Current Slope Research Articles

High-Precision Control for Switched Reluctance Motor With Current Information

Magnetic characteristics of the SRM can be monitored directly in the detection of commutation instants. However, the mutual inductance effect between the adjacent phases is prominent for the switched reluctance motor when the adjacent phases are energized simultaneously. Consequently, mutual coupling will distort the response current profile of the injection voltage phase, thereby affecting position estimation precision. In order to acquire a precise estimation and accommodate it for the SRM drive system, it is necessary to take into consideration the modifications for the sensor-less scheme. This study presents a unique rotor position estimation approach to eliminate the mutual inductance effect by using the phase current slope difference method. The sensor-less scheme is achieved by setting a low and a high threshold, and a series of voltage pulses are injected in the idle phase alternately, synchronizing with the chopping current control. Without prior knowledge of mutual inductance and any additional position sensor, a precisely estimated rotor position is achieved. A dynamic model of a 12/8 SRM model is established to evaluate its validity, and both simulation results and experimental evaluation indicate that the proposed sensor-less control can be accomplished with an adequate precision used in a variety of applications.

Dynamic power management based on model predictive control for hybrid-energy-storage-based grid-connected microgrids

In this study, an efficient and reliable dynamic power management system (PMS) is proposed for microgrids (μGs) based on hybrid energy storage systems. Owing tothe differences in the response times of the different components (i.e., the battery, supercapacitor, and fuel cell) of the μG, efficiently allocating the power between the different devices is a challenging task for system designers. To address this issue and optimize the operation of the μG, a dynamic PMS is necessary. The contribution of this study is the application of model predictive control (MPC) for operating and controlling such μGs. The MPC method is used to manage power electronic devices such as DC-DC converters (for the battery, fuel cell, and supercapacitor) and grid-connected inverters. After the proposed PMS is successfully implemented in simulations, itsreal-time performance is validatedunder different operating scenarios that could occur in actual situations. The proposed PMS is found to be effective in controlling the control and operation of the μG.It can regulate the DC bus voltage during transient power imbalances, control the fuel cell current slope as per the requirement, and smoothen the operation between isolated and grid-connected modes.

Distribution and Morphology of Lava Tube Systems on the Western Flank of Alba Mons, Mars

AbstractIntegrated analyses of Thermal Emission Imaging System (THEMIS) IR, Context Camera (CTX), and Mars Orbiter Laser Altimeter (MOLA) data sets have been used to characterize the western flank of the Martian volcano Alba Mons, which hosts a prominent population of lava tube systems. Identification and mapping of lava tube systems is based on both morphologic and topographic analyses, including the presence of chains of collapse depressions and elongate, sinuous ridges. Lava tubes and adjacent tabular lava flows with lengths of 100+ km form an extensive lava flow field. Analyses of topographic data sets, including slope maps, suggest continuity of the radial flow field pattern across the full western flank. Concurrent surface activity across the western flank is consistent with age constraints from geologic mapping and crater size‐frequency distributions that indicate Early Amazonian ages. The mapped population of 331 lava tube systems in the western flank geologic map quadrangle has a mean length of 36.2 km and a total length of ∼12,000 km. Individual lava tube systems extend up to ∼400 km. Orientation and slope data for lava tube systems show small deviations compared to regional values in 50‐km grid cells defined by the MOLA Digital Elevation Model, suggesting a strong coupling of lava tubes to the current slopes of Alba Mons. Mapping of lava tube systems documents segments both showing collapse and with no collapse, indicating the potential for extensive subsurface cavities that would be important astrobiological targets.

Landslide Processes Involved in Volcano Dismantling From Past to Present: The Remarkable Open‐Air Laboratory of the Cirque de Salazie (Reunion Island)

AbstractThe Cirque de Salazie is one of the large erosional depressions of Reunion Island. Composed of a thick accumulation of loose volcaniclastic materials derived from successive volcanic flank collapses and exposed to high precipitation rates, this large depression is particularly prone to landslides. Of the 133 km2 making up this large depression, at least 19% of slopes are affected by various types of landslides. The diversity and high density of landslides is one of the main issues for inhabited areas. We examine the landslides in this area with the goal of providing key elements for better hazard assessment and understanding their role in the landscape's evolution. For over 20 years, we have been acquiring multidisciplinary data on landslides. In this cirque, eight types of landslides are identified and described following an adapted landslide classification. Using a multidisciplinary approach, we characterize and interpret the surface morphology and internal structure of three large inhabited compound landslides with volumes of 0.1 km3 moving up to 1.15 myr−1. These complex landslides provide an opportunity to investigate the influence of past slope movements on current slope movements. Furthermore, using detailed mapping and volume calculation of the landslides triggered by the last major cyclonic rainstorm, we estimate that rainfall‐triggered landslides contribute up to 20% of the long‐term erosion rate. The Cirque de Salazie is a remarkable laboratory that offers new insights and challenges for future research on landslide hazard assessment and the role of landslides in the short‐ and long‐term dismantling of volcanoes.

