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The article highlights various departments of the journal including the Industrial and Commercial Power Systems Department, the Industrial Power Conversion Systems Department and the Manufacturing Systems Development and Applications Department.

This paper is Part II of a two paper series on electrical machine iron loss predictions. The Part II paper is focused on application of, and experimental data comparisons for, a new and unique method for predicting machine iron losses using transient finite element methods. A significant difference of the new method is the manner in which the predictive surface function of loss versus frequency and flux density is arrived at given lamination steel experimental loss test data. [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]

This paper presents the flexible dc capacitor voltages balancing control method for star-connected cascaded H-bridge converters. In this paper, the power flows are analyzed by investigating all the converter's control freedoms. Based on the analyses, users can accomplish the dc capacitor voltage balancing with both negative-sequence current and zero-sequence voltage. These two kinds of control options are further integrated together with the defined weighting factor $K$. The low-voltage ride-through operation of a proposed control method is also discussed in this paper. The control method is verified with a 220-V 1-kVA static synchronous compensators based on the star-connected cascaded H-bridge converters, and the experimental test results show that all the dc voltages are well regulated at the commanded value with different weighting factor $K$. [ABSTRACT FROM AUTHOR]

This paper depicts an accident that happened in 2010 in a Brazilian chemical plant. A combination of different events, installations, and commissioning errors coupled with equipment failures involving the primary substation resulted in catastrophic failure. A single-phase failure of a 138-kV disconnect switch, during closing, initiated events and phenomena that resulted in a complete plant shutdown. This paper will walk the reader through the events, forensics analysis, and power system analysis that allowed the authors to identify what happened, how it happened, and what to do to prevent it from happening again. This paper will show how the anatomy of the problem, involving equipment failure, single-phase arcing, switching transients, overvoltage, capacitive coupling, transferred surge voltages, ungrounded system, transient overvoltage due to an arcing ground fault on an ungrounded system, insulation coordination, flashover, and lack of adequate surge protection, all of which resulted in a catastrophic failure of an arc resistant switchgear and a potentially serious arc flash incident. The research followed some steps that will be commented on here as well as the lessons learned. [ABSTRACT FROM AUTHOR]

The goal of all circuit protection devices is to mitigate and minimize collateral damage when a failure occurs to either the source (ac line) or the equipment. The circuit protection device is often given little attention, i.e., until erroneous trips hamper performance or unexpected damage occurs within the equipment. Then, the devices are often reviewed for performance characteristics and operating conditions. To meet this need, various devices have been designed for this purpose, and various standards have been written to provide guidance for the usage of those devices. The focus of this paper will be on the interplay between adjustable-speed drive (ASD) short-circuit current rating and protective device sizing, as well as the scaling of such systems, i.e., if a fuse sized for a 10-A circuit should have the same guidelines as that used for a 1000-A circuit. This paper will review the impact of Underwriters Laboratories 508A and 508C, and the National Electric Code on the ASD protection requirements. This paper evaluates a test setup scheme to measure the fuse performance. The peak current and I^2\t test results with both test schemes from three protection devices, a time-delay (TD) Class J fuse along with two non-TD Class J and T fuses, are presented and explained. A novel method of comparing the results is offered by viewing the collateral damage associated with a failure. This methodology has a minor impact at low power ratings, but it has major implications with high power ratings, where equipment is often field repairable. [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]

In this paper, concentrator photovoltaics (CPVs) were used to integrate the extraction of light energy and thermal energy. The water cooling system that is proposed in this paper provides effective cooling by circulating cold water to remove heat in the photovoltaics. The experimental results were subsequently analyzed and compared with the power generation efficiency of the examined photovoltaics. The use of a water-circulation cooling system improves the power capacity of the photovoltaics by 2%–15% and enhances the power generation efficiency of the photovoltaics by 2.29%–3.37%. Through the combined application of photovoltaic and thermal technologies, the total energy of the overall system can be improved by 37%–59% even after accounting for the energy consumption of the cooling system. As a result, environmental protection, energy savings, and an increase in the efficiency of sunlight utilization can be achieved. Finally, a neural network was used to optimize this increase in efficiency. [ABSTRACT FROM AUTHOR]

Overall electric energy conservation and improvement in electrical energy efficiency has been a topic of interest to the electric power industry for long time, since 40% of total primary energy used is in the form of electricity. There are many facets to the energy conservation and/or energy efficiency techniques. Energy conservation by voltage reduction popularly called “CVR” has recently gained some momentum, in particular, to reduce the peak demand. This is also an integral part of the discussion in the future smarter grid technology. This paper addresses the pros and cons of the CVR application including a thorough literature search, practical applications, and a quantifiable measure of its actual amount of energy saving from utilities and the cost associated with it. It is expected that this paper will serve as a foundation to all practicing engineers addressing the issue of CVR. [ABSTRACT FROM AUTHOR]

