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This paper presents a new formulation of the voltage sag state estimation problem based on compressive sensing theory. The growing economic losses for voltage sags have led to a search for new mathematical methods for voltage sags diagnosis. Several studies have been focused on optimization problems based on techniques that are inaccurate when faults with large impedance are considered. To overcome these limitations, we proposed a $\ell 1$-based voltage sag state estimator ($\ell 1$-VSSE). A limited number of voltage sag meters, sensing matrices using residual voltages per unit, and the solution of a $\ell 1-$ regularized least square problem (LSP) for each voltage sag detected, are novel characteristics of the proposed estimator. The $\ell 1$-VSSE has been validated by using the IEEE30-bus power system and the IEEE69-bus distribution system. The outcomes validate the efficient performance in the voltage sags estimation and its robustness to the fault types, fault impedance, and meshed or radial systems.

Power quality information is useful not only to determine electricity fitness but also for another important application: load identification. One approach to identify loads is through non-intrusive load monitoring systems that estimate the nature and operation of individual appliances with measurements in a single point. In this work, load identification is addressed as a classification task by taking advantage of power quality information. Therefore, discriminant analysis of power quality characteristics are proposed, thus requiring simpler design and fitting processes than traditional techniques. In this regard, classifiers based on linear and quadratic discriminant analysis are implemented for laboratory measurements with noticeable performance.

This paper presents the design and implementation of a prototype based on a SEPIC (Single-Ended Primary Inductance Converter) used to measure the characteristic curves of photovoltaic (PV) panels. The SEPIC is controlled to emulate a variable resistance at the output of the PV panel in order to obtain a set of values (voltages and currents) for different operating points at the output of the panel. The set of voltages and currents are stored and sent to a computer in order to display the characteristic curves in real-time. The performance of the prototype is firstly evaluated though simulations in PSIM and subsequently by experimental results. The results show the outstanding performance of the SEPIC converter and its suitable use for this kind of applications due to its low input current ripple and its operation as a buck-boost converter. The resulting prototype allows the characterization of PV panels up to 500 W.

This paper presents the operation of a grid-tied photovoltaic power generator considering a two stages configuration for active power injection. A Neutral Point Clamped Inverter (NPC Inverter) was used for the DC-AC conversion and a DC-DC Boost converter complemented the system configuration. The control system includes the following loops: a maximum power point tracking algorithm, a DC bus voltage control, a reference generator, a capacitors voltage balancing loop, a current controller and a Level Shifted Pulse Width Modulation (LS-PWM) technique. The work is mainly focused in balancing the voltages in the DC bus capacitors by adding an offset level to the modulation signal which ensures the good performance of the NPC inverter. The operation of the system was evaluated in a PSIM® software environment for different irradiance conditions. The results show the outstanding performance of the photovoltaic system specifically in the Maximum Power Point Tracking (MPPT), the DC side voltages balance in the NPC inverter and the active power control.

Nonintrusive Load Monitoring (NILM) systems aim to estimate the individual appliance operation and consumption in a household from measurements at a single point, in order to motivate energy conservation behaviors. Power estimation based on appliance rated powers is not always accurate because of the voltage supply variations, thus misleading load disaggregation algorithms. In this paper we propose models of power as a function of voltage for correcting the power estimation. Measurements in the laboratory of residential loads are performed under multiple voltage levels. These data are processed to find regression models. Moreover, some analytic expressions to calculate the powers are proposed. Proposed models result more accurate than the rated powers and other models in the scientific literature.

The evolution of power converters towards modular and robust topologies for high power applications has led to the development of multilevel converters. One of the main advantages of this technology is the improvement of the output voltage quality. This article presents the characterization of the output voltage waveform for three five-level multilevel converters (the Neutral Point Clamped-NPC, the Flying Capacitor-FC and the Cascaded H bridge - CHB) which are controlled by Pulse Width Modulation strategies. The characterization is made by the determination of the Total Harmonic Distortion (THD), the Lower-Order Harmonic (LOH), the voltage stress of the switching devices and the analysis of the FFT of the output voltage. The results show the outstanding performance of the CHB topology under the parameters mentioned above.

