Multilevel inverters for low-power application

Multilevel inverters are an attractive solution in the medium-voltage and high-power applications. However in the low-power range also it can be a better solution compared to two-level inverters, if MOSFETs are used as devices switching in the order of 100 kHz. The effect of clamping diodes in the diode-clamped multilevel inverters play an important role in determining its efficiency. Power loss introduced by the reverse recovery of MOSFET body diode prohibits the use of MOSFET in hard-switched inverter legs. A technique of avoiding reverse recovery loss of MOSFET body diode in a three-level neutral point clamped inverter is suggested. The use of multilevel inverters topology enables operation at high switching frequency without sacrificing efficiency. High switching frequency of operation reduces the output filter requirement, which in turn helps in reducing the size of the inverter. This study elaborates the trade-off analysis to quantify the suitability of multilevel inverters in the low-power applications. Advantages of using a MOSFET-based three-level diode-clamped inverter for a PM motor drive and UPS systems are discussed.

Dynamic Supply and Threshold Voltage Scaling for CMOS Digital Circuits Using In-Situ Power Monitor

A generalized power tracking algorithm that minimizes power consumption of digital circuits by dynamic control of supply voltage and the body bias is proposed. A direct power monitoring scheme is proposed that does not need any replica and hence can sense total power consumed by load circuit across process, voltage, and temperature corners. Design details and performance of power monitor and tracking algorithm are examined by a simulation framework developed using UMC 90-nm CMOS triple well process. The proposed algorithm with direct power monitor achieves a power savings of 42.2% for activity of 0.02 and 22.4% for activity of 0.04. Experimental results from test chip fabricated in AMS 350 nm process shows power savings of 46.3% and 65% for load circuit operating in super threshold and near sub-threshold region, respectively. Measured resolution of power monitor is around 0.25 mV and it has a power overhead of 2.2% of die power. Issues with loop convergence and design tradeoff for power monitor are also discussed in this paper.

Information-theoretic and communication-theoretic optimal power allocation for fading channels

In this paper we review the most peculiar and interesting information-theoretic and communications features of fading channels. We first describe the statistical models of fading channels which are frequently used in the analysis and design of communication systems. Next, we focus on the information theory of fading channels, by emphasizing capacity as the most important performance measure. Both single-user and multiuser transmission are examined. Further, we describe how the structure of fading channels impacts code design, and finally overview equalization of fading multipath channels.

A power scalable receiver front-end at 2.4 GHz

We propose a Low Noise Amplifier (LNA) architecture for power scalable receiver front end (FE) for Zigbee. The motivation for power scalable receiver is to enable minimum power operation while meeting the run-time performance needed. We use simple models to find empirical relations between the available signal and interference levels to come up with required Noise Figure (NF) and 3rd order Intermodulation Product (IIP3) numbers. The architecture has two independent digital knobs to control the NF and IIP3. Acceptable input match while using adaptation has been achieved by using an Active Inductor configuration for the source degeneration inductor of the LNA. The low IF receiver front end (LNA with I and Q mixers) was fabricated in 130nm RFCMOS process and tested.

Power and Discrete Rate Adaptation for Energy Harvesting Wireless Nodes

Energy Harvesting (EH) nodes, which harvest energy from the environment in order to communicate over a wireless link, promise perpetual operation of a wireless network with battery-powered nodes. In this paper, we address the throughput optimization problem for a rate-adaptive EH node that chooses its rate from a set of discrete rates and adjusts its power depending on its channel gain and battery state. First, we show that the optimal throughput of an EH node is upper bounded by the throughput achievable by a node that is subject only to an average power constraint. We then propose a simple transmission scheme for an EH node that achieves an average throughput close to the upper bound. The scheme's parameters can be made to account for energy overheads such as battery non-idealities and the energy required for sensing and processing. The effect of these overheads on the average throughput is also analytically characterized.

Analysis of non-uniform waveguide in MZI and optimization of the power confinement in the waveguide

The technological world has attained a new dimension with the advent of miniaturization and a major breakthrough has evolved in the form of moems, technically more advanced than mems. This breakthrough has paved way for the scientists to research and conceive their innovation. This paper presents a mathematical analysis of the wave propagation along the non-uniform waveguide with refractive index varying along the z axis implemented on the cantilever beam of MZI based moem accelerometer. Secondly the studies on the wave bends with minimum power loss focusing on two main aspects of bend angle and curvature angle is also presented.

High voltage DC power supply topology for pulsed load applications with converter switching synchronized to load pulses

High voltage power supplies for radar applications are investigated, which are subjected to pulsed load (125 kHz and 10% duty cycle) with stringent specifications (<0.01% regulation, efficiency>85%, droop<0.5 V/micro-sec.). As good regulation and stable operation requires the converter to be switched at much higher frequency than the pulse load frequency, transformer poses serious problems of insulation failure and higher losses. This paper proposes a methodology to tackle the problems associated with this type of application. Synchronization of converter switching with load pulses enables the converter to switch at half the load switching frequency. Low switching frequency helps in ensuring safety of HV transformer insulation and reduction of losses due to skin and proximity effect. Phase-modulated series resonant converter with ZVS is used as the power converter.

