Search

Power allocation in hybrid energy storage systems (HESSs) is an important issue for dc microgrids. In this paper, an integral droop (ID), inspired by the electrical characteristics of capacitor charging/discharging process, is proposed and applied to a cluster of energy storages (ESs) with high ramp rates. Through the coordination of the ID and conventional V-P droop, the transient power allocation in HESSs can be intrinsically realized in a decentralized manner. The high-frequency components of power demand can be compensated by the ESs with ID, whereas the ESs with V-P droop respond to the smooth change of load power. Additionally, the ID coefficient can be designed according to the nominal ramp rate of the ESs with slow response, which helps to extend the lifespan of the HESS. On the other hand, to easily assess the stability of the system feeding constant power loads, a minimum relative impedance criterion (MRIC) is developed. Based on MRIC, it is revealed that the proposed ID can shape the output impedance of the HESS and stabilize the entire system. The feasibility and effectiveness of ID are verified by both simulations and experimental results. [ABSTRACT FROM PUBLISHER]

A novel high-efficiency resonant light emitting diode (LED) backlight driver with passive current balancing and dimming is proposed and analyzed in this paper. The proposed LED driver achieves uniform brightness of each LED string by the charge balance of the resonant capacitor, which benefits from high efficiency. By controlling the output current of one LED string, the output currents of other LED strings can be controlled via current balancing of resonant capacitors, which makes its control simple. The proposed LED driver uses only one active switch, which decreases circuit volume and simplifies the control. Furthermore, a wide load range can be achieved by controlling the turn-on duty ratio of the single power switch of the LED driver with a fixed frequency. Finally, a prototype of a high-dimming-ratio small-size three-string LED driver is provided to verify the studied results. [ABSTRACT FROM PUBLISHER]

Conventional centralized control strategies may reduce the flexibility and expandability of a modular multilevel converter (MMC) system. To tackle this issue, this paper proposes a distributed control architecture that is capable of assigning certain control tasks to distributed local controllers and improves the modularity of an MMC system. A central controller dealing with the output current regulation based on sensed arm currents is adopted. The control of MMC internal dynamics and the pulsewidth modulation (PWM) generation are distributed into local controllers. Unlike the conventional MMC control that needs all submodule capacitor voltages for capacitor voltage averaging, the proposed capacitor voltage control only relies on local submodule voltage measurement. Consequently, communication-intensive capacitor voltage transmission in each control cycle is not required and the communication burden of the control system can be significantly reduced. The control loops and possible control conflicts among submodules are presented and considered for system stability analysis. The effectiveness of the proposed distributed control architecture and capacitor voltage control for an MMC are confirmed by the start-up, steady state, and transient experimental results. [ABSTRACT FROM PUBLISHER]

The increasing algorithmic complexity and dataset sizes necessitate the use of networked machines for many graph-parallel algorithms, which also makes fault tolerance a must due to the increasing scale of machines. Unfortunately, existing large-scale graph-parallel systems usually adopt a distributed checkpoint mechanism for fault tolerance, which incurs not only notable performance overhead but also lengthy recovery time. This paper observes that the vertex replicas created for distributed graph computation can be naturally extended for fast in-memory recovery of graph states. This paper describes Imitator, a new fault tolerance mechanism, which supports cheap maintenance of vertex states by replicating them to their replicas during normal message exchanges, and provides fast in-memory reconstruction of failed vertices from replicas in other machines. Imitator has been implemented on Cyclops with edge-cut and PowerLyra with vertex-cut. Evaluation on a 50-node EC-2 like cluster shows that Imitator incurs an average of 1.37 and 2.32 percent performance overhead (ranging from −0.6 to 3.7 percent) for Cyclops and PowerLyra respectively, and can recover from failures of more than one million of vertices with less than 3.4 seconds. [ABSTRACT FROM AUTHOR]

Compared with other applications in computer vision, convolutional neural networks (CNNs) have underperformed on pedestrian detection. A breakthrough was made very recently using sophisticated deep CNN (DCNN) models, with a number of handcrafted features or explicit occlusion handling mechanism. In this paper, we show that by reusing the convolutional feature maps of a DCNN model as image features to train an ensemble of boosted decision models, we are able to achieve the best reported accuracy without using specially designed learning algorithms. We empirically identify and disclose important implementation details. We also show that pixel labeling may be simply combined with a detector to boost the detection performance. By adding complementary handcrafted features such as optical flow, the DCNN-based detector can be further improved. We advance the state-of-the-art results by lowering the log-average miss rate from 11.7% to 8.9% on the Caltech data set and from 11.2% to 8.6% on the Inria data set. We also achieve a comparable result to state-of-the-art approaches on the KITTI data set. [ABSTRACT FROM AUTHOR]

The dc offset and scaling errors in the voltage measurements cause the injection of undesired dc and harmonic currents into the three-phase output currents of the grid-connected inverter. This study proposes an enhanced current control scheme to eliminate the dc and harmonic currents caused by voltage distortion and voltage measurement error in three-phase grid-connected inverters. The proposed current controller is designed in the synchronous (d-q ) reference frame and composed of a proportional resonant (PR) controller and a repetitive controller (RC). The role of the RC is to regulate the grid current follow the reference value as well as compensate all 6\rmn\omega {\rm{s}} and (6\rmn\pm 2)\omega{\rm{s}}\,(n= 1,\,2,\,3,\ldots) harmonic components caused by distorted grid voltage and scaling errors. Meanwhile, the PR controller helps to compensate the dc current generated by dc offset measurement errors to guarantee that the three-phase grid currents are balanced and sinusoidal with extremely low dc component. Since the RC employed in the proposed current controller reduces to time delay by four times compared to the conventional RC, the proposed control system ensures good steady-state performance of the grid current without deteriorating its fast dynamic response. The effectiveness of the suggested solution is verified by various experimental tests. [ABSTRACT FROM AUTHOR]

