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Chipper motors in pulp and paper mill environment are of special design—the stability on impact loads is one important consideration. The power factor under normal operation will continuously swing due to varying loads. This paper describes the guesswork-free rigorous calculations of pull-out (out-of-step) power factor based on the parameter of an actual installation. Single phasing is rather a rare occurrence; however, such an event has been experienced in an installation due to overheating and arcing at the fuse clips in a NEMA E2 starter of a chipper motor. Discussions on the single-phase protection of synchronous motors and recommended settings are provided. [ABSTRACT FROM AUTHOR]

An improved hybrid unified power flow controller (IHUPFC) is developed in this paper to control the power flow and increase the utilization rate of the existing transmission lines. The IHUPFC is composed of an improved “Sen” transformer (IST) and a small capacity unified power flow controller (UPFC). After a detailed introduction of the structure and voltage regulation performance of the IST, this paper derives the capacity relationship between the IST and the UPFC. Then, this paper introduces the technology of the IHUPFC in power flow regulation and transmission capability improvement. Besides, the advantages of the IHUPFC in performance and structure are analyzed. The IST has simpler structure and larger power flow control area than a “Sen” transformer, and the IHUPFC provides a continuous active and reactive power flow control. Simulation and experiment studies are used to verify the practicability and superiority of the IHUPFC. [ABSTRACT FROM AUTHOR]

With a step-out distance of 161 km and a design power of 55 MW, Martin Linge offshore gas field will be the longest ac submarine cable power supplying an entire offshore oil and gas platform from the shore. This field development comprises a platform with a jack-up rig and a floating storage offloading unit. This paper discusses the criteria that have been considered to select a power-from-shore concept instead of an offshore gas turbine power plant, which is the current practice in the offshore oil and gas industry. Since in a first approach, for such a long step-out distance, the choice of power from shore would be to select a dc transmission line, this paper discusses the design and the main technical challenges of this long step-out ac transmission development. Finally, the system approach that is required for the development of the onshore and offshore parts of the project is described. [ABSTRACT FROM PUBLISHER]

The energy blockchain is a distributed Internet protocol for energy transactions between nodes of a power system. Recent applications of the energy blockchain in microgrids only consider the energy transactions between peers without considering the technical issues that can arise, especially when the system is islanded. One contribution of the paper is, thus, to depict a comprehensive framework of the technical and economic management of microgrids in the blockchain era, considering, for the first time, the provision of ancillary services and, in particular, of the voltage regulation service. When more PV nodes are operating in the grid, large reactive power flows may appear in the branches. In order to limit such flows, a reactive optimal power flow (R-OPF) is solved, setting the voltage at the PV buses as variables within prescribed limits. Each PV generator will thus contribute to voltage regulation, receiving a remuneration included in the transaction and certified by the blockchain technology. For showing how this system can work, a test microgrid, where some energy transactions take place, has been considered. For each transaction, the R-OPF assigns the reactive power to the PV buses. The R-OPF is solved by a glow-worm swarm optimizer. Finally, the paper proposes a method for remuneration of reactive power provision; this method, integrated into the blockchain, allows evaluating the contribution to voltage regulation and increases the transparency and cost traceability in the transactions. The application section shows the implementation of a Tendermint-based energy transaction platform integrating R-OPF and the earlier cited technical assessments. [ABSTRACT FROM AUTHOR]

This paper is concerned with the use of a three-level inverter for a synchronous reluctance machine (SynRM). The SynRM suffers from a poor power factor due to poor machine saliency. This makes it harder to operate the three-level neutral-point-clamped inverter due to a strict requirement to have the two dc-link capacitor voltages balanced. This paper proposes a new nearest three vector modulation algorithm which can balance the two dc-link capacitors even at poor machine saliency ratio (poor power factor). In this paper, a method of sizing the two dc-link capacitors based on the machine power is also proposed. A comparison between two- and three-level inverters was conducted. The SynRM registered lower $d$-axis current ripple with a three-level inverter, indicating lower core losses in the machine. [ABSTRACT FROM PUBLISHER]

The active power distribution network operation with the integration of various renewable distributed generations (DGs), storage units, and dynamic loads are attracting a lot of interest due to substantial benefits in maximizing the penetration of available renewable energy resources (RES). However, the risk of voltage violation in the active distribution system (ADS) is exacerbated due to increasing penetration of DGs. It has become a bottleneck to maximize the DG penetration into the system. This bottleneck can be handled by effective voltage regulation and reactive power support into ADS. Nowadays, power electronic devices are frequently used for voltage and reactive power support over the conventional approaches. In this paper, an approach to maximize the penetration of RES, such as solar, wind, etc., into ADS by maximum utilization of existing solar photovoltaic inverters (SPVI) in the system is presented. Optimal utilization of SPVI may enhance the voltage stability of the ADS and wind power penetration into the system. The proposed SPVI control approaches are depended on active power generation of solar photovoltaic (SPVG), rating and capability of SPVI, and required reactive power in the ADS. In this paper, the problem of maximum penetration of RES is formulated as an optimal power flow embedded nonlinear optimization problem subject to the physical limitations of the SPVI. The results of the analysis performed on an IEEE 33 bus system show that the proposed SPVI control strategies can improve the voltage profile of the ADS with minimization of curtailment of wind power generation. [ABSTRACT FROM AUTHOR]

