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The utilization of voltage-source converter-based multi-terminal HVDC (VSC-MTDC) technology has been envisaged as a cost-effective solution to transmit bulk renewables from multiple sending ends to receiving-end AC systems. However, with complex configurations and various types of components, the reliability evaluation of a VSC-MTDC system is more complicated than that of a conventional HVDC system. In addition, due to stochastic failures and complex operating modes, the application of a VSC-MTDC system can have a significant influence on the reliability of hybrid AC/DC power systems. This paper presents a new technique for evaluating the nodal reliability of a hybrid AC/DC power system based on the VSC-MTDC system. The proposed technique is incorporated within a multi-state model for the VSC-MTDC system. Then, an optimization model for contingency management of a hybrid AC/DC power system is formulated. The model is established based on the optimal power flow technique for a VSC-MTDC based hybrid AC/DC power system. The objective of the model is to minimize the total system cost when determining the load curtailment and generation re-dispatch results for each contingency state. Nodal reliability indices for hybrid AC/DC power systems are proposed to evaluate the reliability performance of customers at each node. The effectiveness of the proposed methods is validated using a modified IEEE reliability test system. [ABSTRACT FROM AUTHOR]

Power loss and voltage regulation are two fundamental and challenging issues in DC distributed generation system. In this paper, a multi-objective optimization problem is established to achieve trade-offs between reducing power loss and decreasing voltage deterioration by adjusting the weighting coefficients. This problem is proven to be a convex optimization under constant impedance load and constant current load. A distributed algorithm based on random coordinate descent method is developed to solve this problem without acquiring the information of line impedance. Thus, the optimal operating point of the system can be found automatically in real-time, and the deviation of optimal solution caused by the fluctuation of network parameters is avoided. In addition, the complexity of this algorithm is low and its computational requirement is reduced in practice. Finally, case studies are implemented to verify the effectiveness of the proposed algorithm under the scenarios of line parameter fluctuation, load variation, communication line failure, and plug-play capabilities. [ABSTRACT FROM AUTHOR]

This paper proposes a semi-consensus strategy for multi-functional hybrid energy storage systems (HESSs) in DC microgrids. Batteries in a HESS are regulated by conventional V-P droops and supercapacitors (SCs) are with integral droops (ID). Only batteries are assigned with local distributed compensators which exchange information through sparse communication links. Those SCs are exempted from data exchange process, which would save system investment costs. Within the semi-consensus scheme, the most essential function is the cooperation of V-P droop and ID that helps to naturally allocate low frequency components of load power to batteries and high frequency components to SCs, thus prolonging the overall life time of HESS. In addition to the transient power allocation function, there are other three functions endowed by the proposed strategy, which are autonomous DC bus voltage recovery to its nominal level, spontaneous SC state of charge (SOC) restoration, autonomous power sharing and SOC balancing among batteries. It is the simultaneous realization of above four functions with limit communications that makes up the main contributions in this paper. A generic mathematical modeling of HESS with the semi-consensus strategy is established. The model allows for dynamic analyses to theoretically validate the effectiveness of proposed method in both frequency and time domains. In-house experimental results are shown fully consistent with the dynamic analyses and also effectively corroborate the intended HESS multi-functional operations. [ABSTRACT FROM AUTHOR]

SIN is constructed to support real-time data acquisition, massive data transmission and processing, and systematized information services. Different from static networks, both the network topologies and the available network resources are dynamic in SIN. However, the existing networking technologies treat SIN as segmented static networks, and ignore the relationship among different segmented subnetworks, which results in low resource utilization and poor transmission QoS. This article exploits the time-varying graph theory to characterize and allocate the dynamic resources of SIN. We first introduce the overall SIN architecture, and discuss its key technologies in terms of network slicing and dynamic routing. Then, we construct a novel STAG to precisely depict the multi-dimensional time-varying resources and reveal their connection relationships in SIN. With STAG, we propose the dynamic network slicing strategy to build the dedicated network slices for different services, and design the intra-slice routing scheme to guarantee the service transmission QoS. Simulation results demonstrate our methods can complete more space missions with higher resource utilization. Finally, we discuss the promising future of the time-varying graph theory. [ABSTRACT FROM AUTHOR]