The dc offset and scaling errors in the voltage and current measurements cause the injection of undesired dc and unbalanced currents into the three-phase input currents and subsequently lead to voltage ripple at the dc output voltage of the ac/dc converter. This paper proposes a compensation scheme for current measurement error where the dc offset and scaling errors in the current measurement are estimated from the voltage ripple characteristics of the dc output voltage ripple combining with simple band-pass and low-pass filters. Meanwhile, the dc offset and scaling errors in the voltage measurement can be rejected by using an advanced current controller developed with a proportional resonant plus a repetitive controller designed in the synchronous (d–q) reference frame. The proposed control algorithm is able to effectively reject the impact of both voltage and current measurement error so that the three-phase input currents are regulated to be balanced and sinusoidal with ultralow dc current component. Meanwhile, the dc output voltage is also well regulated to be pure dc with a negligibly small voltage ripple. The proposed compensation method is developed without the need of extra hardware circuit, sensor, or precise information of system parameters so that it can be considered as more cost effective and robust solution. The effectiveness of the proposed solution is verified by experimental results. [ABSTRACT FROM AUTHOR]

Much of the recent progress in Vision-to-Language problems has been achieved through a combination of Convolutional Neural Networks (CNNs) and Recurrent Neural Networks (RNNs). This approach does not explicitly represent high-level semantic concepts, but rather seeks to progress directly from image features to text. In this paper we first propose a method of incorporating high-level concepts into the successful CNN-RNN approach, and show that it achieves a significant improvement on the state-of-the-art in both image captioning and visual question answering. We further show that the same mechanism can be used to incorporate external knowledge, which is critically important for answering high level visual questions. Specifically, we design a visual question answering model that combines an internal representation of the content of an image with information extracted from a general knowledge base to answer a broad range of image-based questions. It particularly allows questions to be asked where the image alone does not contain the information required to select the appropriate answer. Our final model achieves the best reported results for both image captioning and visual question answering on several of the major benchmark datasets. [ABSTRACT FROM PUBLISHER]

This paper proposes a fault location method based on the adaptive control of neutral-to-earth complex impedance in a resonant grounded system, whose neutral point grounds are via an electromagnetic hybrid Petersen coil (EHPC). The EHPC can be equivalent to a parallel circuit of a negative resistance and an inductance, both of which can be adjusted. When a permanent single line-to-earth fault occurs, the ground-fault current will be compensated to almost zero, and the capacitance to earth and leakage resistance of system can be measured accurately for subsequent fault location. Then, the complex impedance of EHPC is adjusted, and the faulty feeder and its faulted section can be identified online based on the characteristics that the measurements of zero-sequence admittances of points along the faulty feeder change with the system's neutral-to-ground complex impedance. The detection criterion is certain and unique, without comparing all of the feeders. This paper also proposes an adaptive jitter adjustment and decoupling control of neutral-ground complex impedance by EHPC, which is adaptive to the grounding transient resistance and is repeatable, and can ensure that the magnitude of the zero-sequence parameter is large enough to be measured while without arc re-ignition, including in high impedance fault states. Simulations and experiments verified the feasibility of this fault location method and its control strategy. [ABSTRACT FROM PUBLISHER]

The nonlinear loads in distribution grid may generate harmful low-order harmonics, polluting the grid and deteriorating the voltage quality particularly when the grid is weak. The grid interfacing converters in the distribution system, such as the distributed generation (DG) interfacing converters or hybrid ac/dc grid interlinking converters, can participate in distribution grid harmonic control. In this paper, two virtual-impedance-based harmonics control methods are developed for grid interfacing voltage-source inverters (VSIs) to improve the power quality of the distribution grid. As the control parameters are designed based on the virtual impedance theory, clear physical meanings are given to explain their impacts on the system. Also, the proposed methods do not rely on the closed loop feedback control and, therefore, are very suitable for VSIs with low switching frequency (such as those for high-power DGs or interlinking converters for hybrid ac/dc systems), whose closed-loop control feedback bandwidth may be limited for harmonic regulation. The influence of system delay and feedback control loop is considered and modeled in the design procedure; thus more accurate virtual impedance control is achieved for low-switching-frequency VSIs. Moreover, a comprehensive comparison of the two methods, including stability and harmonic compensation performance, are given. Their effectiveness is verified by experiment results. [ABSTRACT FROM PUBLISHER]

In this paper, a beam switching antenna (BSA) based on a reconfigurable cascaded feeding network (RCFN) is presented. The RCFN is engineered by cascading several varactor-loaded quasi-lumped couplers (QLCs). As the output port of the RCFN, the coupled port of every QLC is connected to an endfire radiator. BSAs based on two types of RCFN, the open-loop RCFN and closed-loop RCFN, are designed, simulated, and measured. The open-loop design features flexible beam switching strategies with the dynamic control of operation modes allocating the input power to the intended radiator(s), and single-/multibeam switching is achieved. In the case of the closed-loop RCFN, a power-recycling circuit is introduced to improve the efficiency of the single-beam switching mode of the BSA. Measured results show that the BSA operating in single-beam mode is able to radiate six switched beams each with a 3 dB beamwidth of 60°, covering 360° in the azimuth plane. The return losses and gain fluctuation of both prototypes are better than 15 dB and less than 1 dB, respectively. The corresponding experiments agree well with both the theoretical analysis and the simulation results. [ABSTRACT FROM PUBLISHER]

A high-performance three-phase pulse width modulation (PWM) converter with reduced dc-link capacitor under unbalanced ac voltage conditions is proposed in this paper. The unique feature of the converter lies in that sinusoidal symmetrical ac currents and ripple free dc voltage can be achieved simultaneously without using a bulky capacitor, which was thought to be a dilemma in the past. The control scheme is implemented in an α–β frame, so the complex rotate transformations are avoided, and it does not require the extraction of positive and negative sequence currents, which simplifies the control algorithm. A two-quadrant operation active power compensator together with its controller is developed to suppress the voltage ripple in the dc-link. Compared with the passive compensation method, the compensator is equipped with a smaller capacitor to reduce the system size, weight, and cost. Moreover, the compensator could be integrated with the conventional three-phase three-leg PWM converter seamlessly. The effectiveness of the proposed control schemes is verified by the experiment results. [ABSTRACT FROM PUBLISHER]