This paper proposes a novel open-winding brushless doubly-fed reluctance generator (OW-BDFRG) with dual two-level converters in order to reduce the converter rating and switching frequency for large-scale wind turbine applications. The new converter topology is equivalent to a three-level converter directly connected to the control winding of typical BDFRG. The OW-BDFRG system with this topology structure requires lower converter rating and switching frequency, and has a more flexible control mode, better operation performance, and fault redundancy capability. For the OW-BDFRG, this paper also proposes a new control scheme combining direct power control (DPC) with sliding mode variable structure (SMVS) control to implement the power tracking. The voltage-vector switching table of DPC is redesigned according to the error signals of active and reactive powers of the power winding, as well as the sector location of control winding flux. The active and reactive powers of the OW-BDFRG can be directly decoupled and independently controlled by properly selecting the switching voltage vectors. The novelty of this paper lies in an OW-BDFRG topology driven by dual two-level converters to improve the system characteristics, and the use of SMVS control to improve the DPC accuracy and robustness to parameter variations. Finally, the effectiveness of the proposed system is verified through simulation and experimental studies. [ABSTRACT FROM AUTHOR]

The ever growing penetration of distributed generation (DG) in a distribution network has a profound impact on network protection and stability. Traditional protection schemes and algorithms need to be extensively investigated as more and more DGs get introduced into the network. The current version of IEEE Standard 1547 does not present a comprehensive solution for fault current detection in the presence of various kinds of DGs. Power electronic inverter-based DGs (IBDGs) are of special concern in distribution network protection as they are often incapable of providing sufficient fault current and their controllers play a principal role in the DG behavior. In this paper, the effects of voltage and current controllers for IBDGs on industrial and commercial power system protection schemes are investigated. It is shown that the inverter control mode has a direct impact on its fault current levels and duration. A simplified distribution network model with IBDG operating under voltage and current control modes was tested to verify the effects of these controllers. This paper also proposes an adaptive relaying algorithm to detect the faults in the presence of IBDGs with various types of controllers. [ABSTRACT FROM AUTHOR]

This paper presents an improved dc-link voltage balancing algorithm for a three-level neutral-point-clamped inverter by considering phase current direction. Detailed studies on the effects of change in load current direction on the dc-link capacitor voltages are presented. A maximum value of power factor is numerically derived, above which it affects the capacitor voltage balancing capability. Compared with the previously presented research work, the inputs to the space-vector pulsewidth-modulation block are the three phase currents and the difference between the two capacitor voltages. Depending on the states of the two dc-link capacitor voltages and phase current direction, redundant voltage vector sequences are selected. The selected vectors keep the capacitor voltage deviations within 5% of the total dc-link voltage. Two zero switching vectors (i.e., PPP and NNN) are also removed from all subsectors of the earlier proposed strategy, which one used to produce higher common-mode voltages. Detailed simulation and experimental results are presented in this paper for a 6.0-kW surface permanent-magnet synchronous machine. Both the simulation and experimental results show the required performance of the proposed system. [ABSTRACT FROM AUTHOR]

The operational availability of mining shovels is the focus of this paper. The hypothesis is that energy quality is responsible for the frequent shutdowns of the shovels. Previous engineering studies have highlighted a large presence of harmonics and reactive power in the mine loop electric system. A common solution proposed was to use a combination of active filters, larger mobile substations, shorter mining cables, and equipment location constraints. The aim of this paper is to produce a precise diagnosis of the source and nature of the energy quality issues. Mine loop electric quality monitoring, system modeling, equipment technologies, and shovel's histograms are considered. Results are measured against IEEE standards and shovel's voltage regulation susceptibility. With the diagnosis, the goal was to produce a reliable cost-effective solution. Different alternatives are crosschecked with this paper proposal. The solution presented provides energy quality well within the shovel's susceptibility and improves energy efficiency. The lower energy consumption pays the investment required and is currently under construction. [ABSTRACT FROM AUTHOR]

Reliable operation of multichannel power electronic converters in a large pumped storage power plant (PSPP) is a main concern among policymakers and/or hydropower project developers. This paper aims to design a two-stage protection circuit operation strategy for a large-rated doubly fed induction machine (DFIM) employed for variable-speed PSPPs. This paper initially studies the dynamic behavior of DFIM under symmetrical short-circuit faults in both the 400-kV power system and at stator terminal of the generating unit. Based on the fault analysis, a two-stage protection circuit (dc-link braking chopper circuit and crowbar protection circuit) operation strategy is designed in consideration of practical limitations. The designed operation strategy ensures the continuous operation of large-rated DFIM under marginal grid disturbances. To investigate the effective operation of a two-stage protection circuit, a 250-MW DFIM with multichannel power converters is implemented in MATLAB/Simulink tool. An experimental test is carried in a 2.2-kW DFIM laboratory prototype. [ABSTRACT FROM AUTHOR]

Grid-connected voltage source converter is used to control the flow of active power from renewable energy sources with several functionalities, such as harmonic mitigation, reactive power compensation, and power factor improvement. The reference current calculation and its accuracy decide the performance of the control algorithms during harmonic disturbances. Fundamental signal extraction techniques are utilized to overcome the disturbances present in the system voltage and current. This paper presents a novel orthogonal current decomposition control for load current decomposition into active and reactive components. These current components are obtained through character of orthogonal vector in the inner product space. The block diagram of the proposed technique is implemented with the help of adder, multiplier, and windowed integrator. Phase voltage and load current for each phase are used as inputs to this functional diagram for getting desired fundamental active current signal. Subsequently, adjustable dc-link voltage control is also presented to diminish the switching losses in the converter and to avoid the false tripping of the grid-connected system during susceptible grid conditions. The proposed control technique is simulated in MATLAB/Simulink and verified through developed hardware prototype using ARM Cortex M4-based microcontroller (STM32F407VGT6) using Waijung environment. [ABSTRACT FROM AUTHOR]