Considering the high cost and complexity of multiple-channel blind source separation, single-channel solutions have elicited a significant amount of interest in source separation. Joint maximum likelihood sequence estimation implemented by the Viterbi algorithm (VA) is a seemingly ultimate solution to the problem of data transmission over dispersive channels. However, both joint reduced-state sequence estimation (JRSSE) and joint delayed-decision feedback sequence estimation (JDDFSE) have numerous shortcomings when applied to single-channel blind signal separation. Hence, joint double-direction DDFSE (JDD-DDFSE) is proposed in this article. JDD-DDFSE employs joint VA (JVA) of the low-order channel twice. The estimated symbols from the initial JVA are utilized to equalize the causal and non-causal taps of the channel beyond the trellis state in the second JVA. A method that can derive the log likelihood ratio of the estimated symbols is provided; the complexity of this method is considerably lower than that of soft-output VA or the BCJR algorithm. Hence, the entire computation complexity of the iterative separation structure basically remains unchanged compared with that of the no-iteration structure. For the non-causal channel, the proposed algorithm has the lowest computation complexity and demonstrates a separation performance similar to that of conventional JVA, JRSSE, and JDDFSE algorithms. [ABSTRACT FROM AUTHOR]

Effective detection of multifaults in bearings and gears is a challenging issue in rotary machinery health monitoring. As such, a generalized Vold–Kalman filtering (GVKF)-based compound faults diagnosis method is presented in this paper. The technique includes four main steps: 1) a time–frequency ridge is separated from the time–frequency representation (TFR) of the vibration signal using a peak search method; 2) according to the time–frequency ridge, GVKF parameters corresponding to all the fault characteristic frequencies (FCFs) are estimated; 3) the fault feature components are obtained using the generalized demodulation transform (GDT) and the VKF with the GVKF parameters; and 4) the spectra obtained by the fast Fourier transform (FFT) are used to fault detection. The main contributions of the proposed method are as follows: 1) the influence of speed fluctuations and the unrelated harmonic components are removed through the integration of the GDT and the VKF and 2) the tachometerless GVKF parameters are defined and calculated to quantitatively detect different fault types, which avoids missed diagnosis and misdiagnosis. The proposed multifault diagnosis algorithm is verified by both simulation and experiment data. Comparison with other commonly used techniques has shown the advantage of the new method. [ABSTRACT FROM AUTHOR]

A virtual synchronous generator (VSG) control based on adaptive virtual inertia is proposed to improve dynamic frequency regulation of microgrid. When the system frequency deviates from the nominal steady-state value, the adaptive inertia control can exhibit a large inertia to slow the dynamic process and, thus, improve frequency nadir. And when the system frequency starts to return, a small inertia is shaped to accelerate system dynamics with a quick transient process. As a result, this flexible inertia property combines the merits of large inertia and small inertia, which contributes to the improvement of dynamic frequency response. The stability of the proposed algorithm is proved by Lyapunov stability theory, and the guidelines on the key control parameters are provided. Finally, both hardware-in-the-loop and experimental results demonstrate the effectiveness of the proposed control algorithm. [ABSTRACT FROM AUTHOR]

Electromagnetic pulse (EMP)-induced nonlinear degradation of an L-band gallium arsenide-based low-noise amplifier (LNA) is studied by an injection experiment, failure analysis, and mixed-mode simulation. The experimental results indicate that the real-time response, radio frequency, and direct current characteristic of LNA samples under an EMP show nonlinear and permanent degradation features. In detail, the characteristics first degrade and then recover slightly as the injection power increases. In addition, the nonlinear degradation shows a close dependence on the pulse properties. Failure analysis reveals that the degradation of the LNA is attributed to latent failure defects under and around the gate metal strip of the first-stage high electron mobility transistor, with recovery well interpreted by an EMP-induced “annealing effect.” Simulation results show that if the pulse repetition frequency is smaller than 2.5 kHz, a pulse repetition-induced thermal accumulation effect will not occur and that the pulsewidth τ will mainly determine the actual action duration and the temperature of the “annealing effect.” Based on the above mechanism, the dependence of the pulse properties on nonlinear degradation is well explained. [ABSTRACT FROM AUTHOR]

