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This paper presents a new method for islanding detection of inverter-based distributed generation (DG). The main idea of this paper is to change the dc-link voltage considering the PCC voltage changes during islanding condition. A simple islanding detection scheme has been designed based on this idea. The proposed method has been studied under multiple-DG operation modes and the UL 1741 islanding tests. The simulations results, carried out by MATLAB/Simulink, show that the proposed method has a small nondetection zone. Also, this method is capable of detecting islanding accurately within the minimum standard time. [ABSTRACT FROM AUTHOR]

This paper presents a new solution method that combines state-space and nodal analysis for the simulation of electrical systems. The presented flexible clustering of state-space-described electrical subsystems into a nodal method offers several advantages for the efficient solution of switched networks, nonlinear functions, and for interfacing with nodal model equations. This paper extends the concept of discrete companion branch equivalent of the nodal approach to state-space described systems and enables natural coupling between them. The presented solution method is simultaneous and enables benefitting from the advantages of two different modeling approaches normally exclusive from one another. [ABSTRACT FROM AUTHOR]

This paper presents various synchronous machine models implemented in the computation of electromagnetic transients. This paper proposes new models for achieving better computational efficiency while maintaining precision. In addition to simple infinite bus analysis, the machine models are also compared for a more sophisticated and practical case study. Precision analysis includes the surrounding network accuracy constraints. [ABSTRACT FROM AUTHOR]

This paper presents a generalized, parallel implementation methodology for real-time simulation of ac machine transients in an FPGA-based real-time simulator. The proposed method adopts nanosecond range simulation time-step and exploits the large response time of a rotating machine to: 1) eliminate the need for predictive-corrective action for the machine electrical and mechanical variables, 2) decouple the solution of the dq0 stator currents, and 3) enable the use of one-time-step delayed interface between the machine and the rest of the system which decouples the machine solution from that of the rest of the system. The proposed method simplifies the solution of the machine model without compromising accuracy or numerical stability of the simulation. This paper also presents a massively parallel, customized hardware architecture tailored to the solution of the mathematical model of ac machines. The proposed method and the developed hardware architecture are tested and verified based on the implementation of a permanent-magnet synchronous machine model and an induction machine-based ac-drive system in a field-programmable gate-array-based simulator. Real-time simulation is achieved with a computation time of 44 ns within the simulation timestep. [ABSTRACT FROM AUTHOR]

This paper presents a dynamic model of the active front-end (AFE) converter in the synchronous reference frame under balance input voltage condition. Transfer functions of the closed-loop control based on this dynamic model are verified experimentally in the frequency domain. Bode plots of these transfer functions are given to validate this synchronous frame-based dynamic model. Based on these results, this paper presents the control designs of the AFE converter to enhance the disturbance rejection capability and robustness. The control designs are then verified experimentally in the frequency domain. The frequency response of the AFE converter system is measured by an Agilent 35670A dynamic signal analyzer to validate the performance of the AFE converter system. [ABSTRACT FROM AUTHOR]

This paper describes the field oriented control of a salient pole wound field synchronous machine in stator flux coordinates. The procedure for derivation of flux linkage equations along any general rotating axes including stator flux axes is given. The stator flux equations are used to identify the cross-coupling occurring between the axes due to saliency in the machine. The coupling terms are canceled as feedforward terms in the generation of references for current controllers to achieve good decoupling during transients. The design of current controller for stator-flux-oriented control is presented. This paper proposes the method of extending rotor flux closed loop observer for sensorless control of wound field synchronous machine. This paper also proposes a new sensorless control by using stator flux closed loop observer and estimation of torque angle using stator current components in stator flux coordinates. Detailed experimental results from a sensorless 15.8 hp salient pole wound field synchronous machine drive are presented to demonstrate the performance of the proposed control strategy from a low speed of 0.8 Hz to 50 Hz. [ABSTRACT FROM AUTHOR]

This paper studies microgrids where loads are supplied by parallel-connected inverters controlled by decentralized active power/voltage frequency and reactive power-/voltage-magnitude droop control laws. A paralleled ac system, such as a multiinverter microgrid, is susceptible to circulating currents due to differences in voltage magnitude, frequency, phase angle, or dc offset. Circulating currents due to differences in voltage magnitude and dc offset have been known issues reported in literature. However, an in-depth analysis of the problem is required to ascertain the deviation of the system-operating condition from the desired condition. This paper provides a mathematical model that predicts the effect of voltage-magnitude offsets on reactive power sharing between inverters. Simulation and experimental results verify the accuracy of the analytical results obtained from the mathematical model. We examine the effect of dc-circulating currents and propose a simple capacitor emulation control law implemented in software to eliminate dc-circulating currents. This solution is a possible alternative for hardware implementation to eliminate dc-circulating currents. The effectiveness of the capacitor emulation control law has been verified through experimental results. [ABSTRACT FROM PUBLISHER]