In low-speed applications, variable-reluctance permanent magnet machines are often proposed due to their efficient use of magnet material and high torque density. This becomes even more important in large linear applications, where the translator is longer than the stator. Often, however, very low power factors are experienced by this class of machines. This paper proposes a V-shaped flux concentrated version of a consequent pole linear Vernier hybrid permanent magnet machine and compares it to a surface-mounted magnet variant. Using finite-element analysis validated by two laboratory prototypes, it is shown that the flux-concentrated version increases the airgap flux density, which potentially leads to an improvement in the force density and efficiency or can be used to increase the operating power factor. [ABSTRACT FROM AUTHOR]

Among the renewable energies, wind energy is hosted in selected points helping their penetration to the network. This paper shortly treats the wind power flow and the control of power flow within the wind power plant, focusing on the doubly fed induction generator (DFIG). A general slip–torque relation is derived with three torque components: one component is derived by the stator voltage, the other component by the $d$ component, and the third component by the $q$ component of the rotor voltage space vector. The algorithm for controlling the stator active and reactive power by the rotor-side converter in block diagram form is developed, and its operation is presented by simulation results. The reader can easily check all results as the relations are derived and their physical contents are explained. [ABSTRACT FROM PUBLISHER]

Large-scale wind farms (WFs) are gradually required to participate in power system frequency regulation, especially in a weak grid. Corresponding ancillary frequency control functionalities and the contribution of the WF to system frequency stability are well studied. However, the impact of WF ancillary frequency control on wind turbine generators (WTGs) is rarely considered. It is found in this paper that the ancillary frequency control deteriorates drive-train torsional oscillation of the WTG, which restricts application of the ancillary control. To overcome this problem, this paper proposes an adaptive damping control scheme based on reactive power modulation of the WTG to suppress the drive-train torsional oscillation, which can assist the WF to meet the grid code requirements. Superior to the traditional active power modulation method, the proposed adaptive control scheme can achieve satisfactory damping improvement with less control effort. Furthermore, the adaptive scheme with a torsional frequency updating mechanism can effectively counteract torsional damping deterioration caused by parameter uncertainties, operating condition or control mode variations. Feasibility and effectiveness of the proposed damping control are validated by simulations and real-time experiments. [ABSTRACT FROM AUTHOR]

This paper focuses on the analysis and design of a triple-rotor axial-flux spoke-array vernier permanent magnet (TR-AFSAVPM) machine. By cooperating with spoke-array rotor and coil-wounded winding, power factor and torque density of the proposed machine are much improved and its copper utilization is reduced comparing with conventional vernier machines. First, the machine structure and its operation principles are reviewed. After that, analytical equations of its back-electromotive force and torque are derived to reveal the machine characteristics. Based on both quasi-3-D finite element analysis (FEA) and 3-D FEA, its high torque density performance is verified and a set of optimized machine sizing specifications is ultimately settled. A fractional slot axial-flux permanent magnet (VPM) machine and an axial-flux surface VPM machine are designed to compare with the proposed configuration. Analysis results show that the TR-AFSAVPM machine has high power factor viz., 0.96 and high torque density viz., 24.2 kNm/m3. A prototype has been designed and tested to validate the results. No-load test result is illustrated in this paper and the rated load experiment will be added in the future. [ABSTRACT FROM AUTHOR]

This paper presents a high power factor (PF), low total harmonic distortion (THD) light-emitting diode (LED) driver with dimming capability. In addition, the proposed technique ensures a high PF and low THD at any dimming level. The driver is implemented by using an interleaved capacitor, which is placed between the rectifier and the integrated buck flyback converter (IBFC). In this way, the line current conduction angle is increased, which in return increases the PF and decreases the THD. The operation of the proposed converter ensures that one diode of the conventional IBFC will not conduct, so that it can be removed. Moreover, owing to the continuous power flow, the proposed technique makes a significant reduction of the converter output ripple. The paper presents a prototype of the proposed converter supplying an LED luminaire of 37 V/ 0.67 A. The prototype shows a high PF of 0.997, small THD of 2.5%, output current ripple of 6%, and an efficiency of 80%. [ABSTRACT FROM AUTHOR]

This paper introduces a three-phase grid-connected inverter for commercial-scale photovoltaic systems. The circuit topology combines an ac-inductor-less active bridge with a parallel-connected pulsewidth modulation inverter acting as an instantaneous reactive power compensator. The active bridge, called a 120° conduction inverter, operates at a switching frequency equal to the grid frequency and outputs a 120° rectangular current, while the compensator eliminates the harmonic currents included in the rectangular current. The main advantage of this strategy is the reduction in size of the required ac inductor by a factor of 4, as well as the reduction of power losses in the switching devices. The theoretical analysis clearly shows that the compensator can synthesize a sinusoidal output current by controlling only instantaneous reactive power, thus eliminating the need for electrolytic capacitors. A 5-kW experimental setup validates the operating principle and the control method of the proposed inverter and exhibits an inverter efficiency as high as 99.2% with Si superjunction mosfets. [ABSTRACT FROM AUTHOR]