With ground-based synthetic aperture radar (GB-SAR) discontinuous observation, the effect of rail error, caused by multiple installations, on imaging is difficult to eliminate with difference correction. In this article, the impact of rail error on each point, which is related to the incident angle of each point, is theoretically analyzed. This is the first attempt to introduce a baseline in the application of GB-SAR microdeformation to build a model that estimates the incident angle of each point in the image. Then, the rail error correction model is established using the incident angle, and the influence of the rail error on the image point is weakened using this model. The experimental results show that the precision of the estimated incidence angle cosine is 0.0132, which is comparable to the same angle cosine value measured by the total station. By applying the correction method in this article, different impacts of each point in the image, caused by rail error from multiple instrument installations, can be weakened to below 0.1 mm, meeting the requirement of GB-SAR microdeformation measurement submillimeter accuracy. [ABSTRACT FROM AUTHOR]

High penetration of renewable energies through fast-response power converters results in a considerable displacement of conventional synchronous generators and losing of system inertia for frequency control. Modular multilevel converters (MMCs) can be employed serving as an interface between the large-scale renewable generation and power grids. In a microgrid with high shares of renewables integrating through MMCs, submodule (SM) capacitors can be used as energy storage to provide a degree of synthetic inertia for system frequency support. This paper quantitatively exploits the MMC synthetic inertia in a microgrid with flexible renewable penetration levels. An MMC inertia coefficient concept is proposed. It is mainly affected by the penetration ratio, the SM capacitance, and the modulation index of an MMC, with the system operation constraints. According to the analysis, a substantial portion of system inertia can be provided by properly designed MMCs. Detailed MMC frequency control loops are presented. The capacitor average voltage is proportionally linked to the frequency deviation, in order to flexibly adjust the capacitor energy during frequency events. The MMC output active power is deliberately and simultaneously regulated according to the capacitor energy change rate. By controlling the MMC capacitor voltage, dc side power, and output active power, an amount of energy can be released or absorbed by SM capacitors to improve the system frequency response during the frequency event transients, while the renewable generation is scarcely influenced. The proposed concept is experimentally verified and the results show that, with proper system parameters and control loops, the line frequency deviation and the rate of change of frequency can be significantly reduced. Good agreements of the system frequency characteristics have been achieved between the theoretical calculation and experimental results. [ABSTRACT FROM AUTHOR]

Memristors with small size, fast speed, low power, CMOS compatibility and nonvolatile modulation of device resistance are promising candidates for the next-generation data storage and in-memory logic computing paradigm. In comparison to the binary logics enabled by memristor devices, multi-valued logics can provide higher computation efficiency with simple operation scheme, reduced circuit complexity, and smaller chip area. In this contribution, we demonstrate that all the 27 univariate ternary logic operations can be realized with a single ZnO three-state resistive switching memristor in at most three steps. The nonvolatile modulation characteristics of the memristor allow the read step to be independent of the logic operation and capacitate logic-in-memory applications. The present methodology could be beneficial for constructing future high-performance computation architectures. [ABSTRACT FROM AUTHOR]