This paper discusses typical grounding practices and ground fault protection methods for medium-voltage generator stators, highlighting their merits and drawbacks. Particular attention is given to applications of multiple generators connected to a single bus. The paper also provides an overview of the generator damage mechanism during stator ground faults. Problem areas associated with each type of grounding are identified and solutions are discussed. The paper also provides a list of references on the topic. The paper is intended as a guide to aid engineers in selecting adequate grounding and ground fault protection schemes for medium-voltage industrial and commercial generators for new installations, for evaluating existing systems, and for future expansion of facilities, to minimize generator damage from stator ground faults. These topics are presented in four separate parts, Parts 1-4. Part 1 covers scope, introduction, user examples of stator ground failure, and theoretical basis for the problem. Part 2 discusses various grounding methods used in industrial applications. Part 3 describes protection methods for the various types of grounding and Part 4 provides a conclusion and bibliography of additional resource material. [ABSTRACT FROM AUTHOR]

To prevent the high voltage direct current ground electrode from eroding, it is usually wrapped by a coke bed, which may affect the electrical performance of the electrode, such as current distribution and step voltage. In this paper, the effect is analyzed by a numerical method, which couples moment method with circuit theory by regarding the coke bed as several resistors connecting the ground electrode with soil. The method is simple and efficient. The calculated results are in good agreement with the measured ones. The current distribution, ground resistance. and step voltage of several typical electrodes with and without coke beds are calculated. The effect of the coke bed on the above parameters is summed up. [ABSTRACT FROM AUTHOR]

This paper discusses electrical distribution for refrigerated containers (reefers) in port terminals, characterized as parks of uniform distributed loads. Power systems of uniform distributed loads need configurations with modularity whenever possible, to ensure an easier installation, operation, and maintenance with significant cost reductions. This paper shows what has been the practice at ports in the past to provide Low Voltage (LV) supply to reefers from medium voltage (MV)/LV substations to cluster of reefer outlets panel with group of outdoor receptacles, used to connect power supply cord to each reefer. In the new method of power distribution system for the reefers, it is suggested to use a main MV underground distribution and portable containerized MV/LV transformer substations with close coupled LV distribution panel including reefer outlets. This potable power supply unit can be installed inside the reefer racks to supply locally a modular LV distribution to the reefers. This new method of supplying power to reefer racks has benefits over the past practice. It can offer a relevant flexibility for expansions and endorses development of new fitting components. [ABSTRACT FROM AUTHOR]

In this paper, a fault-tolerant control scheme for a low-speed squirrel cage six-phase induction generator (SC6PIG) connected to a full-scale back-to-back converter structure is proposed and tested on an experimental 24-kW wind turbine test bed that represents a 1/100 of the electrical power of a grid-connected real wind turbine multiphase generator (2.5 MW). The aim of this paper is to define a suitable control algorithm that allows the electrical generation despite the loss of one to three phases on the generator or converter sides. Furthermore, the pole number of the generator is increased to simplify or eliminate the gearbox in such a way as to reduce mechanical sensitivity. Indeed, by multiplying the phase and pole numbers, the robustness against mechanical and electrical faults is improved compared to that of a classic three-phase generator associated with a gearbox. Simulation and experimental tests carried out on a 24kW-230V-24-pole SC6PIG in healthy and faulty mode (one phase missing) assess the feasibility and capacity of the proposed strategy. [ABSTRACT FROM AUTHOR]

Islanding detection is a critical protection issue, as conventional protection schemes such as vector surge (VS) and rate of change of frequency relays do not guarantee islanding detection for all network conditions. Integration of multiple distributed generation (DG) units of different sizes and technologies into distribution grids makes this issue even more critical. This paper presents a comprehensive analysis of the effectiveness of a new method for islanding detection in DG networks. The proposed method, which is based on multiple features and support vector machine (SVM) classification, has the potential to overcome the limitations of conventional protection schemes. The multifeature-based SVM technique utilizes a set of features generated from numerous set of offline dynamic events simulated under different network contingencies, operating conditions, and power imbalance levels. Parameters (such as voltage, frequency, and rotor angle) showing distinguishable variation during the formation of islanding are selected as features for classification of the events. Features associated with different islanding and nonislanding events are used to train the SVM. The trained SVM is tested on a typical distribution network containing multiple DG units. Simulation results indicate that the proposed method can work effectively with high degree of accuracy under different network contingencies and critical levels of power imbalance that may exist during islanding. [ABSTRACT FROM AUTHOR]