Electric grid codes are expected to change in near future to accommodate an increased number of distributed generation units in the distribution power system without impairing its power quality. It is desired that the generators remain connected during voltage sags and provide ancillary services, such as voltage and reactive power control, ensuring the operational stability of the power system. This paper explores how the existing strategies for active and reactive power injection impact the operation of grid-tied inverters in terms of required power, current flowing, and reduction of active power delivery during the voltage sags. Such inputs are relevant to properly size converters for operation under fault events. In addition, this paper contributes to devise: 1) constant peak current control, 2) constant active current control, and 3) constant average active power control strategies for three-phase four-wire grid-tied inverters considering the natural (abc) reference frame. The design and implementation of the investigated power injection strategies are discussed, and their effectiveness and technical viability are analyzed through dynamic computational simulations under symmetrical/asymmetrical voltage sags, and variation of the short-circuit ratio. [ABSTRACT FROM AUTHOR]

Since 1980s, several countries have been committed in the exploitation of wind energy sources. The lifetime of these energy sources is generally estimated between 15 and 20 years. Therefore, these wind turbines must be dismantled and replaced by others that are more powerful and more performing. In this context, the Tunisian Electricity and Gas Company has launched, since 2015, a study of the re-equipment (repowering) of the Sidi-Daoud power plant in the north-east country. This paper deals with the repowering study of the Tunisian wind farm. To verify the impact of new wind turbines on the power grid, we performed simulations for the following two faults: a short circuit at the wind farm connection bus and a loss of a conventional power plant of the Tunisian grid. These simulations are performed using commercial PSSE software containing different generic models of wind turbines. Finally, the robustness test is performed and gives good results. [ABSTRACT FROM AUTHOR]

This paper studies the application of distributed and centralized solutions for voltage control in low voltage (LV) grids with high photovoltaic (PV) penetration. In traditional LV grids, the coordination of distributed PV converters and a centralized device would require massive investments in new communication and control infrastructures. The alternative of exploiting distributed PV converters for voltage control is discussed, showing that it can help to stabilize the voltage in the grid connection points also without coordination between them and/or with a centralized unit. The goal of this paper is to investigate how the setup of the voltage controllers inside PV inverters affects the operation of these controllers taking into account the limits for reactive power injection. In addition, the interaction of distributed PV converters with centralized devices (static var compensators and on load tap changers) is analyzed to assess whether additional benefits may come in these cases. [ABSTRACT FROM AUTHOR]

Grid-interactive inverters allow distributed generation units to provide various ancillary services in microgrids. As the linear modulation region of inverters is restricted by the dc-bus voltage, providing ancillary services may drive the fundamental positive-sequence inverter voltage to the overmodulation region. Therefore, to operate in the linear modulation region the maximum active- and reactive-power of the inverter may have to be reduced unless pulsewidth modulation (PWM) references are adjusted. In this paper, an atypical PWM method is proposed for maximizing dc-bus utilization of grid-interactive two-level voltage source inverters (2L-VSI) providing ancillary services. Two important ancillary services, i.e., negative-sequence compensation and harmonic compensation are considered in this paper. The proposed method increases the maximum active- and reactive-power that a 2L-VSI can deliver when providing ancillary services by injecting a common-mode component in the references computed based on instantaneous reference magnitudes. The validity of the proposed technique is verified through simulation, as well as experimental data obtained using a 208-V three phase grid-connected 2L-VSI. [ABSTRACT FROM AUTHOR]

This paper analyzes the configuration, design, and operation of multi-MW grid connected solar photovoltaic (PV) systems with practical test cases provided by a 10-MW field development. In order to improve the capacity factor, the PV system operates at its maximum power point during periods of lower irradiance, and the power output is limited to a rated value at high irradiance. The proposed configuration also incorporates a utility scale battery energy storage system (BESS) connected to the grid through an independent inverter and benefits of the experience gained with a 1-MW 2-MWh BESS large demonstrator. The BESS power smoothing and frequency regulation capabilities are illustrated though combined theoretical and experimental studies. The behavior of the grid connected PV and BESS combined system is studied using a modified IEEE 14 bus test system implemented in PSCAD/EMTDC. This paper also includes a sizing exercise for energy storage in order to provide dispatchable PV power. [ABSTRACT FROM AUTHOR]

A multifunctional grid-connected inverter (MFGCI) has been a promising solution to mitigate power quality problems in distributed generation system and microgrid applications. However, the capability of a conventional MFGCI is limited when compensating a voltage-based power quality problem. In this paper, a new configuration of MFGCI is proposed to improve both voltage-based and current-based power quality issues and is named shunt-series-switched MFGCI (SSS-MFGCI). The SSS-MFGCI can be connected in series or parallel to the grid by implementing bidirectional switches to provide different modes of operation depending on various grid disturbances. The required compensating current and voltage are analytically derived considering the grid and load conditions for voltage regulation. This paper also presents the compensation strategies, control scheme, and transition scheme between different modes of the proposed SSS-MFGCI. Simulation results to prove the concept are also included for unbalanced sag and swell cases. [ABSTRACT FROM AUTHOR]

The paper aims to provide a guideline for rotor design of permanent magnet (PM) assisted synchronous reluctance machine (PMa-SynRM). Unlike interior PM machines, the PMa-SynRM is essentially an SynRM with dominant reluctance torque. The PMa-SynRM is often designed by directly embedding magnets into an SynRM rotor to improve the performance. However, how the PMs can be arranged in the rotor to enhance motor performance has not been fully discussed. This paper investigates the influence of several key factors concerning the PM arrangements, including number of PM layers, inserted positions, and PM sizes. The torque, flux linkages, power factor, and motor performance are comprehensively evaluated. Based on the analysis, a brief guideline is suggested for PMa-SynRM rotor design. Finite element analysis is used for evaluation and experiments are conducted to validate the analysis. [ABSTRACT FROM AUTHOR]