This paper proposes a new framework in calculating the ex post prices for the spot electricity market. The proposed method finds a set of prices that are as consistent as possible with the actual outputs of resources correctly following their dispatch instructions. Two alternative consistency metrics are proposed in the paper. One measures the difference between the actual performance of an individual resource and its bid-based profit-maximizing response to the ex post prices in a perfectly competitive market. Another measures the difference between the ex post price and the price that supports the actual response of an individual resource. Compared to the existing approaches adopted in the real-time electricity markets in the U.S., the proposed method solves the ex post energy and ancillary service prices directly and simultaneously. It does not require heuristics that are hard to justify, and has a much clear definition for the pricing problem than the existing approaches do. Moreover, the proposed approach is flexible in the price control required by the market operators. Numerical examples are presented to further demonstrate the validity of this approach. [ABSTRACT FROM AUTHOR]

This paper presents two new algorithms for real-time calculation of the wheel angles and speeds of gantry tractor modules. In transport mode, the gantry tractor is, in a sense, a snakelike robot with passive joints and active wheels, with each module having autonomous four-wheel drive and four-wheel steering. The algorithms determine the wheel angles and speeds of each module with the prescription that the four wheels will have the same center of curvature, wheel speeds provide cooperative redundancy, and all hitching points follow the same path, thereby eliminating scuffing and minimizing off-tracking. Details of the analytical algorithm for a predetermined path were presented at the 2009 IEEE International Conference on Industrial Technology, together with a simulation for a single module. In this paper, we also present the results of a newly developed numerical algorithm which enables the gantry tractor to be steered online by an operator. We also show, by simulation, that this new numerical algorithm gives a good approximation to analytical solutions. The numerical algorithm is then used to calculate wheel angles and speeds for a three-module tractor with the results depicted graphically as functions of time. [ABSTRACT FROM AUTHOR]

Thermal energy in railgun is unwanted and generated by ohmic losses that are dependent to the current implied, rail dimensions, electrical conductivity (\sigma), and specific heat (CP). \sigma and CP are functions of temperature. Using achievement L^\prime formula by intelligent estimation method, the current density and ohmic losses on the cross section of the rail are computed. Ohmic losses are the source heat and utilized heat equation that are used to compute thermal distribution and temperature that are compared with other results in some papers. This paper chose h = 30\ \mm, w = 10\ \mm, and copper for the rail material and a method to compute the thermal distribution on the surface of the rail and side rail edges. Effects of rail dimensions on the temperature in time domain are calculated and shown in the figures. Rail materials are investigated with copper and aluminum in which the average temperature of both materials on the rail surface is calculated and compared. [ABSTRACT FROM AUTHOR]

This paper focuses on the scaling study of a capacitor-driven railgun. Railgun is an important kind of electromagnetic launcher. Although the basic principle is relatively simple, due to complicated technologies and extreme conditions, railgun is still far away from practical application. Scaling method is widely used in different field projects, including railgun systems. Subscale-system's test results and experiences can be extremely valuable for the actual system. This paper derives the circuit-scaling relationships based on circuit equations and momentum equations in a capacitor-driven railgun system. Four circuit linear-scaling methods (LSMs) are introduced, and a further approximate LSM is discussed. Finally, numerical verifications of the three models were given, including an original, a full LSM model, and an approximate full LSM model. It is shown that the performances of the full LSM model can be extrapolated perfectly to the original. The results of the full approximate LSM model can get almost the same result as the full LSM model, although some circuit equations are violated. All of the analyses demonstrate the flexibility and exactness of the circuit-scaling method. A detailed derivation and numerical validation are presented in this paper. [ABSTRACT FROM AUTHOR]

Scaling method is an applied scientific method employed in experimental analysis. Also, in the analysis of an electromagnetic-launch system, the scaling method can be an aid in the conversion of test results from models to original. This paper focuses on the capacitor-driven coil-gun scaling relationships between the original and the model. The current-filament method is used to derive the scaling relationships of a capacitor-driven coil gun. If the input scale factors are chosen properly, output scale factors can be calculated by the scaling-relationship equations. Two single-stage coil guns were constructed and tested to verify the scaling method. The calculated scale factors agreed quite well with the test data. Further, three-stage coil guns were simulated based on Ansoft to verify the scaling method of the field results and changes in velocity with respect to the discharge position. It is shown that the scaling method is feasible. These laws allow, with proper application, the construction of experimental models in which phenomena similar to those occurring in the original are reproduced. The result can then be recalculated, using the scale factor for the physical quantity, into the original configuration. A detailed derivation and validation will be presented in this paper. [ABSTRACT FROM AUTHOR]

The technical solution of Unmanned Aerial Vehicle (UAV) has the following features: good controllability; simple thrust control; high precision; long operating life; low cost; strong adaptability, repeatability, maneuverability, and imperceptibility. So the UAV has widespread application prospects. The position sensor of the mover of UAV linear electromagnetic ejection is the key component of control system. It has a direct influence on performance, structure, and reliability of the system. As the sensors such as linear photoelectric encoder and magnetic encoder are not able to meet the demand of high speed control, the paper develops the research on the detection methods of the mover position. First, the paper presents a detection method of mover position based on sliding mode observer. Due to the flicker problem of sliding mode observer, the paper then proposes a detection method based on state observer, and the method can result in smooth detected position of the mover. Finally, the simulated results of the ejection verify the validity of the proposed method. [ABSTRACT FROM AUTHOR]