This paper addresses the impact of the dynamic network reconfiguration (DNR) on the voltage sag observability in smart distribution systems. Optimal placement of voltage sag monitors is generally applied without taking into account the DNR and we show that the voltage sag observability is modified with the network reconfiguration. We also propose two indexes to assess the impact of the dynamic reconfiguration on voltage sag observability. A test case is implemented and the results show the need for new formulations for optimal placement problem, where the DNR should be included to guarantee the full voltage sag observability.

This paper presents a methodology for energy management in residential electrical systems. The methodology is based on the sub-measurement by branch circuit in a scenario that takes into account alternative sources and a differential pricing scheme. The result of this investigation project is part of SILICE III project, whose main purpose is the design and implementation of a smart micro-grid pilot project in an energy distribution circuit in Bogota (Colombia).

Storage systems are a key element to take advantage of renewable energy due to its ability to transfer energy consumption from one time period to another. With high charge/discharge ratios one can increase the short term revenue stream from a renewable energy system whereas with a low charge/discharge ratios one can increase the long term benefits. Hence, when compared against nominal charge or discharge operation, the storage system life can be increased/reduced with a low/high charge or discharge ratios. In order to quantify this fact for different storage management strategies, this work analyze the effect on the life of a lead-acid battery system of three scheduling strategies: linear programming, crisp logic and fuzzy logic. The three cases will be compared against a reference strategy which consist on solving a linear optimization problem with perfect forecast of load, energy price and renewable availability. A photovoltaic system is taken as the renewable source and historic values for eight months are used to study the trend in the life of the storage system. it can be concluded that higher storage capacity leads to higher overall benefits, however, this cannot be said for the maximum storage system power, even when considering only the costs benefits, which suggest that a proper strategy and parameter selection can be better than high power ratio.

This paper presents a comparive analysis between four Maximum Power Point Tracking (MPPT) algorithms in centralized grid-tied Photovoltaic (PV) systems. The algorithms are used to control the duty cycle of a DC-DC converter in order to boost the output voltage of the PV generator and guarantee the operation of the solar panels in the Maximum Power Point (MPP). Three of the analyzed algorithms correspond to the classical Perturb and Observe (P&O) method, the Incremental Conductance (IC) technique and the Constant Voltage (CV) method. The fourth analyzed algorithm is a modification of the classical P&O method and it has been designed to improve the tracking of the MPP under voltage disturbances at the DC-side capacitor (interface between the DC-DC and the DC-AC stage). The performance of the MPPT techniques is compared through simulations in PSIM under two conditions: sudden changes of irradiance and a distortion of second order in the voltage at the DC-side capacitor. The comparative analysis is made according to some criterias such as the number of sensors, the rise time and the efficiency.

This paper presents an analysis of two algorithms used to control the active and reactive powers in three phase inverters for grid-tied photovoltaic systems under unbalanced voltages in the Point of Common Coupling (PCC). The algorithms are focused on injecting balanced currents to the grid despite the voltage unbalances. The analysed algorithms are composed of two control loops: the reference signal generation and the current controller. One of the algorithms generates the reference currents in the abc coordinates and the inverter firing pulses are obtained by using a Dead-Beat controller. The other algorithm calculates the reference current in the dq0 coordinates and considers a Proportional-Integral control technique to generate the firing pulses. The synchronization of the reference signals is made by a Kalman filter in both algorithms. This filter estimates the positive sequence component of the PCC voltages in order to obtain balanced reference currents. The performance of the algorithms is verified through simulations in PSIM and the results were compared based on the following parameters: the Total Harmonic Distortion (THD) of the injected currents and the mean square errors in the active power, the reactive power and the injected currents.

This paper presents a new method for relative location of voltage sags and capacitor switching transients based on voltage measurements only. Voltage sags caused by network faults and transients caused by bank capacitor energizing are considered in this work. The algorithm automatically operates for assessing power quality, characterising and extracting information from voltage records obtained from power quality monitors (PQMs) in distribution systems. Positive sequence voltages are the descriptors used to determine the relative location of the voltage events. Instantaneous voltage changes are the descriptors used to determine the relative location of capacitor switching transients. Finally, proposed method is applied to a study case and it is verified that the method can be helpful to determine the relative location of the voltage events. MATLAB was used for validating this methodology, receiving voltage records from simulated voltage sags in ATP-EMTP and its easy implementation is verified.