This paper introduces a novel H-bridge structured ac–ac pulsewidth modulation (PWM) converter topology based on two-level non-differential ac chopper legs, which can work at the non-inverting and inverting modes for the utility voltage compensation. Compared to the traditional bipolar-type H-bridge ac–ac converter, no bidirectional switches are switched in a complementary manner to overcome the commutation problem due to the delayed response of electronic circuits and semiconductor switching devices. The detailed PWM control signals and operational principles are presented to regulate the output voltage in a bipolar manner. Especially the main advantage is that the proposed ac–ac converter has the same buck/boost operation process for non-inverting and inverting modes, which ensures the continuously average current supply to the low-voltage output side without a high-value capacitor to support power. Additionally, due to the common sharing ground of the input and output, the feature that output can reverse or maintain phase angle with input is supported well. Then, the detailed analysis, design conditions, and experimental verification based on a 1 kW experimental prototype are presented. [ABSTRACT FROM AUTHOR]

Recently, hyperspectral image (HSI) classification approaches based on deep learning (DL) models have been proposed and shown promising performance. However, because of very limited available training samples and massive model parameters, DL methods may suffer from overfitting. In this paper, we propose an end-to-end 3-D lightweight convolutional neural network (CNN) (abbreviated as 3-D-LWNet) for limited samples-based HSI classification. Compared with conventional 3-D-CNN models, the proposed 3-D-LWNet has a deeper network structure, less parameters, and lower computation cost, resulting in better classification performance. To further alleviate the small sample problem, we also propose two transfer learning strategies: 1) cross-sensor strategy, in which we pretrain a 3-D model in the source HSI data sets containing a greater number of labeled samples and then transfer it to the target HSI data sets and 2) cross-modal strategy, in which we pretrain a 3-D model in the 2-D RGB image data sets containing a large number of samples and then transfer it to the target HSI data sets. In contrast to previous approaches, we do not impose restrictions over the source data sets, in which they do not have to be collected by the same sensors as the target data sets. Experiments on three public HSI data sets captured by different sensors demonstrate that our model achieves competitive performance for HSI classification compared to several state-of-the-art methods. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) generators have continuously increased in recent years, whose power is usually controlled through the perturbation and observation (P&O) method. In essence, the P&O method is nonlinear and discontinuous. Hence, the conventional small-signal stability analysis is not suitable anymore when the influence of the P&O-based power control is considered. Focusing on this problem, this paper adopts the nonlinear describing function (DF) method to conduct the accurate stability analysis of PV generators with consideration of P&O-based power control. The detailed procedures about the DF method are introduced, and then the related influence factors like perturbation size, filters, and so on are analyzed quantitatively. Furthermore, the comparison with the conventional stability analysis methods is made, which suggests that the DF method can effectively enhance the accuracy of the stability analysis. All the conclusions are verified by the real-time hardware-in-loop tests. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) is the main sign of the insulation deterioration; therefore, the online PD localization of the power transformers can provide the equipment degradation characteristics and has great value for the power grid. Because of some unique merits, acoustic PD detection is one of the best options for such applications. However, when discharges happen inside the windings, precise PD localization by acoustic method becomes very challenging. As the acoustic PD signal can be reverberated and distorted along its propagation, the type and number of sensors, with their installation, should be carefully studied and selected. In this paper, the acoustic wave propagation inside the transformer is explored via numerical simulation. Based on the understanding of wave propagation, a novel-structure fiber-optic acoustic sensor array is properly designed and installed into one phase winding, which is from a real 35 kV transformer. Experimental verification shows that, by using this proposed design, PD localization with less than 5-cm error can be achieved. Therefore, the novel sensor array developed in this paper, together with the installation and localization method, unveils a novel access to accurate online PD localization, especially for those PDs which happen inside transformer windings. [ABSTRACT FROM AUTHOR]