The traditional finite-control-set model predictive control (FCS-MPC) method for a cascaded H-bridge (CHB) rectifier has two main issues: heavy computational burden and low steady-state current performance. In this paper, a novel FCS-MPC method has been proposed for a single-phase CHB rectifier. The proposed method solves the optimization problem of FCS-MPC for one cell by one cell, like a “pipeline.” In the proposed method, the sampling period is divided into equal intervals by the number of cells. At the beginning of the first interval, the first cell selects its switching state to be applied. Then, the following cell selects its switching state to be applied at the beginning of next interval. Finally, the selected switching state of last cell will be applied at the beginning of the last interval. A cost function presenting the control objectives of common source current error and itself dc-link voltage error is evaluated for each cell. A single-phase three-cell CHB rectifier controlled by a DSpace DS1104 is tested and the experimental results show that a significant reduction in computational time, an improved steady-state current performance, and a comparable dynamic response are achieved in the proposed method in comparison with the traditional FCS-MPC method. [ABSTRACT FROM AUTHOR]

Due to voltage mismatch between phase legs and the dc bus in modular multilevel converters (MMCs), the differential current in MMCs is inherently subjected to circulating even-order harmonics. Repetitive control based active harmonic suppression methods can be adopted to eliminate such harmonics. Nevertheless, conventional repetitive controllers have a relatively slow dynamic response, because all the sampled errors in the past one cycle have to be stored, which causes a response delay for one fundamental period. This paper proposes an improved repetitive control scheme that exclusively copes with even-order harmonics based on the circulating current characteristics of MMC systems. The design details of the even harmonic repetitive control scheme according to the harmonics characteristics are provided. The proposed even-harmonic repetitive control scheme requires halved data memory to store error samplings and the delay introduced by the repetitive controller is also reduced. According to the frequency domain analysis, the even-harmonic repetitive control features faster convergence rate, greater low-frequency gains, higher crossover frequency, and higher tolerance against system frequency deviation, while possessing the same even-order harmonics suppression capability and stability as conventional ones. Simulation and experimental results are presented to show the steady-state harmonics suppression capability, dynamic response, and disturbance tolerance of the proposed even-harmonic repetitive control scheme. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMCs) are multi-input multi-output (MIMO) nonlinear systems. The control systems for MMCs are required to simultaneously achieve multiple control objectives, e.g., output current regulation, submodule capacitor voltage control, and circulating ripple currents suppression. Existing cascaded control strategies for MMCs achieve those control objectives with relatively complex controllers, and the controller parameter design is normally difficult for such nonlinear systems with highly coupled states. In view of this, a feedback linearization-based current control strategy is proposed for an MMC system in this paper. The nonlinear state function model of the MMC is presented and transformed to a linearized and decoupled form with the help of the input–output feedback linearization technique. Based on the linearized system, simple linear controllers are employed to regulate the output and inner differential currents of the MMC, which significantly reduces the difficulty in controller design. The stability of the proposed control strategy is analyzed. The experimental verification results show that, compared to the conventional cascaded control strategies for MMCs, the proposed feedback linearization control strategy is able to achieve improved steady-state and dynamic performances. The robustness of the proposed control strategy against parametric uncertainties is experimentally investigated. [ABSTRACT FROM PUBLISHER]

This paper proposes a modified one cycle control (OCC) for active power filter (APF) to compensate only harmonic components of load currents. The conventional OCC-based APF cannot differentiate between the harmonic and reactive components of load currents, which leads to the increment in device current rating because of compensation of large reactive currents besides harmonics. The reference signals of the OCC control core have been reconstructed and the associated control equations have been developed, following the control philosophy of simplicity. The modified scheme is easy to implement and only three more sensors are required for measuring load currents compared with the conventional OCC. This modified OCC guarantees the excellent performance of harmonic compensation alone and retains the advantages of the conventional OCC, such as no phase locking loop and the constant switching frequency. The feasibility and performance of the proposed OCC has been validated by experimental studies on a 5 kVA APF hardware platform developed in laboratory. [ABSTRACT FROM PUBLISHER]

Cloud storage services such as Dropbox have been widely used for file collaboration among multiple users. However, this desirable functionality is yet restricted to the “walled-garden” of each service. At present, the only feasible approach to cross-cloud file collaboration seems to be using web APIs, whose performance is known to be highly unstable and unpredictable. Now that using inefficient web APIs is inevitable, in this paper we attempt to achieve sound user-perceived performance for cross-cloud file collaboration. This attempt is enabled by two key observations from real-world measurements. First, for each cloud, we are always able to deploy one or several nearby (client) proxies which can efficiently access the web APIs. Second, during file collaboration, significant similarity exists among different versions of a file. This can be exploited to substantially reduce inter-proxy traffic and thus shorten the data sync time. Guided by the observations, we design and implement an open-source prototype system called CoCloud. Currently, it supports file collaboration among four popular cloud storage services in the US and China. Its performance is well acceptable to users under representative workloads, even approaching or exceeding that of intra-cloud collaboration in many cases. [ABSTRACT FROM PUBLISHER]

Encouraged by the success of convolutional neural networks (CNNs) in image classification, recently much effort is spent on applying the CNNs to the video-based action recognition problems. One challenge is that a video contains a varying number of frames, which is incompatible to the standard input format of the CNNs. Existing methods handle this issue either by directly sampling a fixed number of frames or bypassing this issue by introducing a 3D convolutional layer, which conducts convolution in spatial-temporal domain. In this paper, we propose a novel network structure, which allows an arbitrary number of frames as the network input. The key to our solution is to introduce a module consisting of an encoding layer and a temporal pyramid pooling layer. The encoding layer maps the activation from the previous layers to a feature vector suitable for pooling, whereas the temporal pyramid pooling layer converts multiple frame-level activations into a fixed-length video-level representation. In addition, we adopt a feature concatenation layer that combines the appearance and motion information. Compared with the frame sampling strategy, our method avoids the risk of missing any important frames. Compared with the 3D convolutional method, which requires a huge video data set for network training, our model can be learned on a small target data set because we can leverage the off-the-shelf image-level CNN for model parameter initialization. Experiments on three challenging data sets, Hollywood2, HMDB51, and UCF101 demonstrate the effectiveness of the proposed network. [ABSTRACT FROM AUTHOR]