Due to the short end windings of nonoverlap winding permanent-magnet (PM) machines, the end-winding inductance component is generally ignored in the design. In most cases, the end-flux fringing effects in PMs are also not taken into account. It is shown in this paper that these end effects have a significant influence on the performance parameters of the machine. In this paper, several nonoverlap winding PM machines are considered with respect to the effects of end-winding inductance and PM end-flux fringing. A number of calculation methods for the per-phase end-winding inductance of the machines are compared. A new simple analytical calculation method is proposed, which is shown to give a relatively good prediction of the end-winding inductance compared with 3-D finite-element (FE) results. It is proposed in this paper that the PM strength should be reduced by a certain fringing factor to take the end-flux fringing effects into account in the 2-D FE analysis. Practical measurements are also presented to validate the FE calculations and to give an indication on the effects that are caused by the end-winding inductance and the PM end-flux fringing. [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 presents theoretical and experimental discussions on a practical speed-sensorless start-up method for an induction motor driven by a modular multilevel cascade inverter based on double-star chopper cells (MMCI-DSCC) from standstill to middle speed. This motor drive is suitable, particularly for a large-capacity fan- or blower-like load. The load torque is proportional to a square of the motor mechanical speed. The start-up method is characterized by combining capacitor-voltage control with motor-speed control. The motor-speed control with the minimal stator current plays a crucial role in eliminating a speed sensor from the drive system and in reducing an ac-voltage fluctuation occurring across each dc capacitor. Experimental results obtained from the 400-V 15-kW downscaled system with no speed sensor verify that the motor-speed control proposed for the DSCC-based drive system can enhance the start-up torque by a factor of three under the same ac-voltage fluctuation. Several start-up waveforms show stable performance from standstill to middle speed with different load torques. [ABSTRACT FROM AUTHOR]

This paper examines the torque response based on direct torque control (DTC) for an interior permanent magnet synchronous motor. DTC with a PI controller for torque control is used in this paper. The relationship between the gains of the PI controller and the torque response is derived based on the transfer function of the torque control loop. In addition, this paper discusses the influence of the nonlinearity of the torque control loop on the torque response. It also proposes a linearization method for the torque control loop based on gain scheduling, and improvement of torque response is achieved. The effectiveness of the proposed method is verified by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

Intentional islanding operation of distributed generation (DG) can increase system reliability and reduce customer outage costs. Guidelines for the impact study and operation of DG for islanding operation should be implemented. The Provincial Electricity Authority (PEA) plays more attention to intentional islanding operation. To perform islanding operation, PEA has established islanding operation and impact study guidelines for DG. This paper presents the development of these guidelines. A case study was conducted to demonstrate the results of both steady-state and dynamic analyses. Operational issues are also taken into account in this paper. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive power management strategy for photovoltaic (PV) generation units in a standalone microgrid. In existing microgrid configurations, the PV units are controlled using droop control technique, which ensures load sharing among the distributed generation (DG) inverters. However, the intermittency in power generation of PV-based DG poses many challenges to the standalone operation of a microgrid, the ineffective volt-ampere (VA) utilization being one among them. This paper proposes an adaptive droop control, which enables the maximum utilization of the VA rating of the interfacing inverter in a PV/battery hybrid system. With the proposed technique, as the generation goes down, the DG inverter is controlled to support the reactive power demand of the load, thereby utilizing the rating of the inverter switches effectively. The applicability of the proposed adaptive control method is analyzed using detailed simulation and real-time hardware-in-loop studies. [ABSTRACT FROM AUTHOR]

Replacing the batteries of wearable medical devices is an inconvenience to the user. Wireless power transfer (WPT) could be a solution for this problem. However, the structure should be compact to satisfy the wearable device requirements and the power efficiency should be as high as possible for prolonging the user experience. Besides, as algorithms embedded in these devices become more complex, the device power consumption also increases. Fulfilling these specifications in a compact structure with better efficiency is the aim of this research paper. This paper proposes a power processing module for WPT applications. This module is embedded within the WPT path to convert receiving end ac power to dc power, and to simultaneously provide multiple dc–dc power conversion for wearable medical devices. The ac–dc circuit is specifically designed using a compact topology to convert wireless ac power to stable dc power. The dc power is further regulated by different mode controls either to perform battery charging or to provide independent voltage supplies to dc loads. The integrated circuit occupies an area of 1.9 × 2.3 mm when implemented on a 0.25 μm high voltage CMOS process. [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]