Induction Machine Sensorless Control Based on Saliency Extraction That Uses One Single SVPWM Active State

Some induction motors present saliencies that periodically modify the air-gap flux following a sinusoidal shape. Consequently, these modulations are reflected in the transient leakage inductance. Therefore, transient leakage inductance can be expressed as a constant term or offset, which comes from the symmetrical machine, plus all motor saliency sinusoids, modulated by the mentioned saliencies. Since saliencies are linked to the rotor position or flux, calculation of transient leakage inductance enables encoderless vector control. A way to calculate transient leakage inductance is to excite the machine with voltage steps and estimate the resulting phase current slopes since they are inversely proportional to phase transient inductance. For creating a vector, only the three current slopes resulting from a single active state are sufficient. The vector sum of the three current slopes leads to the so-called saliency-offset vector, which is a vector composed of an offset, which is created due to the contribution of the transient inductance offset, plus several saliency phasors, superposed to the offset. To access saliencies, it is critical to accurately identify the offset of the saliency-offset vector, especially in induction motors since offset is much bigger than saliencies. This article presents an advanced signal processing scheme that identifies the offset in the saliency-offset vector, assuming offset amplitude differsdepending on the voltage step applied. Using a feedforward scheme, the offset is eliminated, leading to a saliency vector where rotor slotting can be extracted from. A novel excitation is proposed to reduce additional current distortions coming from the one-active excitation.

Strong anion exchange for improved NiCo2S4 oxygen reduction reaction via interlayer spacing manipulation

Transition metal sulfides as high-performance, cost-effective, and stable electrocatalysts for oxygen reduction reaction (ORR) have attracted much attention. The replacement of sulfur atom by oxygen atom in metal sulfides was considered to be the fundamental reason for its decreased activity. Adequate anion exchange can greatly reduce the generation of oxygen species in transition metal sulfide, which further enhances the intrinsic electrical conductivity and stability of transition metal sulfides. Herein, a novel and simple approach to larger interlayer spacing was provided by introducing interlayer water in layered hydroxides precursor. The NCS-O 1 with treated layered hydroxides precursor exhibits few oxygen impurities and excellent activity for the ORR in alkaline electrolyte, presenting the close limiting diffusion current density and lower Tafel slope (reaches 56 mV dec −1 , vs. Pt/C 70) in comparison to 20% commercial Pt/C. Hence, our results provide an interesting design path for such catalysts. • A novel approach to synthesize NiCo 2 S 4 with few oxygen impurities. • The larger interlayer spacing in Ni–Co hydroxide favors the anion exchange. • The oxygen incorporation in NiCo 2 S 4 causes lower d-band center of metal sites. • The decreased oxygen impurities in NiCo 2 S 4 are conducive to oxygen reduction.

Road Cut Slope Stability Analysis at Kotropi Landslide Zone Along NH-154 in Himachal Pradesh, India

Abstract A landslide is a natural phenomenon that generally occurs in mountainous regions leading to severe damage to life and property. Most of the landslides occur due to rapid snowmelt, rainfall and human activities in terms of road cutting, and mining, etc. In the present study, slope stability analysis of Kotropi landslide along NH-154 in Mandi district, Himachal Pradesh, India was carried out by using circular failure charts (CFC). The various input parameters such as ground water table and shear strength of soil were considered in the analysis. The factor of safety (FOS) was evaluated for different moisture conditions such as completely dry, 25% and 50% saturation for the selected four sections at Kotropi landslide. These sections were found as marginally stable with factor of safety greater than unity when the slope is completely dry while further increase in the moisture made slope sections unstable with FOS <1 in case of slope sections 2, 3, and 4. Hence, the precautionary control measures were suggested based on the factor of safety analysis which will be helpful for various stake holders like engineers, designers, geologists etc., for stabilizing the current slope.