Deriving from the gradient vector of a generative model of local features, Fisher vector coding (FVC) has been identified as an effective coding method for image classification. Most, if not all, FVC implementations employ the Gaussian mixture model (GMM) as the generative model for local features. However, the representative power of a GMM can be limited because it essentially assumes that local features can be characterized by a fixed number of feature prototypes, and the number of prototypes is usually small in FVC. To alleviate this limitation, in this work, we break the convention which assumes that a local feature is drawn from one of a few Gaussian distributions. Instead, we adopt a compositional mechanism which assumes that a local feature is drawn from a Gaussian distribution whose mean vector is composed as a linear combination of multiple key components, and the combination weight is a latent random variable. In doing so we greatly enhance the representative power of the generative model underlying FVC. To implement our idea, we design two particular generative models following this compositional approach. In our first model, the mean vector is sampled from the subspace spanned by a set of bases and the combination weight is drawn from a Laplace distribution. In our second model, we further assume that a local feature is composed of a discriminative part and a residual part. As a result, a local feature is generated by the linear combination of discriminative part bases and residual part bases. The decomposition of the discriminative and residual parts is achieved via the guidance of a pre-trained supervised coding method. By calculating the gradient vector of the proposed models, we derive two new Fisher vector coding strategies. The first is termed Sparse Coding-based Fisher Vector Coding (SCFVC) and can be used as the substitute of traditional GMM based FVC. The second is termed Hybrid Sparse Coding-based Fisher vector coding (HSCFVC) since it combines the merits of both pre-trained supervised coding methods and FVC. Using pre-trained Convolutional Neural Network (CNN) activations as local features, we experimentally demonstrate that the proposed methods are superior to traditional GMM based FVC and achieve state-of-the-art performance in various image classification tasks. [ABSTRACT FROM PUBLISHER]

Economic operation is a major concern for microgrids (MGs). System operation cost is optimized when the incremental costs (ICs) of all distributed generators (DGs) reach equality. Conventionally, economic dispatch of DGs is solved by centralized control with optimization algorithms or distributed control with consensus algorithms. To improve the reliability, scalability, and economy of MGs, a fully decentralized economic power sharing strategy is proposed in this paper. As frequency is a global state in ac MG and dc bus voltage serves as a natural indicator in dc MG, a frequency-IC droop scheme is proposed for ac MG, a voltage-IC droop scheme is proposed for dc MG, and a normalization scheme is proposed for hybrid ac/dc MG. By using the proposed technique, ICs of DGs reach equality with the convergence of the system global indicator (frequency or dc bus voltage). Then power sharing of each DG is automatically achieved based on its relevant IC function and the total operating cost can be optimized without any communication or central controllers. The proposed approach is implemented in an ac MG, a dc MG, and a hybrid ac/dc MG in MATLAB/Simulink to verify its effectiveness. [ABSTRACT FROM AUTHOR]

There have been many attempts to classify imbalanced data, since this classification is critical in a wide variety of applications related to the detection of anomalies, failures, and risks. Many conventional methods, which can be categorized into sampling, cost-sensitive, or ensemble, include heuristic and task dependent processes. In order to achieve a better classification performance by formulation without heuristics and task dependence, we propose confusion-matrix-based kernel logistic regression (CM-KLOGR). Its objective function is the harmonic mean of various evaluation criteria derived from a confusion matrix, such criteria as sensitivity, positive predictive value, and others for negatives. This objective function and its optimization are consistently formulated on the framework of KLOGR, based on minimum classification error and generalized probabilistic descent (MCE/GPD) learning. Due to the merits of the harmonic mean, KLOGR, and MCE/GPD, CM-KLOGR improves the multifaceted performances in a well-balanced way. This paper presents the formulation of CM-KLOGR and its effectiveness through experiments that comparatively evaluated CM-KLOGR using benchmark imbalanced datasets. [ABSTRACT FROM PUBLISHER]

For hybrid energy storage system in dc microgrid, effective power split, bus voltage deviation, and state-of-charge (SoC) violation are significant issues. Conventionally, they are achieved by centralized control or hierarchical control methods with communications. This paper proposes a simple and effective strategy to solve the problem in a decentralized manner. A high-pass filter-based droop (HPFD) controller is proposed to regulate the battery converter, and a virtual capacitance droop (VCD) controller is implemented for a supercapacitor (SC) converter. The cooperation of HPFD and VCD first achieves autonomous power split that high-frequency fluctuation is buffered by SC and low-frequency power is supplied by battery. Meanwhile, the bus voltage deviation induced by the droop-based power sharing is eliminated automatically at steady state. The resulted bus voltage restoration simultaneously enforces SC SoC back to its nominal value, and, thus, ensures continuous operation of SC as a power buffer without the violation of its SoC boundary. A design guideline is developed to ensure expected system dynamics. The effectiveness of the proposed method and analytical results are validated by simulations and experiments. [ABSTRACT FROM PUBLISHER]

This study proposes an advanced current control strategy for three-phase grid-connected inverters to reject the impact of the dc offsets and scaling errors in the grid voltage measurement on the grid current performance. The proposed current controller designed in the synchronous (d-q) reference frame is developed with a proportional integral (PI) plus three vector PI controllers. The PI controller regulates the fundamental current to follow its reference, meanwhile, three vector PI controllers tuned at the fundamental grid frequency ( \omega _s), 2\omega _s, 6\omega _s are employed to eliminate the dc, unbalance, harmonic components in the grid current. As a result, the three-phase grid currents are controlled to be balanced, sinusoidal, and extremely low dc component despite the presence of the dc offset and scaling errors in the grid voltage measurement and distorted grid voltage conditions. The main advantage of the proposed control scheme is that it is developed without the need of additional hardware circuit, dc extraction, and harmonic detection scheme so that it can be integrated into the existing grid-connected inverter system without extra cost. The effectiveness of the suggested solution is verified by experimental results under various grid voltage conditions and the grid voltage measurement errors. [ABSTRACT FROM PUBLISHER]

Dealing with electrical rotating machines fed by voltage converters, understanding the effect of impulsive voltage parameters on partial discharge features is of great importance to select appropriate impulsive voltage to perform partial discharge inception voltage measurements. Similarly, the dependence of insulation endurance on voltage parameters might help to develop qualification tests providing more accurate evaluation of insulation performance. The effect of voltage duty cycle on partial discharge characteristics and endurance of inverter-fed motor insulation were investigated through a large number of tests performed on single-contact crossed enameled wires under bipolar repetitive impulse wave voltages. The partial discharge pattern, magnitude, repetition rate show that short impulsive voltage duration (i.e. small duty cycles), can induce asymmetric PD patterns and reduce the probability of PD inception at the falling flanks of impulsive voltages. Moreover, the endurance tests indicate that the duty cycle of the repetitive square wave voltage can affect the insulation endurance significantly. Repetitive square wave voltages with small duty cycles tend to overestimate endurance. Accordingly, when performing partial discharge inception voltage and endurance tests on insulation of inverter-fed motors, the influence of duty cycle should be carefully considered. [ABSTRACT FROM AUTHOR]