Bidirectional dc–dc converters, which make possible the bidirectional transmission of power, have become indispensable in recent years due to the diversification of the power supply network, including the use of batteries. Of these, the dual active bridge (DAB) dc–dc converter features a simple mechanism and symmetric circuit architecture, making possible the equal transmission of power in both directions. Because of these advantageous characteristics, DAB dc–dc converters are in wide use. However, this circuit has the intrinsic problems that, during light-load conditions, switching surges occur and power efficiency decreases. This paper proposes digitally controlled operation as a new method to resolve these problems and reports on an experiment that was carried out using a 1-kW system. In addition, for both buck and boost modes, output power characteristic equations were derived through application of the extended state-space averaging method, and a loss-included circuit analysis was carried out for the circuit used in the experiment. It was thereby demonstrated that circuit loss was smaller for the proposed operation than that for conventional operation. In the loss-included circuit analysis, for both proposed and conventional operations, equivalent circuits that approximated circuit loss as a single resistance were used. As a result, it was confirmed that, with the operation proposed in this paper, without the use of a snubber circuit, switching surges could be reduced significantly and also that, during light load, there was a power efficiency improvement of up to 16%. In addition, a loss-included circuit analysis with a single equivalent resistance has been done. The resistance value is assigned with the averaged circuit total resistance. By the analysis, a relation between phase difference and output power is obtained. The results were confirmed with the experiment. [ABSTRACT FROM AUTHOR]

This paper discusses the development of new winding configuration for six-phase permanent-magnet (PM) machines with 18 slots and 8 poles, which eliminates and/or reduces undesirable space harmonics in the stator magnetomotive force. The proposed configuration improves power/torque density and efficiency with a reduction in eddy-current losses in the rotor permanent magnets and copper losses in end windings. To improve drive train availability for applications in electric vehicles (EVs), this paper proposes the design of a six-phase PM machine as two independent three-phase windings. A number of possible phase shifts between two sets of three-phase windings due to their slot–pole combination and winding configuration are investigated, and the optimum phase shift is selected by analyzing the harmonic distributions and their effect on machine performance, including the rotor eddy-current losses. The machine design is optimized for a given set of specifications for EVs, under electrical, thermal and volumetric constraints, and demonstrated by the experimental measurements on a prototype machine. [ABSTRACT FROM AUTHOR]

The time-domain correlation information of wind generation is important for wind power utilization. This paper proposes a parametric approach for the short-term multiperiod joint probability density function (JPDF) forecast of wind generation. The approach makes a spot forecast of wind generation by using support vector machine (SVM), and the probability distribution of the SVM forecast error is estimated by sparse Bayesian learning (SBL) which assumes that the forecast error follows a Gaussian distribution. Then, the SVM forecast result is corrected. The correlation matrix of the forecast errors within multiple successive forecast periods is estimated using the historical data. By combining the variance information obtained by SBL and the correlation matrix, the covariance matrix of the forecast errors is formed. Thereby, the JPDF of wind generation is obtained. Data collected from an actual wind farm are used for the study, and the results illustrate the effectiveness of the proposed approach. The justification of the Gaussian assumption of SBL is also explained in this paper. [ABSTRACT FROM AUTHOR]

In rotating ac machines, the saturated flux density waveforms contain harmonics, which create minor hysteresis loops. The minor hysteresis loops in machine laminations constitute an additional loss which requires modifications in traditional core loss formulas. This causes a serious challenge in core loss estimation. The task becomes more competitive under rotating magnetic fields, where the minor loop behavior has not been investigated yet. This paper highlights the problem of harmonics in rotating fields and its effect on the core loss estimation. In addition, the behavior of minor loops under rotating fields is compared with the minor loops under pulsating fields. Measurements were carried out on a nonoriented silicon steel sample of M36G29 with different fundamental frequencies of interest to the industry, 60 Hz and 400 Hz, with consideration of the third harmonic at each frequency. A design of magnetizing test fixture based on an electromagnetic Halbach array is used to perform these measurements. Results are presented and discussed. [ABSTRACT FROM AUTHOR]

In this paper, a complete conjugate heat transfer analysis of a scaled-sized prototype of an integrated air-cooled surface-mounted permanent-magnet generator for the “more-electric engine” application is presented. The selected integration position inside the aircraft's main gas turbine engine imposes the use of an unconventional cooling system, where the coolant directly flows through the machine air gap. To predict and prevent the critical working conditions of the prototype, the adopted cooling system has been investigated using a complete fluid–thermal analysis. Due to the capabilities of computational fluid dynamic software, it has been possible to analyze the temperature and flow fields inside the machine, giving an idea about the distribution of the thermal quantities both inside the solid materials and above the surfaces. The numerical model validation has been provided, comparing computed and experimental results, i.e., imposing the same working conditions, the predicted temperatures satisfactorily agree with the measured temperatures. [ABSTRACT FROM AUTHOR]