This paper presents a comparative analysis between three control techniques based on the Direct Power Control (DPC) algorithm for grid-tied Voltage Source Inverters (VSI). These techniques are used to regulate the injection of instantaneous active and reactive powers in a power system for renewable generation system applications. The first technique corresponds to the Classical DPC (C-DPC) and it is based on the definition of a Virtual Flux (VF). In the second one, the instantaneous active and reactive powers are estimated by using the time derivatives of the injected currents, without any voltage sensors. The third algorithm uses the Space Vector Modulation (SVM) technique to generate additional space vectors and it considers the minimum square error of the instantaneous active and reactive powers to determine the switching states. Simulation results of the three control techniques are presented and their performance is compared based on some criteria such as maximum steady-state power error, the current total harmonic distortion and the rise time.

This paper presents a real time hardware in the loop simulation system of a Shunt Active Power Filter (SAPF) for a three-phase four-wire Voltage Source Inverter (VSI). A digital signal processor starter kit TMS 320F2812 PGFA is chosen as control platform for the SAPF model, which is implemented in a dSPACE 1104. The system is focused on the DC bus voltage control and its purpose is to achieve and maintain a reference voltage level in each capacitor in order to guarantee both the active filter controllability and the balance in the distribution of the DC bus voltage. Direct comparison between real time simulation waveforms and Matlab/Simulink simulation signals are made to evaluate the effectiveness of the implemented system.

In this paper, we first introduce a simple tool called the wavelet or sigma-wavelet scheme. Wavelets deal with coordination among processes which are at most sigma hops away of each other. We propose a self-stabilizing solution for this scheme. Our solution requires no underlying structure and works in arbitrary anonymous settings, i.e., where process identifiers are not required. We show that our solution provides a simple and generic self-stabilizing sigma-infimum computation. Next, we present a self-stabilizing sigma-barrier synchronization protocol based on the wavelet scheme. We show that our protocol provides an efficient device in the design of local coordination problems at distance sigma, such as the sigma-local resource allocation (LRA). In particular, we propose a solution for the popular sigma-local mutual exclusion (LME) problem. The solution to sigma-LME also provides a transformer to transform algorithms written under sigma-central daemon into algorithms working with any distributed daemon.

This paper shows a new strategy to calculate the reference current in a power active filter used to mitigate harmonics injected by non-linear loads. The current is predicted with a Kalman filter a sampling period ahead to reduce and compensate the delay time effects caused by the acquisition times, the data processing and the performance of the filter. The validity of the algorithm is demonstrated by means of simulations in Matlab/Simulink. Several Kalman filters were studied and their capabilities compared to find out the best performance at the lowest computational cost.

Summary form only given. In the present paper, artificially nanostructured uniaxial giant magnetostrictive (Tb/sub x/Fe/sub 1-x//Fe/sub 0.6/Co/sub 0.4/)*n multilayers have been investigated for future MEMS purposes. For this goal, such multilayer films have been RF sputtered onto glass and silicon under various conditions to obtain different Tb ratios in the TbFe layers, with and without a bias field applied along the substrate in order to induce a magnetic easy axis. The authors show that uni-axial magnetostrictive TbFe/FeCo films were obtained with a greatly enhanced magnetoelastic coupling coefficient (b/sup /spl gamma/,2//spl ap/18 MPa) compared to TbFe/Fe (b/sup /spl gamma/,2//spl ap/11 MPa) without an annealing post process.

The lack of information on assembly equipment represents one of the main obstacle for the integration of assembly concerns at an early stage of product design activity. The definition of standardized assembly equipment gives an answer to this problem and permits to reduce considerably the global lead time. This paper is related to the design of a new standardized assembly system developed in collaboration with Fabricom Automation. We first identified three main classes of assembly equipment and examined the main characteristics of current assembly operations. Based on this analysis, we proposed a concept (basic 'G' shape frame in which different functional units can be incorporated) for a systematic organization of assembly workstation and developed this concept for two categories of products (CLII and CLIII). The conceptual process and the detailed design step for CLII are discussed in this paper. The impact on product design activity of such a standardized system is also examined.