Multilevel Dodecagonal Voltage Space Vector Generation using Flying Capacitor topology for Induction motor drives

In this paper, a multilevel flying capacitor inverter topology suitable for generating multilevel dodecagonal space vectors for an induction motor drive, is proposed. Because of the dodecagonal space vectors, it has increased modulation range with the absence of all 6n +/- 1, (n=odd) harmonics in the phase voltage and currents. The topology, realized by flying capacitor three level inverters feeding an open-end winding induction motor, does not suffer the neutral point voltage imbalance issues seen in NPC inverters and the capacitors have inherent charge-balancing capability with PWM control using switching state redundancies. Furthermore, the proposed technique uses lesser number of power supplies compared to cascaded H-bridge or NPC based dodecagonal schemes and has better ride-through capability. Finally, the voltage control is obtained through a simple carrier-based space vector PWM scheme implemented on a DSP.

A scalable network port scan detection system on FPGA

With ever increasing network speed, scalable and reliable detection of network port scans has become a major challenge. In this paper, we present a scalable and flexible architecture and a novel algorithm, to detect and block port scans in real time. The proposed architecture detects fast scanners as well as stealth scanners having large inter-probe periods. FPGA implementation of the proposed system gives an average throughput of 2 Gbps with a system clock frequency of 100 MHz on Xilinx Virtex-II Pro FPGA. Experimental results on real network trace show the effectiveness of the proposed system in detecting and blocking network scans with very low false positives and false negatives.

HD resolution intra prediction architecture for H.264 decoder

High performance video standards use prediction techniques to achieve high picture quality at low bit rates. The type of prediction decides the bit rates and the image quality. Intra Prediction achieves high video quality with significant reduction in bit rate. This paper presents novel area optimized architecture for Intra prediction of H.264 decoding at HDTV resolution. The architecture has been validated on a Xilinx Virtex-5 FPGA based platform and achieved a frame rate of 64 fps. The architecture is based on multi-level memory hierarchy to reduce latency and ensure optimum resources utilization. It removes redundancy by reusing same functional blocks across different modes. The proposed architecture uses only 13% of the total LUTs available on the Xilinx FPGA XC5VLX50T.

Nearly constant switching frequency hysteresis current controller for general n-level inverter fed induction motor drive

A current-error space phasor based hysteresis controller with nearly constant switching frequency is proposed for a general n-level voltage source inverter fed three-phase induction motor drive. Like voltage-controlled space vector PWM (SVPWM), the proposed controller can precisely detect sub-sector changes and for switching it selects only the nearest switching voltage vectors using the information of the estimated fundamental stator voltages along α and β axes. It provides smooth transition between voltage levels, including operation in over modulation region. Due to adjacent switching amongst the nearest switching vectors forming a triangular sub-sector, in which tip of the fundamental stator voltage vector of the machine lies, switching loss is reduced while keeping the current-error space phasor within the varying parabolic boundary. Appropriate dimension and orientation of this parabolic boundary ensures similar switching frequency spectrum like constant switching frequency SVPWM-based induction motor (IM) drive. Inherent advantages of multi-level inverter and space phasor based current hysteresis controller are retained. The proposed controller is simulated as well as implemented on a 5-level inverter fed 7.5 kW open-end winding IM drive.

A Space-Vector-Based Hysteresis Current Controller for a General n-Level Inverter-Fed Drive With Nearly Constant Switching Frequency Control

A current-error space-vector-based hysteresis current controller for a general n-level voltage-source inverter (VSI)-fed three-phase induction motor (IM) drive is proposed here, with control of the switching frequency variation for the full linear modulation range. The proposed current controller monitors the space-vector-based current error of an n-level VSI-fed IM to keep the current error within a parabolic boundary, using the information of the current triangular sector in which the tip of the reference vector lies. Information of the reference voltage vector is estimated using the measured current-error space vectors, along the alpha- and beta-axes. Appropriate dimension and orientation of this parabolic boundary ensure a switching frequency spectrum similar to that of a constant-switching-frequency voltage-controlled space vector pulsewidth modulation (PWM) (SVPWM)-based IM drive. Like SVPWM for multilevel inverters, the proposed controller selects inverter switching vectors, forming a triangular sector in which the tip of the reference vector stays, for the hysteresis PWM control. The sector in the n-level inverter space vector diagram, in which the tip of the fundamental stator voltage stays, is precisely detected, using the sampled reference space vector estimated from the instantaneous current-error space vectors. The proposed controller retains all the advantages of a conventional hysteresis controller such as fast current control, with smooth transition to the overmodulation region. The proposed controller is implemented on a five-level VSI-fed 7.5-kW IM drive.