Modern aircrafts are evolving toward more electric aircraft (MEA), resulting in greater reliance on the electrical system for safe flight. On-board power system of MEA integrates a large number of power electronic converters, and it is reported that semiconductor devices and electrolytic capacitors in power converters are the most vulnerable links impacted by loading conditions; thus, reliability becomes a critical concern in an MEA power system. This paper proposes a hierarchical approach for systematic reliability modeling and evaluation for the on-board power system of MEAs. It consists of three hierarchical levels (HLs): component level (HL1), subsystem level (HL2), and system level (HL3). In HL1, failure rates of power electronic components are modeled considering relevant inner structure and loading conditions; in HL2, the reliability of individual subsystems such as converters are constructed; in HL3, the system reliability is quantified based on the network architecture and reliability of the subsystems. The impacts of different parts (components/subsystems) on the overall system are assessed effectively with the identification of the vulnerable parts. This also provides a guideline for reliability enhancement by using thermal control techniques, adding redundancies or performing maintenance on the vulnerable parts to ensure the satisfactory of system reliability requirements. The proposed method is demonstrated on the future MEA power system architectures (hybrid ac–dc architecture and HVdc architecture). [ABSTRACT FROM AUTHOR]

The digital control system of modular multilevel converters (MMCs) normally synchronizes with the switching actions. The switching frequency of an MMC is generally selected as low as possible from an efficiency point of view, which leads to an unavoidable and relatively long time delay in the control system. Such a time delay might deteriorate the MMC performance and even reduce the stability margin by introducing infinite uncertain eigenvalues into the system state functions. Without a proper time-delay model and quantitative system stability analyses, MMCs might suffer from uncertainties and unstable risks during their operations, especially when the switching frequency is low. This paper derives an MMC model considering the time delay in the digital control system. A Padé-based stability analysis method is then proposed, which consists of three steps: information integration and critical eigenvalue extraction, and trajectory visualization and critical angle (CA) calculation, and quantitative assessment and extreme value determination. By the proposed model and method, the critical eigenvalue can be effectively extracted. With the Hopf bifurcation, the time delay in the digital control system induces a pair critical conjugate eigenvalues into MMC systems, which is detected as an instability cause. The CA and the critical impact are defined to quantitatively assess the stability, while selecting the controller parameters and minimum switching frequency. The proposed method for the MMC stability assessment is experimentally verified. [ABSTRACT FROM AUTHOR]

This paper introduces a compensation strategy to deal with both current and voltage measurement errors in the three-phase pulsewidth modulated rectifier system. 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 current and subsequently lead to voltage ripple at the dc output voltage. 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 characteristic of the dc output voltage ripple combining with simple band-pass and low-pass filters. Meanwhile, an advanced current controller designed with a proportional integral plus two resonant controllers tuned at the fundamental grid frequency $({{\omega _s}})$ and $2{\omega _s}$ in the synchronous (d–q) reference frame is suggested to reject the impact of the dc offset and scaling errors in the voltage measurement. 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]

The rapidly developing data center industry results in a large amount of energy consumption. Considering its unique demand characteristics, it becomes desirable to improve its energy efficiency by reusing its waste heat. In this paper, an integrated energy management scheme is proposed to optimize the operation cost for a data center microgrid. The waste heat recovered from data center operation is optimally scheduled with other resources in the integrated energy management model to minimize the operation cost of data center microgrid. Taking the uncertain nature of renewable supply, power and heat demand into consideration, a two-stage stochastic programming model is formulated and analyzed under different test cases. The numerical study results demonstrate the effectiveness of the proposed integrated energy management model. [ABSTRACT FROM AUTHOR]

CLLC-type dc transformer (CLLC-DCT) is very popular in the hybrid ac–dc microgrid thanks to its high-power density advantage and good bidirectional power transfer capacity. In the hybrid ac/dc microgrid, the open-loop control is always utilized by the CLLC-DCT to cooperate with the bidirectional interlinking converter to realize the power and voltage conversion between the ac and dc bus. This paper first studies the circuit parameters design of the open-loop controlled CLLC-DCT with consideration of such a realistic problem: The real inductors/capacitors values are actually different with their theoretically designed values due to the operation power and temperature variation. To solve this problem, a robust circuit parameters design scheme is proposed for the CLLC-DCT in this paper. With the proposed scheme, the designed CLLC-DCT exhibits good power transmission and voltage regulation ability in the hybrid ac/dc microgrid even when its actual inductors/capacitors values vary with the practical power and temperature. The robust design method is experimentally verified in a hybrid ac/dc microgrid prototype. [ABSTRACT FROM AUTHOR]

