Engineering Commons^™

Modulation Techniques To Reduce Leakage Current In Three-Phase Transformerless H7 Photovoltaic Inverter

Faculty of Engineering University of Malaya

Recently, reduced common-mode voltage (CMV) pulsewidth modulation (RCMV-PWM) methods have been proposed to reduce the leakage current in three-phase transformerless photovoltaic (PV) systems. However, most of these studies only focus on leakage current elimination and neglect the overall performance of the PV systems on issues such as cost, voltage linearity, dc-link current ripples, and harmonic distortion. In this paper, a three-phase transformerless inverter, adapted from the single-phase H5 topology, is investigated. Since the H5 topology has been conventionally developed for a single-phase system, its adaptation to the three-phase system requires the development of corresponding three-phase modulation techniques. Hence, modulation techniques …

Potential Application Of Pure Silica Optical Flat Fibers For Radiation Therapy Dosimetry

Faculty of Engineering University of Malaya

Pure silica optical flat fibers (FF) have been proposed as the basis for a novel radiation sensor by the measurement of the thermoluminescence (TL) produced. In this paper the 17, performance of the FFs were studied. Using a linear accelerator (LINAC) delivering doses in the range 0.2-10.0 Gy, the TL dosimetric glow curves of the FFs were studied with respect to 6 MeV electron and 6 MV photon beams. When exposed to 6 MeV electron irradiation, the pure silica FFs displayed a supralinear response starting from 2 Gy up to 10.0 Gy. While for 6 MV photon irradiation, the FFs …

Q-Switched Erbium Doped Fiber Laser Based On Single And Multiple Walled Carbon Nanotubes Embedded In Polyethylene Oxide Film As Saturable Absorber

Faculty of Engineering University of Malaya

A passive, stable and low cost Q-switched Erbium-doped fiber laser (EDFL) is demonstrated using both single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), which are embedded in polyethylene oxide (PEO) film as a saturable absorber (SA). The film is sandwiched between two FC/PC fiber connectors and integrated into the laser cavity for Q-switching pulse generation operating at wavelength of 1533.6 am. With SWCNTs, the laser produces a stable pulse train with repetition rate and pulse width ranging from 9.52 to 33.33 kHz and 16.8 to 8.0 is while varying the 980 am pump power from 48.5 mW to 100.4 …

A Review Of Safety, Health And Environmental (She) Issues Of Solar Energy System

Faculty of Engineering University of Malaya

Solar energy is one of the cleanest forms of energy sources and considered as a green source of energy. Solar energy benefit ranges from low carbon emission, no fossil fuel requirement, long term solar resources, less payback time and other. However like other power generation sources, solar energy has also some Safety, Health and Environmental (SHE) concerns. This paper presents the overview of solar energy technologies and addresses the SHE impact of solar energy technologies to the sustainability of human activities. This paper will also recommend the possible ways to reduce the effect of potential hazards of widespread use of …

Stability And Performance Investigations Of Model Predictive Controlled Active-Front-End (Afe) Rectifiers For Energy Storage Systems

Faculty of Engineering University of Malaya

This paper investigates the stability and performance of model predictive controlled active-front-end (AFE) rectifiers for energy storage systems, which has been increasingly applied in power distribution sectors and in renewable energy sources to ensure an uninten-uptable power supply. The model predictive control (MPC) algorithm utilizes the discrete behavior of power converters to determine appropriate switching states by defining a cost function. The stability of the MPC algorithm is analyzed with the discrete z-domain response and the nonlinear simulation model. The results confirms that the control method of the active-front-end (AFE) rectifier is stable, and that is operates with an infmite …

Semi-Z-Source Inverter Topology For Grid-Connected Photovoltaic System

Faculty of Engineering University of Malaya

Transformer-less inverters are necessary parts for grid-connected renewable energy resources. Owing to its cost effectiveness, downsize and less weight, great attention has been paid to these inverters development. With these aforementioned advantages, these inverters have limitations like the flow of leakage current through photovoltaic arrays, high total harmonic distortion (THD) at inverter's output and DC current injection to the grid. This study presents coupled inductor-based single-phase transformer-less semi-Z-source inverter topology to lessen those limitations. Since the DC input and AC output voltage share a common ground, the presented inverter system is categorised under doubly grounded topologies. For the purpose of …

Thermoluminescence Response Of Flat Optical Fiber Subjected To 9 Mev Electron Irradiations

Faculty of Engineering University of Malaya

We describe the efforts of finding a new thermoluminescent (TL) media using pure silica flat optical fiber (FF). The present study investigates the dose response, sensitivity, minimum detectable dose and glow curve of FF subjected to 9 MeV electron irradiations with various dose ranges from 0 Gy to 2.5 Gy. The above-mentioned TL properties of the FF are compared with commercially available TLD-100 rods. The TL measurements of the TL media exhibit a linear dose response over the delivered dose using a linear accelerator. We found that the sensitivity of TLD-100 is markedly 6 times greater than that of FF …