This paper proposes a novel multifunctional controller for a dimmable high-power-factor single-switch electronic ballast that can be used with standard phase-cut dimmers. Conventional dimmable electronic ballasts lack the ability to 1) provide smooth dimming and maintain high power factor when phase-cut dimmers are used and 2) regulate the lamp power when the input line voltage varies. A digital controller with multiple control functions is proposed in this paper. The proposed controller allows high power factor to be achieved by controlling the duty cycle during dimming with standard phase-cut dimmers. On the other hand, when dimming is not required, the lamp power is regulated through the regulation of the dc-link voltage. Additional control functions, such as lamp low-power cutoff operation, and protection function are also implemented inside the digital controller. The descriptions of the controller operating principles and its logic flow diagrams are provided in this paper. PSIM simulation and experimental results are provided on a 13-W compact fluorescent lamp to highlight the merits of the proposed work. [ABSTRACT FROM AUTHOR]

This paper describes a systematic method for optimally designing with multiple objectives and differential evolution (DE) algorithms, current regulated electronically controlled synchronous reluctance (SynRel) machines. A large-scale study with thousands of designs calculated with a ultrafast computationally efficient electromagnetic finite-element analysis (CE-FEA) establishes the performance limitations of conventional radially laminated technology with multiple flux barriers. The potential advantages of employing permanent-magnet (PM)-assisted technology with additional ferrites in the rotor are quantified in terms of substantially improved power factor, specific power, and efficiency. Numerical and experimental results for a 10-hp, 1800-r/min typical rating are included. [ABSTRACT FROM PUBLISHER]

In this paper, a control strategy for the parallel operation of three-phase inverters in a modular online uninterruptable power supply (UPS) system is proposed. The UPS system is composed of a number of dc/acs with LC filter connected to the same ac critical bus and an ac/dc that forms the dc bus. The proposed control includes two layers: 1) individual layer and 2) recovery layer. In individual layer, virtual impedance concept is employed in order to achieve active power sharing while individual reactive power is calculated to modify output voltage phases to achieve reactive power sharing among different modules. Recovery layer is mainly responsible for guaranteeing synchronization capability with the utility and voltage recovery. With the proposed control, improved voltage-transient performance can be achieved and also dc/ac modules can be plugged in and out flexibly while controlling the ac critical bus voltage, thus allowing plug’n’play or hot-swap capability. Detailed control architecture of the individual and recovery layers is presented in this paper. An experimental setup was built to validate the proposed control approach under several case-study scenarios. [ABSTRACT FROM AUTHOR]

This paper presents an optimal planning approach toward the design of cost-efficient and reliable microgrids. The proposed approach uses simulated annealing (SA) to determine the optimal size and location of a mix of distributed generation (DG) candidate technologies to achieve stipulated reliability criteria. The deployment plan consists of adding suitable quantities of DG at appropriate locations, and is optimal in that the cost of expansion is minimized. The paper develops the models and the approach, and describes an SA-based implementation. The method is demonstrated on a standard test system, and the application of the method as a planning tool is illustrated by means of two case studies: 1) optimal expansion of an existing distribution system into a microgrid and 2) evaluation of the impact of projected prices on the deployment strategy. Relative penetration of different DG technologies is also analyzed. [ABSTRACT FROM AUTHOR]

Managing power delivery from distributed generation systems is challenging when the grid voltages are unbalanced, since the negative sequence voltage causes power oscillations at twice the fundamental grid frequency. Current regulation using sequence components can be used to manage these real and reactive power oscillations, and thus help mitigate the unbalanced network voltages. This paper presents a consolidated control scheme using double sequence frame current regulators that can readily adjust between eliminating real or reactive power oscillations created by unbalanced grid voltages, or alternatively can simply balance the three-phase currents. The mitigation influence of these alternative control strategies on unbalanced grid voltages is then experimentally examined for a distribution feeder with a resistive and/or reactive series impedance. [ABSTRACT FROM AUTHOR]

This paper proposes a Y-D multifunction balance transformer (YD-MFBT)-based power quality control system (MBT-PQCS) to deal with the power quality problems in the single-phase power system. The MBT-PQCS mainly consists of a YD-MFBT and a three-phase full-bridge converter (FBC). It fully explores the inherent negative sequence current (NSC) suppressing the ability of YD-MFBT, which makes the power flow transformed by FBC less than that of the conventional transformer-based compensating system. In addition, since the YD-MFBT exits three-phase output ports in relatively low-voltage level, FBC can directly connect with the main transformer via the output ports, without using the auxiliary step-down transformer. Therefore, the initial investment cost, installing difficulties and covering space of the whole compensating system, can be reduced significantly. In this paper, the current transforming relationship and the compensating principle of MBT-PQCS are presented, and the detection and control methods are given as well. Both the simulation and the experiment are used to verify the effectiveness of the proposed system. [ABSTRACT FROM AUTHOR]