Internet data centers are booming in the last few years, leading to gigantic amount of energy consumption and greenhouse gas emission. In this paper, a data center microgrid including conventional units, energy storage, and renewable generation is modeled to optimize its electricity bill and carbon footprint. Considering the randomness of electricity price, renewable output and workload distribution, the volatility risk is incorporated to measure the associated operation risk. Then, a day-ahead emission-aware stochastic resource planning scheme is formulated to decide the strategy on power procurement, energy storage operation, batch workload allocation, and unit commitment of conventional units. Simulation results show the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

In this paper, we propose and develop a leaky-wave antenna (LWA) by periodically loading shunt radiation element pairs along a host transmission line (TL). Each pair of radiation unit consists of one capacitive element and one inductive element, which are susceptance-complementary with each other. The complementary radiation element loading leads to an effective open-stopband (OSB) suppression, thereby facilitating a continuous leaky-wave beam scanning from backward, through broadside, to forward. Compared with the previously studied OSB-suppressed LWAs containing only one type of susceptive radiation elements, the proposed LWA features two unique properties: constant radiation efficiency over the operation band, and unit cell period only related to the host TL regardless of parameter values of the radiation elements. The aperture synthesis of the proposed LWA is hence straightforward as the radiation elements can be designed to be equally spaced. Experimental prototypes are designed and fabricated based on microstrip line structure as a proof of concept. Desired measured results agree well with the theoretical predictions. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

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]

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]

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 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]

Unidirectional inductive power transfer systems allow loads to consume power, while bidirectional inductive power transfer (BIPT) systems are more suitable for loads requiring two-way power flow such as vehicle to grid applications with electric vehicles. Many attempts have been made to improve the performance of BIPT systems. In a typical BIPT system, the output power is controlled using the pickup converter phase shift angle, while the primary converter regulates the input current. This paper proposes an optimized phase-shift modulation strategy to minimize the coil losses of a series–series compensated BIPT system. In addition, a comprehensive study on the impact of power converters on the overall efficiency of the system is also presented. A closed-loop controller is proposed to optimize the overall efficiency of the BIPT system. Theoretical results are presented in comparison to both simulations and measurements of a 0.5 kW prototype to show the benefits of the proposed concept. Results convincingly demonstrate the applicability of the proposed system offering high efficiency over a wide range of output power. [ABSTRACT FROM AUTHOR]

It is known that in addition to spectrum sparsity, spatial sparsity can also be used to further enhance spectral utilization in cognitive radio systems. To achieve that, secondary users (SUs) must know the locations and signal strength distributions (SSDs) of primary users' base stations (PUBSs). Recently, a group sparse total least squares method was developed to cooperatively sense the PUBSs' signal strength and estimate their locations. It approximates PUBSs' power decay with a path loss model (PLM), assumes PUBSs' locations on some grid points, and then accomplishes the estimation tasks. However, the parameters of the PLM have to be known in advance, and the accuracy of the location estimation is bounded by the resolution of the grid points, which limit its practical applications. In this paper, we propose a sparse Bayesian learning method to solve the problems. We use a Laplacian function to model the power decay of a PUBS and then derive learning rules to estimate corresponding parameters. The distinct features of the proposed method are that most parameters are adaptively estimated, and little prior information is needed. To further enhance the performance, we incorporate source number detection methods in the proposed algorithm such that the number of the PUBSs can be precisely detected, facilitating the estimation of PUBSs' locations and SSDs. Moreover, the proposed algorithm is modified into a recursive mode to adapt to SUs' mobility and time-variant observations. Simulations show that the proposed algorithm has good performance, even when the spatial measurement rate is low. [ABSTRACT FROM PUBLISHER]