A hybrid generator with a photovoltaic energy conversion system is proposed with supercapacitors and lead-acid batteries in a dc-coupled structure. The objective of this system is to supply the prescribed reactive and active power to the grid. This paper focuses on the strategy, which makes it possible to ensure a high battery state of charge and overcharge security by designing a dedicated local control system. A continuous dynamic model and a control design of the power system studied are proposed in this paper. Simulation and experimental results illustrate the performances obtained. [ABSTRACT FROM AUTHOR]

This paper presents an online procedure for the automatic search of the maximum-torque-per-ampere operating region for a synchronous reluctance motor. The algorithm is based on a signal-injection method with a random-based perturbation pattern applied to a common direct-torque-controlled drive. Among motor parameters, only the stator resistance is required to perform the automatic procedure. Simulations and experimental results are presented in the paper, demonstrating the benefits of the proposed algorithm. The solution is easily extended to any ac drive. [ABSTRACT FROM PUBLISHER]

The black-box arc models are commonly used for describing the interaction between a switching arc and the surrounding circuit during a circuit breaker interruption process. This paper proposes an extended Mayr's equation based arc model for the SF6 circuit breaker to characterize the transients associated with switching off a shunt reactor. The proposed model includes Mayr's arc model with estimated parameters input, a time-controlled switch, and a dielectric recovery voltage control unit. From the transient simulation aspects, the paper not only provides the guidelines for estimating parameters required for Mayr's equation to simulate the arc dynamics, but also describes a method for modeling post-arc behavior that cannot be simulated by conventional black-box models. Several study cases are performed to show the usefulness of the proposed model. Results obtained are compared with the measured and calculated data. It shows that the proposed SF6 circuit breaker arc model is relatively accurate for characterizing the shunt reactor switching transients. [ABSTRACT FROM AUTHOR]

Applying the selective harmonic elimination (SHE) technique to grid-connected-cascaded modular multilevel inverters has been widely discussed in the literature. However, due to the difficulties of solving high-order nonlinear transcendental equations, the SHE technique cannot be implemented in real time so its applications are limited. This paper presents a technique to convert the nonlinear equations to a specific control system and use a look-up table, integral controllers and a decoupling controller to help the system converge to a zero-error steady state. An inner instantaneous observer is introduced to directly extract the harmonic spectrum of the output voltages without applying FFT algorithm to output step voltage waveforms. It can not only simplify software design but also eliminate the phase delay generated by conventional spectrum extracting algorithm. The proposed technique can achieve an accurate switching angle control and a fast response. Simulation and experimental results verified that the system can achieve zero-error steady state within one line period. [ABSTRACT FROM AUTHOR]

This paper introduces a new realization for a phase-domain line model and proposes methodologies to increase its numerical performance. The new realization is based on the management of complex poles that may arise when deriving rational models by means of second-order states. The accuracy and numerical performance of the proposed realization is assessed through its application to representative examples and the comparison against other methodologies. It is demonstrated that the proposed methodology can increase substantially the numerical efficiency of the model. [ABSTRACT FROM PUBLISHER]

To improve the system reliability while conserving the limited system resources, cold standby sparing is often used. In computing tasks, because active components fail randomly, and the standby component has to pick up the mission task whenever required, scheduled backups are often implemented to save the completed portions of the task. The backups can facilitate an effective system recovery where the standby component can take over the mission task from the last backup point instead of resuming the mission task from the very beginning. This paper considers a k-out-of-n cold standby system subject to scheduled backups, where k components are online and operating, with the remaining components waiting in the unpowered, cold standby mode. Whenever an online component fails, a cold standby component is activated to take over the mission task from the last backup point. The backup intervals are deterministic, but can be even or uneven. As the component may fail due to an imperfect switching from the standby state to the fully powered up state, the switching failure is also considered in the system model. A multi-valued decision diagram (MDD)-based analytical approach is proposed to evaluate the reliability of the considered system, and its complexity is analyzed. The proposed method is applicable to systems with non-identical components following arbitrary lifetime distributions. Examples are given to illustrate the MDD-based method. The correctness and efficiency of the proposed method are verified using Monte Carlo simulations. [ABSTRACT FROM PUBLISHER]

There is a current spike in LLC resonant converter during start-up and frequency modulation method is adopted to limit the resonant current usually, which controls switching frequency decreasing from specific high frequency to steady-state frequency in exponential pattern with a time constant tau. However, it is hard to determine the crucial parameter of time constant of the exponential switching frequency sweep curve, due to the complexity in analyzing dynamic process of the converter. In this paper, the operation modes and characteristics under continued conductive mode and discontinued conductive mode are analyzed based on state-plane analysis and the boundary of two conductive modes is figured out. Then, the iteration calculation model of the LLC converter is proposed to predict the resonant current during start-up progress, and time constant of the existing soft start method is optimized using iteration algorithm. Using the proposed iterative design method, the current stress of LLC resonant converter is limited, as well as guaranteeing the response speed of output voltage. [ABSTRACT FROM AUTHOR]

