Montie A. Vitorino

An Effective Induction Motor Control for Photovoltaic Pumping

A new design of an efficient batteryless pumping system powered from photovoltaic panels, comprising a push-pull converter and an induction motor, is presented. Detailed evaluation of the energy processing cycle has allowed the formulation of a set of design principles and the optimization of a sensorless induction motor drive system. The resulting performance enhancement is demonstrated experimentally.

Combining Model-Based and Heuristic Techniques for Fast Tracking the Maximum-Power Point of Photovoltaic Systems

This paper proposes a technique for accelerating the convergence to the maximum power point of photovoltaic (PV) systems based on the model obtained from manufacturers generator data. The influence of the temperature over the PV array performance is considered, and no measurement of solar radiation is required. Knowledge of the load model and expensive sensor circuitry are not necessary. The tracking speed is much faster than nonmodel-based techniques at the expense of an increase in the computational complexity. Simulation and experimental results are presented and demonstrate the feasibility of the proposed solution.

Using the model of the solar cell for determining the maximum power point of photovoltaic systems

This paper proposes a technique for accelerating the convergence to the maximum power point of photovoltaic (PV) systems based on the model obtained from manufacturers generator data. The influence of the temperature over the PV array performance is considered, and no measurement of solar radiation is required. No knowledge of the load model and no expensive sensor circuitry are necessary. The tracking speed is much faster than non model-based techniques at the expenses of an increase in the computational complexity. Simulation and experimental results are presented and demonstrate the feasibility of the proposed solution.

Compensation of DC link oscillation in single-phase VSI and CSI converters for photovoltaic grid connection

In this work it is presented a technique to reduce DC link oscillation in Voltage Source Inverter (VSI) or Current Source Inverter (CSI) that operates connected to a single phase grid. That oscillation can be responsible for losses or malfunctioning of the DC sources (photovoltaic panels or batteries). It is also may cause efficiency reduction of photovoltaic generators. The oscillation reduction can be achieved by adding two power switches and a passive energy storage element to the converter topology. Details about design and control strategies for both topologies, which has demonstrated performance improvements, when compared with others solutions, are presented. Simulation and experimental results are provided to validate the theoretical approach and to evaluate the topologies performance and quantify energy efficiency gain.

High performance photovoltaic pumping system using induction motor

Photovoltaic pumping is one of the most interesting applications for distributed energy generation. Despite that, cost still a concern, when compared with others energy resources. Therefore, efficiency improvement can be seen as one way for cost reduction. Use of maximum power point tracker allows generating more energy with the same amount of panels, which means more energy per panel. Nevertheless, the whole power processing has more than panels. It also includes converters, inverter, electrical motor, pump and batteries, which store energy for further use during solar outrage. The aim of this paper is to show how to achieve an effective photovoltaic pumping system without batteries. In this solution the role of batteries are replaced by fluid storage and, steady state operation depends on the amount of available power. Evaluations of all system devices, for each processed power level, allow to conclude about their efficiency and to clarify how they can be controlled to make the whole system operates at maximum efficiency level. Experimental results help to show how a photovoltaic pumping system can be improved in terms of efficiency.

Compensation of DC-Link Oscillation in Single-Phase-to-Single-Phase VSC/CSC and Power Density Comparison

This paper proposes a technique to reduce the low-frequency dc-link energy oscillation due to the pulsating single-phase energy flow in a single-phase-to-single-phase voltage source converter (VSC) and current source converter (CSC), which operate connected to the grid. This pulsating energy is the major factor for increasing the size of the passive components and power losses in the converter. Pulsation reduction is achieved by incorporating two auxiliary active switches and one passive energy storage element to the rectifier and inverter sides. Additionally, this paper presents the comparison of these converters (VSC/CSC) regarding efficiency and power density. Details of the control strategy are presented. Simulation and experimental results are provided to validate the theoretical approach.

A Method for Averting Saturation From Series Transformers of Dynamic Voltage Restorers

This paper proposes a technique for preventing saturation in series transformers from dynamic voltage restorer (DVR) systems. The method consists in correcting the voltages which are injected through the transformers into the power system to compensate voltage sags. It restricts the compensating voltages during the sag whenever it predicts that a maximum limit for the flux linkage is about to be exceeded. The prediction is carried out at the beginning of a stabilized voltage sag. Moreover, the technique allows a certain level of sag compensation even when the estimated flux is expected to exceed the saturation limit. The voltage sag level and phase are computed through an adaptive recursive least squares (RLS). The RLS estimation incorporates a transient period before it achieves a stable state whenever there is a sag event. The DVR is not supposed to operate in this period. Therefore, this paper also outlines a simple procedure for detecting the RLS estimation stable level. Simulation of different scenarios of voltage sags and the results from the experimental implementation of a DVR show the effectiveness of the method.

Single-phase current source converter with new modulation approach and power decoupling

In this work it is presented a Current Source Converter (CSC) topology that helps to mitigate double line frequency power ripple (low frequency) effect. Low frequency power ripple presented in single-phase systems propagates through DC-bus converter. This low frequency ripple reduction allows to increase the power converter density by reducing the volume of the DC inductor, without lack of stiffness at the DC-bus. The low frequency mitigation is achieved by using a different single-phase CSC topology that uses three series-connected switches per leg. Thus, it allows independent control for two merged CSCs which share the same DC-bus and the middle switches of the leg. This solution is adequate to connect photovoltaic panels to the electrical grid, among others applications. Evaluation of such a solution by assuming grid modeling is useful and may require powerful simulation tools such as real-time simulator. In order to comply with power processing restrictions, a low frequency model is derived. Performance of both models (high and low frequency) are compared to ensure usability of the low frequency model. Control strategies and modulation are presented. Simulation results are provided to validate the theoretical approach, and real-time simulation results, as well.

Low-Frequency Power Decoupling in Single-Phase Applications: A Comprehensive Overview

This paper presents a literature overview of all techniques proposed until the submission of this paper in terms of mitigating power oscillation in single-phase applications. This pulsating energy is the major factor for increasing the size of passive components and power losses in the converter and can be responsible for losses or malfunctioning of the dc sources. Reduction of power ripple at twice the fundamental frequency is one of the key elements to increase power converter density without lack of dc stiffness. Pulsation reduction is achieved by incorporating control techniques or auxiliary circuitries with energy storage capability in reactive elements to avoid this oscillating power to propagate through the converter, creating what is called as single-phase power decoupling. The topologies are divided as: rectifiers, inverters, and bidirectional. Among them, it is possible to classify as isolated and nonisolated converters. The energy storage method may be classify as: capacitive and inductive. For the power decoupling technique, it is convenient to divide as control and topology. The power decoupling technique may be implemented as series or parallel with respect to the ac, dc or link side. This paper represents the best reference on this topic.

Single-phase power compensation in a current source converter

This work presents a single-phase current source converter topology that allows to mitigate typical DC-bus power ripple. Reduction of power ripple at twice of line frequency is one of the key elements to increase power converter density without lack of DC-bus stiffness. In this paper, low frequency ripple mitigation is achieved by adding a third leg connected to the output filter central point. Details of control strategy and modulation are presented. Simulation results are provided to validate the theoretical analysis.