An Accelerated And Accurate Three-Dimensional Ray Tracing Using Red-Black Tree With Facet Mining And Object Bouncing Techniques

Faculty of Engineering University of Malaya

Recent trends show that it is a major challenge to predict the exact propagation path accurately and efficiently for three-dimensional (3D) indoor environments. Therefore, this study introduces a new 3D ray tracing algorithm based on a red-black tree with facet mining and object bouncing techniques. The red-black tree data structure offers a faster object searching operation while repeatedly performing intersection tests. On the other hand, extensive ray-facet intersection tests can be eliminated by using object and facet bouncing techniques, whereas the facet mining makes it easier to trace the transmitted ray paths accurately. The proposed method is compared with ray …

Airborne Hyperspectral Discrimination Of Tree Species With Different Ages Using Discrete Wavelet Transform

Faculty of Engineering University of Malaya

In this article, the capability of discrete wavelet transform (DWT) to discriminate tree species with different ages using airborne hyperspectral remote sensing is investigated. The performance of DWT is compared against commonly used traditional methods, i.e. original reflectance and first and second derivatives. The hyperspectral data are obtained from Thetford forest of the UK, which contains Corsican and Scots pines with different ages and broadleaved tree species. The discrimination is performed by employing three different spectral measurement techniques (SMTs) including Spectral Angle Mapper (SAM), Spectral Information Divergence (SID), and a combination of SAM and SID. Five different mother wavelets with …

Effective Use Of An Edfa And Raman Pump Residual Powers Via A Bi-Edf In L-Band Multi-Wavelength Fiber Laser Generation

Faculty of Engineering University of Malaya

Residual powers of an erbium-doped fiber amplifier (EDFA) and a Raman pump are utilized effectively for pumping a 0.45 m long bismuth-based EDF (Bi-EDF) in linear-cavity L-band multi-wavelength fiber laser generation. A 7.7 km dispersion compensating fiber (DCF) operates as both Brillouin and Raman gain media and a 6.5 dBm fixed-power tunable laser source (TLS) amplified by an EDFA works as a Brillouin pump (BP). By inserting the Bi-EDF in the linear cavity and using the EDFA and the fixed Raman pump residual powers 13.6 mW and 64 mW, at wavelengths 978.8 nm and 1490.6 nm respectively, the gain spectrum …

Optimization Of A Photovoltaic Pumping System In Bejaia (Algeria) Climate, Rahrah Karima Jr, Djamila Rekioua Pr

REKIOUA Djamila Dr

Photovoltaic energy is used in different applications and especially in water pumping and irrigation in remote areas. However, the performances of a photovoltaic pumping system can be degraded with variations of insolation and in order to maximize the efficiency of the photovoltaic energy system, it is necessary to track the maximum power point of the PV array. Many methods have been developed to determine the maximum power point (MPP). In this paper we present the results of performance optimization of a PV pumping system in Bejaia (Algeria) climate. The pumped water is desired to satisfy the domestic needs of three …

Control Of Photovoltaic Water Pumping System, Chafia Serir Jr, Djamila Rekioua Pr

REKIOUA Djamila Dr

Due to the continuous decrease of the solar cells cost, photovoltaic energy is used in different applications. The most important one is the water pumping system powered by photovoltaic generators. These systems can work with or without storage battery. With the increased use of this application, more attention has been paid to their optimum utilization. Many methods have been developed to determine the maximum power point (MPP). In this paper, to control the DC bus voltage, we apply field oriented control (FOC) strategy to induction motor (IM) supply by a photovoltaic (PV) system. And to maximize the efficiency of the …

Nanoimprint Lithography 20 Years On, Qiangfei Xia, R. Fabian Pease

Qiangfei Xia

To celebrate the 20th anniversary of nanoimprint lithography (NIL) we present a perspective of how the technique and its prospects have evolved over the past two decades. We describe how it overcame certain fabrication challenges at the time it was first reported and look at some of the obstacles that hindered uptake in industry initially, as well as likely sectors for future successful commercial deployment. Developments in the technique since that are making NIL increasingly attractive such as 'moving roll to roll' for higher throughput, are also described.