Intermediate couplers have been shown to increase the coupling from primary to secondary pads in inductive power transfer (IPT) systems. This paper investigates embedding a coplanar intermediate coupler coil with the primary coil inside the primary pad to boost the coupling to the secondary pad and improve the efficiency of the system. Several coil designs are simulated and a mathematical model is developed to evaluate the efficiency of parallel–parallel and series–series tuned systems. As shown a coplanar, independently tuned intermediate coupler coil improves the efficiency of a series–series-tuned system since it reduces source losses. However, there appears to be no benefit to having an intermediate coupler with a parallel–parallel-tuned system. Furthermore, boosts in coupling are a result of adding extra current carrying windings to the primary pad and simulations show that operating the system as a traditional two coil IPT system may be simpler and more effective based on tuning topology. An experimental system was constructed to validate the simulations. [ABSTRACT FROM AUTHOR]

This paper presents a 3-D magnetohydrodynamic model of a conducting radiating plasma, which forms the basis for the Euler (in r - \varphi - {z} cylindrical coordinates) FLUX-3-D computer code. Finite-difference methods used to solve the model equations on a stationary regular spatial grid are described. The numerical 3-D simulations of a multiwire Z-pinch based on Shot-51 experiment on Z facility machine (USA) are given for the full ( 2\pi $ ) azimuth angle. The computational geometry was approximated to the real experiment configuration wherein the electromagnetic energy was supplied to the liner chamber using a vacuum coaxial transmission line. During numerical simulations, the acceleration dynamics of the plasma ablated from tungsten wires was studied depending on their number in the original cylindrical array. In addition, the results of 3-D multiwire Z-pinch implosion calculations are considered for two ways of an artificial perturbation imposition on the plasma ablation intensity. The causes for the difference in soft X-rays pulses generated in these cases are discussed. [ABSTRACT FROM PUBLISHER]

Spin-transfer torque RAM (STT-RAM) has been proposed to build on-chip caches because of its attractive features such as high storage density and ultra low leakage power. However, long write latency and high write energy are the two challenges for STT-RAM. Recently, researchers propose to improve the write performance of STT-RAM by relaxing its non-volatility property. To avoid data losses resulting from volatility, refresh schemes have been proposed. However, refresh operations consume additional overhead. In this paper, we propose to significantly reduce the number of refresh operations through re-arranging program data layout at compilation time. An N-refresh scheme is also proposed to further reduce the number of refreshes. Experimental results show that, on average, the proposed methods can reduce the number of refresh operations by 84.2 percent, and reduce the dynamic energy consumption by 38.0 percent for volatile STT-RAM caches while incurring only 4.1 percent performance degradation. [ABSTRACT FROM AUTHOR]

A state-space electromyography (EMG) model is developed for continuous motion estimation of human limb in this paper. While the general Hill-based muscle model (HMM) estimates only joint torque from EMG signals in an “open-loop” form, we integrate the forward dynamics of human joint movement into the HMM, and such an extended HMM can be used to estimate the joint motion states directly. EMG features are developed to construct measurement equations for the extended HMM to form a state-space model. With the state-space HMM, a normal closed-loop prediction–correction approach such as the Kalman-type algorithm can be used to estimate the continuous joint movement from EMG signals, where the measurement equation is used to reject model uncertainties and external disturbances. Moreover, we propose a new normalization approach for EMG signals for the purpose of rejecting the dependence of the motion estimation on varying external loads. Comprehensive experiments are conducted on the human elbow joint, and the improvements of the proposed methods are verified by the comparison of the EMG-based estimation and the inertial measurement unit measurements. [ABSTRACT FROM PUBLISHER]

In the domain of numerical computation, proper generalized decomposition (PGD), which consist in approximating the solution by a truncated sum of separable functions, is applied more and more in mechanics, and has shown its efficiency in terms of computation time and memory requirements. We propose to evaluate the PGD method to solve three-dimensional (3-D) quasi-static field problems coupling with an external electric circuit. The numerical model, obtained from the PGD formulation, is used to study the 3-D examples. The results are compared with those obtained when solving the full original problem. It is shown in this paper that the computation time rate versus the number of time steps is very small compared with the one in a classical time-stepping method, and can be very efficient to solve problems when small time steps are required. [ABSTRACT FROM AUTHOR]

The series of published works, related to differential fault attack (DFA) against the Grain family, require quite a large number (hundreds) of faults and also several assumptions on the locations and the timings of the faults injected. In this paper, we present a significantly improved scenario from the adversarial point of view for DFA against the Grain family of stream ciphers. Our model is the most realistic one so far as it considers that the cipher has to be re-keyed only a few times and faults can be injected at any random location and at any random point of time, i.e., no precise control is needed over the location and timing of fault injections. We construct equations based on the algebraic description of the cipher by introducing new variables so that the degrees of the equations do not increase. In line of algebraic cryptanalysis, we accumulate such equations based on the fault-free and faulty key-stream bits and solve them using the SAT Solver Cryptominisat-2.9.5 installed with SAGE 5.7. In a few minutes we can recover the state of Grain v1, Grain-128 and Grain-128a with as little as 10, 4 and 10 faults respectively. [ABSTRACT FROM PUBLISHER]