Oversizing electrical distribution equipment is a concern in industrial facilities. It adds cost and can increase fault levels. IEEE Std 141-1993 provides guidelines on how to size electrical equipment, but at the early stage of the project, when the equipment is being purchased, much of the process information necessary to properly size the equipment is preliminary at best. In addition, much is left to the discretion of the individual design engineer, who is often not an employee of the facility's eventual owner and, therefore, may have no incentive to reduce equipment size. In fact, depending upon the contractual relationship and due to the preliminary data, compressed schedule, and long delivery, design engineers tend to oversize the equipment. This paper describes an approach for establishing a load-based upper size limit to control oversizing of electrical equipment. This paper will demonstrate that establishing this upper limit can effectively control oversizing of the electrical equipment with information available at the early stage of the project. The resulting safety and economic benefits of the properly sized electrical equipment cascade throughout the power system. [ABSTRACT FROM AUTHOR]

This paper presents a novel finite-control-set model predictive control (FS-MPC) approach for grid-connected converters. The control performance of such converters may get largely affected by variations in the supply impedance, especially for systems with low short-circuit ratio values. A novel idea for estimating the supply impedance variation, and hence the grid voltage, using an algorithm embedded in the MPC is presented in this paper. The estimation approach is based on the difference in grid voltage magnitudes at two consecutive sampling instants, calculated on the basis of supply currents and converter voltages directly within the MPC algorithm, achieving a fast estimation and integration between the controller and the impedance estimator. The proposed method has been verified, using simulation and experiments, on a three-phase two-level converter. [ABSTRACT FROM PUBLISHER]

This paper proposes the enhancement of the control of a grid-connected inverter by a simplified virtual synchronous compensator (S-VSC) model working in parallel with the traditional inverter current control loops. The goal of the integration of this model into the inverter control scheme is to provide grid services, such as virtual inertia behavior, current harmonic compensation, as well as reactive grid support during faults. The S-VSC is only in charge of providing the aforementioned services, working, therefore, always at a low power level. On the other hand, the main power references are sent directly to the inverter control loops. This way, a more stable and damped operation of the inverter is obtained. The proposed structure has been implemented on a 15 kVA grid-connected inverter for experimental validation. [ABSTRACT FROM AUTHOR]

This paper presents a technique based on the novel bat algorithm (NBA) for the design of the parameters of power system stabilizers and the generalized Unified power flow controller-power oscillation damping in a multimachine power system. The objective is to ensure minimal damping rates to low-frequency electromechanical oscillation modes. Simulations were carried out on the New England system to compare the performance of the NBA with three other techniques: particle swarm optimization, bacterial foraging optimization oriented by particle swarm optimization, and the bat algorithm. For the cases analyzed in this paper, the NBA produced results superior to other techniques. Moreover, the proposed methodology was able to obtain solutions with high damping levels, which showed to be robust when a wide range of loading conditions of the power system were considered. [ABSTRACT FROM AUTHOR]

The conservative power theory (CPT) is a time-domain theory applicable to any periodic signal single- or polyphase system with or without a neutral conductor. The principle operation is the orthogonal decomposition of electrical variables, resulting in electrical quantities with physical meaning. An important feature of the CPT is the current decomposition. It consists of decomposing any current into five parts. The label of these parts is active current, reactive current, scattered active current, scattered reactive current, and generated current. This paper proposes the application of the current decomposition of the CPT in distributed energy resources (DERs). A supervisory controller (SC) uses the current decomposition in a load power-sharing strategy. The combination of these two issues is the main contribution of this paper. Moreover, the proposal of this paper is more attractive than the conventional droop strategy since the DERs follow their current reference in a current-controlled mode, making the load sharing faster, more reliable, and more accurate. A clear understanding of how the CPT decomposes load currents into its parts is presented, as well as the drawback found in droop strategy when dealing with load power sharing. Later, the SC load power-sharing strategy is described, indicating that the proposal of this paper makes an SC to have a broad option when managing a smart grid with dispatchable DERs. A case study with experimental results shows the efficacy of applying current decomposition of the CPT in load power-sharing strategies. [ABSTRACT FROM AUTHOR]

This paper presents the design considerations and analysis of a double-sided transverse flux machine (TFM) for direct-drive wind turbine applications. The proposed TFM has a modular structure with quasi U-core stators and toroidal ring windings. The rotor is designed with ferrite magnets in a flux-concentrating setup to achieve high air gap flux density. This paper presents the different aspects of the TFM, taking into consideration the critical geometric parameters affecting the back-EMF waveform, phase inductance, torque density, and power factor. Three-dimensional finite element analysis (3D-FEA) was used to analyze and optimize the critical TFM design parameters to meet the performance specification. A proof-of-concept prototype was developed based on the proposed design considerations. The prototype was experimentally tested at different operating points and the results showed good correlation with the 3D-FEA results. [ABSTRACT FROM AUTHOR]

In this paper, a reduced order state observer for doubly fed induction generator (DFIG) is designed that estimate the states just using stator voltage and power measurements. Further, the proposed state observer is used to provide two control strategies for rotor side converter: 1) state estimator based state feedback control; and 2) state estimator based vector control. The state observer and controllers were tested for varying wind conditions using a full-order dynamic model with a real-time simulation platform. First, the proof-of-concept is verified on a grid integrated DFIG considering aggregated grid model represented by an infinite bus. Then, the architecture is validated on a modified IEEE 39-bus system connected with a wind farm. The results confirm that the proposed state observer coupled with existing control for DFIG provides better tracking of the system output without the need for feedback measurements, and at the same time reduces the controller design complexity. Also, these state estimator based controllers eliminate the need of rotor current sensors. [ABSTRACT FROM PUBLISHER]