Nanoscale Memristive Radiofrequency Switches, Shuang Pi, Mohammad Ghadiri-Sadrabadi, Joseph C. Bardin, Qiangfei Xia

Qiangfei Xia

Radiofrequency switches are critical components in wireless communication systems and consumer electronics. Emerging devices include switches based on microelectromechanical systems and phase-change materials. However, these devices suffer from disadvantages such as large physical dimensions and high actuation voltages. Here we propose and demonstrate a nanoscale radiofrequency switch based on a memristive device. The device can be programmed with a voltage as low as 0.4 V and has an ON/OFF conductance ratio up to 1012 with long state retention. We measure the radiofrequency performance of the switch up to 110 GHz and demonstrate low insertion loss (0.3 dB at 40 GHz), …

General Properties For Determining Power Loss And Efficiency Of Passive Multi-Port Microwave Networks, Ramakrishna Janaswamy

Ramakrishna Janaswamy

Starting from the scattering matrix formulation, three useful properties are derived that characterize the dissipative loss and the corresponding efficiency of a multiport, passive microwave network. Elementary examples are considered that involve both reciprocal and non-reciprocal networks to demonstrate the utility of the expressions provided. When applied to the equal-split, matched, 3-port resistive divider, they recover the known fact that the device is 50% efficient. The relations yield the new result that the efficiency of a 3-port Wilkinson power divider is 2/3 on the average. Using the results presented it is further shown that the Wilkinson power divider belongs to …

High Rate Space-Time Codes For Millimeter-Wave Systems With Reconfigurable Antennas, Vida Vakilian, Hani Mehrpouyan, Yingbo Hua

Hani Mehrpouyan

In this paper, we propose a high-rate space-time block code (STBC) for millimeter-wave wireless communication systems that are equipped with reconfigurable multiple-input multiple-output (MIMO) antennas. We assume that each reconfigurable antenna element has the capability of forming its beam and can independently change the characteristics of its radiation pattern1. We exploit this feature of the antenna elements to construct the proposed space-time block code where each coded symbol is sent over independent beams. As a result, the received coded symbols at different receive antennas will have different power levels, a desired property that can be used in data detection. We …

Hybrid Millimeter-Wave Systems: A Novel Paradigm For Hetnets, Hani Mehrpouyan, Michail Matthaiou, Rui Wang, George K. Karagiannidis, Yingbo Hua

Hani Mehrpouyan

Heterogeneous Networks (HetNets) are known to enhance the bandwidth efficiency and throughput of wireless networks by more effectively utilizing the network resources. However, the higher density of users and access points in HetNets introduces significant inter-user interference that needs to be mitigated through complex and sophisticated interference cancellation schemes. Moreover, due to significant channel attenuation and presence of hardware impairments, e.g., phase noise and amplifier nonlinearities, the vast bandwidth in the millimeter-wave band has not been fully utilized to date. In order to enable the development of multi-Gigabit per second wireless networks, we introduce a novel millimeter-wave HetNet paradigm, termed …

Bandwidth Efficient Channel Estimation For Full Duplex Communication Systems, Abbas Koohian, Hani Mehrpouyan, Mahmoud Ahmadian, Mohammad Azarbad

Hani Mehrpouyan

In this paper, the channel estimation problem in full duplex (FD) point-to-point wireless communication systems is investigated. Because of the existence of two interfering and communication channels, this problem is fundamentally different from the conventional channel estimation problems in half duplex (HD) communication systems. Here, we propose a blind channel estimator that simultaneously estimates the channel parameters of the FD system without requiring time division duplex. A major problem for blind estimators is the identifiability of the parameters. Therefore, thorough analysis is presented to determine the identifiable parameters in this estimation problem. It will be shown that a completely blind …

Image Masking Schemes For Local Manifold Learning Methods, Hamid Dadkhahi, Marco Duarte

Marco Duarte

We consider the problem of selecting a subset of the dimensions of an image manifold that best preserves the underlying local structure in the original data. We have previously shown that masks which preserve the data neighborhood graph are well suited to global manifold learning algorithms. However, local manifold learning algorithms leverage a geometric structure beyond that captured by this neighborhood graph. In this paper, we present a mask selection algorithm that further preserves this additional structure by designing an extended data neighborhood graph that connects all neighbors of each data point, forming local cliques. Numerical experiments show the improvements …

Recovery From Linear Measurements With Complexity-Matching Universal Signal Estimation, Junan Zhu, Dror Baron, Marco Duarte

Marco Duarte

We study the compressed sensing (CS) signal estimation problem where an input signal is measured via a linear matrix multiplication under additive noise. While this setup usually assumes sparsity or compressibility in the input signal during recovery, the signal structure that can be leveraged is often not known a priori. In this paper, we consider universal CS recovery, where the statistics of a stationary ergodic signal source are estimated simultaneously with the signal itself. Inspired by Kolmogorov complexity and minimum description length, we focus on a maximum a posteriori (MAP) estimation framework that leverages universal priors to match the complexity …

Conditioning Of Random Block Subdictionaries With Applications To Block-Sparse Recovery And Regression, Waheed U. Bajwa, Marco Duarte, Robert Calderbank