A semifloating-gate transistor had been proposed and its memory function has been demonstrated recently. In this paper, we further investigate its temperature dependency, device scalability, and device modeling. The high-temperature behavior is studied by measuring its endurance, retention, and disturbance immunity at 85 °C. The device scalability down to the 14-nm technology node is investigated by simulation. Its macrodevice model for circuit design is also developed. Finally, a memory array with the specific peripheral circuits is designed using the device model developed in this paper. [ABSTRACT FROM AUTHOR]

An online measurement system based on Kerr electro-optical effect is developed to investigate the surface electric field of insulator stressed by high-voltage (HV) pulse in vacuum. A basic principle of Kerr effect is narrated. According to this principle, a circular optical polarization configuration is arranged to detect the phase difference caused by Kerr effect. An 180-kV Marx generator and an HV cable serving as pulse-forming line are utilized to output an HV pulse stressing on insulator specimen in Kerr cell. In addition, a synchronous controlling apparatus is developed to make sure that an online measurement on surface electric field is performed during the HV pulse being stressed on the insulator. As a result, distortion of surface electric field of insulator is observed in experiments preliminarily. [ABSTRACT FROM PUBLISHER]

Polyimide nano-composite film (Kapton 100CR) is a special type of engineering plastic film, which is widely used in turn insulation of form-wound inverter-fed motor. Partial discharge (PD) caused by high-frequency surge impulse is one of the key factors leading to premature failure of turn insulation of inverter-fed motors. Aging experiments on turn insulation samples under repetitive bipolar square impulse voltage were carried out in this study. Experimental results show that, in the presence of PD, the damage to the structure of the polyimide nano-composite film under impulse voltage is concentrated on the surface layer of the sample. Moreover, the results indicate that with the increase of aging time, the discharge phase distribution becomes broader. Therefore, the appearance of the discharge at higher phase would be the reflection that the insulation of the sample reaches its terminal stage. Surface microscopic images taken by the scanning electron microscope (SEM) show that, because of PD erosion, the polymer matrix was carbonized and volatilized, the residual nano-fillers remained on the surface and formed a screen layer to resist further damages caused by PDs. It is a symbol that faults expand rapidly when the floccules and voids appear on the surface layer, which indicates the insulation could be breakdown soon. [ABSTRACT FROM AUTHOR]

The area, temperature (160–300 K), and bias polarity dependences of the I–V curves of the self-rectifying n+Si-HfO2–Ni resistance random access memory (RRAM) have been measured systematically. The complementary nonrectifying p+Si-HfO2–Ni RRAM I–V data are also provided for reference. To explain all experimental data, three resistances in series in the RRAM device: 1) the Si-HfO2 contact resistance R \(_{\mathrm {Si-HfO}}\) ; 2) the HfO2 dielectric resistance RHfO; and 3) the HfO2– \(Ni\) contact resistance RHfO-Ni must be considered on an equal footing. Previously reported first principle calculation results for the density of states of the monoclinic HfO2 grain boundary with high and low densities of oxygen vacancy V \(_{O}^{0}\) are adopted for describing the conductive filament resistance RHfO of the dielectric at low- and high-resistance states. The temperature dependence of I–V is controlled by three different energy barriers: Schottky-like barrier, multiphonon trap assisted tunneling barrier, and multiphonon deep trap capture barrier (ECAPTURE). It is demonstrated that all experimental data can be explained in a natural and unified way. This model is valuable not only for understanding the conduction mechanism, but also for guiding the future self-rectifying RRAM technology development. [ABSTRACT FROM AUTHOR]