Input voltage modulated high voltage DC power supply topology for pulsed load applications

High voltage power supplies for radar applications are investigated which are subjected to pulsed load with stringent specifications. In the proposed solution, power conversion is done in two stages. A low power-high frequency converter modulates the input voltage of a high power-low frequency converter. This method satisfies all the performance specifications and takes care of the critical aspects of HV transformer.

Design parameters for earth-wire power tapping

The paper deals with the calculation of the induced voltage on, and the equivalent capacitance of, an earth wire isolated for purposes of tapping small amounts of power from high-voltage lines. The influence of heights, diameters and spacings of conductors on these quantities have been studied and presented in the form of graphs.

Performance of Tuned Half-Wave-Length Power Transmission Lines

The basic concepts of tuned half-wave lines were covered by Hubert and Gent [1]. In this paper the problem of overvoltages during faults and the stability of the system incorporating such tuned lines are discussed. The type of tuning bank and the line arrangements that will be satisfactory from the point of view of stability are suggested. The behavior of a line tuned by distributed capacitor is analyzed, and its performance is compared with the other type of tuned line.

Analysis of ferro-oscillations in power systems

The paper presents an analysis of ferro-oscillations in capacitor voltage transformers and series-compensated e.h.v. lines. The dual-input describing function is adopted to show the regions of existence and the influence of system parameters on such oscillations. A complete analytical method suitable for digital computation has been developed for determining the amplitudes of these oscillations.

Analysis of Natural Half-Wave-Length Power Transmission Lines

This paper provides additional theoretical information on half-wave-length power transmission. The analysis is rendered more general by consideration of a natural half-wave line instead of a short line tuned to half-wave. The effects of line loading and its power factor on the voltage and current profiles of the line and ganerator excitation have been included. Some of the operating problems such as charging of the line and synchronization of the half-wave system are also discussed. The inevitability of power-frequency overvoltages during faults is established. Stability studies have indicated that the use of switching stations is not beneficial. Typical swing curves are also presented.

Improvement of power-system transient stability by phase-shift insertion

Computational studies of the transient stability of a synchronous machine connected to an infinite busbar by a double-circuit transmission line are used to illustrate the effect of relative phase-shift insertion between the machine and its associated power system. This method of obtaining a change in the effective rotor-excitation angle, and thereby the power transfer, is described, together with an outline of possible methods of implementation by a phase-shifting transformer in a power system.

Control technique for non-linear and unbalance compensation of an integrated magnetics-based three-phase series-shunt-compensated uninterruptible power supply

Handling unbalanced and non-linear loads in a three-phase AC power supply has always been a difficult issue. This has been addressed in the literature by either using fast controllers in the fundamental rotating reference frame or using separate controllers in reference frames specific to the harmonics. In the former case, the controller needs to be fast and in the latter case, besides the need for many controllers, negative-sequence components need to be extracted from the measured signal. This study proposes a control scheme for harmonic and unbalance compensation of a three-phase uninterruptible power supply wherein the problems mentioned above are addressed. The control takes place in the fundamental positive-sequence reference frame using only a set of feedback and feed-forward compensators. The harmonic components are extracted by a process of frame transformations and used as feed-forward compensation terms in the positive-sequence fundamental reference frame. This study uses a method wherein the measured signal itself is used for fundamental negative-sequence compensation. As the feed-forward compensator handles the high-bandwidth components, the feedback compensator can be a simple low-bandwidth one. This control algorithm is explained and validated experimentally.

Indium flux, growth temperature and RF power induced effects in InN layers grown on GaN/Si substrate by plasma-assisted MBE

In the present work, we report the growth of wurtzite InN epilayers on GaN/Si (1 1 1) substrate by plasma-assisted molecular beam epitaxy (PAMBE). The growth parameters such as indium flux, substrate temperature and RF power affect the crystallographic and morphological properties of InN layers, which were evaluated using high resolution X-ray diffraction (HRXRD) analysis and atomic force microscopy (AFM). It is found that excess indium (In) concentrations and surface roughness were increased with increase in In flux and growth temperature. The intensity of HRXRD (0 0 0 2) peak, corresponding to c-axis orientation has been increased and full width at half maxima (FWHM) has decreased with increase in RF power. It was found that highly c-axis oriented InN epilayers can be grown at 450 degrees C growth temperature, 450 W RF power and 1.30 x 10(-7) mbar In beam equivalent pressure (BEP). The energy gap of InN layers grown by optimizing growth conditions was determined by photoluminescence and optical absorption measurement. (C) 2011 Elsevier B.V. All rights reserved.