This paper presents a novel method named the Unified Mitchell-based Approximation (UMA) to obtain an optimized Mitchell-based logarithmic conversion circuit for any desired conversion accuracy up to 14 bits. UMA is the first method that is able to obtain a conversion circuit when a specific accuracy is required. In this work, we studied and analyzed five design parameters and their impact on accuracy and hardware merits. We formulate the hardware model of the error correction circuit in the conversion circuit for performance evaluation. Given an accuracy requirement, the proposed method explores the design space of the five design parameters. As the design space is theoretically huge, we propose constraints for the range of the parameter values and develop a systematical search algorithm for exploring the design space. UMA is able to obtain an area-delay product optimized circuit for each of the conversion accuracies achieved by the existing Mitchell-based designs. Synthesis results in 90 nm CMOS technology show that the circuits obtained are comparable or better than the existing Mitchell-based designs with the same accuracy objective. Nine of the fifteen circuits obtained achieve better area-delay product by more than 50 percent. In addition, UMA is able to obtain circuits for any accuracy from 4 to 14 bits, while the best accuracy achieved by the existing Mitchell-based methods is less than 12 bits. [ABSTRACT FROM PUBLISHER]

Battery equalizers are widely used in multibattery systems to maintain balanced charge among individual battery cells. While the research on the hardware realization of battery equalizers has received significant attention, rigorous analysis of the battery equalization process at the system level remains largely unexplored. In this paper, we study three types of battery equalization system structures: series-based, layer-based, and module-based. Specifically, we derive mathematical models that describe the system-level behavior of the battery equalization processes under these equalization structures. Then, based on the mathematical models, analytical methods are developed to evaluate the performance of the equalization processes. In addition, we carry out statistical analysis to compare the performance of the three equalization structures considered. [ABSTRACT FROM PUBLISHER]

A trust management scheme can be used to aid an automated decision-making process for an access control policy. Since unintentional temporary errors are possible, the trust management solution must provide a redemption scheme to allow nodes to recover trust. However, if a malicious node tries to disguise its malicious behaviors as unintentional temporary errors, the malicious node may be given more opportunities to attack the system by disturbing the redemption scheme. Existing trust management schemes that employ redemption schemes fail to discriminate between temporary errors and disguised malicious behaviors in which the attacker cleverly behaves well and badly alternatively. In this paper, we present the vulnerabilities of existing redemption schemes, and describe a new trust management and redemption scheme that can discriminate between temporary errors and disguised malicious behaviors with a flexible design. We show the analytical results of the trust management scheme, and demonstrate the advantages of the proposed scheme with simulation conducted in a Wireless Sensor Network. [ABSTRACT FROM AUTHOR]

Hydraulic circuits can transfer remarkable amounts of energy in the desired direction without taking large space. To implement this technology for harvesting the energy of wind appropriately, models of the system are required. Hydraulic wind power technology has the benefits of eliminating expensive and bulky variable ratio gearbox and its costly maintenance, while enabling the integration of multiple wind turbines in a single generation unit. In this paper, the dynamics of different hydraulic elements are studied, nonlinearities are taken into account, pressure dynamics in different parts of the system are studied, and the motor load effects are considered. Based on these considerations, a novel nonlinear state-space representation of the system is introduced. Results of the mathematical model and the experimental data are compared to verify the proposed model. The comparison demonstrated that the mathematical model captures all major characteristics of the hydraulic circuit and can model the system behavior under different operating conditions. [ABSTRACT FROM PUBLISHER]

Inaccurate inventory data are often found in production/inventory systems, and have a significant negative impact on the performance of raw materials replenishment and production control. In this paper, robust replenishment and production control problem for a single-stage production/inventory system with inventory inaccuracy is investigated, with the objective of minimizing the average inventory and production cost. In addition to the inventory inaccuracy, the lead-time of raw materials ordering and machine unreliability are also taken into consideration. The problem is solved in two steps. First, for a single-stage production/inventory system with ordering lead-time and uncertain production capacity, but without inventory inaccuracy, an approximate optimal replenishment, and production control policy is constructed. Second, we reveal that it is the discontinuity of the control variables in different domains of the state space that makes the policy sensitive to inventory data error. Consequently, we develop a robust replenishment and production control policy to eliminate this sensitivity. This approach maintains the structural characteristics of the optimal policy, but allows the control variables to change smoothly when the state variables cross boundaries between different domains in the state space. Numerical experiments are conducted to examine the performance of the proposed robust policy for hedging against inventory inaccuracy, and a sensitivity analysis is used to study how the parameters of the production/inventory system and the robust policy impact on the average inventory and production cost. [ABSTRACT FROM AUTHOR]

