Sérgio Daher

High gain DC-DC boost converter with a coupling inductor

This paper presents a design, mathematical modeling, simulation results and laboratory implementation of a 300 W high gain dc-dc boost converter with a coupled inductor, to step up the 24 V of a battery bank to 311 Vdc, aiming to supply residential loads with dc voltage in an off-grid PV system. The converter can supply most of the residential ac loads which input stage is a single-phase rectifier. Laboratory tests with the 300 W converter supplying electronic lights, mobile charger and audio-video system ac showed the viability of the proposed idea.

Avaliação de sensor capacitivo para o monitoramento do teor de água do solo

This paper aims to evaluate a capacitance sensor for monitoring soil water content. Capacitance sensors were tested to evaluate the effect of temperature and response time, and to obtain the calibration equation and their sensitivity. Sensors were placed in different environments (soil, water and air) and temperatures (25 oC, 20 oC, 15 oC, 10 oC, 5 oC and 0 oC). The calibration was performed with one of the capacitance sensors installed in a PVC column containing 0.015066 m3 of undisturbed soil and hanged on one side of a scale with a load cell connected to a data acquisition board on the other side. Results showed reductions in the frequency response of the capacitance sensor with increasing temperature. The response time was low (less than one second) as it was immersed into water, as well as to an abrupt change in soil moisture in the soil column. It was verified that the sensitivity of the sensor increases as the soil moisture decreases. Therefore, the capacitance sensor can be used to determine the soil moisture.

Analysis of high voltage step-up nonisolated DC–DC boost converters

ABSTRACT A high voltage step-up nonisolated DC–DC converter based on coupled inductors suitable to photovoltaic (PV) systems applications is proposed in this paper. Considering that numerous approaches exist to extend the voltage conversion ratio of DC–DC converters that do not use transformers, a detailed comparison is also presented among the proposed converter and other popular topologies such as the conventional boost converter and the quadratic boost converter. The qualitative analysis of the coupled-inductor-based topology is developed so that a design procedure can be obtained, from which an experimental prototype is implemented to validate the theoretical assumptions.

Identification and adaptive speed control for switched reluctance motor using DSP

In this paper, a simple adaptive speed control for switched reluctance motor (SRM) is described and implemented using Digital Signal Processor (DSP). The controller structure design is based on PWM control scheme that have been used for the SRM current controller. To realize the speed control, the speed reference is calculated as function of current machine. From experimental results it is shown that the overall switched reluctance motor speed control gives good transient and steady state responses.

Neo-fuzzy neuron model for seasonal rainfall forecast: A case study of Ceara's eight homogenous regions

The knowledge about the seasonal rainfall in some Brazilian regions is essential for agriculture and the adequate management of water resources. For this purpose, linear and nonlinear models are commonly used for seasonal rainfall prediction, while some of them are based on Artificial Neural Networks, demonstrating great potential as shown in literature. According to this tendency, this work presents a rainfall seasonal forecast model based on a neuro-fuzzy technique called Neo-Fuzzy Neuron Model. Improved performance by using this approach has been obtained in terms of reduced root mean square error RMSE and increased correlation between predicted and real output when compared with dynamic downscaling model using the Regional Spectral Model. Experimental results show the effectiveness of the proposed method in predictions regarding the first four trimesters from year 2002 up to the current one.

Comparative analysis of three dc-dc non-isolated buck converters

This paper presents a comparative analysis of three dc-dc non-isolated buck converters. For this purpose, a classical buck converter, an interleaved buck converter, and a three-state switching cell (3SSC) buck converter were analyzed. In order to best compare the performance of these topologies, the switching frequency, processed power, current ripple before the filter capacitor, and specification were considered equals for all tested configurations. A modular prototype of 1 kW, 200 Vdc / 60 Vdc was implemented, allowing to easily configure all topologies by just changing the magnetic components. From the experimental results, it was found that all studied converters present some current unbalance, being the less critical in the converter based on 3SSC.

A high resolution output voltage multilevel inverter topology with few cascade-connected cells

This paper presents a study of a generalized multilevel asymmetric inverter based on a H-Bridge Cell with one Arm Series (CHB-as) and five switches. It is shown several asymmetrical arrangements of input source combinations that produce several equally spaced voltage levels with few components. Equations for determining the switching frequency employed in the low power processing cells are developed, and demonstrate the possibility of high resolution output voltage even at low frequency. The simulations of a two cascade asymmetric cells 1 kW-220 V topology, implemented in the program Orcad Pspice, V. 16.5 validated analyzes showed that the inverter operating with only two cells resulted output voltage with 25 levels. The results presented show that in topologies with three cascade cells it is feasible to obtain output voltages with 85 levels for the first proposed configuration or even 125 levels for the second configuration without redundant instances in the output voltage.

Turbina eólica para agricultura familiar do semiárido com inovações tecnológicas para baixas velocidades de vento

A agricultura familiar e um segmento importante do agronegocio brasileiro e tem grande participacao na producao de alimentos essenciais para a seguranca alimentar do Brasil, por isso, e preciso o fornecimento de energia para esses agricultores. Uma alternativa e a energia eolica, no entanto um desafio para usar o vento em pequenas propriedades no Estado do Ceara e a condicao operacional do vento que e de baixa velocidade (ventos < 6 m s-1). O objetivo deste trabalho foi propor um sistema eolico para pequenas propriedades do Estado do Ceara com inovacoes tecnologicas. Todos os sistemas foram concebidos e dimensionados em uma turbina inovadora e apropriada para as pequenas propriedades. A estimativa de custo indica um baixo valor de aquisicao e atraves de redes inteligentes e da geracao distribuida pode-se gerar renda.

Multi-state and interleaved converters with passive impedances for current sharing

This paper presents multi-state and multilevel switching cells to generate high power non-isolated interleaved DC-DC, AC-DC, and DC-CA converters. The cells are classified in two groups; multistate switching cell (MSSC) based on autotransformer, and interleaved switching cell (ISC) based on inductors. Each switching cell has impedance based on small inductor, Lsh, connected between the legs, named current sharing circuit (CSC), which guarantees a zero average voltage between the terminals of the involved magnetic components, and thereby absorbs the PWM duty cycle differences. The small inductor causes duty cycle reduction; therefore its value should be very small. To verify the current sharing through the magnetic components, two Buck DC-DC converters with 1 kW output power, 200 V input voltage, 60 V output voltage, and 25 kHz switching frequency, was assembled and tested in laboratory.

High gain DC-DC converter applied to photovoltaic system with new proposed to MPPT search

This paper presents the development of a high gain Boost converter applied to photovoltaic (PV) system. This converter raises its input voltage and injects its output current at a constant 311 Vdc bus, using the maximum power point tracking (MPPT). The new proposal seeks the MPPT is to connect each module a converter for a high gain greater accuracy in finding the point of maximum power. The converter will work with input voltage of 17.4 Vdc, output voltage of 311 Vdc and power of 100 W.