To ensure insulation system reliability of rotating machines driven by power electronics, accelerated tests under repetitive impulsive voltages should be performed on turn-to-turn insulation according to the standards provided by the International Electrotechnical Commission. The parameters of repetitive impulsive voltage can significantly influence insulation lifetime, and thus, voltage parameters should be carefully controlled during the accelerated tests. To increase endurance test efficiency when testing many insulation specimens in parallel, the rise time of impulsive voltage should be controlled at certain constant values after the breakdown of one or more specimens to obtain objective endurance test results. This study provides a description of a novel square wave voltage generator used for the insulation evaluation of rotating machines driven by power electronics. A single-channel generator with variable rise times used for one specimen and a multi-channel generator with a constant rise time used to test five specimens in parallel are presented based on a push-pull solid-state switch. In the multi-channel generator, the RC parameter of the high-voltage circuit can be adjusted automatically by resorting to controlling units and a circuit structure after the breakdown of one or more samples when performing endurance tests on parallel specimens to keep the rise time of impulsive voltage at constant values. The multi-channel generator can significantly increase the endurance evaluation efficiency of the insulation systems of rotating machines fed by power electronics. [ABSTRACT FROM AUTHOR]

A new image-based visual servoing method based on sensitive features is presented to separately realize the position control and orientation control. Line features are used for the orientation control because of their sensitivities to rotational motions. Point features and area size features are employed to realize the position control since area size features are very sensitive to the objects’ depths. The translations resulting from rotational motions are introduced into the position control as the compensation in order to eliminate the influence of the camera’s motions on the point features. The depths for all active features are estimated via interaction matrices, features variations, and the executed camera motions. The proposed method can keep the tracked objects in the camera’s field of view in the visual servoing process. In addition, the determination methods of the interaction matrices for point, line, and area size features are proposed. Comparing to the traditional method, the proposed determination method of the interaction matrix for line is independent from the parameters of the plane containing the line. Experimental results verify the effectiveness of the proposed methods. [ABSTRACT FROM PUBLISHER]

In high-resolution synthetic aperture radar (SAR) images, the spatial pattern of a homogenous region conveys rich information regarding the specific scatterers being imaged. Analytical modelings of both scattering and imaging processes are critical to better interpret a specific scatterer’s appearances in SAR imagery and thereafter quantitatively retrieve its physical parameters. Small-scale rough surface scattering represents one of the mostly common scattering mechanisms and yet its SAR image characteristics have not been well studied. This becomes more critical in millimeter-wave/terahertz regime as smooth surfaces would become slightly rough under millimeter/submillimeter wavelengths. In this paper, we recast the small perturbation method (SPM) approximation of rough surface scattering under the deterministic finite-length surface condition. By ignoring evanescent waves, a simplified SPM solution for rough facet is derived as well as the analytical form of its SAR image under the conventional setup. Then, we reformulate the scattering imaging process of rough facet as a signal processing chain that further reveals the underlying mechanism of rough surface as imaged by radar. The proposed method is extensively validated against the method of moments in terms of both scattering coefficients and imaging patterns. It is found that under the conventional SPM validity condition, the error of scattering coefficients is less than 1.5 dB, while the correlation between SPM-calculated and MoM-calcualted SAR images is larger than 0.9. The proposed model of rough facet SAR image could serve as the theoretical basis for parameter inversion and surface reconstruction. Preliminary cases of the inversion of rough surface spectrum using both simulated and real SAR image patches are presented. [ABSTRACT FROM PUBLISHER]

Power allocation is a major concern in hybrid energy storage system. This paper proposes an extended droop control (EDC) strategy to achieve dynamic current sharing autonomously during sudden load change and resource variations. The proposed method consists of a virtual resistance droop controller and a virtual capacitance droop controller for energy storages with complementary characteristics, such as battery and supercapacitor (SC). By using this method, battery provides consistent power and SC only compensates high-frequency fluctuations without the involvement of conventionally used centralized controllers. To implement the proposed EDC method, a detailed design procedure is proposed to achieve the control objectives of stable operation, voltage regulation, and dynamic current sharing. System dynamic model and relevant impedances are derived and detailed frequency domain analysis is performed. Moreover, the system level stability analysis is investigated and system expansion with the proposed method is illustrated. Both simulations and experiments are conducted to validate the effectiveness of the proposed control strategy and analytical results. [ABSTRACT FROM PUBLISHER]

With high renewable power penetration, uncertainty and intermittence of renewable sources become major concerns of power system planning and operation. Large and fast wind speed change may cause great variation of active power generation, which may lead to system stability and reliability problems. The response speeds of the committed conventional generators (CGs) for frequency regulations are critical for system reliable and stable operation. The slow response of the committed CGs may result in power shortage or surplus, which may affect system frequency. This paper proposes a technique to evaluate operational reliability and efficiency problems of power systems with high wind power penetration from frequency aspect. Energy unnecessarily consumed and less supplied during system frequency control processes are modeled in detail. The reliability and economic indexes are formulated with considering system dynamic frequency control processes. The IEEE-RTS79 is used to verify the proposed models and method. [ABSTRACT FROM AUTHOR]

The increasing demand for high power density requires the power converter to operate in high switching frequency. Silicon carbide (SiC) power module is regarded as one of the most promising candidates for high-frequency applications due to the superior switching speed and low switching loss. With the increase of switching frequency, the switching loss will be the limiting factor of efficiency. Hence, it should be minimized during each switching transition. The optimization of switching loss is normally achieved by the repetitive double pulse test experiments. It is time-consuming to find an optimum gate resistance to achieve the tradeoff between switching loss and electromagnetic interface. In this paper, an accurate subcircuit model for SiC power module is proposed to assist optimization of switching loss in converter design. By considering the device physics and structure, an accurate Miller capacitance model is obtained. Moreover, a parameter extraction procedure is presented, which is based on the datasheet. Good agreements are achieved between the PSpice simulation and experiment. [ABSTRACT FROM AUTHOR]