Although motors that use rare-earth permanent magnets typically exhibit high performance, their cost is high, and there are concerns about the stability of the raw material supply. This paper proposes a permanent-magnet-assisted synchronous reluctance motor (PMASynRM) with a ferrite magnet that does not use rare-earth materials considering productivity. The performance of the proposed PMASynRM is evaluated based on the finite-element method and an experiment using a prototype machine. The analysis results reveal that the proposed PMASynRM has the same power density and an equivalent efficiency as rare-earth permanent-magnet synchronous motors for hybrid electric vehicles (2003 Toyota Prius). Furthermore, some experimental results are presented in order to validate the analytical results. As a result, the proposed PMASynRM was found to achieve high-power-density and high-efficiency performance. [ABSTRACT FROM AUTHOR]

This paper investigates the transient magnetic behavior of an interior permanent-magnet (IPM) synchronous machine following a large transient current caused by a fault condition. A combination of finite-element (FE) analysis and numerical integration of the machine equations is used to calculate the currents resulting from a symmetrical three-phase short-circuit fault at the machine terminals, including magnetic saturation effects. FE analysis is further used to simulate the magnetic behavior of the machine when subjected to the fault currents, with a particular focus on the propagation of the demagnetizing MMF throughout the conductive laminations as well as the conductive PM material. Eddy currents induced in the laminations and magnet material are shown to impede the progression of the demagnetizing MMF. However, the transient analysis illustrates the manner in which the fault currents ultimately trigger the onset of irreversible demagnetization of significant portions of the rotor magnets in the analyzed machine. The transient demagnetization analysis method is extended to investigate the influence of several key design variables, including machine operating temperature and segmentation of the rotor magnets. [ABSTRACT FROM AUTHOR]

In this paper, a tuned controller of variable reactors is developed to realize a reliable tieline reconnection of microgrids. It is very useful to solve the problem caused by a synchronization issue during the tieline reconnection, particularly the absence of a large-area communication network to cover all microgrids. The theoretical fundamental of this method is analyzed, based on which a set of tuning processes of the variable reactors' controller is derived. The feasibility and effectiveness of this tieline reconnection method with the tuned controller is analyzed and verified by simulations. This method can greatly improve the transient stability of a nonconventional grid, which consists of multiple microgrids, require the ability of frequent reliable reconnections, and limit system oscillation to less than 50%. The tieline reconnection controller can be easily integrated with power flow control into existing variable reactor devices at low cost. Moreover, the tuning process of the controller is simple and suitable for industrial applications. [ABSTRACT FROM AUTHOR]

This paper proposed a hybrid multiterminal-high-voltage-direct-current system to integrate several distributed offshore wind farms to onshore power grids. A comprehensive frequency support algorithm for the onshore grid was designed based on this system. The configuration and operating principles of a typical four-terminal system are described. System control strategies are proposed for both wind-farm-side voltage-source converters (WFVSCs) and grid-side line-commutated converters (GSLCCs). To obtain smooth operation, the WFVSCs are controlled as a voltage source that automatically absorbs power generated by the wind farm and establish a stable ac voltage for wind turbines. DC voltage–current droop control is designed for GSLCCs to maintain the dc voltage and distribute power between two onshore grids. A utility black start-up process without auxiliary power supply was designed and tested. The simulation results in Power System Computer Aided Design/ Electromagnetic Transients including DC are presented to demonstrate the system performance during black starting-up, converter disconnection, and frequency variation of one onshore power grid. [ABSTRACT FROM AUTHOR]

This paper presents a new approach for simulation of the cogging torque in a permanent-magnet (PM) machine. The method exploits the numerical functions for modeling the magnetic circuit of the machine. This paper introduces two improved functions to model the PMs and the air-gap permeance, aiming to compute the cogging torque in the PM machine. The first function states the magnetomotive-force drop on the machine air gap with respect to the angular position. The other function, named permeance function, models the air-gap permeance accurately, taking into account the stator saliency due to the teeth. The described procedure has been tested on a prototype PM machine. [ABSTRACT FROM AUTHOR]