The IEC-60060-1 "High-voltage test technique" was revised in 2010 and an evaluation method using the k-factor function (test voltage function) was introduced for the lightning impulse voltage test, which involved the overshoot waveform being converted into the test voltage waveform. Test standards for UHV-class equipment are also presently being studied. To date, authors have measured k-factor values with the largest possible model, assuming actual UHV-class power equipment and proposed a new k-factor function for large-scale equipment. The present paper reports on the evaluation results of expanded uncertainty when measuring a k-factor value on the basis of the ISO/IEC Guide 98-3. As a result, it was clarified that significant uncertainty in measuring a k-factor value is brought about by the definition of the kfactor itself because small differences in the 50% breakdown voltage between the smooth lightning impulse and overshoot waveforms with respective uncertainties at a certain level were calculated. The expanded uncertainty when measuring the k-factor value in the present study for an overshoot rate of 10%, which is particularly important for practical use, was a large value of ?0.23 to ?0.36, or 0.46 to 0.72 in topto- bottom width compared to k-factor values themselves ranging from 0.2 to 1.0. However, this is actually considered a minimum level of uncertainty, which is inevitable in principle, and the best achievable measurement result rather than something caused by any problem in measurement itself. [ABSTRACT FROM AUTHOR]

With increasingly large scale of intermittent and non-dispatchable resources being integrated into power systems, the power flow problem presents greater uncertainty. In order to obtain the upper and lower bounds of power flow solutions including voltage magnitudes, voltage angles and line flows, Cartesian coordinates-based power flow is utilized in this paper. A quadratically constrained quadratic programming (QCQP) model is then established to formulate the interval power flow problem. This non-convex QCQP model is relaxed to linear programming problem by introducing convex and concave enclosures of the original feasible region. To improve the solutions bounds while still encompassing the true interval solution, optimality-based bounds tightening (OBBT) method is employed to find a better outer hull of the feasible region. Numerical results on IEEE 9-bus, 30-bus, 57-bus, and 118-bus test systems validate the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

It is known that local filtering-based edge-preserving smoothing techniques suffer from halo artifacts. In this paper, a weighted guided image filter (WGIF) is introduced by incorporating an edge-aware weighting into an existing guided image filter (GIF) to address the problem. The WGIF inherits advantages of both global and local smoothing filters in the sense that: 1) the complexity of the WGIF is $O(N)$ for an image with $N$ pixels, which is same as the GIF and 2) the WGIF can avoid halo artifacts like the existing global smoothing filters. The WGIF is applied for single image detail enhancement, single image haze removal, and fusion of differently exposed images. Experimental results show that the resultant algorithms produce images with better visual quality and at the same time halo artifacts can be reduced/avoided from appearing in the final images with negligible increment on running times. [ABSTRACT FROM AUTHOR]

Conventionally, production system modeling (PSM) has been conducted for the purpose of steady-state analysis, which only facilitates characterizing the long-term performance of production systems. More recently, there has been a rising concern regarding analyzing production system transients, which depict the system behavior before reaching the steady state. Transients are generally undesirable because the performance measures can be quite different from those of the steady state, and such differences will cause substantial production loss. Compared to the rich knowledge on steady-state analysis of production systems, PSM for transient performance analysis is much less studied. In this paper, a novel analytical method has been established to model the production system for both steady-state and transient analyses. This research has overcome the restrictions of existing methods on the number of machines and the capacity of buffers. That is, it has greatly advanced PSM for both steady-state and transient analyses by directly dealing with general serial production systems with multiple unreliable Bernoulli machines and finite buffer capacities. The proposed PSM is a method derived based on probability theory and fixed-point theory. The solvability of the method is proved theoretically. The transient performance metrics, such as second largest eigenvalue modulus, duration of the transients ( t ITER ), settling time of work-in-process ( t WIP ) and production rate ( t PR ), and percent loss of production ( L PR ) have been investigated numerically based on the proposed PSM method. This research can serve as an atomic model for more complex optimization problems in production system design and operation. [ABSTRACT FROM AUTHOR]

This paper investigates the fundamental dispersion properties of surface waves (SWs) supported by a class of metasurfaces (MTSs) that consists of a planar layer made of metal patches and apertures with self-complementary geometries. When the MTS is suspended in free space, the supported SW is TM or TE depending on whether the vertexes of the metallic parts are interconnected or not, whereas the phase velocity is equal in the two cases. A simple analytical model, that depends only on the geometry, is derived to predict the dispersion curves for a quite general class of geometries. The proposed model is also extended to cases in which the MTSs are printed on a grounded or ungrounded dielectric slab, by using an equivalent dielectric constant. Comparisons with dispersion curves obtained through full-wave simulations confirm the accuracy of the model all over the Brillouin region. Finally, it is shown that connecting or disconnecting the metal patches along a given path allows for a confinement of the SWs on such a path. An experimental validation of this concept is also presented. This feature provides the possibility of controlling the wave's direction of propagation by changing the vertexes status by means of miniaturized switches or optical control. [ABSTRACT FROM PUBLISHER]

Dual rotor motors (DRMs) for the electric vehicle application are a competitive alternative to the multi-motor drivetrain configuration to meet the high-power density and better vehicle drive performance. In this paper, a steady-state model of a hybrid DRM is developed using electromechanical energy conversion principles. The developed model comprises electrical equivalent circuit and torque equation. The model helps in understanding the motor operation and can be used for quick performance evaluation. The finite element method has been used to validate the developed model and a good agreement has been achieved for the results obtained. [ABSTRACT FROM AUTHOR]