A new method for defining the local factor of safety based on displacement isosurfaces to assess slope stability

Slope stability is mainly assessed by the factor of safety (FS) parameter. As an improvement to the integral FS derived from the conventional limit equilibrium method (LEM), the local factor of safety (local FS) is used to describe the FS of each material element. However, although current slope stability algorithms with LEM rely on only strength criteria, some areas of a slope show almost no displacement, even though plastic yielding is occurring within the slope. For these reasons, we developed a new approach for defining the local FS based on the displacement isosurface. Adopting the Mohr–Coulomb (M–C) strength criterion, this new algorithm calculates the local FS in the potential sliding zone with a change in the apparent displacement. Based on the shear strength reduction technique, the distributions of the local FS within 2D homogeneous slopes with different shear strengths and within a real 3D slope with a complex topography are analyzed. Firstly, the applicability of the new approach was examined and we found that the local FS decreases significantly only when the direction of the yielding surface approaches the displacement direction, which also reveals that the LEM may underestimate the FS. In addition, the areas of a slope where the local FS strongly changes depend on the slope geometry and also control the instability patterns. Further, the results of a local FS in a 3D slope analysis show that complex topography and internal structure can cause the alternation of stable and unstable blocks in the slope and that the mobilities of the blocks induced by the instability differ in different areas. Finally, some local optimized retaining countermeasures were successfully implemented for supporting a real engineering slope guided by the local FS. Our results indicate that this improved algorithm can provide a more suitable and accurate local FS with which to assess slope stability and reveal more realistic instability patterns than approaches using the integral FS.

Improvement of low‐speed sensorless control with multi‐layer neural network

AbstractIn recent years, there has been an increasing demand for position sensorless control in Permanent Magnet Synchronous Motor (PMSM) drives, and various methods have been studied. Switching noise is a problem in the low‐speed sensorless control method that uses the current slope during PWM. Furthermore, another problem is that the inductance does not appear in a sinusoidal distribution owing to magnetic saturation. In this paper, we improve the sensorless control method that estimates the position from the current slope during PWM, which is greatly affected by switching. Additionally, we build a multi‐layer neural network (NN) that directly estimates the position signals by learning a large amount of current data, and verify the driving results in the low‐speed range when the learned NN is incorporated into real‐time control.

Evaluation of the turn‐off transient controllability for high‐power IGBT modules

The efficient and flexible conversion of electrical energy is increasingly accomplished by megawatt insulated gate bipolar transistor (IGBT) modules. Their dynamic performance is influenced by the gate driver control, operating points and the switching loop parasitics, which are crucial to their optimized operational behaviours, efficiency and field reliability. This paper investigates the controllability of the transient voltage and current slopes of megawatt IGBT modules during their turn-off transitions and proposes an efficient assessment method accordingly. Firstly, the causal relationship of transient characteristic variations and controllability is investigated analytically. Then, major factors impacting the controllability are analysed and validated, including the charge carrier profile, the operating points (i.e. the load voltage, the load current, and the junction temperature), and the gate resistance. Finally, an efficient method using the MOS-channel turn-off point on calibrated gate voltage waveform is proposed for the controllability evaluation, which can guide the IGBT, gate driver, and converter design.

Predictive Current Control for Switched Reluctance Motor Based on Local Linear Phase Voltage Model

In this paper, a predictive phase current control (PCC) scheme based on a local linear phase voltage model for a switched reluctance motor is proposed. The current is controlled by regulating the average voltage through PWM, ensuring a fixed switching frequency. A linear model is proposed to approximate the relationship between the voltage and the current slope in a short period. By using the voltage and current slope information in the previous control cycle, the intercept and slope of the model can be identified online. In the previous control cycle, the phase voltage changes from zero to positive or negative DC-link voltage, and then the identified model is used to predict the average voltage required in the next PWM cycle for the actual current so as to accurately track its reference. The effectiveness of the proposed PCC was verified experimentally. The results demonstrate that the proposed control scheme can significantly reduce the current and torque ripples compared to hysteresis control with the same sampling rate. The proposed PCC is easy to implement, does not need to obtain the motor characteristics in advance and is not sensitive to the changes in characteristic parameters caused by motor aging, etc. It is relatively suitable for applications that need to accurately track the given current curve.

An Optimized Asymmetric Pulsewidth Modulation for Sensorless Control of Permanent Magnet Synchronous Machines

This article proposes an optimized asymmetric pulsewidth modulation (OAPWM) for saliency-based sensorless control of permanent magnet synchronous machines (PMSMs). Compared with the conventional symmetric space vector PWM, OAPWM has merits of longer active vectors and more accurate current slope measurements, which are beneficial to the low-speed sensorless drives. In OAPWM, a distributed zero vector is inserted between two adjacent active vectors. Thus, the current ripple and the power loss can be reduced. Moreover, the length of zero vector is optimized considering the current ripple and modulation index. Then, a current oversampling method and the least square algorithm are adopted to improve the calculation accuracy of the current slope. And the average phase current in one PWM period is calculated using six sampling points. The effectiveness of OAPWM for sensorless control is verified on both 500- and 1500-W PMSMs based on a single field programmable gate array. In comparison with the conventional methods, more accurate position estimation can be achieved during both the transient and steady-state processes.