The load-commutated inverter (LCI)-based synchronous motor (SM) drive that is fed by a 12-pulse ac–dc converter results in harmonics mitigation. These drives have a further improved power quality at the ac mains if an appropriate passive filter is used at the ac mains for power factor (PF) correction and harmonics reduction. This paper deals with a simplified optimization algorithm based on a particle swarm optimization method for the selection of passive filter components. This algorithm is used to design passive filters for three types of loads on an LCI–SM drive, i.e., constant-torque–variable-speed loads, constant-speed–variable-torque loads, and variable-speed–variable-torque loads, to meet the requirements of a wide range of applications. The obtained results show reduction in the total harmonic distortion in the current and voltage at ac mains, reduced supply current, and improved PF. [ABSTRACT FROM AUTHOR]

This paper proposes a technique to reduce the low-frequency dc-link energy oscillation due to the pulsating single-phase energy flow in a single-phase-to-single-phase voltage source converter (VSC) and current source converter (CSC), which operate connected to the grid. This pulsating energy is the major factor for increasing the size of the passive components and power losses in the converter. Pulsation reduction is achieved by incorporating two auxiliary active switches and one passive energy storage element to the rectifier and inverter sides. Additionally, this paper presents the comparison of these converters (VSC/CSC) regarding efficiency and power density. Details of the control strategy are presented. Simulation and experimental results are provided to validate the theoretical approach. [ABSTRACT FROM PUBLISHER]

This paper proposes an LC-compensated electric field repeater to extend the transfer distance of a capacitive power transfer (CPT) system. The repeater contains two metal plates connected with an external capacitor and an external inductor. The plates are used to generate electric fields to transfer power. The external inductor and capacitor are used to resonate with the plates in order to increase the voltage levels. The repeater is placed between a transmitter and a receiver, which also contains metal plates compensated by an LC network. The repeater can increase the transfer distance of the CPT system without significantly influencing the system power and efficiency. In this paper, the capacitive coupler structure and dimensions are designed and simulated using Maxwell software. Considering all the capacitive coupling between plates, an equivalent circuit model is derived. The fundamental harmonics approximation method is used to analyze the working principle of the circuit. A 150 W input power CPT system is designed as an example to validate the proposed repeater structure and compensation circuit topology. The system can achieve an efficiency of 66.9% from dc source to dc load, when the transfer distance is 360 mm and the repeater is placed between the transmitter and the receiver. [ABSTRACT FROM AUTHOR]

In this paper, an online empirical mode decomposition (EMD) based algorithm is proposed for the control of a shunt active filter (AF). Standard EMD algorithm has worked on the principle of time-scale difference between the upper maximum values and lower minimum values of a signal, and for a long time it has been considered good for offline analysis of signals. This paper deals with the real-time application of EMD for the control of AF under balanced and unbalanced loads. Linear interpolators are employed for construction of upper and lower envelopes to avoid computation complexity. Moreover, customized iterative computations for extraction of intrinsic mode functions maintain the efficiency of algorithm. The algorithm extracts the fundamental component of load current and helps in estimating reference currents. Simulations are performed on MATLAB/Simulink platforms. Simulation results are verified with experimental results of a developed prototype of shunt AF. [ABSTRACT FROM PUBLISHER]

Grinding stage has one of the highest production costs in mining operations due to the intensive use of energy needed for the comminution process. Hence, any improvement in the energy use of this process will have an important impact on production costs. Paper presents the results of an extensive testing program to determine the effect of lifter wear on the power demanded by the grinding mill. Selected power–speed curves covering up to 110% of critical speed are reported. Using these results, a lifter wear factor is proposed to include this effect on the power demand expressions of grinding mills. Results show that for dry grinding, as the lifters wear, the power needed for a specific operating condition increases. Using these results, mill operators will have an important piece of information to set the best operating point for an efficient ore comminution and efficient energy consumption. It will also help to define the appropriate date for a liner change. [ABSTRACT FROM AUTHOR]

In this paper, a new generic composite load model structure for industrial facilities is proposed, which consists of four main loads, an induction motor, a synchronous motor, a motor drive system, and a static load. This structure can be applied to existing or future industry facilities. Major factors to be considered when developing this new composite load model are demonstrated. To achieve the final composite load model for an industrial facility of interest, a two-step procedure is recommended in this paper. Step 1 is to create a power system full model for existing or future industrial facilities. In this step, the full model for existing facilities can be created with the known system configurations and electrical single-line diagrams; while the full model for future industrial facilities with unknown system configurations can be created using the template-based load modeling technique. Step 2 is to perform effective load aggregation in order to obtain a simplified equivalent load model in the format of the proposed composite load model structure for industrial facilities. [ABSTRACT FROM AUTHOR]