This paper investigates the convergence and error evaluation of the distributed analytical representation and iterative technique (DARIT-field) which is a new approach for the analysis of field coupling to multiconductor transmission lines. The DARIT-field method has the advantage of high computational efficiency over the other methods. In order to know the convergence speed and the error at each iteration step of DARIT-field, an analytic expression of iterative error is derived by combining the two telegrapher's equations into a matrix equation and using the euclidean norm to explore its upper bound. The expression shows that the convergence speed is mainly influenced by three parameters, namely coupling factor (CF), terminal loads, and the line length to excitation field wavelength ratio $(d/\lambda)$. The convergence speed is a function of CF, terminal loads, and the line length to excitation field wavelength ratio $(d/\lambda)$. These results allow the users to make a compromise between computational cost and accuracy by selecting the number of iterations. [ABSTRACT FROM AUTHOR]

The paper presents a novel fixed switching frequency predictive current control method for switched reluctancemachines (SRM). The proposed deadbeat predictive current controller accurately predicts the required duty ratio for thePWM pulse for a given reference current in each digital time step over the entire speed range of operation. The pulsewidth depends on the operating conditions, machine parameters and the rotor position. The controller utilizes themachine inductance profile as a function of current and rotor position to accurately predict the required voltage. Thecontrol method is studied through computer simulation and followed by experimental validation. The method is suitablefor torque ripple sensitive applications requiring accurate tracking of a given current profile and mitigating theaudible noise due to the switching of the inverter. [ABSTRACT FROM AUTHOR]

High-temperature arc lamps are used for thermal processing of semiconductor wafers. A vortex water wall on the inner surface of the lamp's enclosure is used to provide cooling for the glass. It has been experimentally observed that, above certain levels of injected energy, the arc shows an unstable behavior and is self-extinguished. In this paper, a physics-based model for the water-wall high-temperature arc lamp is derived and implemented in the form of an equivalent electrical circuit. The equivalent circuit is then coupled to the flash power supply equivalent circuit to validate the derived model against experimental voltage and current waveforms. [ABSTRACT FROM AUTHOR]

In this paper, the back electromotive force and power equations of a permanent-magnet (PM) vernier motor are accurately derived considering an air-gap permeance function expressed in terms of practical machine dimensions. Using these equations, the nature of a PM vernier motor is analytically surveyed, and substantial information such as main geometric factors affecting torque and the maximally obtainable torque for a given current are provided, leading to a new relation for torque per air-gap volume. In addition, these equations provide a means to determine the slot and pole combinations to realize greater power density. Finally, the effects of an increased reactance are investigated in respect to machine performance with a given voltage. [ABSTRACT FROM AUTHOR]

At present, companies and standards organizations are enhancing Ethernet as the unified switch fabric for all of the TCP/IP traffic, the storage traffic and the high performance computing traffic in data centers. Backward congestion notification (BCN) is the basic mechanism for the end-to-end congestion management enhancement of Ethernet. To fulfill the special requirements of the unified switch fabric, i.e., losslessness and low transmission delay, BCN should hold the buffer occupancy around a target point tightly. Thus, the stability of the control loop and the buffer size are critical to BCN. Currently, the impacts of delay on the performance of BCN are unidentified. When the speed of Ethernet increases to 40 Gbps or 100 Gbps in the near future, the number of on-the-fly packets becomes the same order with the buffer size of switch. Accordingly, the impacts of delay will become significant. In this paper, we analyze BCN, paying special attention on the delay. We model the BCN system with a set of segmented delayed differential equations, and then deduce sufficient condition for the uniformly asymptotic stability of BCN. Subsequently, the bounds of buffer occupancy are estimated, which provides direct guidelines on setting buffer size. Finally, numerical analysis and experiments on the NetFPGA platform verify our theoretical analysis. [ABSTRACT FROM AUTHOR]

Topic modeling has become a widely used tool for document management. However, there are few topic models distinguishing the importance of documents on different topics. In this paper, we propose a framework LIMTopic to incorporate link based importance into topic modeling. To instantiate the framework, RankTopic and HITSTopic are proposed by incorporating topical pagerank and topical HITS into topic modeling respectively. Specifically, ranking methods are first used to compute the topical importance of documents. Then, a generalized relation is built between link importance and topic modeling. We empirically show that LIMTopic converges after a small number of iterations in most experimental settings. The necessity of incorporating link importance into topic modeling is justified based on KL-Divergences between topic distributions converted from topical link importance and those computed by basic topic models. To investigate the document network summarization performance of topic models, we propose a novel measure called log-likelihood of ranking-integrated document-word matrix. Extensive experimental results show that LIMTopic performs better than baseline models in generalization performance, document clustering and classification, topic interpretability and document network summarization performance. Moreover, RankTopic has comparable performance with relational topic model (RTM) and HITSTopic performs much better than baseline models in document clustering and classification. [ABSTRACT FROM AUTHOR]