Multipath transmission control protocol (MPTCP) has attracted significant attention from standardization bodies, industrial communities, and academic communities. However, an important performance-related aspect is that MPTCP is negatively affected by packet reordering, especially in heterogeneous wireless environments. Although to improve the protocol, the proposed updated scheduling policies and congestion control methods do not solve the problem fundamentally. In this context, by breaking the strong binding between data packets and their sequence numbers, network coding has been demonstrated to be a promising solution for end-to-end multipath transmissions. However, current network coding solutions are based on batch coding without exception, and encoding and decoding operations cannot proceed unless all packets of a group have arrived. In addition, frequent generation and transmission of coding coefficients increase the delay and waste the already limited bandwidth. This paper proposes a novel pipeline network coding-based MPTCP (MPTCP-PNC) which reduces encoding and decoding delay and saves bandwidth by using innovative economic coding coefficient rules. Based on these, a quality-based distribution scheme and a corresponding transmission management policy are introduced to further improve the performance of MPTCP-PNC. Simulation tests involving video delivery over a multi-path distribution network show how MPTCP-PNC outperforms other state-of-art network coding solutions. [ABSTRACT FROM PUBLISHER]

Multiple subpixel shifted images (MSIs) from the same area can be incorporated to improve the accuracy of soft-then-hard subpixel mapping (STHSPM). In this paper, a novel method that derives higher resolution MSIs with more spatial–spectral information (MSI-SS) is proposed. First, coarse MSIs produce two high-resolution MSIs for each class respectively by two paths at the same time. The spatial path produces the high-resolution MSIs by soft classification followed by interpolation. And, the other high-resolution MSIs are derived from the spectral path by interpolation followed by soft classification. Then the higher resolution MSIs with more spatial–spectral information for each class are derived by integrating the aforementioned two kinds of high-resolution MSIs by the appropriate weight. Finally, the integrated higher resolution MSIs for each class are used to allocate hard class labels to subpixels. The proposed method is fast and takes more spatial–spectral information of the original MSIs into account. Experiments on three real hyperspectral remote sensing images show that the proposed method produce higher SPM accuracy result. [ABSTRACT FROM PUBLISHER]

In computer vision, many problems can be formulated as binary quadratic programs (BQPs), which are in general NP hard. Finding a solution when the problem is of large size to be of practical interest typically requires relaxation. Semidefinite relaxation usually yields tight bounds, but its computational complexity is high. In this work, we present a semidefinite programming (SDP) formulation for BQPs, with two desirable properties. First, it produces similar bounds to the standard SDP formulation. Second, compared with the conventional SDP formulation, the proposed SDP formulation leads to a considerably more efficient and scalable dual optimization approach. We then propose two solvers, namely, quasi-Newton and smoothing Newton methods, for the simplified dual problem. Both of them are significantly more efficient than standard interior-point methods. Empirically the smoothing Newton solver is faster than the quasi-Newton solver for dense or medium-sized problems, while the quasi-Newton solver is preferable for large sparse/structured problems. [ABSTRACT FROM AUTHOR]

In this brief, a low-temperature microwave annealing (MWA) method is demonstrated for the formation of ohmic contact to AlN/GaN high electron mobility transistors (HEMTs) for the first time. Compared with the traditional rapid thermal annealing (RTA) technique, MWA-HEMT can achieve a comparable low ohmic contact resistance with much smoother surface of ohmic contacts. Transmission electron microscopy results show that no direct current path connecting the 2-D electron gas and the metal is formed. Temperature-dependent contact resistance measurement indicates that field emission tunneling dominates the current transport mechanism in ohmic contact formation. The maximum dc output current density of 1.4 A/mm and the peak extrinsic transconductance ( G\textsf {m} ) of 270 mS/mm are measured on 2 \times 8 \,\,\sf \mu $m^2$ gate MWA-HEMTs. Besides, MWA-HEMTs have higher {I}_{ \mathrm{ ON}}/{I}_{ \mathrm{ OFF}} ratio due to the lower gate leakage current than that of RTA-HEMTs. [ABSTRACT FROM AUTHOR]

The severe bandwidth shortage in conventional microwave bands has spurred the exploration of the millimeter wave (MMW) spectrum for the next revolution in wireless communications. However, there is still a lack of proper channel modeling for the MMW wireless propagation, particularly in the case of outdoor environments. In this paper, we develop a geometry-based stochastic channel model to statistically characterize the effect of all the first-order reflection paths between the transmitter and the receiver. These first-order reflections are generated by the single bounce of signals reflected from the walls of randomly distributed buildings. Based on this geometric model, a closed-form expression for the power delay profile contributed by all the first-order reflection paths is obtained and then used to evaluate their impact on the MMW outdoor propagation characteristics. Numerical results are provided to validate the accuracy of the proposed model under various channel parameter settings. The findings in this paper provide a promising step toward more complex and practical MMW propagation channel modeling. [ABSTRACT FROM PUBLISHER]

This paper is concerned with the channel estimation problem in millimeter wave (mmWave) wireless systems with large antenna arrays. By exploiting the inherent sparse nature of the mmWave channel, we first propose a fast channel estimation (FCE) algorithm based on a novel overlapped beam pattern design, which can increase the amount of information carried by each channel measurement compared to the existing nonoverlapped designs and thus reduce the required channel estimation time. We develop a maximum likelihood estimator to optimally extract the path information from the channel measurements. Then, we propose a novel rate-adaptive channel estimation (RACE) algorithm, which can dynamically adjust the number of channel measurements based on the expected probability of estimation error (PEE). The performance of both proposed algorithms is analyzed. For the FCE algorithm, an approximate closed-form expression for the PEE is derived. For the RACE algorithm, a lower bound for the minimum signal energy-to-noise ratio required for a given number of channel measurements is developed based on the Shannon–Hartley theorem. Simulation results show that the FCE algorithm significantly reduces the number of channel estimation measurements compared to the existing algorithms using nonoverlapped beam patterns. By adopting the RACE algorithm, we can achieve up to a 6 dB gain in signal energy-to-noise ratio for the same PEE compared to the existing algorithms. [ABSTRACT FROM AUTHOR]