How to build a text knowledge representation model, which carries rich knowledge and has a flexible reasoning ability as well as can be automatically constructed with a low computational complexity, is a fundamental challenge for reasoning-based knowledge services, especially with the rapid growth of web resources. However, current text knowledge representation models either lose much knowledge [e.g., vector space model (VSM)] or have a high complex computation [e.g., latent Dirichlet allocation (LDA)]; even some of them cannot be constructed automatically [e.g., web ontology language, (OWL)]. In this paper, a novel text knowledge representation model, power series representation (PSR) model, which has a low complex computation in text knowledge constructing process, is proposed to leverage the contradiction between carrying rich knowledge and automatic construction. First, concept algebra of human concept learning is developed to represent text knowledge as the form of power series. Then, degree-2 power series hypothesis is introduced to simplify the proposed PSR model, which can be automatically constructed with a lower complex computation and has more knowledge than the VSM and LDA. After that, degree-2 power series hypothesis-based reasoning operations are developed, which provide a more flexible reasoning ability than OWL and LDA. Furthermore, experiments and comparisons with current knowledge representation models show that our model has better characteristics than others when representing text knowledge. Finally, a demo is given to indicate that PSR model has a good prospect over the area of web semantic search. [ABSTRACT FROM PUBLISHER]

The insulation system of a dry-type transformer under the combined thermal, electrical, mechanical, and environmental stresses undergoes gradual deterioration, which ultimately leads to transformer failure. It is hence important to test specimen insulation of transformer coil so as to explore the aging law and the associated characteristic parameters related to the insulation condition. This paper proposes a method to evaluate reliability of the insulation system of a dry-type transformer based on the three models of degradation, regression and expert judgment. The three models are developed based on the quality parameters (QPs) from the lab tests. The method is illustrated by estimating the reliability of the insulation system of a mining flameproof dry-type transformer. The accelerated aging tests on the Nomex paper (i.e. the turn-to-turn insulation of the transformer) are conducted. The QPs of the Nomex samples of degree of polymerization, partial discharges, and photomicrograph were measured periodically during aging test. The effectiveness of the proposed method was proved through the lab experiments. The results show that the parameters from the aging test can be used to represent the condition of the insulation system. [ABSTRACT FROM PUBLISHER]

Based on the decentralized sliding mode control, a load frequency controller is designed in this paper for multi-area interconnected power systems with matching and unmatched uncertainties. The proportional and integral switching surface is constructed for each area to improve system dynamic performance in reaching intervals. The robust controller is proposed by the reaching law method to assure that frequency fluctuation converges to zero after a load and operation point variation. A three-area interconnected power system is studied to illustrate the effectiveness of the proposed decentralized sliding mode control scheme. [ABSTRACT FROM PUBLISHER]

Due to the growing demand on renewable energy, photovoltaic (PV) generation systems have increased considerably in recent years. However, the power output of PV systems is affected by different weather conditions. Accurate forecasting of PV power output is important for system reliability and promoting large-scale PV deployment. This paper proposes algorithms to forecast power output of PV systems based upon weather classification and support vector machines (SVM). In the process, the weather conditions are divided into four types which are clear sky, cloudy day, foggy day, and rainy day. In this paper, a one-day-ahead PV power output forecasting model for a single station is derived based on the weather forecasting data, actual historical power output data, and the principle of SVM. After applying it into a PV station in China (the capability is 20 kW), results show the proposed forecasting model for grid-connected PV systems is effective and promising. [ABSTRACT FROM PUBLISHER]

A novel one transistor and one diode (1T-1D) dynamic random access memory cell for embedded applications is proposed. This memory cell consists of a floating-gate (FG) MOSFET and a gated diode. The anode of the diode is connected to the FG, so that the threshold voltage of the FG MOSFET can be modulated by the current through the diode. In this paper, basic device operations, speed, retention, and disturb performance are investigated using Silvaco technology computer-aided design simulation tools. The process compatibility is also investigated by integrating the memory array and specific sense amplifier. [ABSTRACT FROM PUBLISHER]

The Kerr effect in liquid of propylene carbonate near an insulator surface excited by pulsed high voltage was electro-optically measured with the data produced in the form of finite fringe interferograms. The fringe in the cathode region near the insulator surface was observed to shift inward, which implies a decrease of the cathode field near the insulator surface and somewhere near the cathode on the insulator surface being negatively charged. [ABSTRACT FROM PUBLISHER]