SiC‐based analytical model for gate‐stack dual metal nanowireFETwith enhanced analog performance

AbstractIn this paper, silicon carbide‐based analytical model for gate‐stack dual metal nanowire field effect transistor (gate‐stack DM NW FET) has been analyzed by solving the 2D Poisson's equation using parabolic approximation method for electric potential, subthreshold current and subthreshold slope. The results have been examined for various silicon carbide film depth and channel length. The results predicted by the analytical model have excellent agreement with simulated results obtained by ATLAS 3D device simulator. A gate‐stack having high k‐dielectric material, that is, Hafnium oxide (HfO2) along with aluminum oxide (Al2O3) has been used. Also, performance characteristics of gate‐stack DM NW FET have been compared with the performance characteristics of nanowire field effect transistor (NW FET), Nanowire field effect transistor (NW FET) (Sic) and dual metal nanowire field effect transistor (DM NW FET) (SiC). It is so proved that our proposed device, that is, gate‐stack DM NW FET (4H‐SiC) exhibits superior performance in terms of drain current (Ids), transconductance (gm), output conductance (gd) and cut off frequency (fT) than the existing devices.

Heterostructured nickel/vanadium nitrides composites for efficient electrocatalytic hydrogen evolution in neutral medium

Water electrolysis capable of working in a neutral medium is compatible with direct seawater splitting, solar-driven water splitting cells, and hybrid inorganic–biological systems for renewable energy conversion and storage. Non-precious electrocatalysts for efficient and durable hydrogen evolution reactions (HER) are of paramount significance. Herein, we report that the heterostructured nitrides composites that are made of poor HER electrocatalysts of Ni 3 N and VN show remarkable activity and durability for HER in a neutral medium. Ni 3 N-VN composite rivals the state-of-the-art Pt/C electrocatalyst, requiring an overpotential of only 85 mV to deliver a benchmark current density of 10 mA cm −2 in 1.0 M phosphate-buffered saline. The HER kinetics are significantly promoted in comparison with Ni 3 N and VN, showing 6–17 times higher current densities and lowered Tafel slopes (73 mV decade for Ni 3 N-VN and >120 mV decade −1 for Ni 3 N and VN). The promoted kinetics is ascribed to the interfacial heterostructures, where the electronic structures are tailored for optimal hydrogen absorption and promoted water adsorption and dissociation. This research demonstrates a powerful interfacial engineering strategy in promoting the sluggish kinetics of nitrides for HER in a neutral medium, which deserves further attention to electrocatalysts in other reactions. • A simple method for synthesizing heterojunction electrocatalysts is introduced. • Ni 3 N-VN heterojunction enhances the adsorption and dissociation of water molecules. • Ni 3 N-VN heterojunction shows the extended energy states in the near Fermi level. • 3D hierarchical structure catalyst has excellent alkaline/neutral HER performance.

Fault Diagnosis for Power Transistors in a Converter of Switched Reluctance Motors Based on Current Features

Fault diagnosis technique is necessary for high reliability system. For switched reluctance motor, asymmetric half bridge converter is the most commonly used. The transistor is the most fragile component in converters. To the transistor in asymmetric half bridge converter, a fault diagnosis method is proposed in this paper. When faults of transistors occur, the conducting loop will be changed. The current slope can reflect the change of the conducting loop. Through reconfiguring current sensors, the sign of the measurements will reverse with the change of the conducting loop. By the current slope and the sign of the measurements, present conducting loop is determined. The changes and the fault types are one-to-one correspondence. Therefore, the fault type is known. Conditions that may lead to misdiagnosis are illustrated and avoided in online execution. Comparisons of the proposed fault diagnosis method and relevant existing methods are made according to the cost, the response speed, the application scope and so on. The proposed fault diagnosis method is demonstrated under all possible fault types of the transistor by simulations and experiments, which validates effectiveness of it.

A Coordination Control between Battery and Supercapacitor Energy Storage Systems to Segregate Power for On-Grid Application

Abstract The present work describes a control methodology for a hybrid energy storage system (HESS) to improve its transient performance under dynamic load conditions. The proposed coordination control enhanced life cycle performance by segregating the power between battery energy storage systems (BESS) and a supercapacitor (SC). The BESS and SC are connected parallel to each other, and two individual DC–DC bidirectional converters connect them to a common DC bus. The coordination control is established between the controllers of BESS and the SC of HESS, which helps to utilise the usable energy capacity of the HESS. The charging/discharging current of the BESS is controlled within the allowable safety range based on the slope and magnitude of the BESS current. The high-frequency power component is handled by the SC, which helps to reduce the extra exhaustion on the BESS during operation with a higher current. The proposed coordination control of HESS is validated through simulation and the results show the effectiveness of the proposed controller.