This paper presents the stability analysis of dc distributed power systems with multiple converter-controlled loads. The load converters are tightly controlled, behaving as constant power loads with low-damped $LC\;$ filters. The dynamic behavior of the system in high frequency range is often not studied with the classical tools based on conventional averaging techniques. However, dc power systems with the reduced size filter, and consequently, the high resonant frequency, are widely used in transportation applications. In this paper, the stability analysis of the system is established based on a discrete-time model of the system, taking into account the switching frequency and intrinsic nonlinearities of the system model. The impacts of the filter parameters and interactions among the constant power loads are investigated with the proposed discrete-time method. Moreover, an active stabilizer is developed and included in the dynamic model of the system, in order to extend the stability margin. The theoretical observations are then validated experimentally on a laboratory hardware prototype. [ABSTRACT FROM AUTHOR]

Based upon the analysis of load signatures, this paper presents a nonintrusive load monitoring (NILM) technique. With a characterizing response associated with a transient energy signature, a reliable and accurate recognition result can be obtained. In this paper, artificial neural networks, in combination with turn-on transient energy analysis, are used to improve recognition accuracy and computational speed of NILM results. To minimize the distortion phenomenon in current measurements from the hysteresis of traditional current transformer (CT) iron cores, a coreless Hall CT is adopted to accurately detect nonsinusoidal waves to improve NILM accuracy. The experimental results indicate that the incorporation of turn-on transient energy algorithm into NILM significantly improve the recognition accuracy and the computational speed. [ABSTRACT FROM AUTHOR]

An improved bridgeless (BL) Cuk converter-based electric vehicle (EV) battery charger with high power factor and increased efficiency is designed and developed in this paper. It provides low cost and high-power-density-based charging solution for the EV. This charger incorporates less number of devices operating over one switching cycle, which reduces the additional conduction loss incurred by a diode bridge rectifier of the conventional charger. Hence, it improves the charger's efficiency. The added advantage of the proposed topology is that the unwanted capacitive coupling loop is removed, as well as the unwanted conduction through the body diode of the inactive switch in the previously developed BL Cuk converter is avoided. This significantly improves the charger's efficiency. For the constant current and constant voltage charging, the commands are synchronized by a flyback converter. The proposed charger draws a sinusoidal current from ac mains and the total harmonic distortion in the supply current is reduced to the limits specified by the IEC 61000-3-2 guidelines. The improved efficiency and power quality indices of the proposed charger are investigated to demonstrate its satisfactory charging operation at all operating conditions. [ABSTRACT FROM AUTHOR]

This paper proposes an interactive decision-making model for the operations of electric vehicles (EVs) and power grid, in the perspective of energy and reserve. In this model, EVs optimize their energy and reserve plans considering prices set by the power grid. Meanwhile, the power grid aims to obtain the optimal energy and reserve prices for EVs, in order to maximize its benefits. Afterward, we use the generalized Stackelberg game to formulate the interactive decision-making model, and prove the existence and uniqueness of the generalized Stackelberg equilibrium. Finally, simulation results verify that the proposed interactive model can well enhance benefits of EVs while guaranteeing their quality of charging services. [ABSTRACT FROM AUTHOR]

Power electronic circuits often regulate load power and present a constant power profile to the utility or other electrical source. These constant power loads therefore exhibit a negative incremental input impedance and pose stability challenges when present in either dc or ac systems. This paper presents an energy buffer power converter for a constant power LED lighting load that presents a controllable input impedance to the electrical source. The use of an energy buffer allows the converter to independently control input and output power. The input power is controlled to resemble a resistive load, ensuring that the device exhibits a positive incremental input impedance over short-term input disturbances. Simultaneously, the output power is held constant through high-bandwidth regulation. The control scheme balances the power flow in the long term. Experimental results are presented that demonstrate independence between input and output performance, as well as long-term power balance. [ABSTRACT FROM AUTHOR]

With the increase of the train speed, the pantograph-catenary (PC) detachment becomes more frequent, which results in more serious PC detachment arc. In order to analyze the influence of PC detachment arc on the train system, several arc models are established. However, these models do not consider the actual PC detachment process. In this paper, an extended black-box model of PC arc is proposed, which considers the dynamic detachment process of PC based on the PC dynamics. First, the Habedank arc model is presented and the relationship of the PC detachment distance with the arc voltage and arc dissipated power is established. Next, the dynamic detachment trajectory is obtained from the dynamic simulation of the PC structure model. Then, by introducing the dynamic PC detachment trajectory model into the arc model, the dynamic arc model is built. Finally, the performance of the arc current and arc voltage is analyzed and the effectiveness of the dynamic arc model is verified. [ABSTRACT FROM AUTHOR]

