfiguration is not so effective, If compared to a simple maximum or average demand reconfiguration. These conclusions are based on the decrease of obtained losses add on the amount of commutations involved in the hourly reconfiguration process. [ABSTRACT FROM AUTHOR]

The neutral wire in most power flow software is usually merged into phase wires using Kron's reduction. Since the neutral wire and the ground are not explicitly represented, neutral wire and ground currents and voltages remain unknown. In some applications, like power quality and safety analyses, loss analysis, etc., knowing the neutral wire and ground currents and voltages could be of special interest. In this paper, a general power flow algorithm for three-phase four-wire radial distribution networks, considering neutral grounding, based on backward-forward technique, is proposed. In this novel use of the technique, both the neutral wire and ground are explicitly represented. A problem of three-phase distribution system with earth return, as a special case of a four-wire network, is also elucidated. Results obtained from several case studies using medium- and low-voltage test feeders with unbalanced load, are presented and discussed. [ABSTRACT FROM AUTHOR]

Presents a discussion to the above named paper. [ABSTRACT FROM AUTHOR]