A Hybrid Multilevel Inverter System Based on Dodecagonal Space Vectors for Medium Voltage IM Drives

Dodecagonal (12-sided) space vector pulsewidth modulation (PWM) schemes are characterized by the complete absence of (6n +/- 1)th-order harmonics (for odd n) in the phase voltages, within the linear modulation range and beyond, including over-modulation. This paper presents a new topology suitable for the realization of such multilevel inverter schemes for induction motor (IM) drives, by cascading two-level inverters with flying-capacitor-inverter fed floating H-bridge cells. Now, any standard IM may be used to get the dodecagonal operation which hitherto was possible only with open-end winding IM. To minimize the current total harmonic distortion (THD), a strategy for synchronous PWM is also proposed. It is shown that the proposed method is capable of obtaining better THD figures, compared to conventional dodecagonal schemes. The topology and the PWM strategy are validated through analysis and subsequently verified experimentally.

Medium Voltage Drive for Induction Motors Using Multilevel Octadecagonal Voltage Space Vectors

Multilevel inverters with hexagonal and dodecagonal voltage space vector structures have improved harmonic profile compared to two-level inverters. Further improvement in the quality of the waveform is possible using multilevel octadecagonal (18-sided polygon) voltage space vectors. This paper proposes an inverter circuit topology capable of generating multilevel octadecagonal voltage space vectors, by cascading two asymmetric three-level inverters. By the proper selection of dc-link voltages and the resultant switching states for the inverters, voltage space vectors, whose tips lie on three concentric octadecagons, are obtained. The advantages of octadecagonal voltage space vector-based pulsewidth modulation (PWM) techniques are the complete elimination of fifth, seventh, eleventh, and thirteenth harmonics in phase voltages and the extension of linear modulation range. In this paper, a simple PWM timing calculation method is also proposed. Experimental results have been presented in this paper to validate the proposed concept.

A Multilevel Inverter Scheme With Dodecagonal Voltage Space Vectors Based on Flying Capacitor Topology for Induction Motor Drives

This paper presents a multilevel inverter topology suitable for the generation of dodecagonal space vectors instead of hexagonal space vectors as in the case of conventional schemes. This feature eliminates all the 6n +/- 1 (n = odd) harmonics from the phase voltages and currents in the entire modulation range with an increase in the linear modulation range. The topology is realized by flying capacitor-based three-level inverters feeding from two ends of an open-end winding induction motor with asymmetric dc links. The flying capacitor voltages are tightly controlled throughout the modulation range using redundant switching states for any load power factor. A simple and fast carrier-based space-vector pulsewidth modulation (PWM) scheme is also proposed for the topology which utilizes only the sampled amplitudes of the reference wave for the PWM timing computation.

Fowler-Nordheim Field Emission from Carbon Nanotubes Under Intense Electric Field

In this paper, we study the Fowler-Nordheim field emission (FNFE) from carbon nanotubes on the basis of a newly formulated electron dispersion law by considering the fact that the intense electric field needed for FNFE changes the band structure in a fundamental way. It has been found that the field emitted current increases with increasing electric field in oscillatory manner due to the appearance of van Hove singularities and exhibits spikes for particular values of the electric field where the singularity occurs. The numerical values of the field emitted current in all the cases vary widely and the determined by the chiral indices and the diameter in the respective cases. The results of this paper find three applications in the fields of nanoscience and technology.

k.p based closed form energy band gap and transport electron effective mass model for 100] and 110] relaxed and strained Silicon nanowire