Comprehensive review on electrical noise analysis of TFET structures

Tunnel Filed Effect Transistors (TFETs) have appeared as an alternative for conventional CMOS due to their advantages like very low leakage current and steep sub-threshold slope. In semiconductor devices, noise is considered an undesired signal that can deteriorate the desired signal. In TFET structures different noise sources affect the performance at different frequency ranges. This paper presents a comprehensive review of impact of electrical noise on the performance of various TFET structures. The impact of both low-frequency noise sources and high-frequency sources have been discussed thoroughly. The study of different types of electrical noises occur in simple TFET device and different structures of TFET is presented.

Current Differential Protection for Active Distribution Networks Based on Improved Fault Data Self-Synchronization Method

The uncertainty in the direction and magnitude of fault current is a thorny issue for active distribution network (ADN) protection. Current differential protection (CDP) is suitable for ADN with complex operating modes and multiple types of DGs. However, the data synchronization conditions in transmission lines are usually not available in distribution systems with relatively low investment levels. Fault data self-synchronization (FDSS) algorithm is a low-cost data synchronization method specially used for the protection of distribution networks, but there will be large time synchronization errors under some extreme fault conditions. In this paper, the inherent defect of the conventional FDSS algorithm is first analyzed. Then an improved FDSS algorithm is proposed, which uses the current zero-crossing time and current slope polarity to estimate the starting delay difference at both terminals. On this basis, a corresponding CDP scheme is proposed. Compared with traditional CDP, the proposed scheme does not require additional synchronization equipment and high communication bandwidth. Finally, an ADN simulation model was built using PSCAD, and the improved FDSS algorithm program was implemented in MATLAB. Test results prove that the improved FDSS algorithm can effectively reduce the time synchronization error, and the corresponding CDP scheme is effective under various fault conditions.

Performance analysis of different material based dual electrode doping-less TFET

In this work, the charge plasma based dual electrode doping-less tunnel FETs (DEDLTFET) is simulated with the use of different materials such as silicon (Si-DEDLTFET), Silicon-germanium (SiGe-DEDLTFET) and SiGe at Source (SiGe Source DEDLTFET). The charge plasma technique is used to create source and drain region on an intrinsic body by selecting appropriate work function of metal electrode. The paper provides the comparison among devices on the basis of RF parameters. The on-state current (ION) for SiGe source DEDLTFET, SiGe-DEDLTFET and DEDLTFET are 1.84x10-4, 8.75x10-5 and 8.11x10-6 A/µm respectively for similar off-state current (IOFF). This result show that SiGe source DEDLTFET device provides better drive current along with improved ON-OFF current ratio (ION/IOFF) and subthreshold slope (SS). Improved transconductance (gm) and cut-off frequency (fT) show that the hetero-material device has better RF performance while comparing with the other two devices. Copyright © 2017 VBRI Press.

Quantitative Risk Assessment of Environmental Hazards Generated by a Tailings Embankment: case study Cabeço do Pião, Portugal

The Panasqueira mine is a world-class tungsten mine and probably one of the most important in Europe, having been continuously in operation since 1898. Between 1927 and 1996, the ore was fully or partially processed in a processing plant located on the left bank of the Zêzere River. The tailings were stored along the bank, in an extension of about 1.5 km. The fine particles, locally known as ‘sludge’, were stored in a self-constructed embankment located on a steep hillside. The current average slope is about 36°. The sludge has high concentrations of some heavy metals (Cu, Zn, W and Cd) but has a particularly high concentration in arsenic (about 15%). This tailings storage was not included in the National Plan for Rehabilitation of Abandoned Mines, despite presenting a high environmental risk. A quantitative environmental risk assessment characterises this situation, considering two possible alternatives: the current state with continuous release of contaminants or, alternatively, the situation that would arise from an eventual collapse of the storage embankment. In the first situation, we used a classical methodology of risk assessment to estimate the concentrations of arsenic in the affected compartments using a conservative exposure scenario and inferring the doses to which the local population is subjected. These doses are compared with reference acceptable values. In the second situation, the creation of a dispersed source of contamination encompasses a much higher dispersion area, a larger population and more expensive rehabilitation costs.