Physical activity consists of complex behavior, typically structured in bouts which can consist of one continuous movement (e.g., exercise) or many sporadic movements (e.g., household chores). Each bout can be represented as a block of feature vectors corresponding to the same activity type. This paper introduces a general distance metric technique to use this block representation to first predict activity type, and then uses the predicted activity to estimate energy expenditure within a novel framework. This distance metric, dubbed Bipart, learns block-level information from both training and test sets, combining both to form a projection space which materializes block-level constraints. Thus, Bipart provides a space which can improve the bout classification performance of all classifiers. We also propose an energy expenditure estimation framework which leverages activity classification in order to improve estimates. Comprehensive experiments on waist-mounted accelerometer data, comparing Bipart against many similar methods as well as other classifiers, demonstrate the superior activity recognition of Bipart, especially in low-information experimental settings. [ABSTRACT FROM AUTHOR]

In this paper, we propose an efficient method for the calculation of the cutoff wavenumbers of coaxial elliptical-circular and circular-elliptical metallic waveguides. The cutoff wavenumbers are obtained through closed-form expressions making the evaluation efficient, and moreover, very accurate even for large values of the eccentricity of the elliptical boundary. The resulting formulas are free of Mathieu functions, including only simple algebraic expressions with Bessel functions, and are valid for every different value of the indices n and m, corresponding to every higher order TMnm or TEnm mode. The validation of the method is performed by comparing to the general exact solution. The efficiency and accuracy of our method is presented by illustrative examples. Numerical results are given for the cutoff wavenumbers of various higher order modes. [ABSTRACT FROM AUTHOR]

Substrate integrated waveguide, an emerging technology for microwave and millimeter-wave circuits, is affected by three loss mechanisms: ohmic and dielectric losses, standard waveguides, and radiation leakage. While ohmic and dielectric losses can be accurately determined by the analytical formulas of the equivalent rectangular waveguide, no equations are available for radiation leakage. This paper presents the derivation of a formula to calculate the attenuation constant due to radiation leakage in substrate integrated waveguide interconnects. [ABSTRACT FROM AUTHOR]

In this paper, we solved Poisson equation in cylindrical coordinates using approximations to obtain a compact model for the drain current of long-channel junctionless gate-all-around MOSFETs. The resulting model is analytical, explicit, and valid for depletion and accumulation, and consists of simple physically based equations, for better understanding of this device, and also easier implementation and better computation speed as a compact model. The agreement with TCAD simulations is very good. [ABSTRACT FROM PUBLISHER]

The Ising channel, which was introduced in 1990, is a channel with memory that models intersymbol interference. In this paper, we consider the Ising channel with feedback and find the capacity of the channel together with a capacity-achieving coding scheme. To calculate the channel capacity, an equivalent dynamic programming (DP) problem is formulated and solved. Using the DP solution, we establish that the feedback capacity is the expression \(C=({2H_{b}(a)}/{3+a})\approx 0.575522\) , where \(a\) is a particular root of a fourth-degree polynomial and \(H_{b}(x)\) denotes the binary entropy function. Simultaneously, \(a=\arg \max _{0\leq x \leq 1} ({2H_{b}(x)}/{3+x})\) . Finally, an error-free, capacity-achieving coding scheme is provided together with the outlining of a strong connection between the DP results and the coding scheme. [ABSTRACT FROM AUTHOR]

This paper investigates the interaction of an initially uniform magnetic field with an electrically conducting slab that moves perpendicularly to the magnetic field with arbitrary time-dependent velocity. It is demonstrated that the problem of determining the time-dependent Lorentz force and the time-dependent Joule heat in the slab is mathematically equivalent to solving a 1-D heat diffusion problem with time-dependent boundary conditions and to submitting the solution to a nonstandard postprocessing procedure. For the particular case of an impulsively driven slab we exploit the mathematical analogy between magnetic diffusion and heat diffusion by translating a textbook solution of the corresponding heat-transfer problem into exact and previously unknown relations for Lorentz force and Joule heat. Moreover, we use a 1-D finite-difference code to investigate more general time dependencies of the velocity including smooth accelerations and random velocity changes. Our numerical determination of reaction times ( \(\boldsymbol {T_{98}}\) ) of the Lorentz force in the case of smooth accelerations provides a useful design tool for the development of Lorentz force flowmeters with short reaction times. [ABSTRACT FROM AUTHOR]

High-speed airflow, which is generated around trains running at a high speed, causes uneven pollutant distribution on insulator surfaces and changes their insulation properties. In this paper, a method has been proposed to calculate the residual pollutant resistance on polluted insulator. Based on the analysis of flashover model, the influence of pollution distribution along and around insulator was discussed. Analysis result showed that flashover voltage would increase when the pollutant distribution on insulator decreased compared to conditions with uniformly distributed pollutant, and vice versa. It implied that there should be a maximum pollutant accumulation value above and below the insulator shed. In this situation, the flashover voltage will be the lowest. Model analysis showed that the flashover voltage would increase with the length of the insulated plate and vice versa. The theoretical analysis was in good agreement with experimental result, which implied that this method might be able to provide reference for insulator shed design. [ABSTRACT FROM AUTHOR]