Marco Duarte

The linear model, in which a set of observations is assumed to be given by a linear combination of columns of a matrix (often termed a dictionary), has long been the mainstay of the statistics and signal processing literature. One particular challenge for inference under linear models is understanding the conditions on the dictionary under which reliable inference is possible. This challenge has attracted renewed attention in recent years, since many modern inference problems (e.g, high-dimensional statistics and compressed sensing) deal with the underdetermined setting, in which the number of observations is much smaller than the number of columns in …

Performance Guarantees For Sparse Regression-Based Unmixing, Yuki Itoh, Marco Duarte, Mario Parente

Marco Duarte

Sparse regression-based unmixing has received much attention in recent years; however, its theoretical performance has not been explored in the literature. In this work, we present theoretical guarantees for the performance of a sparse regression based unmixing (in short, sparse unmixing) implemented in the form of a Lasso optimization with non-negativity constraints. We provide a sufficient condition required for the exact recovery of the endmembers and validate it both theoretically and through experiments. In cases in which the condition is not verified, we explore the performance of sparse unmixing in relation to the exact recovery coefficient (ERC).

Enhancing Access To Radio Spectrum In Cognitive Radio Networks, Fatima Salahdine, Hassan El Ghazi, Naima Kaabouch

fatima salahdine

Limiters Protect Adcs Without Adding Harmonics, Chin-Leong Lim

Chin-Leong Lim

High-speed Analogue to Digital Converters (ADC) are used for sampling at either the intermediate frequency (IF) or the radio frequency of wireless receivers. When the transmitter is nearby, the sampled signal can exceed the ADC’s maximum input level. So, amplitude limiting is necessary to prevent ADC damage or degradation. While automatic gain control is effective for controlling IF amplitude excursion in traditional single-carrier systems, it is not desirable in modern multi-carrier applications. One solution is to cap the IF amplitude excursion with a limiter. Unfortunately, a new problem is created – the strong non-linearity that is required of a good …

A Dft Study On An Alkali Atom Doped Decahedral Silver Nanocluster For Potential Application In Opto-Electronics And Catalysis

Faculty of Engineering University of Malaya

A systematic study of the structural, electronic and optical properties of the decahedral bimetallic Ag12X cluster is presented in the framework of density functional theory (DFT), where one atom of an alkali metal (X = Li, Na, K, Rb, Cs, Fr) is added, replacing a Ag atom in the decahedral Ag-13 cluster in core (c-doped), vertex (v-doped) and surface (s-doped) positions. Geometrical optimization of the clusters indicated that Li and Na doped clusters exhibited the highest stability. The binding energy (BE), vertical ionization potential (VIP), vertical electron affinity (VEA) and HOMO-LUMO gaps were calculated to compare the electronic stability and …

A Literature Survey On Different Type Of Energy Efficiently Routing Protocol In Wireless Sensor Network, Innovative Research Publications Irp India, Devendra Patle, Sandip Nemade

Innovative Research Publications IRP India

— Wireless sensor network is an emerging technology which has an immense scope of research and development. It has the potential of quick capturing, processing and transferring data with high resolution to the base station. WSN consists of multiple sensor nodes, these nodes have low storage capability and limited battery life which dies due to the computation and transmission of data. It is not feasible to replace these batteries due to their placement in isolated areas. In this paper we will emphasize on maximizing energy efficiency and improvement of life span of network. Clustering is the technique which balances the …

Compressive Parameter Estimation For Sparse Translation-Invariant Signals Using Polar Interpolation, Karsten Fyhn, Marco Duarte, Søren Holdt Jensen

Marco Duarte

We propose new compressive parameter estimation algorithms that make use of polar interpolation to improve the estimator precision. Our work extends previous approaches involving polar interpolation for compressive parameter estimation in two aspects: (i) we extend the formulation from real non-negative amplitude parameters to arbitrary complex ones, and (ii) we allow for mismatch between the manifold described by the parameters and its polar approximation. To quantify the improvements afforded by the proposed extensions, we evaluate six algorithms for estimation of parameters in sparse translation-invariant signals, exemplified with the time delay estimation problem. The evaluation is based on three performance metrics: …

Chest Worn Pulse Oximeter Integrating Ni-Usrp With Gps Disciplined Clock Transceiver, Innovative Research Publications Irp India, Alfredo U. Ganggangan, Angelo A. Beltran Jr., Evelyn C. Barreto, Princess F. Hernandez, Paul Erick P. De Villa, Mark Tristan Angelo M. Cabatac

Innovative Research Publications IRP India

This paper presents the chest worn pulse oximeter with integrated universal software radio peripheral (USRP) with global positioning systems (GPS) disciplined clock transceiver from National Instruments. It illustrates the respiratory cardio monitoring using the flexible reflective pulse oximeter with ECG. The gathered cardio respiratory data assessed by the microcontroller and the output is sent through to the remote monitor display by means of wireless system. The device also incorporates an early warning feature to alert both the user and the person being monitored. The GPS device is included for tracking and to determine the present location of the client in …