In this paper, we address a physics based closed form model for the energy band gap (E-g) and the transport electron effective mass in relaxed and strained 100] and 110] oriented rectangular Silicon Nanowire (SiNW). Our proposed analytical model along 100] and 110] directions are based on the k.p formalism of the conduction band energy dispersion relation through an appropriate rotation of the Hamiltonian of the electrons in the bulk crystal along 001] direction followed by the inclusion of a 4 x 4 Luttinger Hamiltonian for the description of the valance band structure. Using this, we demonstrate the variation in Eg and the transport electron effective mass as function of the cross-sectional dimensions in a relaxed 100] and 110] oriented SiNW. The behaviour of these two parameters in 100] oriented SiNW has further been studied with the inclusion of a uniaxial strain along the transport direction and a biaxial strain, which is assumed to be decomposed from a hydrostatic deformation along 001] with the former one. In addition, the energy band gap and the effective mass of a strained 110] oriented SiNW has also been formulated. Using this, we compare our analytical model with that of the extracted data using the nearest neighbour empirical tight binding sp(3)d(5)s* method based simulations and has been found to agree well over a wide range of device dimensions and applied strain. (C) 2012 Elsevier Ltd. All rights reserved.

Direct Band-to-Band Tunneling in Reverse Biased MoS2 Nanoribbon p-n Junctions

We investigate the direct band-to-band tunneling (BTBT) in a reverse biased molybdenum disulfide (MoS2) nanoribbon p-n junction by analyzing the complex band structure obtained from semiempirical extended Huckel method under relaxed and strained conditions. It is demonstrated that the direct BTBT is improbable in relaxed monolayer nanoribbon; however, with the application of certain uniaxial tensile strain, the material becomes favorable for it. On the other hand, the relaxed bilayer nanoribbon is suitable for direct BTBT but becomes unfavorable when the applied uniaxial tensile or compressive strain goes beyond a certain limit. Considering the Wentzel-Kramers-Brillouin approximation, we evaluate the tunneling probability to estimate the tunneling current for a small applied reverse bias. Reasonably high tunneling current in the MoS2 nanoribbons shows that it can take advantage over graphene nanoribbon in future tunnel field-effect transistor applications.

Bipolar Poisson Solution for Independent Double-Gate MOSFET

We propose a new set of input voltage equations (IVEs) for independent double-gate MOSFET by solving the governing bipolar Poisson equation (PE) rigorously. The proposed IVEs, which involve the Legendre's incomplete elliptic integral of the first kind and Jacobian elliptic functions and are valid from accumulation to inversion regimes, are shown to have good agreement with the numerical solution of the same PE for all bias conditions.

Physics-Based Solution for Electrical Resistance of Graphene Under Self-Heating Effect

In this brief, we present a physics-based solution for the temperature-dependent electrical resistance of a suspended metallic single-layer graphene (SLG) sheet under Joule self-heating. The effect of in-plane and flexural phonons on the electron scattering rates for a doped SLG layer has been considered, which particularly demonstrates the variation of the electrical resistance with increasing temperature at different current levels using the solution of the self-heating equation. The present solution agrees well with the available experimental data done with back-gate electrostatic method over a wide range of temperatures.

Multilevel octadecagonal space vector generation for induction motor drives by cascading asymmetric three level inverters

Multilevel inverters with hexagonal and dodecagonal voltage space vector structures have improved harmonic profile compared to two level inverters. Further improvement in the quality of the waveform is possible using multilevel octadecagonal (18 sided polygon) voltage space vectors. This paper proposes an inverter circuit topology capable of generating multilevel octadecagonal voltage space vectors, by cascading two asymmetric three level inverters. By proper selection of DC link voltages and the resultant switching states for the inverters, voltage space vectors, whose tips lie on three concentric octadecagons, are obtained. The advantages of octadecagonal voltage space vector based PWM techniques are the complete elimination of fifth, seventh, eleventh and thirteenth harmonics in phase voltages and the extension of linear modulation range. In this paper, a simple PWM timing calculation method is also proposed. Matlab simulation results and experimental results have been presented in this paper to validate the proposed concept.