In this paper, a Volterra-filter-based control algorithm is developed to generate reference currents for a solar photovoltaic-distribution static compensator (PV-DSTATCOM) system in the distribution network. The developed control is analyzed for being stable under Lyapunov stability criterion; consequently, the error function of the system converges to zero asymptotically. The PV-DSTATCOM system is integrated to the grid to compensate the nonlinear load, while supplying solar PV array active power to the grid. The system is modeled in MATLAB and is executed on a developed prototype in the laboratory, under balanced, unbalanced loading conditions, and variable insolation conditions. Moreover, the harmonic distortion of the grid currents is observed under the IEEE-519 standard. [ABSTRACT FROM AUTHOR]

The use of energy harvesting for supplying wireless sensors becomes a new market opportunity. During last years, new low power transmitters, and also power conversion ICs specifically designed for energy harvesting, have become commercially available. However, as any other power supply circuit, the specific load behavior affects to the power converter, doing that just joining the two parts takes to a nonfunctional device. In this paper, we will measure experimentally the transmitter current of some technologies, for the several sensor states. Some practical issues that affect directly the sensor design will be shown. With this information, some required modifications in the power stage will be proposed. A complete temperature sensor design and assembly is showed. The sensor has been tested in a tandem cold mill, and several experimental results are included. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of uncertainty in the allocation of photovoltaic (PV) generation, solar irradiance, and its impact on the power flow in a distribution network. The solar irradiance available in the National Renewable Energy Laboratory Resource Data Center is clustered into two states: high and low irradiance defined by a threshold. The uncertainty is modeled based on Non-Gaussian distribution, obtained using kernel density estimation. This estimation aids in achieving the probability density function and cumulative distribution functions of the solar irradiance. Moreover, the load demand, wind speed, and generator location are modeled according to Gaussian, Weibull, and discrete uniform distribution functions, respectively. As a part of probabilistic power flow, the backward/forward sweep method is used to solve each scenario of the Monte Carlo simulation. The proposed framework is applied to the 33-node test system considering three different test cases. The first case considers deployment of PV systems in three microgrids of the electric grid, and the other two test cases analyze different levels of penetration of randomly allocated PV and wind power systems. At the end, the results indicate potential reverse power flow through certain branches of the grid, and the renewables have a major impact on the system. [ABSTRACT FROM AUTHOR]

This paper analyzes the power-cycling capability of insulated-gate bipolar transistor (IGBT) modules in a conventional matrix converter used as a motor drive. The analysis is made under various conditions for this topology, including low-speedoperation capability, high-speed thermal and power-cycling capabilities, etc. It was found that the power-cycling mean time to failure of IGBT in a matrix converter is low when the input and output frequencies are close to each other or when the output frequency of the converter is low. As a result, the chip size of the conventional matrix converter may be larger than the other candidates. In the end of this paper, some guidance for designing a matrix converter for long-term reliabilities is also discussed. [ABSTRACT FROM AUTHOR]

This is one of a series of papers discussing the application and accuracy of different analysis techniques supporting the determination of industrial and commercial power system reliability and availability. There is a need recognized in the power industry to identify and utilize a standard tool, or a set of tools, to analyze the reliability of power systems. historically, the results of applying different reliability methodologies and tools varied significantly, and comparisons were difficult. The Reliability Analysis Techniques Working Group of the Gold Book (WEE Std. 493-1997) developed a standard network to enable comparison of analytical techniques. This paper describes the approach of simulations via reliability block diagrams as applied to the Gold Book standard network. Reliability indexes of the load points are presented, and are compared with ones obtained from other techniques in the series to determine the accuracy. [ABSTRACT FROM AUTHOR]

This paper discusses typical grounding practices and ground fault protection methods for medium-voltage generator stators, highlighting their merits and drawbacks. Particular attention is given to applications of multiple generators connected to a single bus. The paper also provides an overview of the generator damage mechanism during stator ground faults. Problem areas associated with each type of grounding are identified and solutions are discussed. The paper also provides a list of references on the topic. The paper is intended as a guide to aid engineers in selecting adequate grounding and ground fault protection schemes for medium-voltage industrial and commercial generators for new installations, for evaluating existing systems, and for future expansion of facilities, to minimize generator damage from stator ground faults. These topics are presented in four separate parts, Parts 1-4. Part 1 covers scope, introduction, user examples of stator ground failure, and theoretical basis for the problem. Part 2 discusses various grounding methods used in industrial applications. Part 3 describes protection methods for the various types of grounding and Part 4 provides a conclusion and bibliography of additional resource material. [ABSTRACT FROM AUTHOR]