This paper presents a systematic and comprehensive approach for differential mode (DM) electromagnetic interference (EMI) filter design in a three-phase boost-type power factor correction (PFC) rectifier. Since the DM EMI filter forms a significant portion of the overall filter as well as converter volume, the reduction of DM filter component size is kept as a major objective in the filter design process in order to improve the power density. In addition to the objectives of volume optimization and conducted emission attenuation requirement to comply with the EMI standard, the filter design process also ensures a near-unity power factor operation with the optimal set of EMI filter parameters. To accomplish this, the paper analyzes the effect of EMI filter component selection on the overall lower order (1–100 kHz) frequency response, which is important for evaluating the dynamic response and stability. The results from the proposed design approach are validated through simulation, the DM Bode plot, and frequency response of the input current with and without EMI filter. As a proof-of-concept verification, the proposed EMI filter is implemented in a 4-kW three-phase boost-PFC prototype, which demonstrates minimal phase displacement (<5°) of the input current. [ABSTRACT FROM PUBLISHER]

The safe operation of grid-connected power converters during abnormal condition is a key issue in order to guarantee operation and to avoid undesired trips. In this paper, different control strategies for the operation of a D-STATCOM are introduced, where the reference currents are determined in such a way that not only will none of the phase currents go over the limits, but also the dc voltage fluctuations remain in safe operation limits. Fluctuating active power interchange during unbalanced condition leads to dc voltage oscillation. Severe unbalanced condition and small dc capacitor selection (to meet the size and cost constraints) intensify the dc voltage oscillation. Therefore, the contribution of this paper relies on the combination of the dc voltage oscillations and the current limit control. The effectiveness of three proposed control strategies is verified by simulating a D-STATCOM tied to an industrial distribution network. Moreover, a scaled scenario has been reproduced experimentally which shows that the results cope well with the analytical equations and the simulation results. [ABSTRACT FROM AUTHOR]

This paper proposes a decentralized control scheme for controlling active and reactive power of grid-tied ac-stacked photovoltaic (PV) inverter architecture using single member phase compensation. Reactive power control is required for the next generation of grid-tied smart PV inverter systems in power networks with high PV penetration. The decentralized control scheme proposed in this paper allows for a fully distributed architecture, both in terms of active and reactive power control and physical implementation of a PV system. This will result in higher reliability and potentially lower cost with minimum communications requirements. A decentralized controller enables higher switching frequencies that can shrink passive components. Therefore, string voltage variations due to voltage drop across passive components will be negligible and the system will be controlled with minimum communications requirement. The relative gain array approach has been used to study the feasibility of the decentralized control scheme. Detailed modeling and analysis are provided to show the effectiveness of the proposed decentralized approach and the effect of this approach on control implementation. Finally, effectiveness of the proposed decentralized approach is verified using mathematical modeling, simulation, and a lab-scale experimental setup in different operation conditions. [ABSTRACT FROM AUTHOR]

This article presents the calculation procedure of short circuits adopting the characteristic currents method (CCM). In a previous paper by the author G. Parise, the CCM has been upgraded with the introduction of “characteristic” countercurrents and the generalization of the Kirchhoff laws. For illustrating the calculation procedure, the selected case study deals with a low voltage cold ironing system where multiple ships are allowed to operate simultaneously on one shore power transformer and, so, a comparison has been developed between the IEC approach of the short-circuit calculation and the CCM. [ABSTRACT FROM AUTHOR]

This paper presents an economic evaluation of the hybrid voltage control scheme with distribution static compensator (DSTATCOM) and active power curtailment for enhancing photovoltaic (PV) penetration in Taipower distribution systems. During the peak solar irradiation period, the hybrid voltage control scheme is utilized to avoid the voltage violation problem and, thus, to increase the PV installation capacity and reduce the feeder loss as well. The annual savings from feeder loss reduction, the annual revenue of PV power sales, the initial capital investment cost for a PV project with or without a DSTATCOM, and the operating and maintenance (O&M) cost are then taken into account to evaluate the benefit and cost of the PV investment. This paper covers analyses of net present value (NPV), benefit–cost ratio (BCR), incremental BCR (IBCR), and payback period (PP) for a new PV project or an existing one to employ the hybrid enhancing scheme. With proper selection of PV and DSTATCOM capacities, the investment can be very profitable. Comparison of the results by these indicators is also presented. Moreover, a sensitivity analysis is performed to handle project uncertainty with respect to some affecting parameters and to provide some useful information for making any promotion policy for the development of solar PV industry. [ABSTRACT FROM AUTHOR]

The variable frequency power factor (PF) (VFPF), frequency response of stray losses (FRSL), and dynamic dc winding resistance tests are reviewed in this paper. These electrical field tests provide new and significant diagnostic detail and thereby enable a more comprehensive assessment of the condition of a transformer. These tools are not radically different from three standard electrical tests that have been in use for decades in the industry. In fact, the test setup, connections, and test implementation requirements from a tester's perspective are identical to those for the PF, leakage reactance, and dc winding resistance tests, respectively. The subject electrical field tests have progressed from these traditional tests, gaining their unique assessment capabilities by simply expanding the related standard test's measurement(s) in the frequency or time domain. VFPF, FRSL, and dynamic dc winding resistance tests do not displace these older diagnostic tools but rather supplement them, bringing considerable and, in the case of the VFPF test, disproportionately more value. [ABSTRACT FROM AUTHOR]