We report a multiwavelength mid-infrared laser based on intracavity difference frequency generation in an MgO-doped periodically poled LiNbO3 optical parametric oscillator, which was pumped by a dual-wavelength fiber MOPA consisting of two parts: dual-wavelength seed and power amplifier. The maximum output power of the linearly polarized pump laser was 65.3 W, and the wavelengths were 1060 and 1080 nm. Three idler emissions with different wavelengths of 3127, 3303 and 3346 nm were obtained under the maximum pump power, and the total idler output reached 7.38 W, indicating a 15% pump-to-idler slope efficiency. The signal laser generated in the experiment had two wavelengths, which were 1594 and 1604 nm under the maximum pump power. Three nonlinear progresses occurred in the experiment, two of them being optical parametric oscillation and the one left being difference frequency generation. [ABSTRACT FROM PUBLISHER]

Repetitive control strategies have been commonly applied in pulse-width-modulated (PWM) voltage source inverters (VSIs) for many industrial applications. This paper presents a repetitive controller for voltage harmonic mitigation of VSI-based islanded microgrids. The phase delay in the overall control system, e.g., the delay caused by the digital duty cycle calculation, PWM generation, and repetitive controller, has to be compensated by elaborately designed phase lead filters in order to prevent control performance deterioration and system instability. Nevertheless, quantificational analysis and practical design of the time advance unit in such filters are hardly found in existing literature works. In view of this, this paper proposes an explicit analysis of the phase lead filters and a novel design method of the time advance unit in repetitive controllers to ensure system stability. Moreover, with the help of the proposed method, the overall system stability margin is predictable and improved controller performance is achieved as well. The proposed method is implemented experimentally to show the accurate stability margin calculation as well as the excellent steady state and dynamic performances of the repetitive control scheme. [ABSTRACT FROM PUBLISHER]

Lithium batteries have the characteristics of high energy density and charge–discharge rate, but exhibit high chemical activity. State-of-charge (SOC) estimation is critical to the lithium battery electric vehicle (EV) operation safety. In this paper, a novel SOC estimation method is proposed based on Gaussian process regression. A mixture Gaussian process is used in this model to strengthen the reliability of data description and to increase the estimation accuracy. Optimal number of Gaussian processes is obtained by a revolutionary expectation maximum method. A nonlinear correlation feature selection method is introduced to improve the model efficiency. The effectiveness of the proposed method is verified by an EV field test. Compared with other data-based approaches, this method exhibits higher estimation accuracy and computational efficiency. [ABSTRACT FROM PUBLISHER]

Objective: To model inductive coupling of endovascular coils with transmit RF excitation for selecting coils for MRI-guided interventions. Methods: Independent and computationally efficient FEM models are developed for the endovascular coil, cable, transmit excitation, and imaging domain. Electromagnetic and circuit solvers are coupled to simulate net B1 + fields and induced currents and voltages. Our models are validated using the Bloch–Siegert B1 + mapping sequence for a series-tuned multimode coil, capable of tracking, wireless visualization, and high-resolution endovascular imaging. Results: Validation shows good agreement at 24-, 28-, and 34-μT background RF excitation within experimental limitations. Quantitative coil performance metrics agree with simulation. A parametric study demonstrates tradeoff in coil performance metrics when varying number of coil turns. Tracking, imaging, and wireless marker multimode coil features and their integration is demonstrated in a pig study. Conclusion: Developed models for the multimode coil were successfully validated. Modeling for geometric optimization and coil selection serves as a precursor to time consuming and expensive experiments. Specific applications demonstrated include parametric optimization, coil selection for a cardiac intervention, and an animal imaging experiment. Significance: Our modular, adaptable, and computationally efficient modeling approach enables rapid comparison, selection, and optimization of inductively coupled coils for MRI-guided interventions. [ABSTRACT FROM PUBLISHER]

Large-scale adoption of moving electric vehicle (EV) loads significantly accelerates the integration of power and traffic systems. This paper proposes an approach to assess and alleviate the impacts of stochastic EV charging and movement in an integrated power and traffic system. Level of Congestion (LoC), Nodal Voltage Deviation (NVD) and Energy Loss Rate (ELR) are proposed as nodal indices to spatially and temporally assess the impacts due to the inter-node movement of EVs on power system operation. Nodal Time-of-Use (NTOU) price and Road Traffic Congestion (RTC) price are developed to shift the charging and movement of EV loads. EV driver's charging and driving decisions are modeled by fuzzy logic inference system in response to NTOU and RTC prices. Two transportation systems have been developed and integrated with the Roy Billinton test power system (RBTS) to illustrate the proposed technique and model. [ABSTRACT FROM PUBLISHER]

A small optical fiber temperature sensor employing the fluorescence lifetime of Mn4+ doped oxyfluoride germanate phosphor was presented and experimentally demonstrated, which has a fairly good temperature measurement precision. The performance of the fluorescent materials for temperature measurement was compared and analyzed. A small temperature sensing probe with a diameter of 1.8 mm was proposed. For the first time, the integrated tee-light-path structure was put forward, the transmission and separation of excitation light and fluorescence in only a single optical path was realized. Experimental results showed that standard deviation errors of 0.45 °C were obtained within the temperature range from 0 °C to 90 °C. [ABSTRACT FROM PUBLISHER]

This paper describes the prototype design of an external bypass that provides protection for the ITER poloidal field converter and magnets in fault conditions. The maximum peak pulse current of the bypass will reach to about 350 kA in the worst case. Three kinds of arm structures are compared according to the design requirement and the specific circumstances of branches. The structure, whose current flows in and out on the same side, is selected and combined with the installation and location. The external bypass structure model is analyzed and compared through analytical and numerical methods. Then a 3-D numerical model of an electromagnetic field is established based on Maxwell. Now a full prototype has been manufactured by China, and the dynamic stability test of the prototype has also been accomplished successfully. It shows that the prototype design can fully satisfy the design requirement and the reliability has been improved. [ABSTRACT FROM AUTHOR]

This paper presents the design and testing of the full scale prototype of the international thermonuclear experimental reactor (ITER) poloidial field converter unit (PFCU), which is mainly composed of converter transformer, converter module, external bypass, and dc reactors with a rated capacity of 82 MVA and a rated dc current of 55 kA. Considering the space limitation, the high safety and reliability requirements, the nonsame-phase antiparallel connection structure, and the fault suppression capability criterion are applied in the prototype design. After the completion of the preliminary design of the PFCU in summer 2012, the detailed prototype structure design and the manufacturing of the PFCU were launched and completed at the end of 2013, then the following main type tests, including short circuit current test and temperature rise test on the main components of the PFCU, have been done on the ITER power supply test platform at ASIPP site. In addition, the PFCU integration test has also been done to verify the system operation performance. The prototype test results are well in compliance with the design requirements of the ITER PF converter system. It indicates that the full scale prototype research and development of PFCU has been accomplished successfully. [ABSTRACT FROM AUTHOR]

Transient electromagnetic scattering by composite structures is formulated by time-domain combined field integral equations (TDCFIEs). Traditionally, the TDCFIEs are solved by combining the method of moments (MoMs) in space domain and march-on-intime (MoT) scheme in time domain. The space-domain MoM requires two basic functions to represent the electric and magnetic current densities on material interfaces, respectively, and the conventional choice of \hat n\times \mathrm RWG basis function for representing the magnetic current density may not be good in the TDCFIEs. In addition, the MoT scheme has a well-known late-time instability problem, which will aggravate in the surface integral equations with penetrable media. In this communication, the TDCFIEs for composite structures are solved by a different approach in which the Nyström method is used to discretize the space domain, while the Galerkin method with Laguerre basis and testing functions is employed to discretize the time domain. The proposed approach can fully overcome the drawbacks of the traditional approach as demonstrated by numerical examples. [ABSTRACT FROM AUTHOR]

In this paper, we consider the low-cost design for point-to-point millimeter-wave (mmW) multiple-input–multiple-output (MIMO) systems in rainfall environments. We first show that rain does not always have a negative impact on system performance, provided that accurate instantaneous channel state information (CSI) is available at both the transmitter and receiver. In addition, we propose a practical and low-cost transmission scheme, referred to as hardware-constrained statistical precoding (HC-SP), for mmW MIMO systems in rainfall environments. This scheme only requires statistical channel information at the transmitter and takes into consideration the hardware constraints on transceiver imposed by the high radio-frequency chain cost. Simulation results demonstrate that the HC-SP scheme allows the mmW MIMO system to have near-optimal performance. [ABSTRACT FROM AUTHOR]

This brief presents an inverter-based low-noise single-ended to differential continuous-time variable gain amplifier (VGA) for 2–6-MHz second harmonic cardiac ultrasound imaging probes. The proposed VGA is based on a transimpedance amplifier and composed of resistive arrays and three equal inverters to form the resistive feedback loop. The inverters operate in the class C mode by being biased in the subthreshold region to improve both the power and noise performances of the VGA. The 6-bit thermometer resistive arrays can control the gain range from −1 to 21 dB for a 2-D piezoelectric transducer (PZT) model, and for a 50- \Omega source resistor, the gain range is from 20 to 26 dB. The second harmonic distortion (HD2) is lower than −55 dB in most cases due to the single-ended to differential conversion, and the equivalent input referred noise is 7 \text{nV}/\sqrt{\text{Hz}} at 5 MHz with the maximum gain. The VGA is fabricated in 65-nm CMOS technology and has the power consumption of 54 \mu\text{W}$ at a supply voltage of 0.5 V. The die size of the VGA is 154\ \mu\text{m} \times 102\ \mu\text{m}. [ABSTRACT FROM PUBLISHER]

A precise robotic assembly for large-scale objects is an important application in manufacture. In this paper, we design a new assembly system for large-scale objects based on automatic guidance and alignment with two cameras and three laser distance sensors. The corresponding strategy consists of three stages. First, the object is guided from a remote position to a close one based on our proposed link-line model-based polygon detection and Computer Aided Design (CAD) - View method. Second, the object is aligned to the installation framework based on the proposed visual and laser alignment method. Finally, the object is automatically inserted into the installation framework. An accurate easily applying and close-loop hand-eye calibration method is also proposed. The proposed assembly system has high assembly precision and efficiency. In our test for a 710 \text mm \times 625 mm optical module, the maximum 6-DOF localization error of guidance and alignment is 0.53 mm in translation and 0.10° in orientation. The mechanical constraint-based controlling accuracy, i.e., the final assembly accuracy, is up to 0.2 mm in translation. [ABSTRACT FROM PUBLISHER]

Parameter estimation of internal solitary waves (ISWs) is an important application of oceanic synthetic aperture radar (SAR) images. Several methods have been widely applied for estimating the parameters of ISWs. Most of these methods assume that the ISW signals are corrupted by additive receiver noise. However, the ISW signals in SAR images suffer from both additive (thermal) and multiplicative (speckle) noises. Therefore, the estimation accuracy of previously proposed methods could not reach the Cramér–Rao bound (CRB). This paper proposes an optimal parameter estimation method of ISWs and derives the CRB for parameter estimation of ISWs. The variances of the estimated ISW parameters are shown to reach the CRB. This optimum estimator is validated using ISW SAR signals taken from simulation data and European Remote Sensing 2 (ERS-2) images. The results show that the proposed method is more accurate and effective than other methods. In addition, it should be noted that this optimality could also refer to parameter estimation of other SAR extended targets with an analytical expression. [ABSTRACT FROM AUTHOR]

In this paper, we propose an approach to realize substrate integrated waveguide (SIW)-based leaky-wave antennas (LWAs) supporting continuous beam scanning from backward to forward above the cutoff frequency. First, through phase delay analysis, it was found that SIWs with straight transverse slots support backward and forward radiation of the $-1$-order mode with an open-stopband (OSB) in between. Subsequently, by introducing additional longitudinal slots as parallel components, the OSB can be suppressed, leading to continuous beam scanning at least from $-40^\circ$ through broadside to 35°. The proposed method only requires a planar structure and obtains less dispersive beam scanning compared with a composite right/left-handed (CRLH) LWA. Both simulations and measurements verify the intended beam scanning operation while verifying the underlying theory. [ABSTRACT FROM PUBLISHER]