This paper proposes a comprehensive and systematic approach in developing a new switching lookup table for direct power control (DPC) based on grid virtual flux estimation, implemented in a grid-connected three-phase ac-to-dc converter. The approach provides detailed information regarding the effects of a particular converter voltage space vector to the instantaneous input active and reactive power distributions in the converter system. Thus, the optimal converter switching states are able to be selected by the switching table, allowing the smooth control of the active and the reactive power for each sector. The usage of input ac voltage sensors for synchronization and input power calculation is avoided by applying a virtual flux concept in the control scheme. The grid virtual flux estimation technique is used to extract the grid voltage information from the converter switching states, line currents, and dc-link output voltage. Detailed explanation and analysis regarding the development of virtual flux DPC utilizing the proposed switching lookup table is given in this paper. Finally, the steady-state as well as dynamic performances of the proposed controller is tested both in simulations and laboratory experiments. There exist close agreements between the simulation and experimental results. [ABSTRACT FROM PUBLISHER]

This paper proposes a new circuit configuration and a control scheme for a single-phase current-source inverter with a power decoupling circuit which is called as the active buffer. The proposed inverter achieves a low-dc-input voltage ripple and also provides a sinusoidal current that can achieve unity power factor, without large passive components in the dc bus such as smoothing inductors and electrolytic capacitors. These components are conventionally required in order to decouple the power pulsation caused by the single-phase power source. In this paper, the fundamental operations of the proposed inverter are demonstrated experimentally. From the experimental results, the input voltage ripple is 8.87%, and the output current total harmonic distortion is 4.24%. In addition, an output power factor of 99% and a maximum efficiency of 94.9% are obtained. Finally, it is confirmed that the maximum power densities of the conventional circuit and the proposed circuit are 2.75 kW/L at the switching frequency of 70 kHz and 4.86 kW/L at the switching frequency of 80 kHz, respectively. [ABSTRACT FROM AUTHOR]

This paper presents practical aspects related with the operation, compensation, and protection of high-power cycloconverters used in the mining industry. Practical recommendations related with startup, compensation requirements, operational characteristics, and unexpected shutdown process are described. Fuseless characteristics of modern cycloconverters are also discussed. Relevant current waveforms associated with the operation of a 20-MW synchronous motor semiautogenous grinding mill drive are presented, as well as current and voltage waveforms under fault operating conditions. [ABSTRACT FROM AUTHOR]

In order to enable a variable-speed operation in existing synchronous-machine-based fixed-speed pumped-storage power plant (PSPP), full-scale power converters are required. But it is not economical in case of large-size PSPP. Furthermore, full-scale power converters lead to increase the complexity of civil construction in case of underground powerhouses. Therefore, a doubly fed induction machine (DFIM) with a slip power rated power converter is an acceptable option for the storage dams with wide variation in water head (for e.g., Tehri Dam, India). In view of the reliability of converters used in such projects, thermal stress across the power semiconductor devices is a major cause for the failure of power converters. It is reported that 55% of failures in electric drives are due to thermal cycling or temperature rise in semiconductor devices. In consideration of this issue, this paper analyses active-thermal-control-based reactive power circulation in a five-channel parallel-connected back-to-back power converter fed 250-MW DFIM system (data collected from a 4 × 250 MW PSPP under construction at Tehri dam, India). The allowable limit of reactive power range is calculated in consideration of an operational strategy to be adopted, and the reactive power among the converters is circulated using the vector control technique. It is concluded that because of reactive power circulation among parallel-connected converters, temperature fluctuation is effectively stabilized. PLECS Blockset in MATLAB/Simulink software is used for this analysis. Experimental validation is carried out through a 2.2-kW scale-down DFIM laboratory prototype. [ABSTRACT FROM AUTHOR]

Economic development and changing lifestyles are leading to the extensive use of energy-intensive technologies by consumers. As a result, this has led to a dramatically increased demand for electricity. In addition, the consumers’ increasing demand for a more reliable and uninterrupted energy supply is posing enormous challenge for service providers. This necessitates the development of novel solutions that should be at the system operators’ disposal, particularly at distribution levels. One way to partly address this concern is by automating distribution systems and equipping them with intelligent technologies–a transformation to smart distribution systems. Such a transformation should improve system reliability and operational efficiency because such systems will be capable of operating and immediately restoring discontinued service to consumers. To facilitate this, it is necessary to replace manual switches by remotely controlled ones, improving the system restoration capability, which is one of the key features of smart grids. This paper presents a new framework to determine the minimal set of switches that have to be replaced or optimally allocated in order to automate the system. This is supported by a sensitivity analysis. Different topologies are also assessed taking into account various reliability indices and power losses in system operation following the system's automation. Such an optimization work is done under a massive integration of renewable energy sources and energy storage systems. All this simultaneously addresses the economic and functional requirements of the automated system, ultimately improving system's reliability. The standard IEEE 119-bus standard system is used as a case study, where different types of loads are considered (residential, commercial, and industrial). [ABSTRACT FROM AUTHOR]

The use of a unified power flow controller (UPFC) to improve the power transfer in an EAF is investigated. The implemented equipment used techniques of hardware-in-the-loop to determine the required specific characteristics of the UPFC to improve the stability of the arc. The arc is mainly responsible for the conversion of electromagnetic power into thermal power and heat transfer. The stability studies of power networks help in improving the stability of the arc. These are the topics covered in this paper. This research also shows how it is possible to achieve an increment of the stability of the arc with the enhancement of the power quality between the main transformer and the distribution system through the decrease of the THDI, unbalance, and flicker. [ABSTRACT FROM AUTHOR]